ckk981

OK guys, I noticed yesterday while checking out the tires on my 91 formula a strange thing going on with the wheels/rear end. I jacked it up, and when i push and pull on the tires, it moves in and out maybe about a 1/4 inch. Looking at it from the rear you can see the wheel and the drum moving in and out, and hear it. My father looked at it with me and were pretty sure its the axles, but not really sure what would cause it... any ideas? I will try to take a video of it tomorrow if no has a solid guess or answer. Thanks guys

Gregzz4

Pull the diff cover and inspect inside
Just a suggestion, but sounds like something to look at as there isn't much holding the axles inside the carrier, just a C-clip, if it's the same as most Chevys

tom3

Normal to have some movement in and out, but if it's actually 1/4 inch, too much. Need to check it out since the c-clip and a raised ridge on the end of the axle is all that holds it in.

big gear head

I'm going to guess that you have an Auburn differential (posi) in this rear end. Axle end play will increase as the cones in the Auburn wear. Axle end play would be around .005 inch when new, but as the differential wears this end play will increase. It is much more noticable with the Auburn differential because of the way this differential is designed. Replacing the differential will take care of the problem. This problem also shows up with the Eaton Posi and some other differentilas, but it is much less severe. You can fix the problem in the Eaton by simply replacing the clutches, The Auburn is a disposable differential, so replacing the whole unit is the only option.

Auburn differential

Stephen

iTrader: (12)

Does the entire rear end move? Or just the wheel & tire your pulling/pushing on?

If the entire rear end moves....Could be bad bushings, in the Panhard Bar. I'd look there, before going through the effort of opening the differential.

ckk981

Stephan:The panhard bar is new, and the bushings look good there, so i dont think its there. Unfortunately i have only pushed on the wheels and the car when the wheels were either on the ground or it was jacked up by the pumpkin.. so i dont know if it moves the whole rear or not..

big gear head: How can I tell if it is an auburn? Or do i just have to open it up? And when you replace it, do you replace the pumpkin, or just the peices inside it? I am still learning how the rears work, I didnt know that Auburn and Eaton had such big differences, I guess they are more like different systems then different brands. It is the stock rear, btw.

Also, I have done some research and found that other f-body have had similar things going on with them.. some needed spacers that had worn in the pumpkin, and others it was the top shock bolts and the play in the rear was acceptable. I will check the bolts, hoping thats it cause how nice would that be! If not.. opening it up will not be a big deal. Thanks everyone and anything else you can add would be great!!

tom3

Might check the RPO codes to start with. Look for a code G80 to see if it has a posi rear.

big gear head

The Eaton Posi was never used in these cars, so you can rule that one out. The Auburn was used most of the time and the Governor Lock was used sometimes. You will have to remove the cover to see exactly what it is. If you have the Auburn you will have to replace the complete differential as seen in the picture that I posted above. The internal parts are not serviceable. I highly recommend replacing an Auburn with an Eaton.

ckk981

It is a G80. If everything checks out I will pull the cover later this week and take a look. Thanks so much for all your help, and I will def be back for some input if I wind up doing the diff myself. Thanks again!

Where would you recommend I go if I do have to get a new posi Unit?? Jegs or Summit or something like that?

big gear head

Read this. http://www.nastyz28.com/forum/showth...t=install+posi