Didn't know which section to post this in so I figured Tech/Misc would do. Sorry if that's wrong, mods can feel free to move this.

My car's front end shakes a little when I brake above 40 mph. You feel it most in the pedal and steering wheel but it's there all over and you can hear it too. A very fast bump-bump-bump-bump etc. etc. etc...

Rotors are wearing evenly (off 20/1000s when I measured them today) and everything is properly secured. I am at a loss for what is doing this since nothing shakes at cruising, thus ruling out (in my mind) wheel hub or balancing issues.

By the way it's been doing this since before I replaced everything, now that I think about it. I thought maybe it was that my old rotors were rounded but maybe it was this same deal. The problem was lessened with the new hardware but clearly still exists.

My braking setup is as follows, installed approx. 3-4 months ago:

Brembo front OEM discs
Brembo rear OEM drums
AEM metallic performance pads
New OEM shoes
New OEM front calipers
Goodridge G-Stop stainless-steel braided lines

Could this be something causes by the denser performance pads? I have been told no, but I just figured I'd get more opinions. What could this be? Thanks in advance for your help, people.

Late Edit: Renamed so I would (hopefully) get some responses.


Modified by TS John at 5:01 PM 2/24/2007

 

Check the rotors for runout. Corrosion on the hub face can cause this by lifting the rotor slightly off of the hub.

 

Is runout the measurement taken by that very precise measuring device that you place in contact with your rotor as you spin it? If so, then the measurement of 20/1000s applies to the runout. Sorry I don't know terms for this stuff.

 

Runout is the wobble of the disk, which sounds like what you measured. Have you checked the torque on your lugs?

 

Yeah, sounds like you rotors are warped. If you changed the pads and did not resurface the rotors that will also lead to warped rotors.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by hybridmiklo &raquo;</TD></TR><TR><TD CLASS="quote">Yeah, sounds like you rotors are warped. If you changed the pads and did not resurface the rotors that will also lead to warped rotors.</TD></TR></TABLE>

It is not common for a rotor to warp. Rotor runout or pad material buildup are usually the culprits.

http://www.stoptech.com/tech_i...shtml

 

Very informative article. Thanks, Dogginator.

Two keys:
"The driver can feel a 0.0004" deposit or TV on the disc. 0.001" is annoying. More than that becomes a real pain."

and

"The only fix for extensive uneven deposits involves dismounting the discs and having them Blanchard ground - not expensive, but inconvenient at best."

If my rotors are reading .02" then that would deffo qualify as a real pain. It's odd, since today after taking the wheels off and removing the screws that held the rotors on it felt better but still not perfect. I guess I'll have my rotors turned and see where that gets me.

Thanks for the help.

 

Make sure the hub faces are clean and free of corrosion. If the rotor can't mount true to the hub due to debris, it will exhibit runout.

 

Will do. Thanks again.

I'll prolly ressurrect this thread soon when I get this done in case anyone is curious about the results.

 

check the rotors,make sure they are not warped and get your tires balanced if there not.

 

So today I pulled off my rotors to inspect the wheel hub face. Sure enough there was some rust build-up on there that made a discnernable (yet slight) height difference in certain areas.

I block sanded the heck out of it so that it was as even as I could get it. It took me about an hour, and made a noticeable (but, again, slight) difference. I guess I could potentially have sanded so much that it looked polished, but I didn't have enough daylight left.

It feels better but still does the same thing when braking medium to hard. I'm about ready to go crazy here cuz this is so hard to pin down.

Monday I'm going to measure my runout again to see if sanding off the rust from the hub face made a difference. Originally it measured .02", which is substantially above the .007" recommended maximum for street vehicles, and way above the .001" guideline given in the article linked by Dogginator about racing brakes.

