W212 E63 braking issue, ideas?

[Kris837]

Hi there.

So here's issue.

The drivers side front wheel assembly, after about an hours motorway driving, is considerably hotter than the left side wheel assembly... the car steers, drives and brakes straight

Troubleshooting..

Jack up the front of the car.. both front wheels spin freely, discs not warped
Check for play in the wheel bearings, minimal, but dismantle, clean, re-grease and re-tighten.
Check the pads move freely in the calipers, they do... but, remove the carriers, check the pistons move freely, clean up, apply never seize to the slides, re-assemble.

Apply the brakes.... the discs still spin freely... hmmm..

The brake fluid was changed last service.. bleed the brakes.. no bubbles...HMMM..

Road test... still the same..

Could there be some issue with the 'auto' braking system supplying more brake pressure to one front wheel?

Any ideas?

Thanks in advance..

 

[C36fan]

Hi there.

So here's issue.

The drivers side front wheel assembly, after about an hours motorway driving, is considerably hotter than the left side wheel assembly... the car steers, drives and brakes straight

Troubleshooting..

Jack up the front of the car.. both front wheels spin freely, discs not warped
Check for play in the wheel bearings, minimal, but dismantle, clean, re-grease and re-tighten.
Check the pads move freely in the calipers, they do... but, remove the carriers, check the pistons move freely, clean up, apply never seize to the slides, re-assemble.

Apply the brakes.... the discs still spin freely... hmmm..

The brake fluid was changed last service.. bleed the brakes.. no bubbles...HMMM..

Road test... still the same..

Could there be some issue with the 'auto' braking system supplying more brake pressure to one front wheel?

Any ideas?

Thanks in advance..

try to move the pistons in the caliper you'll find a couple of them a bit stiff.

 

[Hakon]

Difficult one as you've certainly investigated all potential causes, only thought is that something is binding just a little in real world conditions when parts get warm. Not much help, sorry.

 

[Bellow]

Flexible hose collapsed internally?

 

[Kris837]

Hi there, thanks all...

Yes I'm coming round to the idea that one or more pistons might be slightly sticking, I'm going to take it all apart again this morning, use some cable ties to hold the pistons back, three at a time, then gently pump each piston out (trying not to pop it out completely) and push it back by hand to see how things feel.

I did notice previously when I had it all apart, there's quite heavy corrosion in the hollow part of the pistons, I've a sneaking suspicion that the corrosion on the inside of the piston is possibly making the outside of the piston distort slightly, causing it to stick.

I've emailed APracing, Brembo, Brakeparts and Frentech to see if any of them do a piston and service kit for the caliper... Mercedes don't do one and I don't want to spend £900 for a new caliper!

If anyone knows where I might get a service kit from other than the above, please let me know.

Cheers.

 

[Hakon]

Have a look at these

MERCEDES