Brake disk condition that would cause heavy pulsing/hammering on braking?

[Gene in NC]

Brake disk condition that would cause heavy pulsing/hammering on braking? Buddy claims that hammering on light braking that can be damped by HARD braking may be caused by brakes instead of control arms. This leaves me with a problem.

What am I looking for in rotor condition that might cause such a problem?

[Kalevera]

Rotor conditon = warped. Lots of runout/huge lips. Heat cracking.

How long has it been since the brake fluid was flushed?

best, whit

[632 Regal]

Lowels got it, do you have access to a dial indicator so you can check the runout? You might need to tighten the hub to the rotor for an accurate reading.

[Gene in NC]

Holy stinky stuff, brake fluid is seven years old. Car not driven a lot, but what efffect might that have on pulsing?

[Kalevera]

Brake fluid is hygroscopic, meaning that it absorbs water, as well as dirt and air, over time. BMW (used to) recommend(s) flushing the brake system....I believe once every year (might be two, I forget at the moment).

Water = corrosion, lower boiling point than DOT 3/4/5
Dirt = gum moving parts up -- master cylinder, caliper pistons, any proportioning/metering/compensating valves in the system
Air = compresses. Liquid does not.

All of these things can result in bad braking, blown seals, accidents. Especially with something like Super Blue in the circuit, I would be changing it once a year. Everyone seems to neglect this, sadly.

best, whit

[Bill R.]

feel as smooth as the rest of the rotor but the coefficient of friction for it is different than the surrounding metal. It will appear as round or so discolored patches in the rotor.. Through impurities in the alloy, and excessive heat in places causing a wierd heat treat to spots of the metal you can develop these areas...Remachining the rotor will temporarily get rid of this but it will return soon since the affected areas is actually harder than the material around it... On some cars you can actually squeeze the pads together with your hand while spinning the rotor and feel these areas where the pads slip and grab even though visually it doesn't look like much. Thats one condition, another is a warped rotor as the others have mentioned which is easily detected with a dial indicator . Also tires that have defects in the roundness will sometimes cause a similar sensation too.




Brake disk condition that would cause heavy pulsing/hammering on braking? Buddy claims that hammering on light braking that can be damped by HARD braking may be caused by brakes instead of control arms. This leaves me with a problem.

What am I looking for in rotor condition that might cause such a problem?

[grease]

Brake disk condition that would cause heavy pulsing/hammering on braking? Buddy claims that hammering on light braking that can be damped by HARD braking may be caused by brakes instead of control arms. This leaves me with a problem.

What am I looking for in rotor condition that might cause such a problem?

main things to look for:
1. is the vibration/pulsation felt in the steering or more in the seat of your pants.
2. is the vibration noticable while driving, or only under braking.
3. is there a light/steady vibration around 50-60mph
4. is the vib/pulse... pronounced while driving at higher speeds and appling the brake lightly, versus applying brakes lightly at lower speeds, if you understand what I mean.

if you answered yes to one and four, I would probably say rotors,
if you answered yes to all for I would check thrust arm bushing.
also check the forum real helpful hints on thrust arm and shimmy's use the search. I hope that you find your problem I had a shimmy and I know what it's like to want to fix it, lucky fixing it shouldn't be that expensive granted correct diagnosis. GOOD LUCK, hope I was any help.

[632 Regal]

didnt we all read about pad break in regarding the hot spot issue? I think it said something about "re-bedding" the pads and rotors to get a new surface (bluing the rotors first). new pads on old rotors is wrong but if you blue the rotors and put new pads on your good to bed the new pads...but if they are warped thats another problem.

[Bill R.]

.
didnt we all read about pad break in regarding the hot spot issue? I think it said something about "re-bedding" the pads and rotors to get a new surface (bluing the rotors first). new pads on old rotors is wrong but if you blue the rotors and put new pads on your good to bed the new pads...but if they are warped thats another problem.

[liquidtiger720]

so, what if there is a noticable "step" in the rotor? Say, the outer .5-1.5 inches of the rotor all the way around is worn down more than the the inner part of the rotor. No shimmy, nothing...just that one little step on the outer circumference of the rotor.

[632 Regal]

.
K, I didnt remember the whole article was way indepth.

[dacoyote]

K, I didnt remember the whole article was way indepth.

99 bottles of beer on the wall... 99 bottles of beer... take out down... chug it down.... 2 less brain cells.... 98 bottles of beer

[632 Regal]

I have NO CLUE, can you post a picture or something?


so, what if there is a noticable "step" in the rotor? Say, the outer .5-1.5 inches of the rotor all the way around is worn down more than the the inner part of the rotor. No shimmy, nothing...just that one little step on the outer circumference of the rotor.

[Gene in NC]

Confession time. Dumbass! Had checked the right thrust bush and couldn't find any indication of failure. Decided maybe there was an art involved. Assumed both would be in same or similar condition..

Today I checked the left. GGAM, the center was completely separated from the rubber.

Rotors looked fine.

Recommendations on type/manufacturer/source for parts?

Thanks for the help. Sorry to give a half assed report of conditions and symptoms.

[Kalevera]

Lemforder. 750 or M5 bushings. Call Patrick @ BMA.


best, whit

[grease]

Lemforder. 750 or M5 bushings. Call Patrick @ BMA.




I agree 100%, real easy job, they cost about $100 each with the bushings pressed in. Or you can buy just the bushing and press them in, the arm is fine, it's just the bushing which has failed.