W177 - 19 plate. Brake Juddering

[GreenMB]

Hi all,

19 plate W177 A200D automatic. 64k miles.

This is the second time I've had this issue and it's really starting to **** me off tbh. Back in Feb/March time I had this really obnoxious brake juddering issue, it seemed mostly noticeable at high speed or on any journeys longer than 15 mins. Took it to local Merc specialist for MOT as it was due anyway and I mentioned the juddering. They said it was because the wheel alignment was out so they done that. I also as it happened needed new brake pads and discs at the front so they got done too. Got the car back and it was fine and has largely been fine since.

Last few weeks the juddering has come back with a vengeance even worse than before. A passenger mentioned to me one night (before this started again) that he was feeling a bit of a knock/bump in the passenger side but it must have been subtle as I didn't feel a thing. I can't seem to grasp when it happens it does seem to be a bit random but I'm guessing its the wheel alignment again? I had brake discs/pads checked by a friend who is a mechanic and they are all fine. What would cause the wheel alignment to go off?

I am reluctant to keep having to revisit this issue every 6 months to be honest. Anyone any ideas why this keeps happening?

 

[grahamcol]

Welcome.
I'm a bit skeptical as to whether wheel alignment can cause brake judder !
I think the number one thing is the disks themselves and whether they've been fitted correctly (scrupulously clean mating services) and bedded in properly after fitting by gentle braking for the first 500 miles or so.

 

[JoeHorner]

Possibly disks or possibly one of the calipers sticking on its slide.

If the caliper sticks then, instead of "squeezing" the disk from both sides the piston will tend to push it out towards the outside pad. As the pads wear (even a little bit) that forces the disk to flex as it rotates, and that causes judder / vibration.

Tends to be more obvious on light braking from relatively high speed to start with. Pull the pads, remove the caliper, and give the slides / pins a really good clean followed by a little copper grease. Should have been done when they did the pads / disks but......

Do both sides and (as suggested by Graham) pull the disks off and make sure they have good clean mounting faces while you're at it.

 

[EmilysDad]

Welcome.
I'm a bit skeptical as to whether wheel alignment can cause brake judder !...

Likewise
Brake judder can obviously be warped discs but also cheaper pattern discs can give similar effect due to disc thickness variation.
Long story short ..... I only buy OE discs after having problems with aftermarket discs in the past .... & I do know that MB/Ford/Toyota et all don't make their own discs

 

[GreenMB]

Thanks guys. Still not at the bottom of the issue but car is going in for a service soon so will find out I guess.

 

[Uncle Benz]

Warped discs are actually very rare. What’s much more common, but often referred to as warped discs is actually DTV, or Disc Thickness Variation. A high spot on one or more parts of the disc which force the caliper piston back as it passes through the pads and causes the pedal to rise and fall under the foot and if bad enough and on the front brakes, the steering wheel to judder too. It’s commonly caused by one of two things, but there’s a number 3 that’s slightly different, and not strictly a DTV problem - 1. Cheap brake discs. These are often cast of poor quality material. When machine ground flat they work well, but before long the hard spots in the casting are left when the softer material wears away and voila. 2. Infrequent use of the car or being left to sit after washing the wheels. In this case the damp gets into the pads where they are resting idle on the disc and surface corrosion sets in. A “witness” of the pad shape is often left on the disc, and it’s effectively a high spot which again moves the caliper piston as it moves through the pads. Same symptoms as before. 3. Inadequately cleaned mating surface between the disc and the hub. It’s very important to thoroughly clean the face of the hub before fitting a new disc or the disc will not be seated squarely and the runout can wobble the pads with predictable results. I don’t want to see coppaslip or any other product between the hub and the disc, no thankyou. Rolls Royce used to insist that new brake discs were ground to the hubs with carborundum paste and then fully cleaned off back in the day to ensure a perfectly true braking surface. I don’t think they do any more, which is a shame

 

[mioba]

I only buy OE discs after having problems with aftermarket discs in the past ....

Progress fellow

 

[mioba]

Changing disks and pads is easy, any grease monkey can do it,
The art ( like many things is doing it properly), cleaning all mating surfaces, using copper grease, removing and cleaning slide pins and lubricating. ensuring pads slide on the rails.Let alone using a torque wrench for specific bolts. Rattle gun happy.
Not many garages see to these - what appear to be inconvenient but important of the task.

 

[alexanderfoti]

And torquing the ****** wheel bolts properly too! Had lots with bent hubs from 200nm+