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Brake Judder - Printable Version

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Brake Judder - PJS917 - 02-18-2007

My car has started to judder badly when applying the brakes at around 70 mph, the judder stays until about 50mph and then the brakes are fine, any speed below 50 and there is no vibration, I guess it must be a warped disc, but has anyone any other ideas before I replace them?



I am 90% sure it is from the front which has sebro cross drilled discs and new pagid blue pads.

Brake Judder - flash - 02-18-2007

first off, disks almost never warp, though shops love to tell you that - i will first address the issue if it is indeed brakes:



what almost always is the case, is uneven deposits on the rotors - there is actually a website that explains this in great detail, but i can't find the link right now - it also has a great break in procedure



unfortunately, the result and remedy is almost always the same as if the rotors were warped - you end up having to replace pads and rotors



you can try having the rotors skipped, but it may not work - once uneven deposits are laid down, the rotors start heating and cooling oddly, and create "hot spots" - these can be seen in the form of "blue streaks" or "blue spots" - they result in the pads not going over them smoothly, and they speed up and slow down unevely, which feels like juddering - in reality, they are grabbing and letting go grabbing and letting go so quickly that we can't tell the difference



the pads will be toast in either case



now, it may not be brakes - there are a couple of things that could cause this - to determine if it is one of them, i need to be sure that it does not do any juddering or pulsing below 70, regardless of the force applied to the brakes - brakes should be able to be felt, though to a diminishing degree, regardless of speed



if it indeed is only at 70, it could easily be a balance issue - believe it or not, this happens a lot - most shops only spin balance - this is frequently not good enough, and road force balancing is needed - this should be done at least every 10k miles on a car like this



it could also be a bad wear pattern in the tire - carefully inspect the tire - run your hand across the surface of the tire front to rear and then rear to front - if you feel any "stair-stepping" you have likely found your problem - if it is on the inside, you need an alignment at minimum - if it is on the outside, or across the entire tread pattern, unfortunately it almost always means struts - this is the symptom that shows up long before you would feel worn struts in suspension travel



a worn suspension component can cause this - castor blocks are a prime candidate - as the load is shifted to slow the car down, the component moves, making for a change in toe that fluctuates - it often shows up as a high speed judder under braking



lastly, a loose wheel bearing will cause this too - check that out



hope that helps

Brake Judder - mike - 02-18-2007

I think this may be the web site that Flash referred to above regarding the warped rotor myth.



http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml

Brake Judder - SILVY968 - 02-18-2007

I had a problem last year that made the car judder at between 58-64 mph. It had nothing to do with braking, but it may be related.

The problem was a NEW out of round tire. regular balancers will not find the problem as the balance speed it too low. As Flash said you can find this out with a road force balancer.

Brian

Brake Judder - S_Cal968 - 02-18-2007

Have you checked to see if you've thrown a wheel weight - they sometimes part company?

If it's a brake issue it can many times be felt through the pedal and demishes as the speed is reduced.

This is least likely, but did you bed-in the pads when the rotors were installed?

Brake Judder - PJS917 - 02-19-2007

Thanks for the replys, I am going to change the discs aseverything is pointing at them at the moment, if it is not them then I shall have a spare set for next time they need changing.

Brake Judder - flash - 02-19-2007

mike - yes, that is one of them - thanks!



pjs917 - good luck, but i think you now have a number of places you can look if it does not resolve your problem



make sure you bed the new pads and rotors down well though