Thanks for your help on the ID # Now that I have the pumpkin on my bench I notice that the side yokes have some noticeable end play. ( you can pull the yokes in and out of the case )There is no visiable wear on the outside and no leaks. According to the rebuild manual the way I read it is there should be no more than ten thousands play in these shafts? ( I am no expert and get confused with the terminology )I drained and replaced the fluid about 8000 miles ago. I have driven this car about 10,000 miles with no issues of any kind of noise from the rearend. My plan was to clean, refinish and reinstall.I don't have a dial indicator but the end play is probably close to a 32nd of an inch. Should I be concerned with this condition? Thanks again, Bruce
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Re: 66 rear end side yoke end play ?
Positraction clutch pack wear increases yoke end play as does yoke end wear. If everything is new and in spec, end play is typically less than .010"; 1/32" is about average for a used axle.
Chevrolet only specifies a backlash spec for the differential gears, and this affects side yoke end play.
There was an extensive article on this subject in the Corvette Restorer a couple of years ago.
Duke -
Re: 66 rear end side yoke end play ?
You're talking about .0320". Not cause for alarm, but I would look at it if the seals are leaking and/or you plan on doing any other work to the differential. Max tolerance is about .0100", and when setup initially, I shoot for minimum, or about.0030".
The end play that you see is most commonly due to wear on the hardened end faces of the side yokes, where they contact the pin. Once the casehardening is penetrated, the wear process accelerates. Gross end play is dangerous, and in many cases is caused by a combination of the above condition, and/or clutch pack issues. This would be apparent if the breakaway torque of (I believe 70 ft-lbs, minimum) cannot be achieved. A properly setup and fully functional clutch pack can yield breakaway torque of 100 ft-lbs or more.
The good news is that R&R of the side yokes requires removal of the rear spring, and diff cover casting. It can be done in-place. But I recommend complete R7R if you've had to go as far as yoke replacement.
JoeComment
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Re: 66 rear end side yoke end play ?
I believe the preload spec is more on the order of 40-50 lb-ft with the OE clutch pack springs; much more than that would only be suitable for racing.
Yoke end wear is more of an issue with later C3 yokes than C2 yokes and this can result in very high end play, but end play will always increase with use due to clutch pack wear even if the yoke ends do not wear.
Since he has the axle on the bench it would be a good idea to remove the rear cover and side yoke to inspect them for wear. If none is evident the axle is probably okay for typical vintage car use.
If he wants it "perfect" then it's time for one of those time-consuming and expensive precision axle overhauls.
DukeComment
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Re: 66 rear end side yoke end play ?
Hi Duke,
1963 Shop Manual says "40-70 ft-lbs when new". 1965 Supplement says "no less than 40 ft-lbs". Quite a large spread in acceptable values.
I rebuilt mine a few years ago, and found 1 missing clutch spring, 1 mismatched spring, worn yokes and pin. Yoke end play was about 3/16", both sides. Clutches were non-functional (I effectively had an open diff).
New yokes and pin, reused clutches, as they were serviceable, installed 4 new clutch springs. Assembled and set clearances to minimum values. Filled with a 50/50 mix of 80W-90 and 85W-140 gear oil and about 6 ounces friction modifier. Breakaway tested at about 85 ft-lbs.
I think that there's plenty of leeway in the breakaway values........so long as it's at least 40 ft-lbs, it should be sufficient. I always prefer to have my clearances tight, and so the 85 pound reading is with min. clearance. If GM advertises 70 pounds, when new, you can bet that many of their better built units went out the door with 70 plus ft-lbs.
My car always delivers 2 perfectly parallel and equal length rubber patches when I get rambunctious with it. No clutch chatter around turns, full lock, either.
Joe
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Re: 66 rear end side yoke end play ?
Thanks guys, Duke, I found the artical in my stack of old restorers. it is Volume 31 number 3 winter 2005 if any one is looking for it. I remeasured my end play with a tape and it is closer to a 1/16" than a 1/32". Looks like I will take it to a local expert for an evaluation and or rebuild. I don't want to have to remove it again in the future. Thanks again, BruceComment
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