Brake jutter - Cadillac XLR Forum: XLR and XLR-V Forums
 
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post #1 of 7 (permalink) Old 09-14-2010, 09:29 PM Thread Starter
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Brake jutter

When I am coming to a stop, I get "brake jutter" which is when the car does not smooth stop but kind of pulses (makes you kind of rock forward and back in your seat) One would think this is caused by a warped rotor as this only happens when braking, but I used a dial gauge and checked the rotors and they are perfectly straight with no warping. Any suggestions?
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post #2 of 7 (permalink) Old 09-15-2010, 06:13 AM
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I have noticed a similar experience with light braking - but cannot detect it with heavy break applications. I have also wondered if it was a slight warp, but have not checked it as you have. Do you get this all the time or only with light braking - as coming to what I consider a normal, easy stop?
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post #3 of 7 (permalink) Old 09-15-2010, 10:26 PM Thread Starter
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Yes, only during light braking. My car is an 05 with 46000 miles. Has anyone experienced/resolved this?
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post #4 of 7 (permalink) Old 09-20-2010, 10:55 AM
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Quote:
Originally Posted by Hogwash View Post
When I am coming to a stop, I get "brake jutter" which is when the car does not smooth stop but kind of pulses (makes you kind of rock forward and back in your seat) One would think this is caused by a warped rotor as this only happens when braking, but I used a dial gauge and checked the rotors and they are perfectly straight with no warping. Any suggestions?
Did you check the width (thickness) of the rotors too? You will need a good quality micrometer. Brake judder is usually a problem with the rotors, sometimes contamination. It can be on the rears, even though they do much less work they can still cause the whole car to judder, especially under light braking.

Another problem is sudden, hard braking (i.e. very rapid brake application) with cold brakes, this can cause the surface of the rotor to heat locally and so expand locally. This causes judder at the time, because a small section of the rotor is hotter than the rest, but also causes accelerated wear on that part of the rotor, which on the face of it will cause less braking effect at that point, so the next time the brakes are applied rapidly, it should be a different part of the rotor that expands more. In practice things never work out this way and rotors seems to end up with hollows.

For other reasons, the pattern of wear on a rotor tends to be in fives. I.e. there will be five highs and five lows round the rotor. This is one of those 'physics' things to do with standing waves and stuff. It is a bit to do with the way a bell rings too. If you look at a very worn rotor, it often has fine cracks radiating away from the center, it is those that are often grouped in five even regions round the rotor.
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post #5 of 7 (permalink) Old 09-29-2010, 10:57 AM Thread Starter
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I checked the rotors with a dial runout gauge. The rears are only 2/1000ths of an inch from perfect (within spec). Also if I try to stop using the parking brake (rears only) there is no judder. The fronts measured true with no warping at all. Could the problem be in the suspension or steering rack??
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post #6 of 7 (permalink) Old 09-29-2010, 11:12 AM
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Originally Posted by Hogwash View Post
I checked the rotors with a dial runout gauge. The rears are only 2/1000ths of an inch from perfect (within spec). Also if I try to stop using the parking brake (rears only) there is no judder. The fronts measured true with no warping at all. Could the problem be in the suspension or steering rack??
A dial gauge tells you how much the rotor is 'wobbling' from true, but does not tell you thickness variation? OK, you could measure both sides, but now you need to match up the highs and lows on each side, which can be done, but is getting tricky, given the available space.

Can you check the rotor thickness?
Did you check the runout of both sides of all four rotors?
Have you checked that there is no corrosion between the hubs and the rotors and between the rotors and the wheels?
Was the rotor clamped hard to the hub while you were measuring it? (At least 3 lug nuts, maybe all five for a precise measurement)
Does it improve or get worse with heavier braking?
I'll stand corrected, but being 'within spec' does not mean zero judder when braking, it means 'an acceptable level of judder'.

Last edited by xlrlist01; 09-29-2010 at 11:16 AM.
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post #7 of 7 (permalink) Old 11-03-2010, 11:53 AM
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Big Grin Answers?

Gentlemen,

What was the results of this extensive research?

I've got a slight judder only when light braking or at the end of hard bite sliding into a slow halt.

It doesn't bother me in the whole, but I'd like to address small issues before they become bigger issues.

Thanks all,
Pablo-
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