rcronin

Okay so last weekend I washed the car and put it away.
This morning I pulled it out to come to work and noticed that the pads were slightly fused to the rotors since they were obviously wet when I pulled it in to the garage.
So a few miles down the road and the rusted crap was worn off. Cool.
But I have a shimmy/shake under braking that I suppose that I didn't notice before.
The road surface that I am on is asphalt and is brand new so it is smooth as silk. I notice the shimmy while moving alone at 45mph and also noticed the same pulsing pattern when slowly coming to a stop.
For the longest time I was going in to have the wheels re-balanced because I thought that this was the problem and then cursing the dude for not doing it right. Now I am thinking that it is my rotors! Can it be?
The reason I am now leaning towards the rotors is that on my truck they are warped and I know it. This causing some serious wobble while driving and under braking in a bad way but the truck is old and frankly I just don't give a damn.
But my car...my pride and joy...she is acting the same way. Could it be braking issues? She is only 31,000 miles young.
For the last year I have been so pleased with the brakes compared to anything else that I have owned thus far and here I am faced with them possibly being no different that (gasp) a standard car???

Tippy

Hot rotors can warp if they are rapidly quenched from driving through water puddles. Do you recall braking hard, then passing through a puddle?

Riad

Rotors warping under normal driving conditions would be extremely unlikely.

Have you had the rotor's/brake pads changed?

Might be a tire balancing issue - have you had your tires speed balanced? Did you hit a bump that would push the car out of alignment?

pszikla

It may be coincidence with the car washing/brake rust etc..., but I would go along with Riad and think more along the line of tire problem. (Unless the brake pedal is pulsing up and down when braking and that would point towards needing the rotors turned)

Stefan Richter

I have the same problem whenever I wash my car. If I don't take a 10 minute drive to properly dry the rotors right after washing, the next morning I will actually have to "break" the rotors loose as the car won't move. I will then get a vibration from the rear under braking for about 10 -15 miles, until all the rust/crud wears off. My solution is to drive the car after the body is dried for about 10 minutes, making sure the brakes get nice and warm. Before I put the car away, I'll clean the wheel interior of the rust and crud from the rotors.

Stefan

1999Porsche911

Do another break in of the brakes to clean the pad and rotors. Common problem with many cars washed and put away with wet brakes. A few hard long braking applications, both forward and backwards should clean them right up. Rotors do not warp, but pad material can adhere to them.

Tippy

'99 - I heard you make this statement before.

I have seen rotors cut and it looked to me that the parent material of the rotor was being shaved off, not pad material. As the rotor spins, the high sides would turn a bright silver and the low sides would be a low luster silver indicating that the rotors are indeed warped until flatness was achieved.

Also, can you explain how a hot, very hot rotor when quenched in a water puddle doesnt warp? I have experienced it myself several times on inferior non-slotted or cross-drilled rotors. I know this is not pad material bonding to the rotor causing the out of flatness condition.

1999Porsche911

It is possible for a rotor to warp, but only under extreme and exceptional conditions and I have seen it very seldom. What the lathe is removing is one of things. Either a soft spot on the rotor that has swelled or, most often material from the pads that have bonded to the rotor. This often happens when rotors are extremely hot and pads are tight against them.

Tippy

Brake pad material is softer than a rotor. If the cutter of the resurfacer hit brake material that is supposedly bonded to the rotor, it would make less of a cutting sound. Or possibly, no sound at all. On comparison, a screwdriver can easily damage a brake pad.

On softness of the rotor material in places. Arent rotors cast? If they are, the metal is in a liquid state before pouring into the mold, you would think it is pretty "mixed" and uniform.

LVDell

FYI....it is damn near impossible to "warp" a rotor. Uneven pad material build-up almost always mistakenly called a "warped" rotor. Spray em down with water. Let some rust form and then do do some high speed bedding in of the pads. Should clear it right up.

rcronin

As best that I can read from the original owner's paperwork and services, these are the original rotors and pads.
While we have had a great deal of rain, I haven't gone through any standing pools of water.

1999Porsche911

Pad material is constantly being transfered to the disc. If the pads are not bedded properly or are held against a non moving disc under certain cirrcumstances, you then get an uneven transfer of pad material. Aggressive braking often removes this buildup, depending on the type of pad material that was transferred. High content metal and carbon pads form a harder buildup on the disc..

Tippy

Search "brake rotor warpage" and it is commonly accepted as a fact. It is simply from rapid expansion and contraction, all the metal I know of and work around, warps. Can brake material transfer, sure. Is it the biggest cause of "shimmy", I doubt it.

Yes indeed, Porsche rotors are hard to warp because of their design, but they will. Not the same for the rest of the commuter vehicles.

LVDell

Cory, you're running into an argument you can't win.

Does uneven pad material create a feeling of shimmy/vibration under braking? YES.
Do rotors warp? Damn near impossible.

And no it is not commonly accepted as "fact" but rather it is anecdotal evidence accepted what we like to call a myth.

1999Porsche911

Since when does consensus actually mean fact? MOST people get there "so called" knowledge from what they were told or what they read and NOT from practical experience.

Remember, the majority also thought the world was flat and that hormone replacement therapy did not harm woman and that lobotomy was the proper way to treat schizophrenia and that sacrin caused cancer, and most men believe that SIZE DOES NOT MATTER.......an on an on an on.

It is also popular belief that Mobil 0W40 will not harm your engine and that humans can actually affect the global climate, and , I don't think we ever found green cheese on the moon.

Oh Yeah: and DELL actually thinks statistics matter.

Here is a link that does a pretty good job of explaining it the brake disk issue:

http://www.stoptech.com/tech_info/wp...rakedisk.shtml