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I mentioned in a thread a couple of weeks ago that I would be getting in a couple of new Eaton posi's to use. I don't usually post long pictorials anymore and for several reasons but a few people have emailed or PM me to ask about them and if I would explain some things about them so here you go. For new posi's there are Auburn Cone, Eaton clutch type, Yukon clutch type which is a knockoff of Eaton's design and I believe Yukon was sued over it. I like and use Eatons so that is what this will be about. Eaton made them for GM and those were made in the USA and slightly different then the new loaded cases sold today from any Eaton distributor. As with any new part you may find a wide price swing on them depending on where they are purchased. For this example Summit sells them for $635 loaded but I suggest you call other suppliers as well, Tom's, Zip, Van Steel, Bairs, or any non vette Eaton distributor can sell them.. The nos base cases made for GM are no longer available and finding one is not easy with pricing about $600 for the bare case. I would use a nos USA made case as first choice if you can find them. I have a couple left but not for sale.
So if you decide to rebuild your 63-79 diff and open it up and find this, then you have to get a new case. This one is extreme most will have a small crack in the large window radius or by the cross shaft hole if they are bad. Any cracks found in a case makes it junk, do not attempt to weld or drill it, it will fail in use.
The new Eaton cases are pretty good. They are cast in China and assembled in Mexico.
Now these come loaded, meaning they are supposed to be ready to use out of the box. They have powder metal spiders, fiber coated clutches, hd spring pack as you can see in the pictures. Many places will do just that, bolt on a ring gear and install it. Saves a lot of time and increases profit. Customers are only told a new posi was installed so everyone is happy. You can do that as well but I take them apart and these 3 are good examples of why I take them apart. They were assembled in July 2021 so they were only 2 months old when I got them.
With these 3 I found the same thing. The cross shaft was very tight in the case, it should be a slip fit. Once the spring pack was removed the lash on the spiders was pretty sloppy. The last time I used a spring pack in a posi was about 15 years ago in one of these new cases. I never use them. So these would have worked, the spider play would have been assisted by the spring pack and the fiber clutches just smudge once loaded so they will be smooth, as they wear away. If that is ok with you then you bolt on your new or used gear and assemble it.
The inside edge of the large window is cut back on the new cases to allow the spring pack to fit in better I am assuming. The USA cases were thicker at this point and I prefer that but you don't have a choice, that's how they have been cast for the past 15-20 years but interestingly back then the USA ones were still available from any GM dealer and still had the thicker wall.
The first picture shows one of the new cases, sharp edges, burrs, and the cut back. The second picture is after I blend, radius, and polish them so it shows the cut back in better detail
They do come with the flange holes countersunk so you can use ARP bolts. If you use an old or NOS USA case you have to do this if you use ARP bolts, which I recommend over the plain grade 8 bolts that come in master kits.
Here is a fiber coated clutch. The contact pattern is smaller then using the solid steels. I never use these clutches, only solid steels, but that is your choice.
Here is a comparison of the new and old style spiders. You can see the difference in the teeth and between powder metal and cut gears.
Here on the left is the powder metal spider with fiber clutches, just as it is out of the box. On the right is the new cut spider with solid steels. The stack height is the same. However the added thickness of the fiber material doesn't allow the case to hold the same number of clutches, so the clutch pack has one less pair per side. I use the solid steels and get more in the same area.
Here is the assembled cases, one with new 10-17 cut spiders, the other with the powder spiders. Both are built with solid steels and tuned on my machine. The action is smooth and snug on both and there is no lash.
So I hope that answered those who asked me to post this information. Both of these are going into street cars that are not going to have 500+hp and be abused at the track. These improvements made them better but don't forget that anything will break with enough abuse and power. There won't be any fiber floating in the oil and if you have one of these already and drain the oil expect it to be black.
Brought this thread back from last year for two reasons:
1- Guys still think buying a loaded posi is the best way to replace a broken one or someone talked them into it that is either a seller or clueless.
2- I just inspected another new one today
So, the one today is pretty much like every other new one I checked- sloppy and it's covered up with the huge spring pack. This one the cross shaft didn't have to be tapped out, they should slide out easy. With the spring pack out, I checked the way the spiders were setup. There was 025" endplay in each side gear. To compare this to a correctly tuned posi, and the word correctly is important here, there is no endplay or lash.
