Banging noise after rear subframe rebuild - PeachParts Mercedes-Benz Forum

Biodiesel300TD · #1 10-14-2012, 06:19 PM

A couple of months ago I replaced the trailing arm bushings, subframe mounts, differential mount, and springs in my 78 240D. I immediately started getting a hard, loud, metallic banging noise from the rear when I went over large bumps or train tracks. I thought is was the bump stops on the trailing arms hitting since the new springs were making the rear sit so high. The noise has lessened in the past two months but it's still there. I used to be able to drive over a set of train tracks by my house at 30mph smoothly with no noise, now I can't even go 20 with out getting the noise. It's less than it used to be, but still there. Today I put some rubber hose on the bump stops to see if the noise would change but no dice. I'm at a loss as to what could be making the noise. Any suggestions.

vstech · #2 10-14-2012, 09:02 PM

something is put together wrong, or there is something jammed in the subframe area... it could also be the swaybar links or brackets... look everything over. a few months eh? I don't think I'd have been able to drive a day with a new noise after I put together that many parts in the rear.

charmalu · #3 10-15-2012, 01:09 AM

Did you remove the Differential from the Sub frame when you dropped everything, and if you did, are the 4 19mm nuts tight?

Are the upper nuts (17mm) on the shocks tight? or the lower ones?

I was thinking of the Sway bar links also.

The Sway bar couldn`t be hitting the Diff mount as it goes on only one way, found that one out when I had it on reversed.

but could the 4 13mm bolts that secure the Diff mount to the body be loose?

What about the 13mm bolt in the Hub`s?

Charlie

whunter · #4 10-15-2012, 01:43 AM

Quote:

Originally Posted by Biodiesel300TD

A couple of months ago I replaced the trailing arm bushings, subframe mounts, differential mount, and springs in my 78 240D. I immediately started getting a hard, loud, metallic banging noise from the rear when I went over large bumps or train tracks. I thought is was the bump stops on the trailing arms hitting since the new springs were making the rear sit so high. The noise has lessened in the past two months but it's still there. I used to be able to drive over a set of train tracks by my house at 30mph smoothly with no noise, now I can't even go 20 with out getting the noise. It's less than it used to be, but still there. Today I put some rubber hose on the bump stops to see if the noise would change but no dice. I'm at a loss as to what could be making the noise. Any suggestions.

Remove the rear shock absorbers, verify the bushings are all there.
It is possible a flawed bushing crumbled or collapsed.

If the top of the shock is not fully tightening down, it leaves a gap between the bushings.
This sometimes happens because of manufacturer QC issues with washer hole diameter versus shaft diameter.

.

Biodiesel300TD · #5 10-15-2012, 12:25 PM

I did some poking around yesterday. I tightened down the top of the shocks. They were pretty loose, I did reuse the old shock mounts, the ones inside the car under the rear seat looked fine upon inspection. But I couldn't see the ones under the car. After tigthening them down all the way I had no change in the noise. I think I'm going to replace all the shock mounts just to be sure.

After thinking about it some more it seems to make the noise most when the rear suspension end drops suddenly. Like when driving over a set of bumpy train tracks where there is a sudden drop in the surface of the road.

John, I was hoping to avoid having to take it all out again, but that may be what has to happen. It took me two full days to take it out and get it all back in. It's my daily driver, and the only car I have to drive. I've also not had time to pull it all out. I've been out of town alot for work, and only had a few days at home before leaving again.

Charlie, I made sure to double check that all my mounting points and bushings were tight before I put the subframe back in. I did have to fight the whole subframe to get it all alighned. The subframe mounts didn't want to stay in the subframe, but seemed to suck up tight when I bolted it up.

scottmcphee · #6 10-15-2012, 02:16 PM

Spare tire / jack loose in the trunk?

Stranger things have happened.

Biodiesel300TD · #7 10-15-2012, 02:20 PM

Quote:

Originally Posted by scottmcphee

Spare tire / jack loose in the trunk?

Stranger things have happened.

Hadn't thought about that. But I'm not sure that's it. It happened right after the rebuild, and it a really harsh, heavy noise that you can almost feel, not a rattleing noise. I will definetly check, just to make sure. I thought about the exhaust too. But a good shake doesn't seem to make any noise.

Biodiesel300TD · #8 10-18-2012, 09:56 PM

I think I may have found the issue. Hopefully I'm not posting prematurely. I was replacing the shock bushings which all looked fine but I had new one, so I replaced them anyway. Started looking at all the subframe bushings and mounts and the drivers side subframe mount wasn't seated into the subframe all the way. It was out at least a 1/4". I got it seated in all the way, and am in the process of getting mount re-secured. They are a biotch to get lined up right. Hopefully tomorrow I'll find out. I'll report back either way.

Biodiesel300TD · #9 11-11-2012, 06:03 PM

Just reporting back. I think I've really found the issue. The rear is sitting high, and I assumed it was just because I had new springs. But I was looking at the limiter stops that keep the trailing arm and subframe from extending apart to far, and they are nearly touching and mis-aligned while sitting normally on the ground. I've also notice the wheels are canted with the bottoms in closer than the tops. So the tire is riding on the outer edge. I starting suspecting the springs were wrong. I looked up the measurements in the FSM and the new springs wire diameter is a 1mm thicker than the originals, and they are like an inch longer than what the old ones are. So I've got the wrong springs, and it's making the rear sit too high and making the stops bang every time I go over bumps.

charmalu · #10 11-11-2012, 07:53 PM

Where did you source your springs? you were zeroed in on the bump stops early on, so were on the right track.

Charlie

Biodiesel300TD · #11 11-11-2012, 08:26 PM

Quote:

Originally Posted by charmalu

Where did you source your springs? you were zeroed in on the bump stops early on, so were on the right track.

Charlie

I got them from a member here. The were supposed to be 300D rear springs. And I assumed a 300 would have the same rear springs as a 240. They could also be front springs. Never the less I'm going to pull them and put in the original springs. Then I'll measure them and see what car they should be under.

I was thrown off the bump stops because I put some rubber hose on the stops and the sound didn't change. But I think it just cut through the rubber and was hitting so hard the it didn't matter.

wildest · #12 11-11-2012, 10:13 PM

Quote:

Originally Posted by Biodiesel300TD

I got them from a member here. The were supposed to be 300D rear springs. And I assumed a 300 would have the same rear springs as a 240. They could also be front springs. Never the less I'm going to pull them and put in the original springs. Then I'll measure them and see what car they should be under.

I'm interested in them if you consider letting them go.

Biodiesel300TD · #13 11-13-2012, 12:27 PM

They were definetly the wrong springs. Pulled them and put the originals back in and the banging is gone. They've even got the part number on them and they are for a 300D. They are 3/4" of an inch taller and a 1mm thicker than the ones that came out. I guess I should have done a little more research before I stuck them in. Would have saved me a lot of work.

Oh well. Live and learn.