swissie

I just got a rebuilt T-10. What is the best oil to put in? Would you recommend to start with one type and exchange it after a while, with maybe an other type?
Thanks
Adrian

Denney

When I bought, and installed, my B/W Super T-10 I used Mobil 1 Synthetic Gear Lube LS 75W-90 right from the start. And I don't plan to change it out any time soon.

SWCDuke

The original spec was Mil-L-2105B. The current commercial equivalent is 80W-90 GL-5, which is hypoid axle oil. You DO NOT want the limited slip additive in the transmission.

Duke

JoesC5

If you can find it, use GL-4 85W90 gear oil. The last I purchased was Sta-lube brand.

SWCDuke

GL-4 doesn't meet the Mil-L-2105 or GL-5 spec specified by GM.

Duke

Plasticman

I would not recommend using a synthetic lube. While synthetics have a better temp range, I have been informed that they may be too slippery for the synchro rings to "grab" properly. I "found" that out personally - the hard way. Standard mineral GM recommended lube works for me.

I have had great success however, with synthetic lube (Amsoil) in posi (limited slip) rear axles (no need - ever, for the GM additive).

Plasticman

71zman

When I had my T10 rebuilt by a guy (Bill in Lakewood CA) who has been doing these for 40 years he had two things to say on oil:

1) Don't use synthetic, he showed me a main shaft with the main bearing literally welded to it and said that this was the result of synthetic oil in a M22. Made a believer out of me.

2) He recommended Torco gear lube. Said it was the best on the market for T10's and would not put any other oil in his rebuilds.

JoesC5

GL-4 does meet the obsolete Mil-L-2105 spec. and is better suited for transmissions with "yellow" metal components(synchronizers). Great info from another forum.

"Posted by: mikepvg

IS GL-4 OBSOLETE?
By Mike NowickiAll rights reserved
Is a GL-4 rated gear lube really obsolete and who cares? When we go back to the Dodge dealer to purchase some GL-4 manual transmission lubricant, we are asked to pay as high as $25.69 per quart. That’s almost 230% over their cost. What!? When a top of the line synthetic GL-5 gear lube runs anywhere from five to ten dollars a quart at your local Pep Boys, WE CARE A LOT! We are talking over $100 dollars just to change 4 quarts of oil and that would be doing it yourself, Bob… This GL-4 gear lube is only available through Dodge, GM and extremely few aftermarket transmission repair shops (I only could find one that would sell it). What is this costly lube? Castrol Syntorq LT (low temperature), a 75W85 synthetic GL-4 rated gear lube. General Motors & DaimlerChrylser insists that only Castrol Syntorq LT be used for the NV4500 a 5 speed manual transmission.

In fact, GL-4 is equivalent to the obsolete military rating MIL-L2105, which is usually satisfied with 50% less EP (extreme pressure) additive than a typical GL-5 lube. I say usually because it is only a rule of thumb and not a specification. Typical GL-4 applications are manual transmissions, spiral bevel gears, hypoid gears in moderate service and the ubiquitous New Venture Gear 5 speed manual transmission (NV4500). The reason that the NV4500 has a GL-4 rating is that “yellow” metal components are used in the construction of the synchronizers. EP additives are corrosive to the copper alloys like brass and bronze. EP additives are activated with heat and pressure. The result is chemical corrosion, etching, pitting and excessive wear over time. Since a typical GL-5 will contain approximately twice the amount of EP additive as that of a typical GL-4, the possibility that a negative reaction will occur becomes high, especially if excessive heat is present. The use of a GL-5 gear lube in a synchronized transmission will cut the useful life of the synchronizers by typically one half. Since transmissions usually last a relatively long time, you won’t know the effects of using a GL-5 until its too late. There is also a cone clutch style type of material in the NV4500 on the synchronizers that also may be sensitive to high levels of EP additives. A popular auxiliary transmission made by Gear Vendors reports that their cone clutch material is also sensitive to EP additives and recommends a non-EP GL-4 lube. I have found most GL-4’s to be usually mineral based. Remember, GL-4 is an old rating and mineral based lubes are old technology. Syntorq is a synthetic GL-4. The reasons for a synthetic version are to enhance shifting problems/harshness at low temperatures and reduced high operating temperatures. Kenneth Koliba, a Product Specialist at New Venture Gear (NVG) responded: “The NV4500 was first developed with a mineral based oil which resulted in unacceptably high operating temperatures.”

Lets look at the some of the more pertinent performance criteria for gear lubricants. The details of each test are not necessary to get where we are going.
Performance category: Resistance to gear distress under high-torque, low-speed conditions
API GL-4: Test = CRC L-20
API GL-5: Test = CRC L-37
API MT-1: No requirement
The L-37 test simulates a much more severe duty type of service and is more difficult to pass. Therefore, we can safely say that a typical GL-5 can handle high speed, low torque and high torque, low speed conditions significantly better than a typical GL-4. Since a GL-5 can offer more extreme pressure protection than a GL-4, it might lead people to seek out a gear lube in this category.

