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View Full Version : clunk in rear when going over bumps


dcramer
10-26-2012, 02:51 PM
I suspect this is a control arm bushing but wondering if anyone has any other ideas.

I thought it was the muffler, as it happens in corners, but I'm pretty sure it's not. I hear it when I back out of my driveway over the little lip between the road and driveway, mostly when I am on an angle to the bump. Or going around corners.

There's nothing obviously loose. The normal places have been checked. RTAB, and the shock mounts are good.

Anyone ?

Dave

InfiniteDice
10-26-2012, 03:12 PM
Peel the interior trim back on the sides of the trunk. Bounce the car and watch for excessive movement in the shock mounts.

Ahh with your car not sure if you need to peel the cover back or if they poke out, or have an access hatch of some kind.

Could be a number of things, including a broken muffler hanger. Just take a look.

hockeyfan27
10-30-2012, 10:34 AM
I have a similar issue but the noise is not consistent and difficult to reproduce. Usually it goes away on the trip to StanceFactory. Hasn't come back since I had it checked out last.

I'm in to see what you dig up.

T.Dot_E30
10-30-2012, 11:31 AM
Same, haven't pin pointed it. I changed my shock mounts, still there. Changed RTAB still there.

Next I'm just going to rebuild the the whole rear end and change all bushings/rear ball joints. It could be anything from a diff bolt to a sub frame bushing to a rear ball joint, I just can't pin point it, so the plan was to do all at once.

Nick_V
10-30-2012, 11:48 AM
This is a long shot, but you guys should check your parking brakes. I had a rear spring break on me, resulting in the retainers for the brake shoes being partially ripped out of the backing plate. It would cause occasional binding of the shoes on the rotor which manifested as a pretty violent clunk. It was also sporadic and hard to reproduce. I replaced the RTABS to no avail and was losing my mind poring over all the rear end components trying to find the problem. Checking the parking brakes was a desperate last-gasp effort (seemed the least likely culprit) but ended up being the problem.

It's worth a look.

hockeyfan27
10-30-2012, 11:57 AM
best explanation I've heard so far, "make sure the hooker is 100% dead before you stuff them in the trunk"

nevin
10-30-2012, 12:23 PM
+1 on the parking brake. I had the shoe-retaining quarter-turn fasteners pull out of the dust guard. Parking brake would randomly engage while driving, felt like my tranny/diff/rear end was about to explode. Only clue was a subtle brake dragging noise when buildings reflected my car noise back to me.

sb_600
10-30-2012, 12:39 PM
could also be a swaybar endlink...

Dinanstu
11-02-2012, 07:06 AM
Pull the mats from the trunk and examine the metal mounts that the shock(s) is(are) mounted to. Look for hair-line fractures in the metal from fatigue.

It happened to me...

dcramer
11-02-2012, 07:18 AM
Same, haven't pin pointed it. I changed my shock mounts, still there. Changed RTAB still there.

Next I'm just going to rebuild the the whole rear end and change all bushings/rear ball joints. It could be anything from a diff bolt to a sub frame bushing to a rear ball joint, I just can't pin point it, so the plan was to do all at once.


Hmmm. I"m thinking inner bushing but of course the exhaust is on that side which makes it even more of a PITA to do .

going to shannonville tomorrow, one last kick at the can, then I will start tearing it apart.

I'm with you though, one of those bushings must be the problem.

Dave

Dinanstu
11-02-2012, 09:53 AM
You never mentioned if you examined this...

dcramer
11-02-2012, 09:57 AM
In my first post I said I have checked all the usual suspects. Including the shock mounts.

Additionally I didn't mention that I heard the clunk when jacking the car up the other day. I lifted one side up quite high and it clunked.

Dave

Dinanstu
11-02-2012, 10:29 AM
I had to be certain. Some people check the integrity of the rubber mount but not the metal piece.

Subframe bushings might need to be changed...Also check the subframe itself for integrity. If thats the case, change them anyways..

