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C3 Rear End Chatter

XLR8

Gone but not forgotten
Joined
Jun 23, 2004
Messages
6,662
Location
Mississippi Gulf Coast
Corvette
2003 AE Convertible, 1998 LCRM Convertible
I had a similar problem with my 76 that I bought last year......... If it wasn't for this message board, I was almost ready to take apart the entire rear brakes. Thanks!

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rogercoldiron

New member
Joined
Apr 19, 2011
Messages
2
Location
Mount Vernon, Kentucky
Diffential Chatter

Your diffential is probably chattering because the ends of the yokes that go into the diffential have worn down because they tend to rub against the main pinion when the car corners. You'll need to replace the yokes on both sides. I'll even bet that at least one of the clips is laying in the bottom of the diffential housing.
 

GTR1999

Well-known member
Joined
Sep 4, 2003
Messages
1,146
Location
New Haven CT
Corvette
1969,1972,1975
Your diffential is probably chattering because the ends of the yokes that go into the diffential have worn down because they tend to rub against the main pinion when the car corners. You'll need to replace the yokes on both sides. I'll even bet that at least one of the clips is laying in the bottom of the diffential housing.

This isn't exactly true. Yes the side yokes or axles, will hit the posi cross shaft but I've rebuilt enough of them to know the early yokes up to about 72-73 were better quality because they were hardened. The 74-79 were not and they wore out, some to and beyond the snap ring.
Posi chatter is a result of the spider lash setup and the springs/plates.
Many diff's with worn out yokes didn't chatter at all.
 

rogercoldiron

New member
Joined
Apr 19, 2011
Messages
2
Location
Mount Vernon, Kentucky
C-3 Yokes

I've had to replace yokes on both my '71 and '73 because of wear. In the '73, one of the circlips was lying in the bottom of the diffential. There can, I agree, be a number of causes for rear-end chatter but yoke wear is the most likely. Good thing is, they're not that hard to change.
 

GTR1999

Well-known member
Joined
Sep 4, 2003
Messages
1,146
Location
New Haven CT
Corvette
1969,1972,1975
I've had to replace yokes on both my '71 and '73 because of wear. In the '73, one of the circlips was lying in the bottom of the diffential. There can, I agree, be a number of causes for rear-end chatter but yoke wear is the most likely. Good thing is, they're not that hard to change.

Roger I'll disagree again, not that it really matters. The biggest concern with yoke wear is the yoke sliding in/out of the diff causing changes to the rear alignment and if let go will in time cause grinding of the yoke against the 1/8 cast boss in the housing by the seal. The added problem of all the powdered metal mixing in with the gear oil also gets into the bearings and gears as a fine lapping compound.

The chatter is caused by the setup of the posi lash in addition to the springs and plates. It was a problem for many years resulting in the clutch change in 1971 which only made them weaker.

The snap ring or circlip may sometimes fall off but that's not as common as some believe. If they were not installed completely they will come off, if the yoke wears down past the groove they'll fall off.
The cross shaft is about 60 Rockwell on the c scale, the yokes from the 73-79 run are often in the 10-15 range and as a result will wear down but not cause the common posi chatter or hammer as I call it. Many time replacing just the yokes with hardened tip rebuilt yokes helps but it doesn't address the very sloppy posi setup. I've seen many guys just replace the yokes and still have over 025-030 endplay which is not how I would set them up or use them. I still with 005 007 endplay which requires correctly setting up the posi.

This problem is still not addressed and often misunderstood. The new loaded Mexican posi's still use springs and not fiber coated solid steels to try and eliminate the problem. The springs are too heavy and the fiber smudges off. The last one I had apart was one with only 800 miles on it, once I removed the springs I checked the lash and it was terrible, well over 030" sideplay in the gear.

Anyway, good luck with your vettes:beer
 

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