This is just a general question for the group. I will be going to Carlisle next week and intend to ask some of the experts who rebuild diffs but I'd also like to hear from the forum regarding your experiences. I have a stock rear end with a 3.70 ratio that I intend to reinstall this winter. Before I put it back I will install new seals so the yokes are out now. My question is, how much end play should be present in the side yokes and if it is deemed to be too much, is it OK to install a shim behind the snap ring to take out some of the play? I set up my dial indicator and measured 0.067" end play on the right side and 0.077" on the left side. It just feels loose to me and it may not matter if the clearance is simply forced hard up against one side during normal driving, but I would think it would move side to side during cornering. Thoughts?

 

Here is a good thread i learned on.
https://www.corvetteforum.com/forums...ay-advice.html

 

Gary Ramadei (gtr1999) is the resident expert on these differentials. Search the forum for his posts and you will learn everything you would ever want to know about them.

The play you are describing is indicative of the axle tips wearing due to their being too soft. As you will learn from Gary’s vast experience, GM’s QC started down a slippery slope in the 70s and poor heat treatment of the stub axles in the C3 differential was one of the victims. Unless you address the root cause of the problem, anything you do to compensate is a band-aid. Something in the range of 0.005-0.007 is the target but you have to have dimensionally correct (and properly heat treated) axles to begin with.

 

Good luck speaking the differential experts at Carlisle.

I was in Waterford at Harkness state park Sunday, great part of the state.

I just made shims to cut down the endplay in axles I had hardened and only had to cut 012" on If you have truly the amount of endplay you say you have issues with the posi and or the axles, but ask the experts in PA.

 

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, Am I detecting sarcasm,, slightly maybe???.
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Man,, im so glad we have your experience and knowledge Gary. Ill sing your praises always. 🥰

 

i believe there may have been a hint of disdain towards the experts at carlysle in his tone. Gary doesn't usually take that tone. so i would hear what the experts say but don't spend any money. if my diff were that loose i would ask gary when he could get to it.

 

With that much play you're through the hardening of the stub axle ends and wearing the soft inner metal. Any shims at this point is a very temporary fix.

 

ok, i have never messed with a diff...yet. you have lots of end play cuz the ends of the stubs wore off rubbing on the cross shaft. why is it you cannot shim the stubs outward so that they do not go in far enough to continue rubbing on the cross shaft until the c-clip outer edge wears off and the clip leaves?

 

The C2/C3 rear suspension has no upper link which means the weight of the car is pushing the half shafts and stub axles into the diff. There's no shimming that can prevent this. The shims that are being discussed are "on the other side" (diff clutch packs) and prevent the stub axle from pulling out as much. So shims decrease play, but takes it from the opposite side of motion.

Since the stub axles are only surface hardened they wear fast once you're through the hardening.

 

Very perceptive comments. It may, or may-not, matter.

As several have said you probably have stub axles that are worn part way down to the c-clips. With the cars weight on its wheels the stub axles will be in contact with the center pin, hence zero play. You could adjust your camber to correct. They will rub and continue to wear. The rubbing occurs only when you are going around a corner. Now if this is a car that sees very low mileage per year it may not matter to you. You may be around the point where you are through the case hardening , and wear would increase much faster from this point on. But it probably took 100k miles to get to this point, so you can probably get another 10k-20k miles out of it, although It will continue to get worse.

However, second point, if you drive it hard, in a corner, at somewhere around .75-1G the cornering traction at the rear tire patch will suddenly overwhelm the vertical force, at a tipping point, and your yoke will quite suddenly extend outward until it hits the c-clip. This will cause a quite sudden increase in rear positive camber of around triple the yoke play, so around .20" of movement at the tire tread, causing the camber to change around 1 degree positive, decreasing cornering traction, and causing toe-in changes as well, and the sudden tire unloading and clunk you will be able to both feel and hear. Worse case is you feel sudden oversteer. You are correct in that below .5 -.75G this should not happen due to the cars weight keeping yoke/pin in contact. Once the c-clip is worn off, that would cause even more drastic camber changes in a corner. There is around .185" of axle past the c-clip. There was even a go-pro video of this sudden movement on-line somewhere.