Performance category: Thermal & oxidation stability/component cleanliness
API GL-4= No requirement
API GL-5= L-60-1
API MT-1= L-60-1*
The interesting fact here is that the GL-4 has NO REQUIREMENT! The GL-5 must pass L60 & the MT-1 must pass much tighter limits of L60. Again, the GL-5 and the MT-1 both look very good here.

Performance category:Copper corrosion conforming to ASTM D130
GL-4: 3B max after 1 h at 121.1°C
GL-5: 3 max after 3 h at 121.1°C
MT-1: 2A max after 3 h at 121.1°C
That converts to 250degF, which is extremely hot for a transmission. The pass/fail criteria require that there be no blackening with flaking. The industry uses a color picture chart for referencing. The MT-1’s 2A rating indicates a lubricant in this category is LESS corrosive to copper & copper alloys than either a GL-4 or GL-5. Again a GL-5 combined with MT-1 look very good here. I was able to contact a gear lubricant expert at Shell Oil through spokesperson, Ed Brown. His response to my inquiry regarding why the MT-1 has a much better rating than a GL-4; “At the time API GL-4 was created, drain intervals were much shorter than they are today, and OEM warranties were much shorter. With the extension of drain intervals comes the greater need for thermal stability. Since API MT-1 was introduced much later than API GL-4, the folks working on the tests for MT-1 had the opportunity to include a relatively new test, the L-60-1, to accommodate that need. They also upgraded the D 130 requirement recognizing the importance of copper compatibility. That does not mean that applications calling for GL-4 lube don't need that high level of copper compatibility; it just says the industry learned from their experiences and made the requirements more stringent within MT-1.”
There are eight other performance categories required for a standard GL rating but not shown here due to space limitations. In all eight tests the GL-5/MT-1 is equal to or better than anything the GL-4 can achieve or endure.

So, what do you suppose everyone is using in his or her NV4500? I recently conducted a survey on the TDR website. I asked three questions and I was able to obtain approximately 1.5% percent of the 6,600 TDR registered members. The results are as follows:
1)How many used what brand?
2)Average miles used?
3)What % reported an oil related problem?
62% used Castrol Syntorq LT 75w85 GL-4
57,230 Ave Miles 3% rpt oil related problem

24% used AMSOIL 2K 75w/90 GL-5/MT-1
50,400 Ave Miles 0%

3% used AMSOIL 80w90 GL-4
17,700 Ave Miles 0%

3% used Mobil 1 75w90 GL-5/MT-1
47,000 Ave Miles 0%

2% used Redline MT90 75w90 GL-4
45,000 Ave Miles 0%

2% used Castrol Syntec 75w90 GL-5/MT-1
424,000 Ave Miles 0%

1% used Royal Purple 75w90 GL-5
87,000 Ave Miles 0%

1% used Redine MTL 70w80 GL-4
30,000 Ave Miles 0%

1% used TORCO 75w90 GL-5
24,000 Ave Miles 0%

1% used Lubro-Moly MT
50,000 Ave Miles 0%

0% used Lubrication Engineers LE607 GL-5
0 Ave Miles 0%
(Note:I was somewhat surprised to see no one in this sampling using LE after reviewing Fritz’s website on lube alternatives.)

The average of 424,000 miles used with Castrol Syntec (not Syntorq) is somewhat misleading due to the fact that one member threw off the bell curve. That member is “Tdrmbramr” (This is his username on the TDR website) who claims over 700,000 miles recorded with all original components! Castrol SYNTEC is a GL-5/MT-1 rated lube. Of interest, Castrol specifically states in its Data Sheets that Syntec is not for a GL-4 application. Considering this empirical data, it would appear that synthetic gear oil rated to performance criteria GL-5 AND MT-1 is not just an alternative but a pretty darn good alternative to what the OEM originally validated for the NV4500. It would appear the “yellow” metals issue is addressed with the MT-1 rating & the GL-5 rating can take much more severe duty service. There are other TDR success stories with members using synthetic gear oils with the GL-5/MT-1 rating such as Amsoil. But, it would be best to dig as deep as we can since appearances can be deceiving and the NV4500 is not an inexpensive component to be experimenting with!

What does the actual manufacturer, New Venture Gear, have to say about all this? Getting any information from NVG was like pulling teeth. Countless inquires to numerous personnel via email and their telephone tech line resulted in little to no information. Eventually, I got a hold of Charles Armstrong, a NVG engineer willing to say something of interest. Apparently, New Venture Gear doesn’t even specify what to put in its own product! I find it hard to believe that the actual manufacturer of a transmission has no say in this matter. I quote his response to my email inquiry: “In response to your inquiry, New Venture Gear does not set the specifications for the SynTorq LT fluid. We are required to use this fluid by our customers. The fluid is specified by GM and DaimlerChrysler, and must meet their requirements. I would suggest contacting GM and/or DaimlerChrysler for their specification information.” Excuse me…. But didn’t NVG work directly with Castrol to develop this lube? What about all those shift stand tests we keep hearing about? I also pointed out other potential problem areas such as heat. Mr. Armstrong responded: “Concerning the high temperature issue you noted, this is one of the main reasons a synthetic lubricant like the SynTorq LT was required by vehicle manufacturers. In certain applications, transmission fluid temperatures can reach 300F. At such a temperature, mineral-based oils can quickly oxidize, thicken and lose some of their essential properties, reducing their ability to adequately lubricate the transmission. Further, overall useful life of the fluid can be drastically reduced by high temperatures, making the OEM required 'filled-for-life' condition for the transmission questionable at best. Synthetic-based lubricants are less sensitive to elevated temperatures and are not as susceptible to degradation as their mineral-based counterparts.” When I asked for more information regarding the new GL-5/MT-1 rated lubes, I received a very curt reply. “No more response will be forthcoming from NVG.” That was not exactly “happiness” to help me!

