wmf62

the premise of the quote in bold type is that GL-5 is not always downward compatible (kinda like Windows 10 won't run all Windows XP programs, BUT some it does.... ).

as an example, my MY6 transmission had synchro clash using GL-4 but worked perfectly with ATF, apparently GL-4 was too 'slippery'...

right now i'm trying to find the right lube for my Keisler SS700; I don't think GL-5 is the answer, and i'm not sure what it is...

one size doesn't always fit all...

Bill

tuxnharley

...... and so we have yet another topic to add to the contentious list of "my product of choice is better than yours" debates.

I think maybe I'll start another thread to develop a master list of all those topics - no debates on the merits, just a listing of them

Nowhere Man

For most it's I payed more for that product so it's better then your cheaper product of the same ratting

SWCDuke

I wrote Mil-L-2015D (actually the suffice was B in the fifties and sixties)/SAE 80W-90 GL-5 because the latter is the modern equivalent of Mil-L-2105.

So let me restate:

All vintage Corvette three-speed, T-10, Muncie, Saginaw, and Super T-10 four-speeds were factory filled with oil that met the requirements of the then current Mil-L-2105 revision.

The milspec was cancelled decades ago and replaced with the SAE 80W-90 GL-5 API spec, so the latter is the modern equivalent of the old mil spec and should be used to service these old design transmissions.

Beginning in the early to mid-seventies GM service manuals reflected this change by recommending SAE 80W-90 GL-5 for older design manual transmissions that specified the milspec in previous years.

Duke

SWCDuke

I don't know what was used in prewar transmissions or axles. I have only addressed vintage transmissions for post war GM cars that specified Mil-L-2105, and believe the entire auto industry followed suit.

If you have a older non-GM car you'll have to research the original spec and then determine the equivalent modern spec.

If you have replaced the original transmission of a vintage GM car with something different, consult with the transmission manufacturer.

Duke

4speeds

So here is my take. Yes in "theory" GL5 can corrode yellow metals but only if you boil the oil. The only corrosion you will get is a tarnished ring. I have never seen damage to rings using conventional Gl5 fluids.

You will not get corrosion. If anything its a play on words. The ring can just turn to a black color. I've seen black rings typically when transmissions get overheated, possibly with a GL5. But they still work, but just were discolored.

Marketing 101. If you can get someone to switch to your brand because it is better it may be possible you will use their engine oils and diff oils as well. That's how it works. As a result you will notice that in the past 2 years oil companies have come up with specific GL4 oils now to jump in the game. It's this perpectual banter on forums that helps market it even further with people cutting and pasting data sheets and feeling smart about their internet research.

I've built 1000's of transmissions and never seen any proof of this problem. I've always recommended Valvoline conventional gearlube or Royal Purple Max 75wt because both have worked well especially Royal Purple in our endurance transmissions which are non cooled and subject to extreme heat.

However because of forum banter people are asking for GL4 because of what they read on forums. So, I carry the Brad Penn GL4 as well as the Driven Racing Oils GL4. I have done extensive testing with both oils and drivers say they feel smoother shifting with the Driven oil GL4

When it comes to motor oils, you are basically using a lighter weight oil and will feel the benefits from it in terms of shifting and cold weather. You won't see it used in Nascar but you will see lighter weight "qualifying" oils used only for that short run. Transmission journal clearance, gear backlash , and oil flow dynamics all come into play when choosing the right viscosity. Example the T5 5 speed used conventional Dexron III. People who decided to use 90wt lube in them usually ended up with burn't up pilot needles because the higher viscosity couldn't flow through the small oil bleed holes on the input shaft. In regards to motor oils being used, I've noticed that units where people used a 50wt oil ended up with more scuffing on the gear teeth in race applications compared to Royal Purple 75wt Max or the Driven GL-4 which both show no signs of galling or scuffing. Keep in mind these transmissions are getting hot and running sometimes for 6 hours at 100 plus MPH speeds.

