car pulsates/hops when braking?

attila_

This is really baffling me.

The car is a 2003 polo tdi (discs all round). When I brake I feel the car pulsating back and forward (no steering wheel wobble or pedal pulsation) just the feel as if the car is pulsating forward when coming to a standstill.

The sensation is like there is an oil patch on half of the disc and the other half is fine (there are no oil patches by the way). I changed new discs and pads last year and this only happened few weeks ago.

I don't think its the rears as I have pulled the hand brake up during driving and comes to a standstill with no pulsation.

I'm really confused and worried as MOT is up soon.

Any help would be greatly appreciated!

tykesi

Sounds to me like either a warped disc or a sticky caliper.

I had the same symptoms on an old Honda Civic I had and expected the worst ie warped disc. Turned out one of the calipers was sticking on the front, I opted for a brand new caliper which cured the issue completely. I'd get it in for a free brake check somewhere avoiding the large chains who will tell you the world will end if you don't replace all parts on the car there and then.

If it's the caliper like mine was you can probably get it solved for less than £100 and not a huge amount more if it's a disc.

gilbert_and_sullivan

Does the handbrake work on the rear calipers and pads or does it operate small shoes inside a top hat design of rear disc?, in which case the handbrake test won't show.
If its got all drum rear brakes then i suggest removing those too, to check for lining contamination or seized slave cyls or adjusters etc.

Either way i would remove all wheels and remove all pads too (you cannot examine pads properly by peering through the wheel as is the common method of garage 'servicing'), and check everything is working correctly, especially the calipers as suggested above, i would also check all suspension bushes, drive shafts etc whilst down there.

You can spin the hubs whilst there and check for disc run out.

attila_

Thanks both for the replies. I hadn't thought of stuck caliper, will whip the wheels off and have a look.

epninety

attila_ wrote: »

I'm really confused and worried as MOT is up soon.

You really are confused... the important thing here is not that you will fail the MoT, it's that there a fault with your brakes...

I reckon tykesi is on the money - though sometimes pads can twist and jam when worn, which is even cheaper - just a new set of pads.

I once had similar symptoms on a car only used for short journeys... we never found the cause, because I jetwashed it before starting to work on it, and the problem went away and never came back. Presume some contamination on the disk, or dried mud in the caliper, but hasn't happened again in 5 years or so.

EDIT : I just re-read the OP - no feeling in the brake pedal suggests contamination of the disk surface to me - leaking CV boot, brake pipe, something like that?

hartcjhart

Abs ?????????????

UncleZen

It could be a patch on the disk where rust has formed, usually after the vehicle has been standing for a while (weeks), usually where water get trapped between pads and discs.
Its quite common of the disks are made of particularly soft metal.
A lot of new cars get this when they've been standing in a field for weeks before being delivered to a dealers.

Strider590

Warped brake disc is a MYTH

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

victor2

I had a similar problem several years back, with the "pulsating" braking when braking at speed although not particularly harshly - it turned out to be one of the wheel sensors for the ABS. It only came to light when the sensor completely failed and the brake warning light came on. When the sensor was replaced the "pulsating" issue went away.

NewUserHere

Do the brakes appear to be less efficient than before?
Does the car pull in any direction when braking?

Prothet_of_Doom

Strider590 wrote: »

Warped brake disc is a MYTH

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

Really? I've noticed if I put a dial test Indicator on my discs and rotate it they are like 7 inch singles left out in the sun. If I replace them with new discs the DTI barely moves and there's no vibration or grabbing.