Mystery : 1 Thunk from Brakes When Almost Stopped - Page 2 - PeachParts Mercedes-Benz Forum

bruce.g.cameron · #16 05-06-2018, 08:11 AM

Not sure, can you tell me what that is? The steering rack has an idler arm (a separate hardmount) and an associated damper to make the steering feel smooth.

tangofox007 · #17 05-06-2018, 02:01 PM

Quote:

Originally Posted by Junkman

Does this car have a guide rod and guide rod mount?

No.

kuene · #18 05-06-2018, 10:25 PM

have you tested the vac line to the transmission modulator yet? I'm really curious to eliminate that possibility. the clunk that I experienced when I had that line disconnected felt nothing like a transmission thing, I was certain it was the breaks or some kind of loose suspension part or driveshaft.

vstech · #19 05-08-2018, 03:37 AM

When exactly does the clunk occur?

As you apply the pedal?
As the car stops after applying pedal.

As the car rocks back after stopping.

will_t · #20 05-08-2018, 09:47 AM

Quote:

Originally Posted by vstech

When exactly does the clunk occur?

As you apply the pedal?
As the car stops after applying pedal.

As the car rocks back after stopping.

My car has an identical single thunk. I occurs about 80 to 90 percent into the braking sequence - in other words, just before the car comes to a complete stop. It seems to happen most with moderate to heavy braking, but I don't mean slamming them on. I mean going from 30 to 0 at a stop sign in like 4 to 6 car lengths (or so.) If I start braking rather sooner and bring it in with light to moderate braking it usually doesn't do the thunk.

vstech · #21 05-08-2018, 11:44 AM

Quote:

Originally Posted by will_t

My car has an identical single thunk. I occurs about 80 to 90 percent into the braking sequence - in other words, just before the car comes to a complete stop. It seems to happen most with moderate to heavy braking, but I don't mean slamming them on. I mean going from 30 to 0 at a stop sign in like 4 to 6 car lengths (or so.) If I start braking rather sooner and bring it in with light to moderate braking it usually doesn't do the thunk.

This sounds like suspension unloading. Check the 4link bushings and the lower bearing/ball joint...

will_t · #22 05-08-2018, 12:47 PM

Quote:

Originally Posted by vstech

This sounds like suspension unloading. Check the 4link bushings and the lower bearing/ball joint...

Thank you. That sounds really likely.

BillGrissom · #23 05-08-2018, 10:12 PM

I hear a click in my 1985 when braking certain places, like before a guard shack at a speed bump. My guess is the pad to bracket clearance is too high. Many new pads come with a little bag of spacers you can clip over the pad to take up such play. I have seen those for slider type calipers, like my M-B. Haven't been motivated enough to pull the wheels and check.

bruce.g.cameron · #24 05-19-2018, 07:12 PM

@vstech Thunk happens while applying pedal. If I spent 10 seconds slowing from 20mph to 0mph, the thunk comes up through the pedal at about the 9th second mark. Before the car rocks back and you come off the pedal.

kuene · #25 05-20-2018, 08:14 AM

I sound like a broken record, but I still think it could be a very clunky final downshift into 1. These symptoms sound almost identical to mine. And I thought I had a loose suspension/driveshaft/brake part. It was only on testing that I found the black line to trans modulator was cracked - apparantky happened during a valve adjustment.

bruce.g.cameron · #26 05-20-2018, 08:46 AM

@kuene working on it this morning, appreciate the suggestion!

bruce.g.cameron · #27 05-20-2018, 11:27 AM

@Kuene, are you referring to the driver's side line that goes in midway down the transmission (which has a yellow quick disconnect and is two separate lines encased in a plastic harness)? I didn't take the plastic harness off, but the exterior of the line looked fine.

There was a separate white line running down passenger side of the vehicle coming at the forward end of the transmission.

Here's a couple pictures

bruce.g.cameron · #28 05-20-2018, 11:32 AM

Images of trans line

bruce.g.cameron · #29 05-20-2018, 11:34 AM

@vstech, I checked the four bolts that hold on the lower control arms today. I added a little extra torque to them - they were tight, but not as tight as I would hav expected. I don't think that was the culprit judging by the torque.

I also replaced all four sway bar bushings this morning (and had fun repainting the sway bar - very rusty). One of the bushings was worn (but not oil-soaked). Haven't test driven yet.

bruce.g.cameron · #30 05-20-2018, 12:46 PM

OK, @kuene I found the trans vacuum line going to the rear of the trans (sorry, the earlier one was the electrical connection). Here are some pictures. Nothing obviously wrong, although there was a little oil on the transmission line end.

How did you end up diagnosing yours? Would you suggest disconnect trans side and putting a vacuum gauge on it? I can't quite see where the line starts (it goes through firewall near fuses at drivers side of engine bay).