Basically it is not right, and how much trouble you want to go thru to fix it is your call, and in part depends on how often and how hard you drive the car. Cruiser? Push it hard? Or race it? Feels squirrelly?

Good luck in your decision. This is a common achilles heel problem with these cars, and many of us have to go thru the same mental decision process. I intend to drive mine hard, and race it, so I got mine down to .001-.002" with Gary's help. I did the entire diff blue-printing process myself (PITA), and I still spent $1000 in parts. But it would have been 3-4-5X that costly if I had paid someone else..... But mine is blue-printed, tuned, and strengthened, far beyond a typical "rebuild". A typical $1000 "rebuild" just does $100-200 worth of seals & bearings and does not really fix the yoke end-play issues. New aftermarket yokes run a few hundred and many of them have horrible quality. Contact Gary if you need quality work or parts. He is the premier expert in restoring these diffs. He is a machinist and will rebuild it to any performance level that you desire. But just beware, it is a slippery slope deep into the proverbial "money pit".

 

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.Awesome, simple explanation 👏 👍

 

Leigh,
No one else would build it like I coached you on, they would charge you a lot more as you said but the work would not be the same. I have seen it way too many times and every single one of them were overpriced junk. You did good kid.

 

Hi Teddy, hope you're well. Sarcasm, me, nah!

If I really went 100% and told the truth on what I know and what I have repaired from many of the "experts" out there I would probably PO a few people and make others wonder what they overpaid for.

I will say and I think you can confirm -anyone who has met me, been to one of my seminars at Carlisle, visited me in CT, leaves knowing more about these diff, than anyone you're going to find this week in PA. I will bet a nice dinner on that, but than what do I know.

 

Ah grasshopper you may approach this job and do it. I say this and wonder if people know to whom I am referring, it's an age thing.

Ok so here is the deal on axles from 1963-79.

The axles were all the same from 63- 67/68 when the so-called HD axles started showing up in production. I have the original specs on the axles but I am not listing them here. I will say the axles were hardened correctly from 1963-about 1970. Then GM must have decided to go cheap and the axles were case hardened which is about 030" deep.

So, Joe Corvette buys a new corvette between 1970-79 and drives the car. All is well with the axles until about 40-50k miles are clocked on it. Many times, Joe Corvette sold the car a year or two later or blew up the diff racing it. By the time the 40-50k miles are on it the case hardening has worn away, leaving a soft face riding up against the hardened cross shaft at every corner. As mentioned, the axle, 1/2 shaft into the outer axle makes up the upper link in the IRS. This works fine as long as the parts are good and dialed in, with the C3's wearing down the axle the endplay increases and the play in the suspension increases. Now many geniuses out there, yes this is sarcasm, drove the cars as the axles worn down to the point of hitting the differential, some grinding into the seal bore lip, then the seal and sometimes with u-bolt axles, they cut into the ears of the housing. By that time the diff is wrecked, leaking oil all over the underside of the car.

So the cottage industry was born rebuilding worn axles. It was a great idea however you do need to have something some of the rebuilders, past and present, didn't think of- QC. Anyone who has ever working in industry knows what QC is and how it is an important part of what ever you are making. There is a problem when you buy say 10 rebuilt axles and 5 fail inspection. The 5 that passed worked great. Then you have those that have different methods of rebuilding them, there are much less of these rebuilders today. Same thing happened with SS lined calipers 40 years ago. There were a lot, now not so much but the QC was better 40 years ago.

One of the things I show in a seminar is a before and after version of a rebuilt axle. This one is what I call a cored axle, I would not use a cored axle on a go cart yet they have been sold for many years continuing to this day. If you have been to my shop you know what this cored axle looks like and you would not want it.

