How can I cut down on rotor warpage?

[pdx 528e]

My independent mechanic recommends replacing the rotors every other set of pads. In the 16,000 miles ive driven the car since its rebuild, Ive warped all 4 rotors, first the fronts, and then the rears. I had each replaced when the vibration became too obvious. Its been about 9000 miles since the fronts were replaced, and maybe 3000 miles since i had the rears done. Starting to notice braking vibration ever so slightly through the pedal again. Should I change pads? Whats a good way to safely check for a dragging caliper. If i put my hand near it will I feel the difference in heat radiated? Im not sure that is it though, because the last times they warped in pairs.

Thanks in advance.

[fastpat]

What type rotors and pads are you using?
To detect a "dragging" caliper, by that I'll assume you mean a piston that isn't retracting properly due to rust or corrosion, jack the vehicle up, place it on jack stands, and turn the suspected wheel. You should notice significant drag.

[FirstFives Dictator]

[QUOTE="pdx 528e"]My independent mechanic recommends replacing the rotors every other set of pads. In the 16,000 miles ive driven the car since its rebuild, Ive warped all 4 rotors, first the fronts, and then the rears. I had each replaced when the vibration became too obvious. Its been about 9000 miles since the fronts were replaced, and maybe 3000 miles since i had the rears done. Starting to notice braking vibration ever so slightly through the pedal again. Should I change pads? Whats a good way to safely check for a dragging caliper. If i put my hand near it will I feel the difference in heat radiated? Im not sure that is it though, because the last times they warped in pairs.

Thanks in advance.[/QUOTE]

Are you sure they are warped? Did your mechanic measure run-out with dial-indicator? Seems like hardly anyone does anymore. Sometimes brake judder is caused from worn steering and suspension parts and sometimes from pad friction material being transferred to the rotor. It's happened to me.

Try this whitepaper from Stoptech http://www.stoptech.com/whitepapers/war ... s_myth.htm

This transfer can occur from improper pad bedding or leaving foot on brake after hot laps and baking the resin from the pads on to the hot disc
It's also a function of suspension design; this is much rarer in E12's yet I don't suspect the above factors occur any less often with e12 cars. Something about the front thrust bushing design appears to make the front suspension less tolorent of variations in rotor thickness and friction

[pdx 528e]

[QUOTE="fastpat"]What type rotors and pads are you using?
To detect a "dragging" caliper, by that I'll assume you mean a piston that isn't retracting properly due to rust or corrosion, jack the vehicle up, place it on jack stands, and turn the suspected wheel. You should notice significant drag.[/QUOTE]

I'm just using OEM replacement discs and equivalent pads, nothing more than street use equipment. I'm wondering if I should have some part of this system upgraded, even if its just pads.

Thanks for the response.



[Edit by pdx 528e on [TIME]1109096168[/TIME]]

[pdx 528e]

[QUOTE="FirstFives Dictator"]Sometimes brake judder is caused from worn steering and suspension parts and sometimes from pad friction material being transferred to the rotor. It's happened to me.
Try this whitepaper from Stoptech http://www.stoptech.com/whitepapers/war ... s_myth.htm
This transfer can occur from improper pad bedding or leaving foot on brake after hot laps and baking the resin from the pads on to the hot disc
It's also a function of suspension design; this is much rarer in E12's yet I don't suspect the above factors occur any less often with e12 cars. Something about the front thrust bushing design appears to make the front suspension less tolorent of variations in rotor thickness and friction[/QUOTE]

I am less likely to suspect suspension components at this time but I will check into it. My independent is a reputable shop, but I cant answer whether they used a dial indicator or not on the rotors. Each time the rotors are replaced I have perfect judder free braking for thousands of miles, last week I had one emergency braking situation, after which I tried to keep the pads off the rotors, and I could feel the slightest judder later during the same drive. That article is very interesting to me, and something I'll investigate. Specifically this point:

"If the vibration has just started, the chances are that the temperature has never reached the point where cementite begins to form. In this case, simply fitting a set of good "semi-metallic" pads and using them hard (after bedding) may well remove the deposits and restore the system to normal operation but with upgraded pads."

Any pad upgrade recommendations, does the break-in procedure from the article seem like the best approach?

Thanks.



[Edit by pdx 528e on [TIME]1109096197[/TIME]]

[Guest]

If your running Metal Master pads to reduce dusting this may be the cause of your warped rotors. The 528e has marginal brake (Think Thin) rotors and easily warp. My deceased 533i which used the same rotors as the Euro 528i warped rotors when using Metal Mssters. I switched back to the OE pads from BMW and BMW rotors, end of warpage, say hello to brake dust.

Or you could do want you really want to do, BIG BRAKE UPGRADE !!!!

Rich

[FirstFives Dictator]

I think the break-in/bedding procedures make sense but it's difficult to find a place to do repeated 60-5mph stops.

I would ask your mechanic if he actually measured warpage or not.

I checked few of mine that shook and never measured run-out.
I did burnish them with fine garnet paper and it helped.