question that really could apply to all cars... or just mine

[scheistermeiste]

so i got my dads old baby, an 85 IROC-Z. 1 catch though. when he gave it to me he said there was something wrong with it. he didnt know what for sure, but he definately knew something was wrong with it. well its been sitting in my garage for a few months because i havent had the money to work on it. well today i decided id take it to fill up the tank and see if i could determine what was wrong with it. put it in reverse, pulled out of the garage and started down the street. all was fine and well as i came up to the first stop sign. then the second, still nothing. then i started driving down a longer road at about 40mph all was fine and peachy... until i let off the gas... i heard the most GOD AWFUL grinding noise i have ever heard come from a car, i mean this sound was worse than when i shot a connecting rod through the side of my block in a civic. well i stopped at the stop sign i was slowing down for then started driving again, everything peachy, slow down again and the same noise, it sounded like the longer i coasted the worst it got. BUT i did find out that if i stepped on the brakes with my left foot to slow down while giving it slighty less gas until i stop it doesnt make the noise. the car as i said is a 85 IROC-Z, auto, with posi

so what would it be? u joints? wheel bearings? rear-end? evil elves? any ideas?

thanks guys!

[Rufblackbird]

I doubt it's u-joints, wheel bearings, or evil elves. Where is the sound coming from?

[scheistermeiste]

i personaly thought it was coming from the tranny area, but my dad insists its from the rear

[Rufblackbird]

well you could drain both the gear and trans fluids, drop the pan/cover, and look for big chunks of metal.

[IROC]

I would guess something in the rear end (ring/pinion and or bearings) that is only loaded in the "coast" position. In other words, under load, everything is fine, but when you let off the gas, the loading changes on the ring and pinion and the bearings and other problems pop up.

I had a similar (but not as bad from the sounds of it) problem in my old beloved '83 Toyota 4WD. Ended up being bad pinion bearings.

Good luck,

Mike

[ronin]

Originally posted by IROC
In other words, under load, everything is fine, but when you let off the gas, the loading changes on the ring and pinion and the bearings and other problems pop up.

exactly. the noise is coming from the driveline being loaded in reverse. that's why you're (sheister) not getting the same noise when applying the brakes, as this takes the load off the driveline (similar to coasting). positive load or no load = no noise. negative load = noise. most likely diff related in your case

[RANDY P]

2nd the ring and pinon. Nice thing is that those cars aren't exactly rare - you could probably find a whole rear end for under $100 somewhere. Forget repairing it, just swap it out for good used.

rjp

[Rufblackbird]

agreed....those 10 bolt posi's are everywhere, or you can always get the stronger BW 9 bolt