Take care,
Paul Cangialosi
GearBoxVideo.com

4speeds

The clearances of that transmission were designed to work with Dexron based ATF not conventioanl gear lube

SWCDuke

The statement does not apply to vintage transmissions that were designed for Mil-L-2105 oil. The current replacement for the milspec is GL-5, not GL-4.

Duke

Workin On 59

Well this has turned into an "interesting thread".....So, not to muddy the waters but to throw in another Muncie lubricant option, I am currently using 50 wt. Valvoline racing oil in a Muncie M-20.

The transmission man I had rebuild the M-20 with a new Muncie super case back in 2002 highly recommended the Valvoline 50wt. I thought that was a bit unusual as I had always used a 80/90 wt gear lube in manual transmissions, but I followed his advice.

The transmission is in our 79 L-82 and it is silky smooth shifting and very quiet. We have only driven it a few thousand miles since 2002 but I am very satisfied with the results to date. One thing I have noticed is really easy shifting when cold and it also works well in hot conditions when the gear lube gets heated up.

Just my experience with one Muncie...... Doug

PAmotorman

we used 30W motor oil in them for drag racing and never had a transmission problem

TCracingCA

I personally would rather measure my bearing clearances and determine the oil to use! There are some charts on this type of stuff! New engine rebuilds should be done targeting an oil viscosity. Example would be the clearances in modern cars with synthetics are generally tighter, leading to longer life. The multi viscosity oils like a 5w-30 are common on many stock cars which allows for less warm up needed to get cold flow and protection. I am trying to write the above in the very simplest explanation, as there are plenty of high tech explanations to read online!

But in real world and with real people, I would hook up a very new modern quality oil gauge and test the pressures throughout operation or the ability to hold oil pressure, with different weight oils. The primary thing I worry about is the ability of the oil layer to be at a high enough pressure, so keep a film or layer on rotating parts, and then sufficient to keep the valve train lubricated and take heat away.

MikeM

After reading through all 91 posts on how to "out think" the guys that designed the transmissions, I think I'll just leave the 50-55 year old transmission grease in the several four speeds I have.

They don't leak, grind, growl or scrape so why not?

GTOguy

FYI, motor oil dues not have the HP additives that gear oil does. New motor oil doesn't even have the zinc and Phosphorus. Many old motorcycles I had back in the day used motor oil in their transmissions. Back then, it had plenty of ZDDP additives....not so much these days. A whole 'nuther rabbit-hole to go down! I personally would not run anything but gear oil in an old T-10 or Muncie. YMMV........

SWCDuke

What does engine oil have to do with a thread on transmission oil?

Duke

SWCDuke

Your statement is utterly false! Current S-category oil is limited to 800 ppm P, and C-category is 1200, which is about the same as dual rated oils before the first P limitation showed up for SL. For a given P concentration the Zn is about 100-200 ppm higher.

Where have you been for the last 10 years?

Duke

wmf62

Mike

BECAUSE it is not the latest and greatest.... ...and the reason you remain a "deplorable", and an "ordinary' one at that....

Bill

wmf62

I agree, and, at this point, i'm still searching for the correct lube for my SS700. apparently the synchro rings are not brass, so I don't have a clue what the best fluid should be to eliminate synchro clash...

Bill

GTOguy

Obviously, not spending enough time hanging out with you, Duke. Sorry about that. What I meant to say was that the new oil does not have as much ZDDP as the old stuff. In the '80's, when I serviced Honda Accords and Civics, the transaxles specified 10/40 motor oil. Using regular 10/40 motor oil today in the same cars could result in damage from the lack of ZDDP in regular, car-spec motor oil. Love and healing to you, and all the best.

wmf62

Bill

Workin On 59

I have a quart of the 50wt Valvoline racing oil left over from 2002. It contains friction modifiers and ZDDP......Current 50 wt. Valvoline might be a different formula without the ZDDP.

Doug