The rear is out of the car and is exhibiting some yoke end play (identified by a friend who said this is common for Vettes). I'm trying to do as much work myself and i'd love to learn how to do a rear-rebuild, but is this one of those things i should leave to a professional? A local Vette shop quoted me $450 for the job. Should i just take this?

Are there special tools here? Gotcha's?

 

I'm in the same boat with you. My 79 rearend is out and apart in my fathers garage. My yokes are mushroomed, but don't know how much is too much. Keep me on this thread. Thanks Jim

 

If you are just replacing the yokes that is an easy job. The yokes if worn have put a lot of metal shavings in the rear. If you are going to rebuild the rear I would suggest you take it to a pro. It has to be set up right or it will howl or maybe even worse. I put all new bearings in mine but am leaving the setup to a pro. I have done a frame off on my car so there is nothing that I am afraid to tackle but this is one of those jobs that is better off left to someone whoi has experience and the right tolls. 450 sounds a little steep. Is that with a new ring and pinion or just a rebuild. The parts are about 170 for bearings and clutch pack. 300 is a little much for setup I think. It can be done by some but if it is wrong there is alot of work for nothing.

 

Not sure why but 79's seem to have a big problem with worn yokes. My friends 79 had worn so much, the u-bolt was cutting into the housing?

We ended up cleaning the housing with gears in place and just replacing the yokes and yoke seals. That was 10 years ago and it still drives great!

The yokes are relatively easy to replace once the rearend is out of the car, or at least the rear cover is removed. On pre 80 cars, you remove the center pin which is held in buy a locking bolt . once the locking bolt is out rotate the diff until up can push the center pin out. Warning - make sure the side yoke spin together or the spider gears can come out once the center pin is removed.

With the center pin out, the yokes can be pushed in so the c-clips can be removd (80 and up uses locking rings). Now pull the yokes out (do not allow spider gears to rotate (I sometimes put the center pin back in to make usre the spider gears stay in place)

reverse process to put back together. Not that if the yoke has mushroomed aginst the center pin real bad you may have to pry the yoke out.

This is really an easy job! I'm not a certified mechanic, but did sleep at a holiday inn select

 

So, regarding the end-play (or yolk movement) this is generally solved by a yolk replacement (as described above) with out "rebuilding" the whole thing?

Here's what i gather:
-Yolk replacement - do it yourself
-Full rebuild - give to a professional

 

That is correct, you just replace just the yokes if there is excessive play without a rebuild.

 

Sure enough. I opened up the rear and the yolks (one in particular) was "mushroomed" pretty bad. We removed the center pin and couldn't figure out out to get the "c-clip" out. It's pretty stiff. I had to run to the store to pick up some special snap ring pliers.

One yoke came right out. It had just a tiny tiny bit of play. Didn't appear to be mushroomed. Is this ok? Or should it replaced?

The other one was very mushroomed and had lots of play. Because of the mushrooming it doesn't want to come out. How should we get it out without doing damage to any of the other parts?!!


[Modified by tzavaleta, 2:13 PM 12/1/2001]

 

The one yoke should be okay, if no wear was noted on the end of the yoke and the end play (movement) is less than 1/8". Now the other one is another story, I know that others have "driven" theirs out by tapping on the yoke (outside.) I have no idea if that will work in a badly mushroomed yoke or not. You are going to have to replace the two seals anyway, and I don't know what else might be damaged.
Shannon (SB69) had to drive his out, but I don't other than the seals anything else was damaged.
Good Luck!

 

Thanks for all the good information. I had to drive mine out. Luckly the disatemer of the yoke at the bearins is greater then that of the splines, so passing the yoke through the splines broke off the "mushroom" and the yoke slid right out. Actually the whole job was pretty easy.

One yoke looked appeared to look ok, but i have no way of knowing what "ok" is. It did have some end play (albeit minimal) but i'm not sure what is in acceptable range. Is there a way that i can measure the yoke to see if it's been worn any? Does anyone have any specs on it?

Thanks in advance!

 

Recently, I had the same question. http://forums.corvetteforum.com/zerothread?id=190129
I still haven't found the specs either.

 

Look on the "good" yoke, at the end where it rides on the center pin. It should be slightly beveled at the tip. If you still see the bevel, it's probably OK. If there's no bevel visible, I'd replace it. The hardest part of the job is the disassembly and reassembly. Spend the extra $65 for another rebuilt yoke if there is any doubt.

My personal opinion, is that if the rear end wasn't howling or exhibiting any strange noises before you dropped it, you should be OK with doing the yokes, side seals, and fresh fluid.