The loaded posi will work. Anyone that installed one and says they have no noise I do believe them. What they don't know is that 025" endplay is going to continue to open up on every turn they make. The spring pressure is keeping the clutches quiet by smudging them away. The oil will be black and once the fiber is gone there won't be any posi action.
I recall about 20 years ago, asking my friend Tom about the "new" clutches. They installed a set in a customer's car who drag raced it a few times and pulled the diff for inspection. Anyone who knew Tom would understand his answer "Dude, the fiber came out with the black oil"
So, for those who don't do their due diligence on what they use or someone else uses in their diff, good luck. I still get calls asking, "why does my, (cheap), rebuilt diff have black oil, I have a new posi?" Maybe this will help someone, maybe not.
Gary, Your information is very valuable to the Corvette Community (Especially C2/C3).
As cast-iron differential parts Availibility continues to change and shrink, rebuilding one of these differentials to OEM or an upgrade specification is becoming a big-challenge. Your experience captures both Your drive for perfection and the experience brought from countless multiple unit operations. We are all fortunate to have Your skill & knowledge displayed on this Forum. Hopefully someone on this Forum that is smarter than myself is preserving Gary's Posts, photos and all.
Again - THANK YOU Gary for Your time, skill and professionalism.
Thank you, glad to help if I can.
Yes a lot of the good parts are getting harder to find, add in the con men still out there with their scams, and the fact most don't know how to do custom work anymore so yeah things have changed a fair amount in just the past couple of years.
Thank you, glad to help if I can.
Yes a lot of the good parts are getting harder to find, add in the con men still out there with their scams, and the fact most don't know how to do custom work anymore so yeah things have changed a fair amount in just the past couple of years.
Has anyone designed and sell an aftermarket forged or cast case for the C2-3?
How about adapting a Ford 9" case to a C2-3?
Yes the MW case has been discussed before and I suspect there is not a huge demand for it other then diehard track users who have already moved on to spools or a complete different rear suspension. While it is a good piece I can't think many are going to pay that kind of money for a bare case. Maybe, but life long experience with these cars and owners tells me otherwise.
Many forget or just don't know when they drop in an a new engine with 2-3x the power and torque of the original that everything south of the flywheel needs attention. Some will go by the theory of replacement once broken, others will get the best systems they can but in the end power and abuse will determine what and when things fail, and they will.
Yes the MW case has been discussed before and I suspect there is not a huge demand for it other then diehard track users who have already moved on to spools or a complete different rear suspension. While it is a good piece I can't think many are going to pay that kind of money for a bare case. Maybe, but life long experience with these cars and owners tells me otherwise.
Many forget or just don't know when they drop in an a new engine with 2-3x the power and torque of the original that everything south of the flywheel needs attention. Some will go by the theory of replacement once broken, others will get the best systems they can but in the end power and abuse will determine what and when things fail, and they will.
Learned that lesson helping my big brother modifying his 74 Camaro when we were in high school. Engine had headers added, dropped in a solid lift cam, put on a set of 1.92 (96? long time ago) fuelie heads, and topped off replacing the stock 2 barrel carb with 4 B that was likely overkill from Holley. Also put a shift kit in the TH350. That was the first thing to blow. So, dropped in a TH400 with shift kit. That snapped the drive shaft. So, put in a custom made replacement. Then the engine blew when a valve lock couldn't handle the stress from the solid lift cam. We didn't know they made heavy duty locks. Then he replaced the engine with a 400 small block which could be had for $50 back then (25 hours work), sold the Camaro, and bought a 280 ZX which he drove for many years just as the factory had built it.
Last edited by vince vette 2; 10-17-2021 at 03:23 PM.
FYI
Opened another new in the box Eaton and found it like the others. The cross shaft had to be tapped out and now I will have to fit it correctly. So, if you guys are buying new posi cases you better check them and if someone installs one for you then I would be asking a lot of questions before they start.
Now this is better then being too loose for sure but still not right.
Brought this thread back from last year for two reasons:
1- Guys still think buying a loaded posi is the best way to replace a broken one or someone talked them into it that is either a seller or clueless.
