Front brakes shake at times when stopping

[ShaneHayes]

Something I noticed is sometimes when I stop quickly, I can feel the front brakes clatter/shake. Also, when I have the windows down and going very slowly, I can hear the rotors making a metal to metal noise. Does this mean I need to pads or rotors, or both? Car always still stops on a dime though. Thoughts? Thanks.

 

[SlowSVT]

Sounds like warped discs to me

 

[jm@ReischePerf]

Does the pedal pulsate a little when stopping? If so +1 on a warped rotor.

 

[wheelhopper]

+2 for the warpage.

 

[ShelbyGuy]

rotors dont warp. check your wheel bearings.

 

[beabout]

Do a brake job on it.... that metal to metal sound is the warning that you need to do it.

 

[jm@ReischePerf]

rotors dont warp.

Excuse me? :shrug:

I have personally seen tens or even hundreds of rotors shimmy from side to side on a lathe. If that's not warp, what would you call it?

 

[Venomous281]

rotors dont warp. check your wheel bearings.

LOL they do guy. Sounds like your rotors are warped. Get them cut and some new brake pads will do...

 

[ShelbyGuy]

rotors cockeyed on the brake lathe.

cutting rotors is an unneeded procedure meant only to bilk the customer.

put a dial indicator on the knuckle and measure the runout, rollout, and backlash of the rotor before putting it on the lathe. you'll find that the rotor is fine.

if you get chattering brakes its not due to a warped rotor, but an uneven transfer of brake pad compound onto the rotor. naturally cutting the rotor takes the pad film off the rotor, so the problem goes away, and the shop gets money for doing unneeded work. a set of hawk blue pads and slow speeds will clean the rotors just as well.

the original poster said the car SHAKES. this points to worn wheel bearings.

isolate and test
isolate and test
isolate and test

Excuse me? :shrug:

I have personally seen tens or even hundreds of rotors shimmy from side to side on a lathe. If that's not warp, what would you call it?

 

[SlowSVT]

rotors cockeyed on the brake lathe.

cutting rotors is an unneeded procedure meant only to bilk the customer.

put a dial indicator on the knuckle and measure the runout, rollout, and backlash of the rotor before putting it on the lathe. you'll find that the rotor is fine.

if you get chattering brakes its not due to a warped rotor, but an uneven transfer of brake pad compound onto the rotor. naturally cutting the rotor takes the pad film off the rotor, so the problem goes away, and the shop gets money for doing unneeded work. a set of hawk blue pads and slow speeds will clean the rotors just as well.

the original poster said the car SHAKES. this points to worn wheel bearings.

isolate and test
isolate and test
isolate and test

That is not entirely true. I admit I don't know much about the pad material transfer to the disc, something that someone just brought up to me in a similar thread last night. The disc surface gets pretty well polished by the pads which would make pad material sticking to them a but difficult but that is something I don't have much knowledge of. But the claim of rotors not getting warped is something I have first hand experience with. I've done quite a few brake jobs due to brake chatter to the point of shacking the steering wheel whenever the brakes were applied. Took the rotors off and had them turned down. On the brake lathe when the machinist made the first skim over the dics you can hear and see the cutter taking down the high spots (working at a Porsche dealership I saw this repeated many times). After turning the rotors the steering wheel shimmy disappeared. It has been my experience that rotors do warp and is the leading cause of brake shimmy.

Regarding the runout thing. Not sure if your referring to the bearing, hub or disc but I broach this subject on the post I mentioned earlier. Rather then repeat what was said here is the link to the thread.

http://www.svtperformance.com/forums/showthread.php?t=455659

Diagnosing problems like this the answer can get a bit more complicated then first appears. But it's been my experience that the vast majority of brake chatter problems can be traced to warped disc. There is a lot of heat involved and the flatness of the disc going out by only take a few thousands can effect the brakes. Uneven cooling due to clogged cooling veins in the rotor is one place I suspect is the cause of this.

 

[1svtfan]

An interesting read discussing people quick to blame warped rotors. You need to isolate the problem first.

Is it the rotor or is it not....

 

[jm@ReischePerf]

Is it the rotor or is it not....

Ok well instead of a warped rotor they're calling it disc thickness variation (DTV) out of tolerance. I think this is a bit of semantics. The article goes on to say that excessive runout (total runout after installation), and other factors, leads to excessive DTV, which can then lead to pulsation. I think the moral of the story is that the rotor is the effect not the cause. I never have argued against this point. Possible causation factors:

1. Unclean rotor/hub mating surface
2. Rotors improperly machined (Shelbyguy - I noticed that occasionally the rotor was improperly positioned and after some adjustment had less runout, but to assume this is the sole reason for excessive runout/DTV in every rotor is highly improbable)
3. Caliper issues: not sliding properly, or piston not retracting properly. This is where I feel the problem usually lies.
4. Bad bearings: Ok I can see where this could lead to DTV also.

 

[ShaneHayes]

Hey thanks for all the inputs guys. At first I was thinking warped rotors; however, the brake pedal doesn't pulsate all the time. Only at times, when I have to stop abruptly (on occasion). It perhaps may be a caliper issue...no sliding properly at times. At least that is what it feels like. I guess I may have to take it to a brake specialist?

 

[jm@ReischePerf]

Only at times, when I have to stop abruptly (on occasion).

That could be just the anti-lock system engaging. This will feel something like a vibration or a quick side to side shaking/pulsation under hard braking.

 

[SlowSVT]

There are some very valid points on this threads and brake shimmy is certainly caused by more factors then just warped rotors. I have done many brake jobs on both automobiles, motorcycles and a few airplanes. In every case tuning the rotors (or getting new ones) resolved the issue of brake shimmy. Not saying hub issues, stuck caliper sliders or bad bearings are not the cause. But it has my experience that the vast majority has to do with warped rotors. If there is no shimmy at all and the friction surface is smooth, I just clean the disc with brake cleaner and drop-in new pads. For a road racer who cooks his disc and plows his two ton car under lots of G's into every corner will stress other parts of the system that can become the source of the problem. But the vast majority of these cars are driven on the street and it is a rare occurance when something other then warped discs are the problem. That is the first thing I check for.

 

[ShaneHayes]

thanks again guys...as far as braking hard and the abs engaging. could very well be the abs, but i don't think it was a hard enough stop for the abs to engage. however, i wouldn't rule that out. the car does have 31k miles, and i just bought it several months ago, so i will get it looked at. i'll most likely get the rotors turned, and new pads.

 

[jm@ReischePerf]

could very well be the abs, but i don't think it was a hard enough stop for the abs to engage.

You may have just hit an oily patch in the road or some loose gravel. Once in a while I'm surprised to see the ABS kick in but I just chalk it up to a poor traction situation that may not have been visible.

 

[SnakeBit]

Whenever a shop pulls my wheels, I put a torque wrench on them when I get home. Even torquing of the lug nuts is a must and will prevent other problems down the road.

I would also check for other problems in the front suspension. There are several parts and any one of them could cause a shimmy, including a bad wheel (like from hitting road debris or a curb) or a defective tire. Any good front end shop should be able to find it.