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boobert 09-21-2012 11:55 AM

12 bolt axle play
Hey all, I have a 67 Nova with a big block 402. It has a pretty fresh (about 2000 miles) 12 bolt Posi rear end. 3.73 Richmond gears with an Eaton posi. Toms axles. I noticed awile back while backing up and turning I was getting thumping noise from the drivers side. You could actually feel it. Anyways today I got around to checking it out and it seems to me that the drivers side axle has a little too much play causing this problem. I don't beat up on this car too much and everythings fresh built by a well known diff builder. Any ideas? Thanks in advance.


big gear head 09-21-2012 03:32 PM

The noise is coming from the cutches in the Eaton. Did you use the GM oil additive when you filled it up?

ssimpala 09-21-2012 03:47 PM

Sometimes the 12 bolt takes 2 bottles.

boobert 09-21-2012 04:20 PM

Ya I used the additive

big gear head 09-21-2012 04:56 PM

Was it the GM additive or was it something else?

boobert 09-21-2012 05:13 PM

It was GM, but why only in reverse and while i'm cranking the wheel.

boobert 09-21-2012 05:38 PM

The gear shop out in Paramount,ca. built this diff I had it shortened and some perches added. When I picked it up they gave me Lucas gear oil and 2 bottles of GM LS additive

big gear head 09-21-2012 09:25 PM

This is a comon problem with clutch type limited slip differentials. Most of the time you only hear the noise and feel the car jerk at low speed and when making a sharp turn. Most of the time the GM or Ford additive will take care of the problem.

A new Eaton Posi should have the clutches tight enough that there will be very little axle end play. If you have a lot of axle end play then you might have some damaged clutches. A Eaton Posi that is set up correctly should have about .005 to .010 axle end play, but factory set up clutches might have more.

lmsport 09-22-2012 11:00 AM

Another variable is the thickness of the c-clip button when using aftermarket axles

big gear head 09-22-2012 03:13 PM

The c clip button on a 12 bolt axle is suppose to be .312 inch thick. Good axles are right on this number, but some of the cheap axles like Alloy USA will vary.

vinniekq2 09-22-2012 09:03 PM

are you still using C clips?I would think a shortened diff would have good axles?

boobert 09-22-2012 09:40 PM

Still using c clips, the axles are Toms and very good.

vinniekq2 09-22-2012 11:22 PM

Take it back to the guy that built the diff. I really dont understand why you still use C clips? The pressed bearing axle is less like to lose a wheel "when " the axle breaks. 12 bolts do break if you race or have good traction and a healthy engine. On my car,the tires are the fuse,,,

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