Rear Brake Judder?

[alistair260661]

I have a CLK 270 CDI - 2004. 82k miles - 5 speed auto

Have had a problem for sometime with a rear braking judder type noise and feeling coming through the body of the car (rather than the steering wheel) when I perfom firm (as against light or hard) breaking from about 40/60 mph (below and above that there is no issue) particular when coming down a slope to stop at a junction.

This has got worse recently - and indeed is now quite alarming with more vibration and noise like I'm running over rumble strips on the road, and it has also just started to do it when braking on long sweeping bends - particularly to the right). However the car does still stop quickly enough. I did notice that it got worse after being laft for a week at the airport (with the parking brake applied - I never normally use it)

The rear tyres are to MB spec (size) and don't appear to be warped, tho they are quite low on tread, but legal. Rear pads quite new, and the discs don't have any markings or scoring on them. Front tyres and pads are new.

So I took it into kwikfit to get a look underneath (for free), they found that both rear springs were broken - at the last turn at the bottom - so I replaced them. They checked the braking performance and found brake pressure on the rear wheels to be constant and balanced. So the discs aren't warped, and I know the pads have plenty of life in them. They also checked all the rear suspension mounts / prop shaft and could find nothing wrong. the symtoms continue.

So any ideas what it can be. I wondered about an ABS fault (a wheel sensor?), but surely that would have shown up in the brake test? I have no dash fault warnings at all.

The mechanic suggested that it could need to have gearbox/torque convertor fluid and filter replacing (he said due at around 80k miles) - I don't understand his reasoning - I have no problems with the gearbox - it changes smoothly and there seems to be no slipping - but I am doubtful about fluid (not the place to start in cost terms alone).

[keyhole]

Hi. I know that you are new, but would you please complete your profile with User CP, showing model/year/location as this is often useful in future posts

First, about your ATF change. Your mechanic was quite right about advising you to change the ATF and the filter - if they have never been changed before. We all know that MB originally said that it was not neccessary - but they changed their mind later after some problems.

So get that filter changed asap, (should have been done at 60k miles) and the ATF will also get partially changed, as the TC cannot be drained on your model of transmission. Get someone who knows they are doing to change the ATF. It must be done properly. Probably needs about 5 liters to do the job.

Read the 'stickies' in the W210 forum for details on this task (they use same 722.6 transmission there)

About the brake issue. Are you sure that you are not just feeling the normal ABS pulsing through the pedal that occurs with sharp braking?

I know that you think that your rear rotors (discs) are not warped - but how do you know this?

[alistair260661]

thanks re the transmission - I will get that done.

Braking - its definately not just the normal ABS effect when it cuts in. This is much stronger with a solid thumping like going over rumble strips on the road - its also fairly new and I've had the car 2 years. the thump varies with the road speed - and is very pronounced in long sweeping curves, or going down hills under braking.

As to the discs - I know they aren't warped because when the car was on the rolling road brake test machine in applying the brakes the readings on the machine stay constant as the wheels turn/slow down. If they were warped then the reading would rise/fall in a regular cycle as the wheel turned (so the guy in the kwikfit said) - at least they should know about this for sure. Hence my thought about a faulty ABS sensor - kicking in when there is a load on the car (going down hill) when braking.

The only other thing I can think of is a fault coupling / joint in the prop shaft............but I had a shaft go on me years ago (in a BL) and it doesn't sound the same..............

[keyhole]

Originally Posted by alistair260661

...... Hence my thought about a faulty ABS sensor - kicking in when there is a load on the car (going down hill) when braking.

These are simply speed sensors located on the front/rear axles that pick up a pulse on every revolution of the wheel. I don't see how they can be speed sensitive.

The only other thing I can think of is a fault coupling / joint in the prop shaft............but I had a shaft go on me years ago (in a BL) and it doesn't sound the same..............

There is a flex disk coupling at the transmission end of the prop shaft that does degrade over time. You ought to be able to see if the material has begun to break up. I suppose this might give you a vibration problem at certain loads/speeds when braking.

The service docs advise checking them every 4 yrs/ 50k miles

[alistair260661]

could needing a tran fluid change cause my judder problems? braking and the engine/gearbox trying to drive at the same time?

I'm stumped, and scunnered

[keyhole]

Originally Posted by alistair260661

could needing a tran fluid change cause my judder problems? braking and the engine/gearbox trying to drive at the same time?

No - that doesn't compute...

You reported a noise & judder while braking, so we must assume that the problem is closely associated with those parts. Why not change the pads. You said that they are not worn out - but change them anyway - they are not expensive. Check that the required 'retaining plates' are there. (thin plates that stop the pads moving sideways) A previous owner might have left them off. I can post a drawing if required.

Check that the pistons in their calipers move smoothly in/out. No jamming by rust, etc.

Let us know how you get on.

[keyhole]

Another question..

How long have you had the car, and did the braking noise start after any special work on the brakes/tyres, etc?