C3 rear end education needed

[tom444634]

After spending a few weeks replacing all of the worn out parts in my front suspension and steering, I was off to the alignment shop today. After we got the car up on the rack, then lifted it off of the rack for initial checks, we went over the front end and all was tight ( as I expected). When we checked the rear there was a good amount of movement when pushing in on the top side of the tire on each side. Upon further inspection, you could see the half shaft moving in and out of the differential as you pushed on the tire.

Now I would expect some movement to be normal, but this seemed real excessive. Needless to say we did not continue with the alignment and I am now faced with rebuilding the rear suspension as well. (No problem, I like getting my hands dirty.... really)

I'm trying to educate myself before I start removing bolts. Is the problem more with the differential or the trailing arms. I know I'll need to rebuild both, but I am curious. The trailing arms did not seem to move much when we were doing the test, just the half shafts.

The car seems to drive fine and straight. Although it does seem "loose" in the rear when braking sometimes.

BTW, 71 LS5, 4 spd, 119k miles

[Joe L.]

Re: C3 rear end education needed

Tom------

This is a VERY common problem with 63-79 Corvettes. The inner ends of the stub axles wear and end play on the shaft becomes excessive. There is no definitive spec for this end play ever published by GM. However, when new, the end play is less than 1/16".

The main problem is that the wear on the axle does not occur at a constant rate. That's because the axles are case hardened. So, while the case hardening is intact, the wear progresses very slowly. After the case hardening is worn through, the wear progresses rapidly. If you have more than 3/16" of end play, that's definitely cause to rebuild the differential assembly and replace the stub axles as well as any other worn parts.

The trailing arms are unrelated to wear on the differential. However, if they've never been rebuilt at 119K and 35 years, then you won't be wasting any money by doing these at the same time.

[Wayne K.]

Re: C3 rear end education needed

Tom,

If the axle stubs can be moved excessively in and out of the pumpkin ( thanksgiving on my mind ) then there is a good possibility that the C clips in the pumpkin are not inplace. You'll need to go inside to remedy.

Wayne

[tom444634]

Re: C3 rear end education needed

Joe, we were easily seeing 1/2" of end play. My mechanic doing the alignment (He is the only guy I trust with my cars. I had a 71 frame off SS-454 Chevelle that took me 10 years and he was the only one that I would let touch it. So I trust his opinions) told me the same thing. He remembers needing to repair many C3's with this problem over the years.

Looks like a differential and trailing arm rebuild are in my near future!

Now I need to find a way to heat the garage!

Thanks!

[tom444634]

Re: C3 rear end education needed

Wayne, I thought the same thing myself. Probably the excessive play I was seeing was because the clips were (are) off. Hmmm, a long weekend. I can get a lot taken apart over the weekend! Just wish it was warmer! Thanks

[Joe L.]

Re: C3 rear end education needed

Tom------

With that kind of end play, I'd say that the stub axles are worn to the point where the c-clips FALL OFF. This means that the car is really not safe to drive and immediate repair is in order.

It's also a POSSIBLE sign that this car actually has more than 119K miles, like, possibly 219K. I would not expect that kind of wear at 119K for a pre-75 Corvette. I won't say it's impossible, but I would consider it unusual.

[tom444634]

Re: C3 rear end education needed

Joe,

I tend to agree about the C clips. Although if I remember correctly, isn't there a shaft that goes into the posi carrier between the two axle shafts that would prevent the axle from being pushed in far enought to allow the clip to come off? I think the shaft holds the spider gears and you need to remove the shaft and gears then push in the axle to release the C clip. I'll find out when I get it opened up.

The mileage is accurate though. Bought the car from the 2nd owner who had it for 20 years. Nobody has been in the engine...yet and it runs well. It is complete to the point that the only thing I can find that is not original is the alternator and possibly the starter which has a small block part number on it (discussed in a previous thread) but that too could be original to the car. All of the gauges work and the interior is in great shape with the exception of a small (1") wear mark on the drivers seat and a hole that somebody drilled in the shifter plate.

I have had many cars over the years and done a few restorations mostly on Chevelles and Camaros. This is my firat Corvette. I've always wanted one since I was a kid and it took me almost 9 months to find an "unmolested" big block that I could afford. Got this one back in the end of September.

Thanks for the help!

[William C.]

Re: C3 rear end education needed

Tom, excessive wear on the shafts will eliminate the groove causing the clips to fall off, usually the problem when as much play as you have described is present.

[Joe L.]

Re: C3 rear end education needed

Tom-----

Yes, there is a shaft that the stub axles "back up to". This is, indeed, the shaft that the differential spider gears rotate on. This shaft has a Rockwell hardness considerably greater than the stub axle case hardening. It often survives relatively unscathed while the stub axles are worn down to the "nub".

However, when the stub axles wear, they eventually wear down to the c-clip groove. When this occurs, the c-clip falls out; there is nothing to retain it any longer. That does not mean that the axle comes out of the differential, though. The trailing arm still "forces" IN the half shaft and attached stub axle to remain in the car. Under certain conditons, though, the axle can be forced out of the differential causing catastrophic damage.

[Gary R.]

Re: C3 rear end education needed

The shaft referred to is also called the center pin,although it's just under.750" They will get worn too, but as Joe said, not too often. One thing to be concerned about is the yokes will continue to wear until they start hitting the housing. There is a boss there that will "protect" the yoke seal for a while, but I've rebuilt some that have been "faced" off by the yoke grinding it down.If it hits the seal there might not be much left to support it.
The snap ring groove is machined .187" from the end of the yoke. Consider too that all the metal that was ground off has no place to go except in the oil. If yours are that worn I would replace the bearings as a good precaution. When I get them in that shape I usually go through the whole unit so you don't have to pull it down again.
Good Luck,
Gary