Jerky braking & tracking question

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BenzB82

New Member
Joined
Mar 21, 2021
Messages
8
Location
Milton Keynes
Car
W209 CLK 240
Hi everyone,

I own a 2004 Mercedes CLK 240 and it recently had a new lower front suspension arm changed by the garange and subsequently they re-did the tracking. I was told, but stupidly enough didn't ask any further, that they needed to re-gas it to do the tracking. Any idea what they could mean with that?

One thing I noticed since they did the work was that the car now seems to jerk back and forward quite a bit when braking, especially when braking relatively slowly, before a traffic light. It's not as bad when I brake harder, so I'm just trying to figure out what the cause for that could be. I don't feel anything through the brake pedal or steering wheel. It's rather the whole car that seems to jerk for a bit.

Thanks for any help!
 
They redid the tracking but did they check the geometry?
The pulsing you are feeling sounds more like pad material deposited on the discs. Try a few high speed hard braking (but not to a complete stop) and see if it clears the pulsing.
I'd also ask to get the suspension geometry checked and set properly
 
They redid the tracking but did they check the geometry?
The pulsing you are feeling sounds more like pad material deposited on the discs. Try a few high speed hard braking (but not to a complete stop) and see if it clears the pulsing.
I'd also ask to get the suspension geometry checked and set properly

No I don't think they checked the geometry.

I did try the high speed, hard braking but it didn't seem to make a difference. The strange thing is that I can't feel it when I brake at higher speeds, only at lower speeds, and I don't feel anything through the brake pedal or the steering wheel. Both of them feel absolutely fine while the car just rocks back and forth quite a few times braking slowly to come to a complete stop at a traffic light. It almost feels like what I guess would be an ABS braking? It feels like the brakes get applied slightly and then let go, applied, let go, etc.
 
ABS you would feel through the brake pedal. What you describe is classic symptoms of disc contamination.
I wonder did they remove the brake disc at any point? If they may have trapped grit between the disc and the hub, causing the 'wobble'?
Worse case scenario, they've not torque up one of the bushes properly?
 
To me, it sounds like they haven't tightened the arm properly and it's moving slightly under braking
 
ABS you would feel through the brake pedal. What you describe is classic symptoms of disc contamination.
I wonder did they remove the brake disc at any point? If they may have trapped grit between the disc and the hub, causing the 'wobble'?
Worse case scenario, they've not torque up one of the bushes properly?

To me, it sounds like they haven't tightened the arm properly and it's moving slightly under braking

Thank you! I'm going to give them a call tomorrow morning to see if they can check that its all properly torqued to spec.
 
So a little update: They just called and couldn't find anything wrong with it. All bolts are tight and nothing really stands out. They said there's a little bit of play in one of the wheel bearings, but nothing that would cause the jerky braking. They test drove it as well and can feel it, but just can't find the reason for it 🤷‍♂️
 
Just picked the car up again. We talked a little bit further and he said there's a little bit of play in some of the suspension components, but nothing major. He described it as feeling a little bit spongy when testing it with a pry bar, so that could possibly be a reason for it.
 
Only changing one control arm is never a good idea, generally speaking you should always do both sides of the axle when it involves suspension or brakes etc. Checking the tracking is only one part of the job, you need four wheel alignment as the camber may be out after the new arm was fitted. Is the steering wheel centralised, does the car pull to the left ? Without proper alignment the front tyres will be destroyed very quickly. The issue with the brakes may or may not be related to the work done on the suspension.
 
Only changing one control arm is never a good idea, generally speaking you should always do both sides of the axle when it involves suspension or brakes etc. Checking the tracking is only one part of the job, you need four wheel alignment as the camber may be out after the new arm was fitted. Is the steering wheel centralised, does the car pull to the left ? Without proper alignment the front tyres will be destroyed very quickly. The issue with the brakes may or may not be related to the work done on the suspension.
Agreed general rule of thumb if one parts worn the rest is not far behind may as well bite the bullet and do it all at once chances are its done 100k+ at that point so it will all be a little sloppy
 
If they found play in the front wheel bearings they should have adjusted it out to eliminate it as part of the problem , it's easy enough to do. You might have to get this car up on an MOT four post lift with wobble plates to give the front links a good looking at.

Brake disc contamination has been mentioned. look at the inside of the disc rotors they are often in much worse condition than the face you can see through the wheel spokes.
 

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