Can anyone provide a "guesstimate" for removing, rebuilding and reinstalling the 308 differential on my 69? I know this will vary widely depending on the part of the country. I'm in south Louisiana. Only 60,500 miles. This morning a respected alignment shop said there is "slack" in the differential resulting in wheel "wobble." This would not allow alignment. I was not experiencing any unusual noises or vibrations. I understand that noises and vibrations are common in C3s. The car hasn't been driven for years as I've "recently" had the T/As rebuilt, replaced the half-shaft u-joints and much more.
Thanks,
Mike

 

Bairs Corvettes says $895 for a typical rebuild.

I would not let a normal transmission shop do it.
It is a loaded part of the suspension, unlike any other diff in any other muscle car.
It needs to go to a good Corvette shop.
So you are likely shipping it.

My first choice:
Gary Ramadei GTR1999 on here in CT
2nd: Bairs in Pa
3rd Van Steel in Fla
4th - Zip in Va
no 5th choice - maybe somebody else knows of more

Getting it in and out is another story.

I would lift the car, and push and pull on the top of the tire, and measure how much the yoke moves at the diff.
Or perhaps it is the rear wheel bearing?
Push at 3 & 9 for those.

 

Need to know what your shop defines as “slack”. Did they measure the end play of the inner axles?

 

I agree with having Gary the #1 place to have it worked on. Personally, would not use any one else. At 60 000mi your at the limit of its life expectancy. If its had a fairly easy life it MIGHT be rebuildable. Removal is not difficult, just a laborious endeavor.

 

Thanks folks for the replies. The alignment shop didn't measure the movement, but did demonstrate the movement with hands at 12 and 6 positions. Very visible even with my untrained eyes. Right side worse than left. I told the shop manager that both trailing arms had been rebuilt (by Bairs). He said they were not a problem. I did find a small shop that specializes in vintage cars including Vettes. Now waiting to fit into his schedule.

 

also, suggest local circle track race shops. Rebuilding and Changing ratios are an everyday job at many. Just might have a diff perfectionist in your own backyard ?

 

What “movement”? You need to get measurements for axle play (movement in and out of the differential).

 

were they pushing at 12 and 6 then pulling both at the same time or pushing at 12 and pullling at 6 and alternating....personally, unless the folks in the shop are in their 60s or older, I wouldnt trust them to change the tire let alone align it. Was ther an align issue or symptom that required you to bring it to them or did you just go in for an alignment? Have you tried aligning it yourself?

 

I would thnk you can still align the car with worn axles?
should still get fixed and for sure will help handling and obviously out of tolerance when loading axles.
i was very surprised how tight the handling was when thrown around after axle repairs.

 

Some thoughts for you and this is by no means a solicitation, just thoughts from years of doing this work. I have repaired the work of many of the known places, speed shops, hot rodders, and owners.

You need to decide on what the car will be used for, how much power you will have, trans type, traction, and your right foot.

You will find many places offering rebuilt or exchange units. Some will say they're racers, sell race diff's, have many parts installed, use the best parts, build it stock, and who knows what else. I love talking to those guys because it doesn't take long to weed out those who know what they're talking about and those that don't.

Many offer one size fits all, which is usually a bearing kit, paint job, and maybe posi clutches and axles. Some do a great stock build using quality parts like Timken, ARP, Koyo, and good axles. Some use the cheapest parts they can get to offer low ball, bait and switch quotes. If you need axles, what will be used? - New, rebuilt, HD, 30 spline, etc. They are not all equal. New are imported, some with steel not originally used by GM. Some rebuilt axles have huge QC issues and have for the past 20 years, still other are hollow like a straw. They will look good and for a car rolling off a trailer or drove around the block once every 8 months they will work- for a while. One hard punch or launch and they may become 2-piece axles.

Ask questions.
Ask what parts and brands are used. Many shops use whatever their supplier can get, or they shop vette parts online like anyone else.

1969 was a transition year. There was a big strike that delayed production. Parts like steering boxes were revised during the run. Diff's in 69 depend on when they were built. Early diff's used carry over parts from 68 or 67. Posi cases used in 68 are different than what was used in later 1969, but are found in early 69's. There is a difference between them, and both had issues.

Axles were starting to be case hardened around this time. I don't have an exact date but for the sake of this info I'll say C3 original axles were case hardened. A rebuilder needs to know about the posi cases, axle types, along with the other issues each year had, and they all had issues from 1963-1982. Some lasted a long time; others failed within the 1-year warranty.

New gears are imported today, almost all from China. Some setup ok others I had to "work" to get right. Is the steel used today better, the same, or worse than what GM used? Gm had poor QC too, check any used GM ring gear for bolt hole depths and see what you find. That is a good example of experience from a builder, if someone is reusing GM gears and doesn't check them, that might come back to haunt them with backed out ring gear bolts.

You speak of movement or "slack" a good question is how will that be addressed? What will the final endplay in the axle be? What is a good dimension, what is bad?

The point is simple. A common diff built with a bearing kit it not the same as one with 40+ hours of labor by an experienced builder. If the car is low power and not going to be pushed it may be fine with those low buck cheap builds or maybe not. Ask how many diff's they built, some good diff shops may not have too much old vette experience. Watch out for the knock off guys and those claiming to have done this without any real backup of those claims as they may be learning with your build.

Good luck, I hope you found a good shop local to you. It will save you time and money for sure.

 

Thanks GTR1999 for the detailed information. Much of it is far beyond my understanding, but I will ask about the source and brand of any parts used.

The car has a C36 with 4sp and will be a “casual driver.” No hard driving…at least not by me. Won’t be a show car or trailer queen. Just trying to get it back to its condition when I drove it off the dealership lot - new. It’s a July build, but of course that doesn’t indicate the age of the differential (it is the original).

 

You're welcome and good luck.

 

The worn axle will not affect the alignment either.
Physics will force it all the way into the diff at rest. All the time.
It is not until you are in a pretty hard turn, at .5G or more, that it will pop-out of the diff under sideload.

See the video, especially 1:44