Brake Pedal Thump!

[samdring]

Help! Looked on threads and found nothing similar. 4 times in 2 or 3 journeys of some 15 miles have had a thump through the brake pedal. Feels as if the pedal rises slightly then down to normal position and with window down this evening could hear noise from outside underneath.

Most of the ‘happenings’ have occurred at lowish speed. No apparent fluid loss or anything else visible.

Any ideas welcomed please

Cheers

Sam

[GreenV8S]

While braking, or just driving along?

[samdring]

sorry - stupid of me not to say
It is whilst braking although not necessarily severely.
The pedal jumps back up against the foot almost like ABS but certainly with more force and is a single movement.

[shpub]

Cracked or broken discs can cause this as the pad moves over the crack. Worth checking immediately. Could also be a leak or problem with the servo as well.

Steve

[samdring]

Thanks Steve

Am checking discs this morning but suspect that given only happened 3/4 times over 40-50 miles (in 2/3 journeys) perhaps more likely to be servo related. Have also noticed now I think about it that high pitched noise (quite faint) goes on and off on entering overrun (might be off and on rather than on and off!)

Cheers
Sam

[ninja_eli]

Sounds like a a similar problem with my runaround car once, it was warped discs. I had been canning the crap out of the car and after loads of heavy braking I went through a massive puddle. Apparently that can warp the discs. Under braking the pedal would go up and down against your foot. It was really annoying but didn't cost much to sort out!

Good luck

[samdring]

Thanks for the helps guys
Followed Steve's advice - inspected discs - no problem. But!!!on turning jacked wheel felt knocking.
Decided to inspect pads - nice and thick - sort of newish. Nevertheless took apart and inside pad fell off the backing plate!! It was rusted for some 2/3rds of its length where its should have been bonded and was totally free from the plate. Very clear signs of bits chewed out which was causing my occasional thumping on the pedal.
Good job Derbyshire police were around alot last week - hate to think what emergency braking might have done.

Is this a symptom of 19000 mile S2 rarely used over last 10 years (400 mpy till I got it)?

Thanks again

Sam

[Dave_H]

quote:
Thanks for the helps guys
Followed Steve's advice - inspected discs - no problem. But!!!on turning jacked wheel felt knocking.
Decided to inspect pads - nice and thick - sort of newish. Nevertheless took apart and inside pad fell off the backing plate!! It was rusted for some 2/3rds of its length where its should have been bonded and was totally free from the plate. Very clear signs of bits chewed out which was causing my occasional thumping on the pedal.
Good job Derbyshire police were around alot last week - hate to think what emergency braking might have done.

Is this a symptom of 19000 mile S2 rarely used over last 10 years (400 mpy till I got it)?

Thanks again

Sam

My mate next doors a mechanic and I'm sure he had this on a BMW once that had not covered many miles per year over many years. But I don't think this happens too often.

The pads on my cars over the years usually last me about 12-20k, And I've normally covered this distance in about 1-2 years. I don't think the bonding proccess with the pads is meant to last for years and years. If your car is doing such little mileage, and bearing in mind the cars performance does require decent brakes, then I'd personally change the pads/rear shoes every couple of years regardless of their condition.

Never skimp on brakes - it's just not worth it.

Cheers,

Dave.