Hey fellas,

I've been reading through a lot of differential threads lately and I'm starting to wonder if my rear end is shot. I originally thought that it may have been the 4spd. automatic causing all the clunking, or even the driveshaft, but I'm not so sure anymore. I guess when I finish the 5 spd swap, and the tranny and driveshaft are replaced I'll know for sure. From what I have read people describing in other threads, I think it may be the diff. that was clunking under the car, not my driveshaft or tranny. Keep in mind that this is on an 85 GS with drum rear brakes. Nothing fancy.

Symptoms. Car sounds fantastic on acceleration, no knocking or clunking of anykind. Once you let off of the gas and start coasting though, it has a constant, knock knock knock knock knock. It has to be something that is turning under the car because the knock happens at evenly spaced intervals. I don't think it is something that came loose, because it would just do it randomly it that were the case. It also makes one big "CLUNK" if I ever go over a large bump, or a speed bump. It does it when the car is coming back down over a speed bump, not when it first hits it. As long as you've got your foot on the gas when you're driving it doesn't do it though.

I am fairly certain that the previous owner was pretty rough on the car. He had incorrectly installed a header and a few other things on the car before I purchased it, for the sake of "performance". I imagine that he beat it up pretty good, and was probably dropping the 4 spd. auto from neutral to drive doing burnouts. Would the rear take the abuse from this or the tranny? I'm guessing both. I know this may seem irrelevant, but I want all the facts out on the table so you guys can make a proper diagnosis for me. I wouldn't be at all suprised if the rear was damaged, I just hope it isn't.

Is there any way that I can go out and run a check on my rear diff somehow? The car has no engine, or tranny in it right now, so driving it is pretty much out of the question for another month. I found another rear diff setup for really cheap locally, so if mines bad I wanna snap up this deal I found, and get it fixed. Any and all suggestions welcomed. Thanks in advance guys!

 

C'mon fellas! I'm in need of some quick help here. I gotta snap up this rear end if mine is bad. If I don't find out soon someone is gonna beat me to it!

 

doesn't sound like a internal rear end issue.....it sounds more suspension related by the way you describe the speed bump clunkcheck all you suspension bushings really well.

 

I'm thinking U-joint ! Best to wait for the 5-spd and see how it goes.

 

I would say put it up on jackstands and check all of your U joints.

But that is just a shot in the dark. Exhaust all options before going for the big switch.

 

I'm having the same problem with my 85 GS auto. Same story, everything is fine until I decelerate, then I get an evenly spaced clunk until the car comes to a stop. I've never noticed a clunk over speed bumps, etc, but I'll start watching for it. Tried another used drive shaft with no change. I have an 84 GS 5-speed that is the organ donor for a 5-speed conversion. I'm going to swap the center section of the differential from the 84 to the 85. I'll let you know how it turns out.

 

I'm hoping to have the car running with a 5 spd. and a different driveshaft in the next few weeks, so hopefully the problem will disappear. I just am rather skeptical that it will still be there. The clunking is coming from the rear end somewhere, so it may be exhaust, suspension, driveshaft u-joint. I just don't think its the tranny because of where the noises are coming from.

What could be doing this as far as the suspension is concerned? Why would my car do it on deceleration only? Any ideas? Thanks for the responses so far.

Jamie

 

Check the back lash on your diff, borrow beg steal a mag mounted dial gauge indicator, place it on the houseing, and bend its adjustment ionts until the dial gauge sut touchs the ring gear on one of the teeth. wiggle the pinion shaft clock, counter clock a litle and record the back lash, then check with a service manual. the backlash is easily adjustable on the sa/fb's by the two adjustment rings on the side of the assembly, screwing them in or out moves the ring gear right or left depending upon which you need, more, or less backlash. my guess is of course less backlash. if you can't get a dial guage then mark the adjusters, and tighten it down a little on one side, and loosen on the other to move the ring over, and try. beware of going to far, it would change the contact patch on the gears, and increase wear if you go to far.

the slop between the gears is probably the culprit for the knocking you here.

ken

 

Ken,

Thanks for the great advice. I'll definitely give that a try once I get my hands on a dial indicator. I never thought to check my Haynes manual. I don't have a factory service manual. I really should get one. They have lots of stuff that the Haynes manuals don't, or so I hear....