Electronic Handbrake On X7

[twoseefives]

Problem ..  brake pedal pulsing and vibration through car when braking.This was traced to rear discs and  pads  not expensive to change .Have done less than 15000 miles problem has resurfaced On examination the rear discs are badly scored and clear evidence of disc pad outline can be seen on both discs.The car is used most days so whats going on here .Ive told her indoors not to use the handbrake just place in park.It might be me but  ive never felt the brakes are up to the performance of the car .I renewed the fronts at the same time they are perfect .Awaiting comments!

[paul.h]

Is the abs working as you brake since this would give a rapid pulsing felt in the pedal ? Otherwise, a pulsing pedal could be the run out on one or more discs could be too much or possibly a brake piston is a bit seized or a caliper slider. When the discs are replaced the runout should be checked and if high the hub/disc contact faces checked again for being clean/smooth and possibly the disc rotated against the hub 90/180 degrees and checked again. If it is high then problems may not happen immediately but come to light later, which could be your case.

 

I think the max runout is 0.05 mm and needs to be checked using a dial gauge resting against the disc face as the hub is turned. You can still do this check with the wheels removed in turn. The dial gauge needs to be clamped to something and I usually use an axle stand base on the ground with the dial gauge clamped to it with something like mole grips. Then position it so the gauge rests against the outer area of the face and rotate the hub watching the readings on the dial. I would also check the front discs so these can be eliminated.

 

Whilst you have the wheels removed it would help to clean up the brakes so everything is easy to move and not seized by brake dust. Something that should be due anyway after 15000 miles. This may not be that easy with the electric handbrake and if new pads are fitted I think you are supposed to have the handbrake calibrated with a diagnostic.

 

I have seen on our cars the rear discs do not seem to wear as smoothly as the fronts so this in itself may not be too much to worry about.

 

This is also some thing else to check from the Common Problems topic:

59. C5 X7 front discs warping.

Something to check, copied from a post by taximan61:

Got the car October 2015 when it was 4 years old and had 115k on. One owner and with a full dealer history, paid £4500 for it. Had a recurring problem with front discs warping, 2 sets only lasted a couple of months. Garage eventually sorted it, inside the caliper pin rubber guides there are plastic spacer rings, these go brittle with the heat and jam the caliper, used to be a problem on the old AX models I'm told. These were removed and all is well.

[twoseefives]

Thanks for reply,all comments noted.I have been looking  cars with electronic handbrakes and the majority have badly scored discs when compared to the fronts so something going on here.As alot of pad material uses various metal inclusions i,m wondering if electrolisis is at work here also.Cast iron when cooling causes condensation obviosly if the pad is clamped on the disc no air is present condensation cannot occur but i does occur arround the pad hence the outline.The pad has to rub this rust off this is where the scoring is occuring.I have the ability to drill the discs so will see what happens in another 15000mls

[paul.h]

I would not drill holes in the discs, it will weaken them and as a modification you would need to tell your insurance company. The rear discs on our C4 (manual handbrake) are slightly scored unlike the fronts and when I cleaned the brakes a few weeks ago I used 180 grit emery paper on them to remove the glaze and also on the pads as usual.

[twoseefives]

I have drilled discs before with excellent results.Nearly all hiperformance  machines have drilled discs check most motorcycles.these are just the rears I will do the fronts later. Past disc drilling resulted in sharper feeling brakes and longer lasting discs particualy on vented ones.

[coastline taxis]

have u got hill assist on the car. this eats the pads and disc 

[twoseefives]

I,ll hang my head in shame to say I have no idea ,its auto so i would think not.I,ll keep an eye on them to see how quickly they score.

[paul.h]

Just thinking, if it is an electric handbrake then I guess you put it on but it puts itself off, so effectively the same as hill start assist.

 

This is copied from a 2011 handbook:

Release

The electric parking brake

releases

automatically and progressively

when you press the accelerator:

ï†

with a manual gearbox (first

gear or reverse gear engaged)

 

press down fully on the clutch

pedal then press on the accelerator

pedal and move off.

 

with an automatic gearbox , accelerate

with the selector in position

D, M or R .

[Routemaster1]

have u got hill assist on the car. this eats the pads and disc 

 

Really? It only applies the brake and releases as soon as you start to move!