BMW M5 Forum and M6 Forums banner

1 - 3 of 3 Posts

·
Moderator Emeritus
Joined
·
4,273 Posts
Gop-Dogg said:
My front brakes are showing signs of warping (shuddering under braking from medium speeds). Can X-drilled rotors be resurfaced or do they have to be replaced?
Hi Gopp-Dogg
The disc faces can be skimmed as long as the process does not take the disc below the manufacturers recommended min thickness.
An added complexity with cross drilled rotors is that you should closley inspect the gas vent holes in the rotor faces for fatigue cracks eminating from the holes. If there are any, the rotor should not be re-worked.

If the discs have warped from medium braking, I would check the hub face for any irregularities & sand the face flat to remove any surface rust & high spots.
I would then proceed to check the rotor to hub mounting face to ensure a clean mounting face, then move on to measure the run out of the rotor faces relative to the rotor to hub mounting face.
It takes surprisingly little runout caused by manufacturing or incorrect installation to warp a disc.
The bigger the diameter of the disc, the greater the exageration of error caused by improper mounting of the rotor to the hub.

Finally, assuming all is good with the world on the disc installation, check that the caliper piston seals have not been compromised & the piston has not
seized causing hot spots on the disc.

Hope this helps.

Regards
Farrell
 

·
Registered
Joined
·
970 Posts
I found these Guys 'Autofarm', a well known Porsche specialist who use this piece of kit to skim brake discs. You must have somebody like this Stateside?

url: http://www.autofarm.co.uk/new.php3/BrDisc.html




farrell said:
Hi Gopp-Dogg
The disc faces can be skimmed as long as the process does not take the disc below the manufacturers recommended min thickness.
An added complexity with cross drilled rotors is that you should closley inspect the gas vent holes in the rotor faces for fatigue cracks eminating from the holes. If there are any, the rotor should not be re-worked.

If the discs have warped from medium braking, I would check the hub face for any irregularities & sand the face flat to remove any surface rust & high spots.
I would then proceed to check the rotor to hub mounting face to ensure a clean mounting face, then move on to measure the run out of the rotor faces relative to the rotor to hub mounting face.
It takes surprisingly little runout caused by manufacturing or incorrect installation to warp a disc.
The bigger the diameter of the disc, the greater the exageration of error caused by improper mounting of the rotor to the hub.

Finally, assuming all is good with the world on the disc installation, check that the caliper piston seals have not been compromised & the piston has not
seized causing hot spots on the disc.

Hope this helps.

Regards
Farrell
 
1 - 3 of 3 Posts
Top