T.Dot_E30
11-02-2012, 10:49 AM
That's a good point, I've been checking that area for cracks each time I look at my mounts but haven't found anything.
My trunk carpet has been out for years, so I do have easy access to it. My shocks have been in and out many times due to the stupid externally adjustable koni setup.

Blades
11-02-2012, 01:17 PM
it could be hundreds of things .. you could be a loose tire iron or spare tire

richie_s999
11-02-2012, 07:03 PM
also check the diff bolt, sub frame mounting points on M3's are reinforced from the factory, so shouldn't be torn, if they are I wish you luck, I tore them right outa my e36, was a hell of a job welding them back in and welding on the M3 reinforcement plates, but it was an excuse to upgrade all the bushings when I had it apart

dcramer
11-02-2012, 10:39 PM
I just put a new diff in the car, so the bolt is good.

I'll let you know what I find after I pull it apart.

Axxe
11-02-2012, 11:20 PM
Exhaust hanger rubber weak from years of heat exposure. Mine got so bad that they broke the seal on the midpipe. Just figured it out the other day. They get too soft laterally and the muffler bangs around in the tunnel. Easy way to check, see if the heatshield in the muffler tunnel has gouges in it from the pinch weld. Could also be the top from over extension over negative curvatures.

iverson03tj
11-03-2012, 07:52 PM
That's a good point, I've been checking that area for cracks each time I look at my mounts but haven't found anything.
My trunk carpet has been out for years, so I do have easy access to it. My shocks have been in and out many times due to the stupid externally adjustable koni setup.

how come u have to take the shocks on and off? im guessing u got he Koni SA's?

dcramer
11-05-2012, 09:12 AM
Exhaust hanger rubber weak from years of heat exposure. Mine got so bad that they broke the seal on the midpipe. Just figured it out the other day. They get too soft laterally and the muffler bangs around in the tunnel. Easy way to check, see if the heatshield in the muffler tunnel has gouges in it from the pinch weld. Could also be the top from over extension over negative curvatures.

Yes, even new they aren't worth a crap on the track. What do people do with track cars ? There must be a decent aftermarket hanger ?

That being said that isn't the clunk that I am hearing I know about that one.

Dave

Axxe
11-06-2012, 08:56 PM
I am going to fill the voids on the new ones with urethane. Also I completely missed the part in your initial post about eliminating the muffler. Mine makes the weirdest noise leaving the driveway, took me a while to pinpoint.

dcramer
11-07-2012, 05:11 AM
I am going to fill the voids on the new ones with urethane. Also I completely missed the part in your initial post about eliminating the muffler. Mine makes the weirdest noise leaving the driveway, took me a while to pinpoint.

Interesting. I'd like to see that and to see how well the urethane stays in.

Dave

InfiniteDice
11-07-2012, 09:21 AM
It stays in well. I've done it. Many bushings come with a wax like coating over the rubber to protect it. You'll need to use a dremel or something on low to just scuff up the rubber (inside the void) a bit, then wash the void out with some alcohol. Fill the void wait 8 - 12hrs or whatever the working time is, then install.

In the case of the e30 rear carrier mounts: The urethane in the void would form a solid 3" long chunk, the carrier mount bottom plate would prevent that from coming out even if it did come loose of the rubber.

The urethane stuff I bought is awesome, hardens up and feels like a hockey puck. Oil/gas resistant, I think it was nearly 20$ at Carquest.

dcramer
07-08-2013, 08:50 AM
OK, I just replaced the rear lower ball joints. I am willing to wager this is where the clunk comes from.

M3's have solid rear lower ball joints. My guess is it takes quite a bit to move them when they are partially worn. So you won't really be able to feel them until they get quite bad. But the car will be able to move them going over bumps etc.

Before you get all excited about replacing them, the bolts are likely rusted in. Mine were. What appears to be a 1 hour job is more like 4. I had to destroy the old ones to get the bolt out.

Now if you had replacement arms and you didnt mind cutting the bolt and damaging the arms it would be much quicker. Course you still have to get the inner bushing and bolt out ....

If I were dropping the subframe I'd be replacing these as a maintenance item.