Brake Pedal Pulsing/Judder

[Andrew850]

Hi,

My 1999 MY S70 T5 developed a pulsing/judder of the brake pedal during firm braking - no sign of the symptoms under gentle braking. I'm certain it isn't the ABS kicking in as it happens in all road and weather conditions.

My initial thoughts were corroded or warped discs so I changed both front pads and discs. As the inside faces were badly corroded I thought that was it - but the pulsing of the brake pedal is still there.

I'm going to get a dial test indicator to check if there is a run out on the discs, but I think it's unlikely. The hubs were thoroughly cleaned before fitting the discs and it was metal to metal - no grease was used there.

Any suggestions on possible cause of pulsing?

Thanks,

Andrew.

[Juular]

Does it happen at lower speeds?

If not, it may just be your wheels needing rebalanced at a tyre place.

[Derek UK]

You might like to remove the calliper slider pins and give them a good clean. Clean the through holes in the calliper if you can. Lube pins with some good ceramic grease when refitting. It may not fix the problem but it's a good thing to do now and then, perhaps every pad change.

[RollingThunder]

If you've only replaced the front discs, I'd check the run out on the rear discs - while it is unusual for those to warp, it isn't unheard of.

I also wire brush the mounting surfaces to make sure there is no rust or debris between them - this ensures the disc is running as true as you'll reasonably get.

[Luxobarge]

I'd say it's the ABS kicking in - these are typical symptoms of corroded or cracked front reluctor rings, you apply the brakes and the uneven signal coming from that wheel makes the ABS unit think that the wheel is skidding, so it does what it's supposed to do. Well worth a check, very cheap and fairly easy to change if it's that.

[DaveNP]

Originally Posted by Luxobarge

I'd say it's the ABS kicking in - these are typical symptoms of corroded or cracked front reluctor rings, you apply the brakes and the uneven signal coming from that wheel makes the ABS unit think that the wheel is skidding, so it does what it's supposed to do. Well worth a check, very cheap and fairly easy to change if it's that.

From when I broke a reluctor ring recently I could also hear the ABS unit activating while I was braking, a sort of clicking from the passenger side dashboard area.

[Andrew850]

Hi,

Thanks for the suggestions - some good ideas.

I did thoroughly clean and lubricate the caliper pins so I don't think it's that. One of the pistons wouldn't fully retract, even with a wind back tool, but I don't see how that can cause the pulsing.

I'll check the conditions of the reluctor rings and then the run out of all 4 discs.

Andrew.

[Kev0607]

Originally Posted by Andrew850

Hi,

Thanks for the suggestions - some good ideas.

I did thoroughly clean and lubricate the caliper pins so I don't think it's that. One of the pistons wouldn't fully retract, even with a wind back tool, but I don't see how that can cause the pulsing.

I'll check the conditions of the reluctor rings and then the run out of all 4 discs.

Andrew.

A pulsing pedal could be the rear discs. As the fronts have been changed, its unlikely to be the front (possible though). It’d be a good idea to check the run out on all rotors, as you suggest.

[volvo again]

"One of the pistons wouldn't fully retract, even with a wind back tool, but I don't see how that can cause the pulsing."

If the piston is seized you will only get pressure on one side, not sure if this will cause judder, may be worth checking though

[Kev0607]

Originally Posted by volvo again

"One of the pistons wouldn't fully retract, even with a wind back tool, but I don't see how that can cause the pulsing."

If the piston is seized you will only get pressure on one side, not sure if this will cause judder, may be worth checking though

Well spotted…

To the original poster, this caliper needs changing, even if its not causing the pulsing. You’ll end up with uneven brake wear & warped rotors again over time if you don’t.