So, let’s at least analyze some of the important pieces of information that NVG gave us. 300degF! How can a transmission get so blazing hot? Many TDR members might say their NV4500 never overheated and that they monitor their NV4500’s with a temperature gauge. I posted a question on the TDR website; “Who has a temp gauge in a NV4500?” to get a response. TDR members reported seeing as high as 225degF pulling hard in hot ambient conditions and averaged 190-200degF pulling hard in normal temperate conditions. NVG says temperatures can reach 300degF. Why the discrepancy? Kevin Dinwiddie is a TDR member who works for LE (Lubrication Engineers) and is a Certified Lubrication Specialist by the STLE (Society of Tribologists and Lubrication Engineers). Kevin has worked in the oil business for over 22 years and responded; “An overheated condition does not always show up on the temp gauge. It happens between the gear faces with lugging or heavy loads and happens over time. I have not seen any high temps that are over 230 degF in any transmissions all the time. 230 degF is where the sulfur additive starts to have problems. Since you will not see the actual temps between the gear faces on your temp gauge then you will not know that you are having any problems.” So even with a temperature gauge, we can’t see the whole picture. We certainly can’t see what NVG can see with the test equipment specifically designed for that purpose. They did test it didn’t they? I think we all thought that the filled for life concept from DaimlerChrysler was “questionable at best”! It stems from the liability problem of demanding a specific lubricant and not supplying that lubricant to the customer for free. Making it factory “filled for life’ came out of the legal department, not the engineering department, and obviously is not in the customer’s best interest. The Magnuson-Moss Act is not the scope of this discussion, so we won’t go there.

OK, what about the repair companies that rebuild transmissions? Standard Transmission of Texas is a transmission rebuilder of countless NV4500’s. They tried some different lubes in the very beginning to try to offset some of these lubrication costs. Mike P. of Standard Transmission responds: ”When we first began rebuilding the NV4500s, we couldn't find a good reason to use the expensive oil. We advocated using 30w oils of various kinds to keep the cost within reason. We soon found out that the Dodge units HAD to have the Castrol, but the Chevys were okay with just about anything. The Dodge units burned the gears up. The reason we came up with is that the GM units just don't have enough engine to make them work as hard as a Dodge, so they wouldn't burn up. The Dodge is usually used much harder than the GM, so it builds up more heat. So actually, we never did any exhaustive testing, just trial & error that led us back to the Castrol..” I can understand why Standard Transmission experimented with 30wt oils. A lot of transmissions required just that. For example, between 1988 and 1991 either Synchromesh OR 5w30 engine oil was perfectly acceptable in the NV3500. The reason many manufacturers use motor oils is that petroleum gear oils frequently do not shift well at low temperatures. Motor oils and ATF’s are more fluid at these reduced temperatures and are not harmful towards the synchronizers. Unfortunately, these oils provide little to no extreme pressure protection. The shearing action of a manual transmission is much greater than the shearing action in an engine or automatic transmission. Also, a 75w85 gear lube works out to be closer to a 10w40 motor oil than a 30wt oil. When the relatively large amounts of torque produced by the mighty Cummins powerplant was applied to the NV4500, it simply did not have enough protection with engine oil it and it simply over heated.

Technically speaking, MT-1 is NOT a designated replacement for GL-4. GL-4, which contains some obsolete test procedures, WILL BE DELETED in the future and replaced with a new category. Industry insiders refer to this as the “GL-4 Upgrade”. This new category would also address the needs of light duty axles & commercial Synchromesh transmissions. The CURRENT RATING GL-4 IS IN FACT OBSOLETE!
I pointed out these deficiencies in the GL-4 rating to Ed Brown. His reply; “This gentleman makes a very good argument and he seems very knowledgeable on this topic. The API (American Petroleum Institute) recognizes that there are deficiencies with GL-4 quality lubricants, and has created a new category for ASTM to work on which will replace API GL-4. We often refer to this as the new manual transmission category or the "GL-4 upgrade." Because most of the tests specified under GL-4 are no longer available.” The GL-4 rating may be obsolete, but the GL-4 APPLICATION CERTAINLY IS NOT. Oil technology has advanced dramatically. We will have to wait for the new GL-4 “upgrade” to be implemented if you want to know absolutely, positively what you can put in the NV4500 as a safe alternative. Brown continues; “The quality of gear lubricants has improved tremendously over a relatively short time period. This is mainly due to improved additive technology. It is very likely that an old GL-4 lubricant (based on a non-thermally stable additive), at twice the additive treat level, would not meet both GL-5 and MT-1 performance requirements. However, a GL-5/MT-1 quality lube at half the additive treat level would meet GL-4 performance and benefit from improved thermal stability and copper compatibility.”

