I need some help here. I have an 87 Formula 350 and I am having an on and off again weird problem coming from the rear of the car. Not sure if it's the rear or what it is, but sometimes, while taking turns or per say driving through a parking lot swaying/steering back and forth, I have a terrible vibration and a metalic sound of some sort. It is not a constant problem, but it has occured twice in the lasw two weeks and it sounds like something is gonna come apart back there. ANy idea what this is.? Is my posi going? It is the wierding thing and like I said, sometimes it there, sometimes not, but it's not a good feeling when it's there. Can this be U Joints or a bad tranny mount. I have a bad feeling the rear is going or my posi, how would I be able to tell? Any help would be greatly appreciated

 

Your posi shouldn't go like that. It is exaclt like a clutch, friction to friction contact, so if it wore off it would do so smoothly and almost unnoticably. The only way to notice it is poor tration or a peg leg burnout! :rockon: (Oh those peg-leggers!)

I am thinking it is the differential of the diferential, The 4 gears in the differential case seem to be engaging a disingaging, so your tolerances may be shot. Check em, you could also be chewing gears if your tolerances are shot.

 

If you're running an Auburn (cone clutch) posi, you need to run "friction modifier" additive with the gear lube or it will make noise similar to what you're describing. If the gear lube was changed and this wasn't added, just grab a tube from your local GM dealer and squeeze it in thru the fill/level hole.

I'd try this first, then take it to a shop if it doesn't clear up and you can't find anything external causing the noise.