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Brakes judder

Pilot

Well-known member
Joined
14 Nov 2011
Messages
56
Hi all. I have a c4s cab. The car has been driven very little since December (about 10 miles a week). I've now started driving it regularly again. The brake discs and pads have little wear but are at least 2 years old. After driving for 10 minutes or so, the brakes feel weak and judder. The steering wheel also vibrates when applying the brakes and coming to a stop. This appears to be intermittent but once it happens, it continues to do so for the entire drive.

Is this likely to be warped discs? The brakes were fine when I was driving it on a daily basis until December. Any views?
 
One explanation could be that your brake pad and disc surfaces have picked up a coating of rust/pad material debris due the car's infrequent and light use, which could be removed by a programme of repeated heavy braking from high speeds on a suitably deserted road or track. (Both for safety's sake and so some bystander doesn't call the boys in blue because they think you are just being a hooligan).
If the discs have rusted severely, then they may be pitted beyond redemption. You wouldn't necessarily be able to see this by just looking through the wheels, as the inboard disc surfaces on our cars seem to suffer more severely from rusting than the outwardly visible ones.
 
Do what Red says.

There is no such thing as warped discs, only discs with contaminated surfaces which can be cleaned as above.

IIRC it is roughly 10 decelerations from 60 to 10, then allow to cool completely, then repeat. You must NEVER sit stationary with the brake pedal applied during this process.

ETA

http://zeckhausen.com/bedding_in_brakes.htm
 
Thank you. I will try and find a secluded road tomorrow.
 
Can also be a sticky piston in a caliper, as they get hotter this compounds the problem and it will not unstick until the brakes cool down, we use a a machine to skim the discs on the car and its acurate to within a human hair. Discs do warp and we test for run out all the time, surprising how far out a lot of cars are.
 
Question for Johnny: when skimming discs on the car, how do you get away with spinning the hub you're working on without cooking the diff? I've often wondered and assume there is a workaround?
 
orangecurry said:
Do what Red says.

There is no such thing as warped discs, only discs with contaminated surfaces which can be cleaned as above.

IIRC it is roughly 10 decelerations from 60 to 10, then allow to cool completely, then repeat. You must NEVER sit stationary with the brake pedal applied during this process.

ETA

http://zeckhausen.com/bedding_in_brakes.htm

+1


or else, rub down with Emery paper
 
JohnnyDangerous said:
Can also be a sticky piston in a caliper, as they get hotter this compounds the problem and it will not unstick until the brakes cool down, we use a a machine to skim the discs on the car and its acurate to within a human hair. Discs do warp and we test for run out all the time, surprising how far out a lot of cars are.

Discs don't warp, unless you park too close to the sun.

Many discs are fitted out of true, and many get unevenly covered in pad material and rust and so on, but discs don't warp.
 
orangecurry said:
JohnnyDangerous said:
Can also be a sticky piston in a caliper, as they get hotter this compounds the problem and it will not unstick until the brakes cool down, we use a a machine to skim the discs on the car and its acurate to within a human hair. Discs do warp and we test for run out all the time, surprising how far out a lot of cars are.

Discs don't warp, unless you park too close to the sun.

Many discs are fitted out of true, and many get unevenly covered in pad material and rust and so on, but discs don't warp.

So why do you not sit with your foot on the brake after a very heavy stop or the disc cleaning procedure and how would you explain runout on the discs when fitted correctly to a flat clean hub ???
 
JohnnyDangerous said:
So why do you not sit with your foot on the brake after a very heavy stop or the disc cleaning procedure

Because the hot disc would translate a layer of pad material onto itself, causing a high-spot.


JohnnyDangerous said:
and how would you explain runout on the discs when fitted correctly to a flat clean hub ???

You can't, so they weren't, or post-fitting they have suffered something like point 1 above,

Discussions on Pistonheads are not my cup of tea. I prefer this sort of thing.

http://www.stoptech.com/technical-support/technical-white-papers/-warped-brake-disc-and-other-myths
 
OK so how do you explain the fact that when measured in a lathe runout can be massive?

Ive read the stoptech article before and no doubt 90% of judder is pad material on discs and maybe missaligned discs which is why our grinder that centres on the hub results in a vast improvement BUT my mate bought a new Land Cruiser to tow heavy boats down to Spain and that would need new discs evry 5K miles and they were warped to buggery when we checked em.
 
orangecurry said:
JohnnyDangerous said:
So why do you not sit with your foot on the brake after a very heavy stop or the disc cleaning procedure

Because the hot disc would translate a layer of pad material onto itself, causing a high-spot.
 
I'm thinking I need to give you more words.

As soon as the pad material starts to be deposited unevenly onto the disc (for whatever reason, either not being bedded-in properly, overheated and then sat with the brakes applied, or poor installation) the problem gets worse with normal driving.

As there is now at least one high-spot, this has slightly more material deposited onto it each time the brakes are applied in normal operation.

So it gets higher/more extensive.

...and so on.

Read the article - it's very good :thumb:
 

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