W203 brake imbalance and grabbing fronts

[flwtcher7751]

Hi all

I have the above on my 06 W203 C220 CDi saloon with sports pack
Had new discs and pads nine thousand miles ago at dealers, discs are ridged already !!!!
Braking around 100mph, (private road obviously) it seems to pulse as if grabbing the
discs, it can be felt in the pedal too

Just passed MOT with advisory information
Measurement "RBT brake imbalance : 7%", and
Advisory "Front brake imbalanced, requirements only just met."

Also rear pads wearing thin, so will get these done

Any suggestions on cause and remedy

Car always serviced at dealers so far, but Indy nearby might be the choice now it is eight years old - or will age related discount may make it viable with dealer?
All advice welcomed.

Thanks

 

[markjay]

Ridge (as in deep grooves) or lip?

Lip around the edge at 9k is not unreasonable, depending on how 'deep' it is, obviously.

Ridge within the swept area of the disc is result of either heavy use (regularly braking too late and too hard), or issue with pads or caliper.

With regards to imbalance... could be a few things. Seized piston or caliper guide, or badly and unevenly grooved discs.

Also, when was the last time the brake fluid was changed? If left for too long, it will absorb moisture, and internal caliper parts or master brake cylinder may corrode, or the caliper on one side may have higher water content than the other (keeping in mind that brake fluid does not circulate).

Also - if the flexible rubber hose between the metal brake pipe and the caliper is in poor condition, it will expand and bulge when pressurised which can also cause brake imbalance. Though this would have been picked-up during the MOT.

As for pulsating... assuming these are 'soft' pulses and do not have a 'clicking' sound to them - i.e. not the ABS - there could be a few reasons, uneven or warped disc surface is one, and contamination or corrosion on the mating surfaces between the disc and the hub is another.

In short, strip, clean, replace discs/pads/calipers where necessary, replace brake fluid, and try again....

Also - I am assuming there is no loss of brake fluid (other than very gradual fluid level decrease as the pads and discs wear), or visible leakes anywhere, because if this was the case then it opens-up further possibilities.

Hope this helps.

 

[flwtcher7751]

Hi Markjay

Thanks for your reply and advice

Brake fluid changed by dealers last service, no loss since
Flexis look good, no signs of bulging

Ridges are undulating regular waves across the friction area. disappointed this started soon after replacements.

No imbalance felt, MOT failure is 25% so surprised 7% was an advisory, but l knew the pulsing grabbing needed diagnosing and sorting - shame they weren't able to identify the cause.

I expect another set of pads discs, might do it myself to ensure calipers are free to travel and the pistons too.

How can l test whether the calipers need replacing aside from leaks?

The pulsing/grabbing are severe. l backed off from high speed braking when taking it for a blow out pre MOT - wifes care so doesn't get much swift driving.

I do have a highly recommended indy nearby but am happy to do it myself to ensure the calipers are free to do there work and the disc to hub is clean .

Thanks again