Empirical data suggests that certain synthetic GL-5/MT-1 rated gear oils will do the job, especially with their good copper compatibility. In one of my queries to Mr. Brown I pointed out the “cleanliness” of the new MT-1 category and talked about the corrosive nature of EP additives and their reaction with heat etc. I pointed to some empirical data suggesting a gear lube with a GL-5/MT-1 rating looks like a better choice than an ordinary GL-4. Apparently even Shell Oil has heard anecdotal claims that GL-5/MT-1 gear oils have performed well, but no OEM is confident that they will provide satisfactory field performance. Certain OEM’s have dropped their recommendation of long drain intervals to relatively short ones. GL-5/MT-1 gear oils work but no one feels comfortable with how long they will work. Brown explains; “Despite the fact that GL-5/MT-1 lubricants meet an ASTM D 130 requirement of 2A max. (after 3 h @ 121.1C) and GL-4 lubricants have a D 130 requirement of 3B max. (after 1 h @ 121.1C), we do not recommend GL-5/MT-1lubricants for GL-4 applications. GL-4 lubricants are frequently used in synchronized manual transmissions. These transmissions frequently have yellow-metal-based components such as synchronizers and thrust washers. We have heard anecdotal claims that GL-5/MT-1 gear oils perform well in these applications. Depending upon the drain interval, the duty cycle and the additive treat this may be true in certain situations. However, I would be concerned with pitting of the yellow metal when using a GL-5/MT-1 lubricant, especially with an extended drain interval or severe duty cycle. Note however that OEM's are not confident that a GL-5/MT-1 lubricant possessing satisfactory D 130 performance would provide satisfactory field performance. Therefore, Meritor does not allow use of GL-5/MT-1 lubes in their transmissions, and Eaton allows them in transmissions only with a fairly low drain interval (60,000 miles; on-highway service). Given the problems with transmission oil cooler corrosion (the coolers are copper), Eaton dropped its specification allowing for 250,000-mile drain intervals for approved GL-5/MT-1 gear oils, and recommends a maximum 60,000-mile on-highway service oil drain interval if MT-1 oils are used in their transmissions.“ Oh Mr. Brown, I love that detail! Now, that was “happiness” to help me!

Also remember that we don’t know how much EP additive is a GL-5/MT-1 rated lube. I did not find any test currently performed on gear lubes to detect the presence of EP additives. Which gear lube has EP additives and how much? We don’t know unless the manufacturer tells us. Dinwiddie comments: “I believe you are right in stating that there should be a test for buffer package amount or type and it's effectiveness over the long term. I do not know of any test like that but it may exist somewhere.”

We also don’t know what buffers are added, if any, to offset the corrosive EP additive. And if they are buffered, we don’t know how long these buffers may work. Dinwiddie adds; “I believe that you’re fighting an uphill battle, why? Because there is no way to determine if a company has used a buffer package or if the buffer package that they used will last for the oil change that the owner wants to go.” Kevin continues; “Yes the LE Gl-5 oils will reduce wear that a GL-4 will not, however, if it was my own truck, even I would use a GL-4---Why? Because you never know what you are going to have to pull or who might drive your truck and lug it or spring a leak and over heat it”

To confuse matters further, we don’t even know how much EP additives is in a GL-4 lube either. Brown states; “we often use the rule of thumb that an API GL-4 treat rate is half that recommended to meet the requirements for API GL-5. That is because API GL-4 applications do not require the high levels of EP performance (manual transmissions use spur of spiral bevel gears) and these high sulfur levels can be detrimental to copper compatibility. However, this rule of thumb is not the optimum situation, and this fact has finally been recognized within the industry.” Rule of thumb? That is not exactly a precise measurement, is it? Is any GL-4 safe or just the one the OEM recommends?

Is this risk really worth the reward? Brown continues; “Since applications calling for a GL-4 oil don't need the EP performance of a GL-5/MT-1 oil, the very real possibility for yellow-metal corrosion is not worth the risk. We suggest that customers follow the OEM lubricant recommendations for their equipment. If an OEM recommends a GL-4 lubricant, we would not recommend using a GL-5/MT-1 lubricant for the application.”

