Clunk from rear

[Wasatch7]

Hey guys just picked up my Z3 2.3 and was driving when I realized a clunk coming from the rear when shifting. It's worse in higher gears. I'm hopefully gonna have it up on a lift today to check everything but anyone have any suggestions? I've read that it may just be drive train play but I don't think it would be this loud with just some play... Let me know what you think

 

[GazHyde]

There are a few things which may go clunk under there, so a visual inspection is definitely first port of call.

The diff mounts and the prop shaft bush are possibles.

 

[vintage42]

... just picked up my Z3 2.3 and was driving when I realized a clunk coming from the rear when shifting...

Did you just pick it up from buying it? Or did you just pick it up from a service shop, and the clunk was not there before?

 

[zedonist]

Diff mount
Detached ARB links
Worn ARB bushes
Broken rear spring
Worn damper
Worn damper top mount
Hand brake cable loose
Han brake mechanism in the drum worn
Fuel tank straps perished

All easy to check for, nearly all easy to fix, fuel tank straps a little more difficult but doable

 

[pgunter]

Have a similar issue on my 99 z3 2.0. Seems it's a case of slowly replacing the worn and tired bushes etc until you find the one. Rear axle and diff bushes replaced.. Now onto rear ARB and onwards.

Still the pleasure you get from the open road makes up for the workshop time.

 

[oldcarman]

Check your boot also, could be a little kid hiding in there wants out. I chased a clunk for a week only to find a tire wrench stuck in the fender well. HTH JIM

 

[Wasatch7]

I looked at it and I had a trusted mechanic look at it and from what we both saw everything looks good. The only thing we couldn't see was the prop shaft carrier bearing under the heat shield.. Other than that it looks good. I just bought the car a few days ago so just trying to figure everything out.

 

[oldcarman]

Hang in there, you'll figure it out. My money's on a U-joint! Grab the prop shaft like you're a 19 yr old at your first porn party and shake the thing in all directions. Any play anywhere's where the clunk is coming from. HTH JIM

 

[EnthuZiaZT]

Perhaps it could be something quite simple, like a loose exhaust bracket, even that would make a clunk as you change gear!!
Mike.

 

[Wasatch7]

Hahaha well since I am 19.... I thought it could be the exhaust as we'll cause it is missing one of the hangers, but I was trying to move the exhaust and it has no where near enough play to move every time I shift. So yeah I'm thinking it has to do with the drive shaft. I'll see what I can find when I get it in the air next.

 

[vintage42]

There are a few things which may go clunk under there, so a visual inspection is definitely first port of call. The diff mounts and the prop shaft bush are possibles.

Two others are the differential mount and the trunk floor channel it's attached to.
http://www.aboutautomobile.com/Complaint/2000/BMW/M+Roadster/Frame
http://forums.bimmerforums.com/foru...nt-Diff-Mount-Failure&p=27394422#post27394422
http://forums.bimmerforums.com/foru...he-definitive-subframe-strategy-thread/page37
http://forums.bimmerforums.com/foru...frame-strategy-thread&p=25841928#post25841928

 

[Wasatch7]

So I got the chance to look at everything again today. Found three things I didn't like. First my spare tire was blown, so it's completely useless. Decided to just take it and the plastic box out to save some weight. Second it looks like a few of the spot welds have been compromised. One isn't holding anymore.. Third the diff mount has a very small crack in it and the bushing is torn. I couldn't really get to the prop shaft to check play but I don't think that's the problem.. I think it's the diff bushing being torn that's causing the problem.... Here are a few pictures. There is the 2-3 bad welds, and the rest that look good as well as the diff mount and bushing. Let me know what you guys think...

 

[vintage42]

... First my spare tire was blown, so it's completely useless... Second it looks like a few of the spot welds have been compromised... Third the diff mount has a very small crack in it and the bushing is torn...