I'm also going to have my rotors turned, and I'll remeasure to see what kind of a difference that has made. If it's still doing it after that then I'll have officially run out of ideas.

v.i.gsr suggests that it could be a wheel balance issue. I also read somewhere else that it could possibly be a wheel bearing. Both of these seem odd to me, as these would contribute to a shakey feel all the time, and not only when braking. Am I off-base with these thoughts? Should these be things I actually look into?

Thanks again for everyone's help.

 

I would take them off and take them down to get resurfaced. Just tell them to make a few small passes on the smooth cut and not a rough cut. Stick around and watch them do it.
You can notice right away on a semi-warped rotor.

 

Yeah, I know what you mean. It's like a fireworks show on a warped one. But those tend to look warped going in and you really can't see anything like that going on with these.

I'll prolly have them turned at my friend's shop, so I'll deffo get to watch and make sure it all goes down right.

Keep the suggestions coming.

 

So I remeasured my runout today after having tried to sand off the rust from the wheel hub. It took it down a few thousanths of an inch on either side, but it was still above twice what it should have been.

Then I pulled my rotors off and had them turned at my friend's shop. Remeasused the runout after that it it was about 5 thousanths.

So problem solved. It feels great. Very smooth and silent. I'm gonna go easy on them for as long as possible to keep it that way. They say go easy for a full tank of gas, so....

Moral: Take the time to do the job right the first time! I may have replaced every conceivable piece of my brake systems (see OP) but I neglected to properly clean the wheel hubs. This caused the rotors to sit improperly and gradually wear improperly. So I had to refix them 4 months after putting them on.... And deal with them being off for the last two or three. Bummer.

But it all has worked out. Thanks for everyone's help.

 

at the dealership i work at, most brake problems are caused by rotor parallelism not runout. runout can cause problems but you usually feel the brakes pulsate from parralellism. becuase that causes the caliper piston to get pushed back into the caliper and causes the peddle to move. runout can do the same but is usualy not as bad. to totaly eliminate the braking pulsation use an on car lathe. that way runout and parralellism are both fixed. if you take the rotor off, and have someone resurface it with an off car lathe, your runout can be just as bad as before because the hub/bearing may be causing the runout issue. also make sure to clean the inside of the rotor where it mounts to the lathe or hub so it doesn;t get installed wronge from rust or corrosion. same with the hub before installing the clean rotor.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Snail Tuning &raquo;</TD></TR><TR><TD CLASS="quote">if you take the rotor off, and have someone resurface it with an off car lathe, your runout can be just as bad as before because the hub/bearing may be causing the runout issue. also make sure to clean the inside of the rotor where it mounts to the lathe or hub so it doesn;t get installed wronge from rust or corrosion. same with the hub before installing the clean rotor. </TD></TR></TABLE>

Yeah, I think I understand what you're describing. Basically I did something similar to that by installing new rotors on corroded hub faces, which quickly led to runout. So not only did I have to get my rotors turned, I had to really work hard to clean up the hub faces so that it didn't happen again.

Good info. Again, thanks for everyone's help.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TS John &raquo;</TD></TR><TR><TD CLASS="quote">

Yeah, I think I understand what you're describing. Basically I did something similar to that by installing new rotors on corroded hub faces, which quickly led to runout. So not only did I have to get my rotors turned, I had to really work hard to clean up the hub faces so that it didn't happen again.

Good info. Again, thanks for everyone's help.</TD></TR></TABLE>

Cleaning the hub is always a good idea. Turning the rotors while mounted on the car can mask the source of a problem: if you were to unmount and remount a rotor for whatever reason, the orientation can change (180 degrees for 4 bolt rotors) and the problem can reoccur. Whereas if both the rotor and hub are true, there will be no problem.

 

Ah yes. When I said "rotors turned" I was actually referring to having them "turned" in a grinding machine. I guess the term is "blanchard ground." But that's what I did, call it what you will.'

Anyways, it's all good in the hood now.

Thanks specifically to you, Dogginator, for your help and especially that article you linked to.

 

unmatched tires, worn steering and suspension components, and alignments must always be checked first before the brakes although in this senario it was the brakes.