In spite of NVG’s lack of cooperation, we do know Syntorq LT is a very good gear lube, compliments of Castrol USA. Lubricants are often designed to provide a viscosity that is low enough for good flow characteristics in cold weather and high enough to provide adequate film thickness and lubricity in hot, high-severity service. When this hot and cold performance is required, a small response to changes in temperature is desired. The oil industry expresses this response as the V.I. (Viscosity Index). From the Data Sheets of Syntorq we find that it has a relatively high V.I. of 166. A high V.I. also indicates it is a better quality base stock to begin with. Lubes that have a high V.I. also have a lower sulfur content. Sulfur is also part of the corrosive equation that we need to avoid. Multigrade oils were first additized with polymers to increase the V.I. of an oil. Additives do not last the lifetime of the base oil, so the benefit of having a high V.I. without the additives are obvious. I also found out Syntorq is uniquely polymer free.
Specification SAE J306 was revised in June 1998 and became mandatory in January 2000. This is the first time that an SAE gear oil specification has had a shear stability requirement. It must meet the 100degC kinematic viscosity stay-in-grade requirement after a 20-hour KRL Shear Stability Test. It is quite possible many gear oils may fail to satisfy the new shear requirements due to a variety of reasons; for example, being formulated too close to the low end of the 100degC viscosity limit, or using a pour point depressant or viscosity modifier with insufficient shear stability. You guessed it, Castrol claims Syntorq meets SAE J306 too! And before 1998, Castrol used the Kurt Orbahn Shear Stability test on Syntorq to qualify its performance.

Trust me when I say my entire goal was to research a viable alternative to the OEM recommended lube. I had trouble finding any gear lubes even in the same viscosity grade. I only found one lube that even comes close in rheological terms and it wasn’t a GL-5 but a synthetic GL-4 specifically made for synchronized transmissions. Remember that the NV4500 is splash lubricated. There is no oil pump or filter in this unit, so the viscosity of the lube is extremely important and not all 75w90’s are created equal in that respect.
As far as base stocks, EP additives, buffer compounds and who uses what; knowledge is pure profit in the science of the lubrication industry and no one is sharing. There might be an equivalent gear lube at a more reasonable cost, but without a degree in petroleum engineering and the resources to test it, I won’t find it before the new GL-4 “upgrade” category comes out.

Syntorq is specifically tailored for the NV4500, no 75w90 GL-5/MT-1 I looked at even approaches it in rheological terms. It meets the new SAE J306 shear stability test. It has a higher V.I. than any of the GL-5/MT-1 alternatives I looked at and is polymer free. The NV4500 doesn’t need the extra protection of a GL-5, so why take the risk? It’s my opinion that Syntorq is the “Holy Grail” of gear lubes for our beloved under engineered NV4500. Unfortunately, Syntorq LT also comes with the “Holy Grail’s” price too! Well, what should you do? Use a less expensive GL-5/MT-1 lube (change it frequently to mitigate the risk), use the expensive Syntorq and be sure, or wait for the new GL-4 “upgrade” category to see what life brings us? Me? My only temptation would be to try a qualified synthetic GL-4 specifically made for synchronized transmissions, but I’m more inclined to just bite the bullet, pay for the Syntorq and not worry about a thing…

Your best dealer choice for Syntorq is General Motors. Ask any GM dealer for P/N 12346190. It will be substantially less than any Dodge dealer will. You can also obtain a wholesale price for Syntorq plus shipping charges from Standard Transmission of Texas.

Remember, “Tdrmbramr” and others that are experiencing good results with gear lubes rated GL-5/MT-1 have rolled the dice and won. My hats off to this pioneering spirit but can you be the same type of pioneer? For example, their frequent lube changes may have mitigated the corrosive chemical reaction that takes place over time under heat and pressure. “Tdrmbramr” changed his lube every 6 months or 100,000 miles, whichever came first. He also took the transmission apart and measured it! Will you? And what really was the duty cycle in these cases? How hot did they actually run? Were these lubes really put to the test? They are too many variables to objectively give these lubes the unconditional thumbs up. Rockland Standard Gear in New York is another transmission rebuild shop not happy with Syntorq cost. They also are using a GL-5/MT-1 gear lube marketed as their own private label “Rockland Standard Synthetic Gear Lubricant” with good success in urban fleet vehicles. But Rockland’s GL-5 has a 1B rating which far exceeds the MT-1 standard for copper compatibility. This also indicates that it’s very likely a mild EP version and would have a much greater chance of success than a typical GL-5/MT-1. I don’t have any more data on that lube to objectively comment further. These new generation synthetic GL-5/MT-1 gear lubes appear to work OR maybe it’s like the eating. It takes putting the wrong fluids and food in a body over time. It’s not like you eat one bad thing and BAM your sick with congested arteries etc! No, that takes time and that time varies depending on how that body is used. Then the end comes and you realize what you have done. But it’s too late…

If you currently use a GL-5/MT-1 rated gear lube, change it religiously and on a fairly short interval basis. You will be probably be OK in most situations. Is probably OK an acceptable risk factor? That’s up to you. If there is harsh shifting present under cold conditions until it warms up, your lube probably doesn’t have the correct viscosity characteristics and not flowing properly. What else might it not be doing correctly?

Research acknowledgements:
Southwest Research Institute, Inc. (SwRi) , Lubrizol Reference Library, Society of Tribologists and Lubrication Engineers(STLE), Don Johnson (NOT from Miami Vice but VP of Product Engineering @ Pennzoil Products Co SAE & STLE member), American Society for Testing & Materials, American Petroleum Institute, Ed Brown of Shell Oil Company, Kevin Dinwiddie of LE & STLE, Kenneth Koliba & Charles Armstrong @ New Venture Gear, TDR members participating in NV4500 OIL SURVEY, and the Wacky World Wide Web."

