pulsing brake pedal after rear discs fitted

[rossco19872011]

after having my car serviced I decided it was time to have my rear discs fitted, the discs weren't new but I had the skimmed by a friend. I took the car to the garage and they fitted the new discs and new pads. I picked it up around 6pm. started to drive it and I come to brake for the first time and the pedal pulsed a little, I thought nothing of it as I thought the new pads were settling in. after driving a few miles with it doing it I knew there was something up!! the pedal moves up and down as I brake. It was fine before I took the car in. my friend assures me the discs are 100% true!! Any ideas?? I've got to take it back to the garage tomorrow but he thinks its warped discs?? could an abs sensor be at fault or a wheel bearing??

[Batfinnk]

I would be very surprised if you would feel the pedal pulse from the rear discs tbh. Fronts maybe but not rears as they only do a small percentage of the overall braking. Might be worth asking if they removed all the wheels as the front and backs may have been swapped over and one might have a slight buckle and would show itself if now on the front.

[Ian_C]

I'd put brand new discs on asap whilst your new pads are still fresh.

[Shoppinit]

They haven't been skimmed true. Too much run-off.

[rossco19872011]

What do you mean too much run off?? I spoke to my friend and he said he clamped them
Correctly, then he trued one face of the disc. Then he trued the other side off the first side he did. Is this wrong?? Thanks guys!

[chunky79]

Either the discs faces are out, or when the discs were fitted they have contamination behind the mating faces.

[armyair]

How long was your car standing?

I had the same yesterday after not driving my car for nearly two weeks whilst waiting for parts. After a few miles with a variety of braking it subsided as the cause was corrosion.

The fronts didn't look that corroded however in comparison to the area under the calliper they must have been!

[rossco19872011]

thanks for all the replies guys its really appreciated!! I've spoke to a local mechanic and he agrees that the faces might be flat but the disc thickness could possibly vary. but to be honest my friend only took a smidge off the discs to get rid of a tiny lip. I did have a knock to the back wheel along time ago and he suggested that it could of bent the hub and the old disc so that when I've offered a straight face up to it, it shows as being out?!?! what do you guys think?? tbh if im 100% honest the wheel does look like it toes in at the top! the alloys are new ones as I changed them a few months back. cheers

[ant1]

The way I see it if you have a problem look at the last thing you changed, in this case your rear discs. Either the alloy is not sitting on the hub Evenly when refitted, or there is a issue with the discs after being skimmed. Light skim or not, you still have to take a certain amount of mm off to skim correctly.

[rossco19872011]

cheers ant. is it even possible to bend a hub?? maybe an arm or wishbone? my mechanic did say what you've just said that they may be skimmed level but the thickness may vary. guess im going to have to get some calliper's on them in several points

[Shoppinit]

Nah, it's the disk. I'll bet a beer on it.

[rossco19872011]

Shoppinit, what do you think has happened?? if you say its the disc then its defiantly the disc! do you think it has a high spot or different thicknesses ??

[ahoooga]

what thickness was the discs before they was skimmed ? and what thickness are they now ?

[rossco19872011]

Im going to whip the disc off now and measure it in 6 places to see the thickness

[bilko1]

Im going to whip the disc off now and measure it in 6 places to see the thickness

Check for play in the wheel bearing while you are at it as you said it has had a knock on that side.