I am curious of exactly how many thousands of side yoke play is supposed to be correct of a 1977? I have my differential at a shop locally here that deals mostly in corvettes and I have about 10-20 thousands of in and out play and he opened it up and says it is good. There is a post over in the general section post number 4 jesse has a video of his end play check it out and let me know what the factory specs call for.
http://forums.corvetteforum.com/c3-g...u-find-it.html

 

Don't know what the spec is but .010 to .020 would not be an issue for me and I am the guy that usually argues this point. I would suck the old fluid out and put new differential fluid and posi additive in it and call it good.

 

 

Are you near Dallas?

If you are, you should have tracdogg2 check it out.

 

No one has ever found a factory spec as far as I know.

 

Here is a post off another forum by a guy who's opinion on corvette differentials I respect the most.

 

As has already been said, I don't think anyone has ever been able to come across a spec for it, but i too wouldn't get to bent out of shape at .050. However, it I had it out and was looking at it I would shim it up under the snap ring and take it down to near zero.

It's not like con rod bearing clearance where nothing really changes until you get too far out and then things really go south. This is more an issue of what optimum performance is. If you are really looking to optimize the handling you do things to minimize the "give" in the suspension so part of that would be to have the min amount of camber change from the upper control arm. Pretty easy to stick a shim somewhere under the snap ring.

Steve g

 

Guys thanks for the quick replies I have the diferential out and I am going to call Mike today and talk to him about it.

 

No specs available? Anyone know who bought the '78 with six miles on the odometer at the B-J auction? There lies the answer or on any very, very low mile, untouched, 'vette.


Edit: It was a '79 with four miles.

 

That will give you the min, or close to it (manufacturing tolerance) but won't identify what the GM engineers might have had in mind for the max.

I must have walked right past that car Fri and not noticed the mileage. Even if I had I doubt they would have let me jack it up and check the end pay in the yokes tho.

Steve g

 

If the yoke moves as much as 0.25" on a "new" car then it would be within tolerance. No? There are several of us that have this much play from what I've read in the forums. Not sure of the maximum but if 0.25" from the factory is OK then maybe there just isn't a maximum?

 

There is no set amount. But here's some specs. Average wear on a set of clutches is .020 per side. On the stub axle from the snap ring groove to the tip is .180 average. Midyear stub axle tip hardening is nearly its total thinckness. Throughout the C3 era the hardening was reduced with 78-79 being the softest with a rockwell rating of 6. Once it wore the hardened outer skin, approx .020, they wore very fast. The cross shaft is hardened throughout its entire thickness. As the stub axle tip wears it damages the contact surface on the shaft which then eats away at the stub axle which is already now into the softer metal.
C3's have slotted inner clutch discs that have a habit of exploding. Lose a disc and you will get .100+ end play in the stub axle. This also put excessive side loading on the cross shaft and carrier bore. You will not notice a broken disc when driving. You will have massive backlash in the spider gears on that one side.
Almost always any end play over .020 will be from stub axle wear. Add in a few thounsandts for spider gear and cross shaft wear. On midyears .050 end play can be acceptable. On C3's you are into soft metal and wear will be accelerated.
Hardened metal wears away in minute particles. Soft metal rolls over and breaks off in large chunks. But yet you pull the rear cover off and there is no metal or clutch material in the bottom of the case. Why? Look inside the diff and on the upper left side you will see a passage. This is how the diff circulates fluid thru the pinion bearings. Anything over 300 ring gear rpm the ring gear grabs the lube from the bottom of the case and throws it into this passage. Commonly known as oil roping. This roping will pick up anything in the bottom of the case. Metal particles, clutch pieces and snap rings. All this gets deposited in the cavity between the pinion bearings. Now take a 1.00" X .150" piece of metal, grind it into dust, add some clutch disc material which is also steel, and mix it with the gear lube. This is exactly what is happening with worn stub axles. You can't drain or suck out or flush out this trash because it is stuck in the cavity between the bearings, not in the bottom of the case.
Right around .150 wear the stub axle starts to eat the case at the seal, depending on gear ratio. Due to the raised lip outside of the seal you have a .050 cushion that can be worn away. After that the reinforced area of the seal will no longer have any material to press against. Vtech mentioned that they just recently had to replace 3 cases in customers cars due to stub axle wear.
So less than .050 wear in a midyear might be alright but in a C3 the excessive wear process has already started.
Mike

 

The side yokes in my '73 were .180 and .250. After Van Steel rebuilt the rear, the end play was .008 and .015.

John

 

Yes. What he said.

 

Per the GM power guide which shows how to race prep a C3 corvette, the posi clutch pack is to be shimmed so that the yoke clearance is .005" maximum - quite tight. There is no "in-service" wear allowable.

 

So now we know where part of the myth and confusion comes from.

 

The above is correct. A downloadable .pdf copy of the Corvette section of the Chevy Power Book can be found 1/3 of the way down the page here - http://corvette.wikia.com/wiki/Misc_Overall

The part that addresses the yoke clearance is found on page 6-12.

 

I can understand wanting the clearsnce set @ .005 on a new setup. The question was, is .010 and ,020 ok on a used differential. Tracdogg says .020 is average clutch wear. Add in the original .005 you get .025. This could be your number with 0 wear at the sideyoke ends and average wear of the clutch pack confirming no broken clutch discs and little to no sideyoke wear. The op was wondering if his was acceptable. I said yes, Apparently GTR1999 agrees. and Tracdogg agrees that .010 and .020. endyoke play is not a problem requiring a rebuild. If there in no visable damage, correct backlash at the gears and it don't leak I would flush it out, seal it up and add new fluid and posi lube and put it back in service.

 

Everyone's always asking for numbers so I'm going to stick my neck out and post guidelines. If anyone has an opinion or thought go ahead and post so that we can use these numbers for future questions.

End play:
Less than .025 No problem
.025 - .050 Starting to wear, consider inspection
.050 - .100 Beyond normal cluth wear, possible clutch damage
and/or heavy stub axle wear. Needs attention
.100-.150 Excessive wear and/or damage. Needs immediate
attention.
.150 -.200 Severe wear and case damage


Mike

 

Excellent info Mike. This is a common question and it is helpful to have someone with recognized, extensive experience commit to a guideline. This is good info to have when these guys come on here spouting that 1/4" of play is nothing to worry about as they have been running thiers like that for years and so have thier buddies with no issues.