Please help diagnose Rear end clunk!!

[Kylar]

Hello All, ever since i swapped driveshafts to a 1 piece aluminum and back to stock, as well as doing the upper control arm with an adjustable unit, upper bracket, and rear diff bushing I'm getting a clunk.

Car stats for reference
2005 Mustang GT 5 spd
DOB supercharged
25,000 miles

Parts used
Metco ADJUSTABLE UPPER CONTROL ARM MOUNT
J&M ADJUSTABLE REAR UPPER CONTROL ARM
Steeda Spherical bushing for the Diff side
All new bolts and hardware

The clunk was not present before the mods were done, and the clunk was present with the aluminum driveshaft, so i know its not the stock driveshaft.

Basically if i blip the throttle in any gear I will get a clunk sound, sounds more like metal then like a loose/worn bushing. Also in between shifts if i shift slowly i get the same clunk. Almost like its driveline slop in the rear end itself.

My Mechanic buddy who did the work just zipped off the pinion nut and zipped it back on. He says that he has done hundreds of rear ends and never had an issue. He also said that he didnt torque it enough to crush the collar more. He also said that the spider gears could be worn, or my clutch packs worn out.

We put the car on the lift and he turned the rear wheels and it does look like there is some play in the rear end, he also tried to turn both wheels while i held one, and said that since i could that the lsd is worn out.

Today just to test that theory i found a spot and did a quick burn out, I am still putting down 2 strips, so the lsd seems to be working.

Sorry for the book, but any ideas? Could he have messed up my gear lash causing extra slop? if the spiders and clutch packs were worn would i still be able to lay 2 strips? Could something else be making the noise? Or is it somewhat normal for there to be some slop and clunks

 

[TexasBlownV8]

My Mechanic buddy who did the work just zipped off the pinion nut and zipped it back on. He says that he has done hundreds of rear ends and never had an issue. He also said that he didnt torque it enough to crush the collar more. He also said that the spider gears could be worn, or my clutch packs worn out.

THAT is NOT how you properly tighten a pinion nut. If that was done to "try to fix a clunk" that just showed up, well, that was wrong and may have introduced other problems.
When installing suspension parts, all bolts need to be properly torqued with normal load on them when possible. If parts are put in with wheels hanging from the air, you won't get proper location of them when torquing, and that can lead to clunks. This is of course assuming things were torqued to spec to begin with and not just zipped on with an impact.
Some parts require lubrication as well. If anything had a grease fitting, it should have been lubricated.

 

[mfergel]

I'll tell you what I think it is............that stupid J&M upper control arm. I have the same thing for upper and lower and it didn't exist till I put them on. I think it's slop because the holes in the control arm/control arm mount and the diameter of the bolt are all different and I think that's where the clunk is coming from. My plan is to swap for a different upper control arm AND mount.

 

[Carperson87]

When you replace it let us know if it fixes it. I have the same problem and the same uca and mount.

 

[Brezick]

Spherical bushing for the Diff side

Is this solid? because everytime you accelerate and put load on the rear, this thing is going to make a hella racket. Not saying it is an issue, but it defiantly gives off a metal on metal sound every time you load the rear. at least mine does.

 

[Kylar]

THAT is NOT how you properly tighten a pinion nut. If that was done to "try to fix a clunk" that just showed up, well, that was wrong and may have introduced other problems.
When installing suspension parts, all bolts need to be properly torqued with normal load on them when possible. If parts are put in with wheels hanging from the air, you won't get proper location of them when torquing, and that can lead to clunks. This is of course assuming things were torqued to spec to begin with and not just zipped on with an impact.
Some parts require lubrication as well. If anything had a grease fitting, it should have been lubricated.

I agree, i dont believe it was torqued or done with load on the suspension. im going to make him redo all of that. Everything was greased though.

I'll tell you what I think it is............that stupid J&M upper control arm. I have the same thing for upper and lower and it didn't exist till I put them on. I think it's slop because the holes in the control arm/control arm mount and the diameter of the bolt are all different and I think that's where the clunk is coming from. My plan is to swap for a different upper control arm AND mount.

I actually checked that before the install and im pretty sure the bolt and hole were the same sizes. There was no slop, maybe they fixed the issue in the versions i got.

When you replace it let us know if it fixes it. I have the same problem and the same uca and mount.

Well that doesnt sound promising...haha But Yes i will update for sure.

Spherical bushing for the Diff side

Is this solid? because everytime you accelerate and put load on the rear, this thing is going to make a hella racket. Not saying it is an issue, but it defiantly gives off a metal on metal sound every time you load the rear. at least mine does.

Yes it is Steedas solid metal spherical bushing.

I was thinking it might be the culprit as well. My noise only happens with a quick tap of the throttle, is your similar? I just wanted to narrow it down before removing parts.

On the same note i dont want to have my rear end rebuilt for no reason...lol

 

[Brezick]

yes, mine is only noisy when i load/unload the rear. cruising or highway driving is fine. I want to change to a poly bushing, but that sold one is a bitch to get out.

 

[Kylar]

yes, mine is only noisy when i load/unload the rear. cruising or highway driving is fine. I want to change to a poly bushing, but that sold one is a bitch to get out.

Yeah it will probably be a pita to remove, and most of the poly bushing want you to reuse the sleeve from the stock bushing. So you would have to buy a new stocker, destroy it, then put in the poly bushing...lol

I might just live with the minor clunk if this is what it ends up being.

 

[Kylar]

Minor correction, my upper mount bracket is a Metco, not the J&M. I just looked though my purchase history and noticed. Maybe thats why mine fit better?

 

[05gtowner]

I know when I installed my UMI upper arm I bought some aluminum step down spacers to fix the slack between the size of the bolt and the hole for it in the mount. Check to see if the clunk is there.

 

[Kylar]

I know when I installed my UMI upper arm I bought some aluminum step down spacers to fix the slack between the size of the bolt and the hole for it in the mount. Check to see if the clunk is there.

This is a good idea, but those spacers are for the stock mount which was replaced. I even checked and they wouldnt fit in the new Metco mount, the hole in it was the correct size for the bolt.

 

[nawagner]

I don't remember and not near my car but are the u-joints part of the drive shaft? That might be it if u-joints are the same with either drive shaft.

 

[408Stang]

I'd be checking the following.... In this order:
1. Suspension arms and bolts... Don't forget the one under the rear seat.
2. Driveshaft components.
3. Differential components. Including a complete check of the ring and pinion set up.

I personally think it has something to do with the pinion nut issue based on how you described it being taken off and put back on. If there's slop in there.... Even a little... You'll get a clunk sound on acceleration and deceleration. It's supposed to be set with zero play and about 8 to 15 INCH pounds of rotational resistance.

 

[mfergel]

I need to do some testing on mine as well. I have the UMI UCA and mount and hoping that helps resolve the issue. I did have my rear gears changed out to 3.73's at the same time but pretty positive that isn't where the issue is. Maybe with this UCA I can get the pinion angle a little closer to stock as well since that can't be done with the J&M I have. I have the step washers but they aren't installed. I really don't have the facilities at home to get at the UCA properly. I'll be curious to know your results.