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Old 04-23-2012, 08:47 AM   #1
Mashman
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Play in the side yokes

I took my 72 in for an alignment, and the shop braught something to my attention, I'm not sure if it's a problem or not, so I thought I'd ask.

They noticed that with the rear tires in the air, they noticed that if you grabbed the rear tire (both sides are the same) at 12 and 6, you could puch the top in. When doing this, it looks like the side yoke will push into differential around 1/8th of an inch.

Is this normal? If not, what do I need to replace?

Thanks!
Matt
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Old 04-23-2012, 12:33 PM   #2
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No, an 1/8 inch is way too much. Time for a rebuild. If the yokes themselves are not bad, then it may just need the posi redone, but I'm not a diff expert, just know some basics. GTR1999 is our resident diff expert, hopefully he will see this and chime in.
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Old 04-23-2012, 12:45 PM   #3
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Here's a picture. I've highlighted the gap - this is with the rear up on jack stands. The other side looks identical. I can grab the tire at 12 and 6, and I can push the top in, and the yoke goes in the amount of the gap - which I'm estimating is about 1/8th an inch. Could it be bad c-clips?


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Old 04-23-2012, 01:31 PM   #4
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The c-clips (actually snap-rings) don't go bad. There's no wear on them. It's either worn ends on the stub-axles or worn posi clutches. Or most likely both.

If you don't fix it the stub axle eventually starts eating the diff case as the stub axle keeps going further and further inward. That ruins the area where the stub axle seal goes and at that point you need a replacement case. So get it fixed soon.
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Old 04-23-2012, 02:22 PM   #5
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Actually, if the C clips are missing, you would see exactly what the OP has going on. The C clips keep the yokes from coming out, not in.

Most likely, the inner ends of the yokes are worn and the c clips have fallen off or broke. He may just need a new set of side yokes, which is a DIY weekend job.

Or the rear could be worn out. Won't know that until it's opened up.
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I'm taking care of my procrastination issues, just you wait and see.
Old 04-23-2012, 02:55 PM   #6
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If you actually see the side yokes moving an 1/8" that is a problem as mentioned. This can sometimes be deceiving so rather then pull the diff out, remove the 1/2 shafts and use a dial indicator or machinist scale to measure the full movement.

Things to consider with this very common problem.

1- The 73-74 era to 79 side yokes were not hardened correctly, if at all, and wear out much faster then the correctly hardened yokes used from 1963-1972. You have a 72 so they may still be good. I have rebuilt plenty of 63-72 diffs and reused the yokes because they were not worn out. I got the endplay down from 030-050 to 005". The '63-'72 hardened yokes were case hardend which is about 030" deep give or take 005-010" The rebuilt yokes on the market use a hardened button pressed in the end of a worn yoke to recondition it. These work pretty good although QC on them is not the best at times. The "new" yokes I have seen and used failed in use. I do not trust the new yokes I have seen and stopped using them altogether. These "new" yokes are not new at all and have been on the market for years. I had to recently replace one that was only 5 years old but worn down 030"

2-The yokes are held in place by snap-rings, that is what we call them here anyway. The more common C-Clip is a C shaped solid steel spacer. This is used on the other chevy lines and my super 10 & 12 bolts.The axles have to be pushed inward, after removing the cross shaft, to remove them. The snap rings use special pliers to expand them and allow them to be removed. The cross shaft does not have to be removed.

With worn yokes, the ends mushroom over so even with the snap ring removed they will have to be driven out. If let go long enough the yoke face will wear down and the driving action will cause the yoke to finally hit and grind into the seal boss,then the seal, then you have issue.

3.-Yoke endplay is caused by 4 things:
A- Worn faces as I described above
B- Worn out cross shaft holes in the posi case
C- Sloppy posi clutch setup
D- labor- inexperieced rebuilder(s)

4- Replacing yokes and seals alone usually does not solve the problem. Many times guys have called me to say they replaced yokes with either new or rebuilt and still have 030" or more endplay. Again this falls into the catagories above adding in poor QC as well as I have received bad new & rebuilt yokes.

I can't tell from your picture if the seal boss has been hit or not but I would check it.
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Old 04-23-2012, 04:37 PM   #7
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Thanks guys!

Gary, So I dropped one of the half shafts, and used a dial gauge, and I got 073.

So I'm thinking I need to rebuild the differential? If I need to rebuild is this kit OK ( http://www.ecklerscorvette.com/corve...Product_Viewed)? Do you think that would suffice, or do you think I need to put in a new clutch pak (http://www.ecklerscorvette.com/corve...1964-1979.html).

Also, I noticed in another thread that you had put together a paper with your rebuild process, is that still available?

Thanks for all the help!
Matt
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Old 04-23-2012, 06:09 PM   #8
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Matt
I use the kits I buy or put together. Can't comment on ones I don't use or see. Some kits are good others are not about as simple as I can put it. If you want the parts I use just let me know.

I looked at that picture again and it appears the boss is still intact so that is good.

You have to decide what you're going to do, if it were my car I would take the diff apart, replace those snowflake clutches, polish and tune it, check the yoke faces and replace if needed. The gears should be checked as well and possibly reussed if you like the ratio and the pattern isn't running off the teeth. Go by the coast pattern to judge them. check the lash.

No, I stopped the paper after some took advantage, sorry. You can find a lot of information right here in the C3 Tech link on the top of this page. A factory Overhaul manual will also help a lot.

If you never have done a diff before then you have to take your time, I have walked plenty through it. The easiest way to do them is the quick vendor/rebuilder type of job. No machine work, nothing custom, nothing impressive in my book. I don't build them like that but plenty do and they work ok as long as you don't beat up the car.

72 diff's are pretty good. Rarely do they crack but check it. The side holes have to be checked as well. If there is a crack the posi is all done. If the side hole is sloppy and you see a step in it then I can bore it and fit a 12 bolt cross shaft and save the posi case.

Use ARP RG bolts not the ones in the kits and I always replace RG bolts. Many do not replace RG bolts in this job and you will never know as long as it doesn't lock up.

If you buy side yokes check them good and measure from the face to the snap ring should be over .180 but some are not and if you are not tuning the posi then you will have end play. If you properly tune it then you may have to grind the yoke faces to setup the endplay. All the cases setup differently so there is no standard shim set to use. Some dial in with the kit shims many do not and require grinding within 001-002" to dial in. You can see all this on You Tube just look up Tom's Eaton posi tuning.

If I can help just let me know. Good luck. If you really want to do then go ahead and don't let someone tell you it's impossible. You'll never learn younger and probably will do a better job then most out there, if you follow my builds.
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Old 04-24-2012, 08:54 AM   #9
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Thanks Gary!

This car is lightly driven about 5k miles a year. I like to learn new things, so I'm going to go ahead and rebuild it myself. I've found that I can do pretty much anything as long as I follow the proper steps, and don't rush it.

I don't have machine tools, but if I need anything machined, I will take it down to the local machine shop.

I'm sure I'm going to have lots of questions, so thanks again for the offer.

Matt
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