JoesC5

Torco MTF (manual transmission fluid) is a synthetic blend recommended for GL-4 applications, according to their tech sheets.

JoesC5

Some additional info on why GL-5 should not be used in transmissions, only GL-4.

Red Line MTL & MT-90 Technical Information
Presented by Jeff Lucius


The information and figures below are directly from Red Line's printed material and all rights are reserved by them. I present this information solely for educational purposes.

RED LINE MTL® and MT-90 are designed to provide excellent protection and improved shiftability for manual transmissions and transaxles. MTL and MT-90 have cured the problem of hard shifting in numerous transmissions which have notoriously difficult shifting. The secret to their success is two-fold. First, they have the appropriate coefficient of friction for most manual transmission synchronizers. Many gear oils, engine oils, and ATFs are too slippery for proper synchro engagement. Secondly, the viscosity characteristics of MTL and MT-90 allow proper shifting over the entire temperature range which the transmission will experience. The synthetic base oils used have a very high viscosity index which provides relatively constant viscosity as temperature changes. MTL is a low 75W, almost a 70W, at very low temperatures and a high 80W, nearly an 85W, at elevated temperatures, providing adequate viscosity to prevent wear and deaden gear noise. MT-90 is a thicker 75W90 version of MTL. The shear stability and oxidation stability of these products are excellent, thus the physical characteristics of Red Line MTL and MT-90 will change little with use.

Red Line MTL is classified as a 75W/80W gear lubricant satisfying the API Service requirements of GL-3 and GL-4. MTL also satisfies motor oil viscosities SAE 5W/10W/30, and the viscosity requirements for ATFs. MT-90 is a 75W90 GL-4 and also satisfies motor oil viscosities SAE 10W/1 5W/40. The additive chemistry used is non-corrosive, so even though they will provide GL-4 performance, they will not corrode synchros or bushings. Because of its low corrosivity, Red Line MTL and MT-90 could also be used in transmissions requiring GL-1 or GL-3 lubricants. Seal compatibility is designed to be similar to petroleum-based lubricants.

BENEFIT SUMMARY
Eliminates notchy shifting
Designed for manual transmissions and transaxles
Perfect synchronizer coefficient of friction
Enables high-speed downshifting
Excellent shifting even when cold
Eliminates gear whine and rattle at high temperatures
High-performance gear protection
Non-corrosive toward synchronizers
Satisfies manual transmissions and transaxles requiring motor oils, or GL-1, GL-3, or GL-4 gear oils

IMPROVES SHIFTING
Red Line MTL and MT-90 are able to improve shifting in most manual transmissions and transaxles. They provide a relatively constant viscosity as temperature changes and provides the proper coefficient of friction to allow synchronizer engagement. Most gear oils are very viscous at lower temperatures. This higher viscosity requires increased shift effort to move the synchronizer gears with the shift fork and to squeeze the oil from between the synchronizer cone and the mating surface attached to the gear. Without contact of these two surfaces, the gear speeds will not be synchronized and locking of the synchromesh gears will not occur. Excessive viscosity results in a longer time required to synchronize before locking occurs.

Viscosity of common lubricants at OºC (32ºF) is compared with Red Line MTL in the chart below. Note that the viscosity of ATF and 10W30 motor oil seems to be adequate. These lubricants are not well suited for transmission use because of two factors - shear stability and improper coefficient of friction - which will be discussed in more detail later. At even lower temperatures such as -17.7ºC (OºF), the differences between conventional lubricants and Red Line MTL are even more dramatic. At such a temperature many of these lubricants would prevent shifting into certain gears, depending on the design of the transmission.

All oils are slippery, and with most lubricated components, the slipperier the better, but this is not so with manual transmissions. The synchronization of shifting gears requires friction to transfer energy from the synchronizer, which is locked to the input shaft, to its mating surface attached to the gear to be locked in as the drive gear. Few modern transmissions use sliding gears to change gearing other than for reverse gearing. Synchromesh transmissions have the gear pairs constantly in mesh. The drive gear is selected by using the shift forks to slide a synchronizer ring, which rotates at the same speed as the input shaft, in contact with the selected drive gear. Once the drive gear is brought to the same speed as the input shaft, the locking ring on the synchro assembly is allowed to slide over and lock into the drive gear.

The time this process takes depends on how easily the synchro ring moves and the rate of frictional energy transfer between the two synchronizer surfaces. Higher viscosity lubricants slow the sliding of the synchro ring on the input shaft and require a longer time for the oil to be squeezed out from between the mating synchronizer surfaces. After the lubricant is squeezed out, the coefficient of friction of the lubricant determines the rate of frictional energy transfer between the two surfaces. Slippery lubricants such as hypoid gear oils can take too long to synchronize the gears, which promotes synchronizer wear. Red Line MTL and MT-90 has a coefficient of friction which is greater than conventional oils, allowing a quicker transfer of frictional energy. The graph below shows the desirable friction curve demonstrated by Red Line MTL compared to conventional lubricants. Note how the coefficient of friction is greater for the MTL than all others except the motor oil. Some motor oils have an adequate dynamic coefficient of friction, but most have problems with the static and low velocity coefficient of friction which can result in clashing.