2- I just inspected another new one today
So, the one today is pretty much like every other new one I checked- sloppy and it's covered up with the huge spring pack. This one the cross shaft didn't have to be tapped out, they should slide out easy. With the spring pack out, I checked the way the spiders were setup. There was 025" endplay in each side gear. To compare this to a correctly tuned posi, and the word correctly is important here, there is no endplay or lash.
The loaded posi will work. Anyone that installed one and says they have no noise I do believe them. What they don't know is that 025" endplay is going to continue to open up on every turn they make. The spring pressure is keeping the clutches quiet by smudging them away. The oil will be black and once the fiber is gone there won't be any posi action.
I recall about 20 years ago, asking my friend Tom about the "new" clutches. They installed a set in a customer's car who drag raced it a few times and pulled the diff for inspection. Anyone who knew Tom would understand his answer "Dude, the fiber came out with the black oil"
So, for those who don't do their due diligence on what they use or someone else uses in their diff, good luck. I still get calls asking, "why does my, (cheap), rebuilt diff have black oil, I have a new posi?" Maybe this will help someone, maybe not.
Brought this thread back.
Maybe this will help someone, maybe not.
,, Thanks again Gary, for all you share with us. This certainly should help someone who really thinks, and cares about what it takes to do the job 'CORRECTLY'..
So happy to have you in my contacts,,,
i can verify Gary's fiber clutch advice. I had a shop rebuild mine with fiber clutches because they said that's all they could get (covid excuse), but the end play on the differential quickly returned and noticed the diff oil was black when I did the first change. This was using an excessive amount of limited slip additive to an already formulated limited slip diff oil and the normal spring pack.
I don't really push my car, so I didn't think it would make that much of a difference, but this is after less than 1000 miles, and I have to think the rear suspension is suffering as a result of the end play.
I really should have just waited however long it took for the solid steel clutches to be back in stock, and I've been regretting it since.
The main reason I was rebuilding mine was I swapped ring and pinion from the stock 3.08 to 3.70, as I was going from a TH400 to T56. You always have to find a silver lining in life, so maybe this will push me sooner to go to open it up again, get a new carrier and go to 4.11
I have had people tell me I am harsh with my statements and responses. That you can't setup a posi without the spring pack. That I don't know what I am talking about. That the 80-82 Dana diff's were good. That carbon Fiber clutches are the best out there.
I used to get fired up but don't anymore. If some think as above that's their choice to do so and I can't help them. I know I have helped a lot of people with their cars and saved them a lot of money and stress, but there will always be the naysayers that know more than anyone else.
Again, good luck. If you think you got a good deal on a diff, box, TA's, etc I'm happy for you. I am on the other side of the fence and see how many of those builds really are since many end up coming my way to fix.
That was a general statement, not directed to anyone in particular.
To Mongoose, your clutches started smudging away the first corner you took. There are only 14 total in your posi not the 18 that solid steels have and that don't wear down a lot. In addition to the fiber turning the oil black, they are getting thinner and thinner. If you used a new out of the box posi, it was sloppy to begin with. If you used new fiber clutches and tried to tune the posi correctly it's not going to work. Solid steels have been backordered a lot, they are right now in fact. Some places may have them in stock, I usually have them in stock but won't sell them directly if they are backordered as they are today.
PS good luck finding 411's. US Gear is gone, they made the thick 411 for 20 years for Tom's. The only one that makes the thick 411 now are Yukon, who knows it and jacked up the price of everything they sell. Motive only make 355 & 370, Richmond I wouldn't trust and some of the "new" gear suppliers are just reboxing Yukon or Motive.
I think Gary's points futher support the fact that so many Corvette owners never drive their cars.....you can buy junk from any big name vendors...or internet experts,......and if the car sits in a garage, only to be driven once a month to some parking lot car show.......it really doesn't require much in terms of build integrity. It has to be the explanation why so many vendors are producing junk,.....selling it, and it never coming back to them. Just like the flat tappet cam issues discussed recently......same thing. Quality can only be judged by use. Add to that....think about the numbe of "projects" that get started, and never finished, or at a minimum, take years to be back on the road. A differential built three years ago......sitting in a garage on a bare frame....that won't be driven for another five. By the time the parts fail....no warranty left.
You want stuff built right....you have to find the right people. Gary is the right person for differentials, steering boxes, and trailing arms....and probably for anything else he would choose to build.
10-16-2021, 10:27 AM
New Posi Case Review
