Clunking...I'm running out of things to replace

[T-Bone028]

Hoping to get some additional ideas on where else to look for the infamous Z "clunk".

 

Little history:

 

I snapped two u-joints about a month ago. Since then, I have replaced all 6 u-joints (both half-shafts and driveshaft), re-torqued every single thing underneath the rear, and still, upon initial acceleration and in between shifts, I get the clunk.

 

Most people would say, "its your diff mount, search "R/T mount" and you will find your solution"...unfortunately, I dont think thats the case, which is why I'm posting. My stock rubber differential mount was replaced with a solid unit, so I doubt that its my diff lifting upon acceleration or shifting. I know most people will chime in and say that a solid mount is overkill for anything other than a track only car, but I would think that regardless of whether or not its necessary, the fact that I have a solid differential mount should eliminate it as the culprit, correct? Since all of my u-joints were replaced within the last month, and they have all been properly greased and inspected for binding before install, I should be able to eliminate the u-joints and driveshaft/half-shafts as the source, correct? I have re-torqued everything underneath the rear, so I dont think its something easy like loose bolts on the mustache bar. So where else to look?

 

When I jacked up the rear of my car yesterday (again), I did a non-scientific test to see if I could replicate the clunk. When turning the wheel/tire by hand, I can replicate the clunk that I hear in-between shifts or during the initial acceleration. To me, it seems like a bit of slop that I just cant find. The only other thing I can think of is to drain and refill the differential and hope that helps smooth it out. The differential fluid was replaced just about a year and half ago, so I dont really suspect it as the source. Any other suggestions? Could it be that the solid diff mount is just amplifying what would normally be masked by a rubber style mount? I'm on the list for another production run of R/T mounts on classiczcars, but I'm not sure if swapping will actually help or resolve my issue. Any help would be appreciated.

 

My rear-end setup:

 

Refurbished driveshaft with new Neapco u-joints

3.7 LSD R200

New Neapco Brute Force u-joints on both halfshafts

Energy Suspension bushings

Solid differential mount

Stock arrestor strap on top of the diff

MSA rear sway bar

All re-installed components were installed with lock-tite, everything else was re-torqued

[KillerBjt]

Well i am not a expert by any means but it sounds to me like you have to much play in the differential between the ring gear and the pinion.

[T-Bone028]

Thanks KillerBJT, thats something I DIDNT want to have to address HAHA. Ugh...I'm a shade-tree mechanic at best and this is something completely out of my league and out of budget right now. I mean the car is completely driveable, I just dont want to be driving down the road when all of the sudden my differential explodes while cruising at 60 mph. The only thing I've started noticing since I replaced all of my u-joints is some sublte gear whine on deceleration. Seems new to me...but then again maybe I never paid attention to it and couldnt hear it over my radio. (I replaced all of my u-joints because I broke 2 of them on an overly aggressive launch at the drag-strip). I'm going to drain my diff soon and see if there are any obvious signs of metal shavings or debris, but other than that, I'm out of ideas for my skill level.

 

Any other Drivetrain doctors want to chime in on how to diagnose excessive play in the differential for the average weekend mechanic wanna-be with limited tools?

[Kevin.pk]

This is a long shot but a loose gland nut on the strut can cause a clunk. You would also hear it on big bumps though. This happened on my car the other day, so I figured I'd through it out there.

Edited July 26, 2010 by 280zcar