Intermittent Braking Force...

[C.A.R.]

When I bought the HDi it had recently had new OE discs and pads (brembo I believe) so I didn't think I would need to look at the braking system for some time...

However...

When braking at low speed you can feel the brakes 'pulsing' almost. It's not like ABS, which is more of a judder you can feel through the pedal.

It's like if you hold the brake pedal in one position you get 'Brake-----brake-----brake----brake----- and you can feel the car rocking under the braking force.

Higher speed braking is unaffected, although the ABS does seem over-intrusive at times. I know the car had a driveshaft replaced due to dodgy ABS, but believed this to have been fixed. Could this point to a possible culprit?

Servicing the car on Saturday so will be an ideal opportunity to have a butchers as it were.

[Joe]

sounds more like a slightly more warped brake disc

[C.A.R.]

That's my thinking, but usually that causes a slight vibration at higher speed braking? Ie. on a sliproad exit or something. I get nothing above sort of 30mph...

[Dan!]

My mx5 does this slightly too, I would be inclined to say it's a slightly bent/warped ABS ring. Try unplugging the abs sensors and see if it still does it then.

[Rippthrough]

Could be a warped/fooked rear disc rather than front.

[C.A.R.]

How could I possibly ever track it down though? Whip the discs off and lay them flat? Even then I don't know how obvious it would be?

[Rippthrough]

It's more likely a shadow on the disc from the pads being stood while warm - you'll probably see a faint transparent print of the brake pads on there somewhere where they've transferred some pad material across. That'll give a touch more braking power at one spot without actually giving you vibrations as such. Just makes the car bob up and down slightly when rolling at low speeds with the brakes on.

You can try scrubbing the rear disc down with some wire wool and brake cleaner and seeing if it goes away.

[C2K]

Pull the ABS fuse and try your brakes, see if the sensation goes. You'll find that it is likely to be a hairline crack in an ABS ring, or potentially a dying sensor. I would believe the former as i've had the same issue before.

My brothers HDI had the shrunk on rings, not the notched shaft. One of his rings cracked through and split and his ABS went bananas.

[Niall]

It's more likely a shadow on the disc from the pads being stood while warm - you'll probably see a faint transparent print of the brake pads on there somewhere where they've transferred some pad material across. That'll give a touch more braking power at one spot without actually giving you vibrations as such. Just makes the car bob up and down slightly when rolling at low speeds with the brakes on.

You can try scrubbing the rear disc down with some wire wool and brake cleaner and seeing if it goes away.

This! If the cars been sitting for a while this normally happens. My rear discs are like this and it gives you sea sickness when braking slowly. You may be lucky and find its just the rears that are buggered when the handbrake has been left on for a long period.

[C.A.R.]

How do you check the ABS rings?

Would the light on the dashboard not flicker if the ABS was intervening? Or not necessarily?

One thing the seller mentioned was that it had a recent ABS ring replaced at the time one of the driveshafts was done. I want to jack the car up and give it a good look over.

One thing it has started doing this weekend is a symultaneous squeak/squealing from the brakes when this pulsing force can be felt, but like I say, you don't get any feedback through the pedal suggesting that it's not the ABS? I dunno!

[kyleo92]

This could explain my wobbly braking and my ABS light being on... Despite new tyres, pads and discs...

Thanks Guys!!

So new sensors or ring

Epic!

[C.A.R.]

My problem is getting worse - now showing symptoms more similar to that of a warped disc - the wheel will vibrate braking from higher speeds now.

Will whip the front wheels off when I service the car at the weekend and have a looksie.

[Niall]

testing sensors is very easy, multimeter on the two pins on the plug, set meter to ac voltage and run a spanner back and forth over the sensor and it should pick up voltages.
rings are simple. if there intact (they can fall off easily), and where they should be, they will work