You will not be able to find a new tire. I got one of the last a year ago. My old tire was good as new and is for sale:
http://forums.bimmerforums.com/forum/showthread.php?2074255-Z3-Spare-Tire

The spot welds fail progressively, those that are left getting more stress. Maybe you can find a body shop that is qualified to install Randy Forbes' kit.
http://www.bimmerfest.com/forums/showthread.php?t=575148
It is the best solution to rear subframe failure. Look through all the sub links in here:
http://www.bimmerfest.com/forums/showpost.php?p=7483980&postcount=2

 

[Wasatch7]

Ive been looking and cant find anywhere to actually get the kit. From him only probably..... The thing is that is a bit outta my budget right now, so is there anyway to strengthen the diff mount and the bad welds? Also what is a good diff mount bushing to use? Ive heard the OEM rubber is best for reducing stress on the diff mount...

 

[vintage42]

Ive been looking and cant find anywhere to actually get the kit. From him only probably... outta my budget right now, so is there anyway to strengthen the diff mount and the bad welds? Also what is a good diff mount bushing to use? Ive heard the OEM rubber is best for reducing stress on the diff mount...

I have watched the threads for almost two years and have seen no alternative to Forbes' method. He is the sole source. He says any highly qualified body shop can read his instructions and install the kit. They just have to be willing to do the radical surgery of cutting out and replacing the trunk floor channel.

Drilling and bolting, and piecemeal welding, are temptingly easy, and buy time, but are not permanent. There are threads on those measures.

A cracking differential mount can be cut out and re-welded back doubled up, two mounts fused into one. This restores full stress to the trunk floor channel.

The rubber bushing is said to cushion the stress transmitted from the differential mount to the trunk floor channel.

 

[Wasatch7]

So no way to re weld the spot welds or something? So OEM bushing would be best? Also the Flex Disc isnt gonna make a clunking noise would it? cause it has some cracks in it and I know that needs replacing soon.

 

[vintage42]

So no way to re weld the spot welds or something? So OEM bushing would be best? Also the Flex Disc isnt gonna make a clunking noise would it? cause it has some cracks in it and I know that needs replacing soon.

Some people have replaced popped welds with bolts:
http://forums.bimmerforums.com/foru...riveshaft-clunking!!!&p=26357354#post26357354
https://www.facebook.com/photo.php?...31875586.55834.100001086122733&type=3&theater
https://www.facebook.com/photo.php?...31875586.55834.100001086122733&type=3&theater
One person made a brace using the differential:
http://forums.bimmerforums.com/foru...ear-Subframe-Question&p=27669262#post27669262
Others have welded pieces of metal and brackets here and there. I think that is what the Dinan kit does:
http://forums.bimmerforums.com/foru...an-Subframe-Reinforcement-and-Camber-Kit-pics
http://forums.bimmerforums.com/foru...r-work-completed-Dinan-sub-frame-kit-and-more
From what I have read, over time, the only repair known to be permanent is the Forbes kit.

A cracking differential mount can be repaired and strengthened:
http://www.z3bimmer.com/Garage/Fixes/DiffCrack/index.html
The OEM rubber bushing cushions the forces going into the mount that in turn stress the trunk floor channel. A poly bushing would be hard on the mount.

The flex disk can make a clunking noise if beginning to disintegrate.

 

[t-tony]

I would think the rubber bush is the source of the clunk, which in turn has caused the spot welds to start to fail.

 

[vintage42]

I would think the rubber bush is the source of the clunk, which in turn has caused the spot welds to start to fail.

There may be a connection between a failing giubo and failing trunk floor welds, but not what you think.
If the engine is powerful enough, and applies that power to clutch dumps and hard upshifts, the giubo in the front of the drivetrain can be torn up, and the stress on the differential mount in the rear of the drivetrain can split it and also pull the trunk floor welds loose.
This stress is hard to generate with a 1.9 or automatic unless they are practically abused. The manual 6's can generate this stress if driven hard, or auto crossed.
Both the giubo and the trunk floor subframe can make clunks, but one is not the cause of the other. They are both the result of handling a lot of stress.

 

[Wasatch7]

Awesome!! Thank you so much!! Well what I think I am gonna do is put a new OEM bushing in the rear, new guibo, and since there are only 2-3 bad spot welds for now, put 3 10mm bolts with steel brackets on each side to make that part a little tougher until I can afford and have the time to do the Forbes kit, (which i think looks a lot stronger than the Dinan...), also when I get some time to pull the rear end apartt I will add some stiffer subframe bushings. Any other things I should do for now?? Again thanks guys for all the help!!