Getting a strong vibration in steering wheel during braking at 70+mph and 40/50. Search of the archives provided some very good info. A link referenced by Graham:

http://www.stoptech.com/whitepapers/...otors_myth.htm

Suggested using GARNET PAPER on the rotors to remove any pad deposits materialized on the surface, which I suspicion is the cause. It said not to use regular sand paper.

A search on the web indicates Garnet Paper is used for woodworking finishes and is NOT to be used on metal surfaces......??? WTF ??

Has anyone used something other than what's mentioned to clean /scrub the surface of the rotor ????

Side note: After a good rotor scrub, I'll try the 60-5mph, 70-5mph, 80-5mph brake in to rebed the pads.

Thank You for any replies.

 

Keith,

Hawk Blues are great for cleaning off any deposited material. Try posting on the racing board to see if anyone has any really thin pads that they're on the verge of throwing out.

 

My experience has been when I felt vibration, the rotors (fronts) are warped. Replacement cured the problem. Never found a rotor cleaning/sanding that did anything.

 

Likely you have warped front rotors, in my recent experience. The shop turned them for me, and the vibration was gone. I don't know what method, or if they use any abrasion material.

 

Before you throw out your rotors or have them "turned", do this one simple thing. Take an air hose and blow out your cross drill holes and then take a small drill bit and and stick it through the hole to make sure it is cleaned out.

I had this same problem with a set of 993tt rotors. Everyone told me that they were warped. I asked someone at the track and was told to do what I have outlined. It cured the problem.

It's worth a shot.

 

I have some HAwk Blues I could send you. That should take car of any uneven brake pad deposits.

 

I have found that sometimes just driving around for a few weeks will cure the problem if it is not really bad. However, I have also had rotors blanchard ground at a machine shop which also cured the problem.

 

Get a caliper measurer, measure at different spots of the rotor to compare thickness of rotor. If they vary too much, your rotors are warped. If any measurement is lower than spec, your rotors should be tossed bc they aren't thick enough. If they are all higher than spec (stamped on rotor's center), you can have a shop turn them. They put it on a lathe and shave off excess metal to make it even in thickness.

Sanding to remove dust is fine but don't get too abrasive on the rotors bc you won't be sanding evenly and can make warping worse.

 

The machine shop, even a pep boys can tell you if the rotors can be turned or if they are beyond hope. I'm not sure I have ever heard of a street car rotor warping but I'm sure it has happened.

Another cause could be a cracked rotor. You will have to pull them to get them turned, so do a good inspection to make sure they are not cracked.

 

I had pretty bad shudder at a track event with my 964. Once I cleaned the rotors well (and got rid of any build-up in the holes) it went away. No sanding, no turning, no replacement was necessary. I cleaned with soap & water and used a "scrunge" type pad from the kitchen. I also poked every hole with a small srewdriver to ensure they were clean.

 

I use a pressure washer to blow out the crud in the holes. Safer on your lungs than compressed air and is quicker than a drill bit.

 

Regular cleaning w/ high pressure air and a garden hose goes a long way.

Regular kithcen scrubbies work will to clean pad deposition. Garnet paper does work well.

the big thing not to use is steel wool

 

My thanks for the tips and advice, particularly to Greg Fishman for offering up his Hawk Blues to help clean up the rotors.

I was able to eliminate the front end shudder in the brakes by doing the following:

-Power washed the front rotors followed by compressed air to dry them out.(took Clbrcr-Jim Newman's recommendation) and inserted a drill bit thru each hole in the rotor to ensure no buildup was left.

-"Dragged the Brakes" ...put the car in 2nd gear and drove it to 35mph while keeping one foot on the brake and the other on the gas maintaining a constant speed.

Followed the process in this link... http://www.pagidusa.com/bedding_in_procedure.htm

Shudder is GONE !! Although it worked for me, I won't go so far as to say it will for everyone. Just another option to try before going thru the expense of rotor replacements or turning them.

Additional thanks to AGRO1 for passing along the Pagid Link.

 

Anybody know of a good shop to blanchard grind rotors in the Long Beach CA area?

-Damon
'94 325i
'95 993