vrs brakes

[moanthebairns]

just picked up my new to me vrs today and have my first little question.

 

the car in general seems fine and has an extensive service history from star performance. No expense spared looking through the invoices.

 

however there seems to be a slight pulse under braking. I noticed it on the test drive last week and it happens maybe 1/5 times braking, that to me rules out warped discs, plus its just had pads and discs 12 months ago. the brakes also perform quite well be it braking from 30 or 120.

 

as I say its just the faintest pulse. its not the abs kicking in as it tends to happen under medium braking and I know what abs feels like.

 

I doubt the pads are glazed as the previous owner doesn't scream the kinda guy who would thrash it even though he remapped it to 254 bhp and the performance is still there under braking

 

next thought is maybe it just needs a fluid change but I would tend to think it might not be that as the brakes aren't spongey, ive ridden/bought plenty of other peoples bikes with decades oil fluid in them and even cooked brake fluid after track days and never had the pulsing due to **** fluid.

 

I turned the esp off after getting fed up of the thing kicking in on cornering well before it needed to (ive never driven with any driver aids, bloody weird I should add). this seemed to stop the slight pulsing or least it never cropped up.

 

so I have a question about the esp now bare with me as ive never driven or ridden anything with any sort of brain apart from my foot and wrist,

 

I know it kicks in the event of a driver losing control while cornering or in a emergency situation and applies the brake it sees fit but under braking does it also redistribute the braking force so its even? I wasn't trail braking all the braking was done in line.

 

as I say its the smallest of pulse could this be why? many wouldn't notice it to be honest but im like the princess and the pee with anything I drive or ride I can normally feel something that feels odd before a mechanic can spot it going on the way out.

 

is it common with the vrs its got me puzzled. its not worrying me Id just rather know

 

 

 

[radders567]

If it is pulsing back through the brake pedal it would suggest that one of the discs has a slight warp. I have not long replaced all of my discs and pads. One of my rears were slightly warped. I was able to diagnose this by driving down the road and applying the handbrake slightly, a light pulse could be felt coming from the back. discs and pads changed and hey presto fixed. You could get a DTI gauge and check the discs.

[moanthebairns]

the front discs have done less that 5,000 miles, but then I remembered cars have linked brakes so the back ones might have a slight warp on it.

 

ill keep any eye on it see if it worsens then I know the discs are ****ed, ill try the old hand brake trick

 

just puzzling that it only happens every once in a while.

 

I should point out thought that the front left was down to 15 psi so that MIGHT have something to do with it especially with winter tyres on.

[D@z]

What year is the car?

[moanthebairns]

2007

[Aspman]

Prob not warped, that's quite rare and would probably mean a duff caliper. It would judder quite strongly all the time when braking, I had that on a Focus, it ate 3 disks on one side before it was picked up properly.

 

It's probably pad deposits baked into the disk. It makes a raised area on the disk face that can pulse when braking.

 

My Pagid disks and pads are prone to this. Solved by taking the car out and driving like a loon. Repeated hard long braking to get the disks nice and hot scuffs off the problem area.

 

http://www.stoptech.com/technical-support/technical-white-papers/-warped-brake-disc-and-other-myths

Edited 20 January, 2014 by Aspman

[moanthebairns]

it seems to have worked a trick, well it hasn't done it since beaker....

 

drove like a "loon" enough to make the brakes stink, made the ABS kick in a dozen times or so under hard braking from high speed and no presence of the pulsing after. I suspect the previous owner took it to the shops and back and up the A9 without touching the brakes much. with brand new discs and pads on it I doubt they have ever really been bedding in properly.

[moanthebairns]

its back.....driving around town you never notice it, driving spirtedly you do. but then i slam the abs on a few times to heat up the pads and it goes.....wtf, then it comes back....

 

i think, possibly it might be the wheel alignment.....or something out of balance or a knackered bearing....

 

at "max" speed im getting a wheel wobble so something is out of balance. 

 

a trip to a hunter machine might be in order....

[Aspman]

Mine comes and goes.

 

I think some disk and pad combos are just prone to it.

 

A wobble off the brakes does sound more like a wheel balance issue.

 

Nothing to stop you having a bit of both

 

Bearing would be noisy, no? Any knocks or bumps when on full lock?

[moanthebairns]

No thats what puzzles me...no noise, no obvious symptoms, its probably never had wheel alignment done in years though.

 

as for the brakes its just under medium braking it happens. hard braking when your close to the abs kicking in and locking up - nothing, light braking - nothing.

 

i wonder, is it a sticky piston.....is it because he has fitted new pads forcing the piston back that dirt has got under the dust seal and the caliper isnt returning when pushed at times. it would explain why it doesnt happen at heavy braking.

[mikey vrs]

I would have thought the "wheel wobble" at higher speeds will be rectified by having the front wheels re-balanced,the fact that the fault goes for a while after hard braking suggests its brake related,id strip the brakes down & check for the pads sticking in the caliper or the caliper slides sticking & have a look at the pistons & seals. 

[moanthebairns]

I have to be honest I haven't bothered my arse to whip the callipers off and inspect the pistons but miracle of miracle its gone.

 

be it braking lightly, medium or heavy.

 

looking through the service history I see the same fault was recorded after 20.000 miles (feels like abs is coming on brakes pulsing) and discs were replaced. then another set as a then another.......so a 57,000 mile car is on its 4th set of discs.....

 

first owner was female, second wasn't the type that seemed to drive it hard. I wonder if a lot of stop start or light braking builds up a glaze on the pads or discs

 

once ive finished working on the bikes ill rebuild the callipers if it comes back but its certainly a weird one

 

I still need to get it set up on a hunter machine ill do that soon

Edited 20 February, 2014 by moanthebairns