Brake Judder

[ggrum]

Interesting little problem that has developed over the last few months with my Cabrio. Applying light brake pressure results in juddering of the steering wheel not dissimilar to a wheel being out of balance. As I increase the brake pressure the juddering goes away. My first thought was a front brake disc running out of true but I checked and both sides are within the limits for run-out. Anyone got any thoughts before I start ripping bits of the car off?

[stevejgreen]

Re: Brake Judder

I would vote for a seized brake piston and a very slightly distorted, but within tolerance disk, causing the disk to heat up and distort more. Applying more brake pressure, deflects the disk onto the static pad so the vibration goes away.
Look for the easy stuff first.

[dogoncrazy]

Re: Brake Judder

As Steve say's - possible caliper sticking.

[greyV8pete]

Re: Brake Judder

I had the same problem some while ago. It eventually got better with use. So if Steve's theory is correct then further use and subsequent heating and cooling may have been enough to free the piston. Looks like the old lack of regular use thing rearing its ugly head again! I will watch this thread with interest.

[stevejgreen]

Re: Brake Judder

I had the same problem some while ago. It eventually got better with use. So if Steve's theory is correct then further use and subsequent heating and cooling may have been enough to free the piston. Looks like the old lack of regular use thing rearing its ugly head again! I will watch this thread with interest.

Nah! I had a random judder on a 350+hp RWD rear braked car. Looked at everything except a caliper piston. Both CV joints, drive shaft, nothing.
I put an infrared thermometer on it after a hard run out, and it went off the scale, didn't believe it, so stupidly burned my finger on the caliper, had a blister/scar for weeks.
I had refurbished the brakes a few weeks before so had eliminated them. Wrong. It didn't get better with time.

Finally checked my own work, found seized caliper piston on one side!
Repeated use and heat cycles did not help it took me weeks to find.
Boiling brake fluid in an overheated caliper is not a good idea. You have to flush it out, and then replace the grease and sealed bearings in the hub and CV joints.

Thats my vote and reasoning.

[ggrum]

Re: Brake Judder

My car is used at least twice a week as it is my only drive if my wife is using the family hatchback so I don't think lack of use is a factor. I can't remember the figure but the disc run-out is well within the limits specified in the Haines manual for the Sierra. I'll certainly check out the caliper pistons although when I had a sticky piston on my Roadster some time ago it made a 'groaning' noise as the disc rubbed on the disc slightly but it didn't have any effect on the steering. Having said that the Roadster has a 4:1 steering rack whereas the Cabrio has a 2.5:1 rack so the feedback would be very different. Thanks for the suggestions.

[philcoyle]

Re: Brake Judder

What type of front suspension do you have, are the tie rod rubbers or equivalent to a tie bar in good condition. What I call tie bars are the rods that stop the lower wishbone going backwards under braking, others may have a different name for them.

[cabrioman]

Re: Brake Judder

Back in the day as a young lad working as a mechanic for the local Ford main dealers this used to be a common problem on Sierras. As an in warranty repair replacing the pads with abrasive pads ususaly fixed the problem. Not sure if you can still get abrasive pads but they were genuine Ford parts, which had abrasive material bonded to the face of the pads. Effectivly did a light skim of the discs before the abrasive material wore away, then they could be left in as normal pads.

As I say not sure if you can still get them, but they certainly used to work.

John

[ggrum]

Re: Brake Judder

In answer to Phil's question, my Marina based Roadster has adjustable rose bearings on the tie rods or radius arms (like you, I'm not sure of the correct term) so there is no movement there. Prior to fitting them the car would wander a bit under heavy braking, maybe because the toe-in changed a bit as the rubbers compressed. That all disappeared when I fitted the rose bearings. As an aside I didn't use the adjustment to change the castor angle but left it as dictated by the preset front geometry.

Not heard of abrasive brake pads - interesting idea. I have Mintex pads on the Cabrio at the moment. Think I'll check out the caliper piston first.

[andyf]

Re: Brake Judder

Used to run 280 capri disks on my sunbeam and they used to start juddering after a couple of stages. Once I found that the juddering went away under hard breaking I stopped changing them. That's not an option on a road car though. I'd see if you can find the abrasive pads first. I have seen a resurfacing tool used on wheeler dealers

[Mike]

Re: Brake Judder

I had several Sierras as company cars, and brake judder was very common.
It used to bug me that it meant a new set of discs each time (even though I wasn't paying).

My money is on new discs being your final solution ....................

(Another one watching with interest)

[philcoyle]

Re: Brake Judder

Back in the early days of disc brakes and replacement rotors were hard to come by, there were abrasive pads the garage mechanic would fit and drive it down the road, applying the brakes to remove the shine/rust etc. before fitting new pads. This idea fell by the wayside when brake manufacturers found out they could make more money by getting you to by new.

You could try having them skimmed or surface ground, but for what new rotors and pads cost nowadays it's hardly worth it. Choose a well known manufacturer, some firms are interested in making money, not saving your life.

As an after thought is your servo pipe one-way valve working okay and not fluctuating when the brakes are applied?

[milliemarlin]

Re: Brake Judder

Since abandoning asbestos they seem to use something quite abrasive and I’ve had several production cars requiring new discs at remarkably low mileages. I also have me doubts about the quality of steel used in discs.
In addition to runout you might want to check disc thickness. It could vary around the disc.
Paul

[davidmartin720]

Re: Brake Judder

I had a new Seat Altea in 2010 and within a couple of months the discs showed signs of grooving. The dealer said that was normal and the discs were designed to wear as well. When the car had its first MOT the Seat dealership wanted to change the discs as they were "grooved and rust pitted". The car passed the MOT and the following ones with an advisory re the condition of the discs. I changed the front discs and pads prior to this MOT and, Yes, the brakes are sharper but have always worked well. Meanwhile my 1981 Roadster's discs are shiny and groove free after many years use. One thing I was advised was to always drive the car after washing it, to warm the brakes and dry them out. David.

[philcoyle]

Re: Brake Judder

There is a grey area about grooved or pitted discs, otherwise every boyracer, sports car, and high performance vehicle with drilled/grooved discs would fail every homoglamation declaration by manufacturers, and MOTs by us ordinary folk, we would not make it past the garage door. So if any mot chappy gives you an advisory ask him if he is going to fail or advise all drilled/grooved discs on vehicles that come his way. The perplexed look is always a sign of defeat.

As an afterthought, how many testers have you seen or heard of who have removed brake drums to inspect the condition, yes, none.
It's only because one side of the disc is always visible they feel that they have to comment, but brake drums that may be scored or rusty because the vehicle has been stored over the winter, not interested, unless it fails on the brake tester.