Next are the new axles sold today, they're imported as far as I know. All the ones I checked in the past and again this past Winter were hardened but the snap ring groove is wrong. Again, lack of QC shows up. This past winter a good friend of mine was finishing up a 63 SWC he built and gave to his wife. It is not an NCRS car, it has a 69 Diff and 65 TA's. I helped him build them and showed him many things in the process, He knows more than anyone in PA. Anyway, he needed axles as his 69 were worn or maybe had been replaced many years ago. He bought a set from a well-known vendor, one who would complain about me if I mentioned their name. He asked me to check them. I had a stone stock spring loaded posi on the bench and just finished tuning one. So we tested them, out of the box, in both posi's. With the stock one the endplay was 045"- that is beyond bad, it's in the lousy range. Next we put them in the tuned posi and they were still out 020"- this is in the bad range. I had a couple more of them come in and the same results, the only difference was they were purchased from a different vendor. See the way things are going here?

I referenced shimming. Now there is shimming in the posi as Marcus started but that is not what I was going to do. In this case since I know the QC on axles I wasn't going to go through that again. This was a 65 diff and the axle may or may not have been original, but they did have about 015-018" endplay in them, in a tuned posi, and that was not going to leave my shop like that. I hardened them and, in this case, ground some steel arbor shims to use to shim the axle inward 020" Next, I parallel ground the snap ring for square shoulder on both sides and dialed in the endplay to 005-007". I fit them and checked that they slide smoothly in the groove, as they should. I have seen wrong size snap ring forced into axles and they would not move, they were loaded and most likely popped off in use. Mine were not loaded, fit square, and I dialed in the endplay where I like it. They should outlive me and many other of us.

Now I hope you understand a little more about axles, some of the "experts" may see this as well. If you go you might want to ask some about this, or what a tuned posi is, maybe if they check the bearing caps and fit them, if they check posi cases for cracks and how they address them.

Sarcasm, no - just the facts Jack! again showing my age.

 

Awesome post Gary! I always learn something new from you. And "we" appreciate it.

And the "grasshopper" quote is spot on.
You see guys, I learned a little bit about Gary during my mentoring and subsequent shop visit, that many of you may not know.

Any "mechanic" can "rebuild" a posi, and by that I mean put seals & bearings in one, nothing else.
A "machinist" will go much farther and knows various ways to correct backlash, endplay, etc. Which is the minimum amount of effort needed in these C3 diffs IMO. Since it affects suspension geometry unlike any other diff on the planet.

But what I learned is Gary is not only a "machinist", no not at all, he is the "professor". He is too humble to brag about it, so I will, for him.
He spent decades with Bridgeport, a world reknown mfgr of machine shop equipment, and spent 30 years, installing, tuning & repairing said equipment, and training regular machinists how to use it.

We are so lucky he loves Corvettes and to have someone with his skill level in our hobby!
Don't question the authenticity of what he says, just respond: "yes sensei" ! LOL

 

Thank you, Leigh, you're pretty sharp yourself. If you go to Carlisle have a great time but watch for those sudden heavy rainstorms.
Stay safe

 

This is a simple warning to the OP of this thread.
I hope it does not derail your thread and I apologize if it does.

Please be extremely cautious about what some of the so called professionals at Carlisle tell you or try to sell you.
I trusted one, he gave me what I thought at the time was excellent advice and lead me to believe he was the best of anyone who builds C3 rear differentials.
$4,700.00 and a year later I was still waiting for my rear differential that would never come.
This person was a forum member who has since been banned.
He is still out there selling his inferior product, ripping people off and conning his customers.
Last I heard he was selling at Carlisle and Facebook.

After my experience, I was introduced to Gary Ramadei, GTR1999, who is the guru for all things Corvette differentials.
The thing about Gary he is all about helping you, so you learn.
He won’t try to sell you, he’ll try to get you to do it yourself and will offer to help you all the way through to the end.
As stated above he is the professor, and not only will he tell you what needs to be, but how to do it and the complete history of why it’s done a certain way.
If you call Gary to ask a question, make sure you have time to invest on the phone and are ready to take copious notes.
Gary spent hours of his time with me explaining what he was going to do with my differential build and why it needed to be done this way.
He sent me hundreds of photographs of “my” build, and referred me to purchase the best quality parts and where to purchase them, Tom’s Differential.

The rear differential I received from Gary is a work of art.
He is the best and that’s why he not only built my rear differential, he built my trailing arms, set up my rear rotors and parking brakes and why he is currently rebuilding my steering box.

Good luck on your project and be cautious!