Clashing of the gears (actually clashing of the synchromesh gears, since the drive gears are always in contact) can occur if excessive shift effort is used in order to shift the locking ring into place before the surfaces have achieved equal speed. It may also occur at the end of a reasonably smooth shift if an instability exists in the coefficient of friction, causing stick-slip to occur. In this form of clashing, the ring slides on the mating synchro gear, but a sudden slippage causes a grinding of the gears. In order to prevent stick-slip from occurring and the gear clashing which results, the coefficient of friction should inflect downward as the relative speed drops to zero.


GEAR AND SYNCHRONIZER WEAR PROTECTION
Most manufacturers of manual transmissions and transaxles recommend an 80W or 90W GL-4 lubricant. GL-5 gears oils which are required in hypoid differentials are not used in most synchromesh transmissions because the chemicals used to provide the extreme pressure protection can be corrosive to synchronizers, which are commonly made of brass or bronze. Typically, the use of a GL-5 lubricant in a synchromesh transmission will shorten the synchronizer life by one half. The extreme pressure, requirements of spur gears and helical gears found in transmissions are not nearly as great as found in rear-wheel drive differentials. A GL-4 lubricant provides adequate protection for most manual transmissions, unless a unique design consideration requires the extra protection of a GL-5.

The reason that many manufacturers have made recommendations of motor oils or ATFs is that petroleum 80W gear oils frequently do not shift well at low temperatures. Motor oils and ATFs are much more fluid at lower temperatures and they are not corrosive toward synchros, but they provide very poor gear protection. These lubricants provide almost no extreme-pressure protection. In addition, petroleum multigrade motor oils and ATFs have very poor shear stability. The shearing action by a manual transmission on thickeners is much worse than in an engine or automatic transmission. Within 5,000 miles the thickeners can be rendered ineffective and the transmission will be operating on a much reduced level of protection, as shown in the graph below. In hot weather these transmissions will whine and rattle because of poor vibration dampening and metal contact. Red Line MTL and MT-90 provide the excellent gear protection of a GL-4 gear oil in a synthetic lubricant which spans hot and cold temperatures and will not shear or oxidize with use.


DIRECTIONS FOR USE
Red Line MTL may be used in transmissions which recommend 75W, 80W, or 85W GL-4 gear oils, or SAE 30 or 5W/10W30 motor oils. If a 90W GL-4 or SAE 40, 10W40, or 15W40 is required, MT-90 may be used. If the transmission or transaxle requires an SAE 90 GL-5 gear oil, then Red Line 75W90NS or 75W140NS Gear Oil may be used. In transmissions which recommend Dexron or Mercon fluids we recommend our D4 ATF which is very similar to the MTL, being a GL-4 Gear Oil also. The D4 ATF will provide better low-temperature shiftability, and the MTL would provide better wear protection for racing use. MTL is not designed for use in rear-wheel drive differentials. Those generally require a GL-5 lubricant such as Red Line 75W90 Gear Oil. It is not necessary to flush the transmission before replacing with MTL. Remove the drain plug and drain while warm. Seal compatibility has been designed to be similar to petroleum lubricants, and leakage should be no greater than any other oil of comparable viscosity. Being formulated with extremely stable synthetic basestocks, MTL and MT-90 will last much longer than conventional petroleum lubricants. However, we do not recommend extended drain intervals, since without a filtration system, there is no way to remove metal shavings other than draining the lubricant. The regular maintenance intervals are also recommended to insure that the proper level of the fluid is maintained.

SWCDuke

Call Redline and ask them what they recommend for a vintage T-10 or Muncie.

You may be surprised at the answer!

Duke

JoesC5

GM Axle Lubricant, GM part No. 12345977, or SAE 80W-90 GL-5 is what GM recommends for rear axles, including the C5 and C6. For manual transmissions like the C5 and the C6 use, GM either recommends ATF, which is not a GL-5 lubricant, or, for manual transmissions, like the New Venture 4500 transmission used in their HD trucks,with yellow metal sycnro's, GM recommends their manual transmission lubricant GM part No. 12346190, which is a GL-4 lubricant. GM does not recommend a GL-5 lubricant to be used in manual transmissions with yellow metal scnro's. A GL-4 lubricant was recommended by GM for their manual transmissions when the original T-10's and Muncies were being used and that's what should be used if you want to save the sycno's. A GL-5 is basically a upgraded GL-4 with additional EP (extreme pressure) additives to handle the high shear forces that a hypoid rear axle design imposes on the oil. The GL-4 has 50% of these additives. A GL-4 can more then handle the low shear forces found in transmission gears and can also handle the moderate shear forces found in hypoid rear axles used in low torque applications like was found years ago. Why put a gear lube in your transmission that can damage it, when the proper gear lube is available? Using a GL-5 lube in the rear axles of the old cars won't hurt a thing as there is no yellow metal used in their construction, but a GL-4 can be used. If GM's recommended GL-4 transmission fluid (GM part no.12346190) can handle the torque of a modern HD truck with a high torque engine output, both GM and Dodge, it will handle the requirements of a low torque application like found in a vintage vette. For drag racing with very high horsepower engines and drag slicks, where high shock loads are encountered, the use of a GL-5 would be to an advantage over a GL-4. Sycro wear would not be a consideration in that application. I prefer to use a petroleum base GL-4 as it has more "tackiness" that will help the syncro's function properly, that the synthetics don't have, even though Red Line has friction modifiers to make their synthetic GL-4 less "slippery". The Sta-Lube and the Torco brands are both petroleum based, but the Torco has some synthetic stock added. I'll take Red Lines tech info for what it says. They recommend their GL-4 transmission lube in synco manual transmissions. Is it printed anywhere that Red Line recommends a GL-5 in the B-W T-85, T-10 or the Muncie M-20, M-21 and M-22's?