Shannon

 

I read the responses to how much yoke end play is okay, and now I am really confused about the design. I have no formal mechanical training and I have never taken a diff apart. I had taken my newly bought all-original '78 to a Vette shop and had them install the engine (355) that I had built at a reputable builder to my liking. I told them I figured about 400 foot pounds torque and 300 - 320 HP. He put it in and said everything should be okay with the rear end as it was. He drove the car and seemed to be unimpressed with the acceleration. So after break-in, I went to a track to have a good time (my girlfriend said okay). When I took it in for another service and asked him to change the diff fluid, he called me to come in and take a look at the mess. The centre pin was worn down, the case holes were distorted, the pin screw was broken off and the shaft ends were mushed down past the c-clip rings. He told me I had pushed it too hard and the rear spring had gotten fully compressed, letting the yokes push in on the center pin and destroy the whole mess! In addition to rebuilding the rear end, he put in a much stiffer rear spring set. Much money later, I am wondering why GM did not design in a travel-limiter so this could not happen. So, is it true that if the engine torque is too much for the rear spring to control, the yokes will mash themselves into the center pin and distort the whole assembly to poopie? Why can this happen? I thought that this design was engineered to stand up to big block torque! Please let me sleep, knowing that I didn't get screwed by this guy. (I never even got kissed!) Is it Okay to think this design is stupid? Thanks. :boxing

 

The rear end needed some work, but he is woefully mis-informed as to how it works.

 

I don't know of any published spec on the length of the yokes- but there must be an engineering drawing somewhere. The only meaningful figure would be based on the U-Joint saddle. Anyhow- that BS about the spring causing damage- better find a better mechanic. The amount of wear on the tips of the yokes and on the shaft is a function of use.... particularly side-loading. Could it have been designed better? Probably. But remember, this was designed in 1961 or 1962 for use in 1963. Things have changed since then. If the bevel is gone, and/or the yokes are mushroomed enough to notice, then they need to be replaced. You do not need a length measurement. The measurement you do need is the distance between the end of the yoke and the shaft. This should be around .010 with new yokes. The entire clutch case & ring gear moves from side to side during the setup process. This will determine yoke end-play figures. Some guys weld metal to the end of the yokes to get them to almost zero clrearance AFTER the ring & pinion are set up. Replacement yokes should put you in the ballpark without getting into rocket science.

 

Even if the one yoke looks good, I would replace it in favor of a new yoke / rebconditioned yoke that has a hardend end (say that 3 times fast).

If not, you may be doing this all over again, soon.

 

The dammage more than likely came from the fact that the c-clips were no longer in place. That allowed the yokes to move in and out for farther distances. A heavier spring will more than likely reduce suspension travel assuming nothing else is changed. Reduced suspension travel will introduce decreased camber change which means the yokes will have less lateral travel than before. Probably enough that the side yoke play was significantly reduced under a fully loaded suspension situation. I think that's all the mechanic had in mind. It's not the correct way to fix the problem, but it helps a little. The biggest flaw in the rear suspension is the camber change. The c-clips help hold that problem to a happy medium but they have a life span as well. AT all cocts make sure the clips are still installed.

 

I might buy some of that... but...
He said he needed to buy snap ring pliers. This means the snap rings (they are snap rings, not c-clips) to get the yokes out. This means the snap rings were in place. Anyhow, I have both a 66/327 with a 300 spring and a 70/454 with a heavy duty spring and the yokes on the 70 with the heavy spring are worn more than the yokes on the 66 with the light spring. There goes that theory... at least for me.

I'll buy some of the concept, but not all of it.
I still think that the biggest wear occurs under high acceleration (squat) and in autocrossing. IMOP

Edit- later years have C-clips eh?



[Modified by Tom454, 2:24 PM 12/4/2001]

 

Ok, looks like I should read my threads a little closer but in theory what I have explained can and has happened

Right, and the same goes for drag strip style launches. Enough of them could cause the ring to break loose and then your in the situation I explained earlier. If you could lessen the travel of the suspension and thus lessen the travel of the yokes with a stiffer spring you reduce your chances of the rings coming off and the ends of the yokes hitting the shaft in the diff. Less wear altogether.

Don't get me wrong, I think i'm in agreeance with you but i'm putting myself in the shoes of a mechanic that might not fully understand that type of suspension. What he did to fix the problem was for him was probably the most logical thing to do.

 

This is why I hate the internet. I can't tell if your making reference to my naming the part wrong or inquisitive into wether the later models really do have c-clips. Anyway, I was just using a general term. You know what part i'm talking about. Someone must have told me c-clips and for some reason it stuck.

 

Yah. I apologize for using the term "BS". I get feisty sometimes, and my choice of words is not always appropriate.

I think we are all in agreement as well. If you take two identical diffs, one with a 300 lb spring, and one with a 400 lb spring, and subject them both to the identical abuse (test), it makes a bit of sense that the 400 lb spring is going to hold the yokes away from the shaft, on the average, a longer period of time. This, in turn , can imply that a 400 lb spring will ultimately result in less yoke & shaft wear. That is the part that I think we all agree on. Where I believe I diverge, is in the question of where most of the wear comes from- the difference in spring rates, or plain old abuse. My 66 327/300 lb has probably 120,000 miles on it. The yokes are worn, but not yet toast. My 70 454/360 lb has about 75,000 miles on it, and I had to replace the yokes last year. I've owned the 66 since 1975, and the 70- since 1986. The 70 gets far more abuse than the 66... and the yokes showed it. That's why I believe that the useage is far more important than spring rate in yoke wear. Hope that clears it all up.

I don't think any of us has any hard cold scientific evidence to back up our arm chair speculation. So it's all conjecture anyways (but it's good conjecture, right?)

RE: The snap-rings- sorry again- didn't intend to jump on anyone... just wanted to clear that issue up.