UK member here with an R56 factory JCW.

Just recently i've noticed a problem which can best be described as :

- Pulsating feel when applying brake pedal, but can only be felt at low speeds and lightly pressing the brake pedal, hard braking and higher speeds it cannot be felt at all.

- Thought this might be tyres, but just had all the awful runflats replaced for some Uniroyal Rainsport 3s (non runflats) and the issue is still there.

- Cannot be felt through the steering wheel, just pedals (chassis and seat slightly too)

- Almost feels as though i'm driving over a road that's got a constantly rippled surface, and could almost be mistaken for engine hesitation / as if it's going to stall.

So my thoughts were :

Sticking caliper (How common is this on the JCWs front 4 pots?)
Broken wheel bearing
Buckled wheel (surely would have been noticed when tyres changed)
Or an outside bet of knackered coilpacks / plugs / clutch / flywheel? (don't ask how I reached these possibilities - I think this problems slowly driving me mad!)

I really hope you can help.

Anthony

 

It's certainly hard to try to diagnose from the armchair. In my experience, a failing wheel bearing will make a lot of noise that increases in volume and pitch as you go faster, but no feel through the pedal.
Are they original rotors? This would be my first guess, based on the symptoms you're describing. As you increase speed, the imperfections in a "warped" rotor tend to smooth out and become less noticeable. I doubt it's the pads, as they have a sensor that's supposed to tell you when you don't have much pad left.
If they're old enough, I'd change the rotors and pads anyway. If the rotors have imperfections in them, they'd be nearly impossible to see with the naked eye.
I'm sure others will chime in. Just throwing in my two cents.

 

If you aren't feeling it in the wheel I would be more inclined to say it's something with the rear brakes. 9/10 times you have a warped rotor or pad issue in the front of the car you'll feel it in the wheel too.

I've never seen the JCW calipers with a seizing issue, let alone the factory front calipers but anything is possible. What I have seen is the rear caliper piston boot gets twisted and torn when whomever is doing brakes and ends up causing the rear calipers to lock up solid when exposed to the elements.

Short of seized calipers I've also seen the rear pads get jammed due to the anti rattle clips being covered in crap and rust which caused overheating issues and warping.

 

Welcome to NAM. +1 for a warped rotor being the source of your problem. Till it's fixed try not to go bonkers. We're already full up with crazy round here

 

Many thanks for all the responses - are warped rotors common on these? Never heard of a car getting a warped rotor, always thought it was internet hearsay.

Trying to find the correct sized discs is a nightmare - just to check, on a 2013 JCW, fronts are 316mm and rears 280mm - am I right?

Many thanks

 

Yep