JoesC5

Additional info.

Varian EP Gear and Transmission Oil GL-4
A highly refined shear stable gear lubricant suitable for most of the limited slip rear axels.
Recommended for most gear transmissions and final drive applications. It is strengthened to prevent wear, rushing and foaming.
The winter grade is almost fluid at -22C.
Made according to MIL-L-2105 B and API
service GL-4.

PM 103 PM Synchro-Gearlife L.V. SAE 75W85
API, GL4, MIL-L-2105B, MIL-L-2105C, MIL-L-10324
Manual Transmission



API SERVICE DESIGNATIONS FOR GEAR OILS

Classifications
Type
Typical Application

GL-1
Straight mineral oil
Automotive manual transmissions (tractors and trucks)

GL-2
Usually contains fatty materials
Worm gear drives industrial gear oils

GL-3
Contains mild EP additive
Manual transmissions and spiral bevel final drives (GL-3 not widely used)

GL-4
Equivalent to Obsolete MIL-L-2105

Specification. Usually satisfied

by 50% GL-5 additive level
Manual transmissions spiral bevel and hypoid gears where moderate service prevails

GL-5
Equivalent to present MIL-L-2105D

Specification. Primary field service recommendation of most passenger car and truck builders worldwide
Used for moderate and severe service in hypoid and all other types of gears. Also may be used in manual transmissions

GL-6
Technically Obsolete – Same performance as Ford M2C105A (Still in use for Ford light trucks)
Typically recommended in service conditions where more anti-scoring is needed than provided by GL-5 lubes

JoesC5

Additional info: notice that the gear oil rated for GL5 service is for SEVERE duty, where as the gear oil rated for GL-4 service is for normal service which was/is the case for vintage cars with manual transmissions and hypoid gear rear axles such as the C1 and C2 corvettes. The reason the GL-5 gear oil is able to take the SEVERE use is because it has twice the amount of EP additives as the GL-4 gear oil, but the extra EP additive is hard on the synco's, cutting their life in half compared to using a GL-4 gear oil. Use what you want, but the GL-4 gear oil is all a vintage transmission requires and will not harm the synco's. Besides. GM still recommends using a GL-4 gear oil in their synchronized manual trnsmissions except for those that are designed to use ATF, which is not a GL-5 gear oil either.


SPIROL EP
These oils are designed for use in gear boxes and rear axles where Extreme Pressure properties are required, particularly for Hypoid and bevel gears.

Performance Specification

Meets IS:1118-1992, US MIL-L-2105, API GL-4
Recommendations

Gear boxes and rear axles of the vehicles. Multigrade oils are recommended for hypoid and bevel gears and are suitable where ambient temperatures are low.


SPIROL XEP 80W
These are heavy duty Extreme Pressure lubricants meant for high load carrying, high speed. High torque service and recommended for axles with hypoid or bevel gears and steering boxes, where bulk oil temperatures can reach upto 150°C.


Performance Specification

Meets IS :1118-1992, US MIL-L-2105D, API GL-5 specifications.
Recommendations

Gear boxes and rear axles of the vehicles operating under severe duty.Multigrade HD Extreme Pressure lubricants are meant for severe operating conditions of axles with hypoid or bevel gears and steering boxes boxes. Ideal for low ambient temperatures.

JoesC5

maybe this will help

API класификация за трансмисионни масла (лубрификанти)

Име Описание Приложение
GL-1 Чисто минерални масла Трактори и комерсиални превозни средства с ръчна трансмисия
GL-2 Масла съдържащи мажещи съставки Индустриални трансмисии за червяци
GL-3 Масла без антиизносващи добавки (Много високи налягания, т.е. Extreme Pressue - EP) Ръчни трансмисииКонични предавки под по-малко натоварване
GL-4 Масла със средно ниво на ЕР добавки - еквивалентини на MIL-L-2105 спецификация Ръчни трансмисииХипоидни предавки под средно натоварване
GL-5 Масла с високо количество на ЕР добавки - еквивалени на MIL-L-2105 D спецификация Хипоидни предавки под високо натоварване. Могат да се използват за ръчни трансмисии