Brake Rotor Recommendations

#1

I am preparing to bring my car back to the track. It had new pads and rotors put on it 5 years ago and then I tracked the car on the rotors for two seasons of HDPE. They still appear to be in good condition, but could use a resurfacing. I would like to know your thoughts on rust prevention. I do not believe their is a paint or powder coating that will hold up to racing temperatures. I have read about an electroless coating referred to as E-coat. It is basically an electrically applied paint, but seems to hold up better to higher temperatures. Does anyone have experience with this? The same goes for the calipers.

Should I:

  1. Resurface them and deal with normal rust; Just clean the calipers and deal with it?
  2. Find a shop that can E-coat them?
  3. Purchase new rotors that are already E-coated?
  4. Other?

I have a 1991 325i with Girling brakes. I ran the Hawk HT10 pads 3 years ago. I will be rebuilding all the brake calipers and installing new bearings with the rotor service. Currently the brake indicators have be bypassed for racing purposes, but I really do not like things that do not work, so I plan on replacing the sensors as well.

I am located in Richmond, VA.

Thanks in advance.

Roddy

#2

BMW rotors can hardly ever be turned. The total wear limit is only 2mm and surfacing of even slightly worn rotors will take them below the wear limit.

Just get plain OE rotors and don’t worry about the rust. Rust on the area swept by the pads will be gone after a few applications of the brakes and rust on the hubs doesn’t matter at all.

#3

When you have a crack that you can catch a finger nail in, and the crack extends to the outer edge of the rotor, replace it. It will look pretty until it’s first over-night when the early morning dew will cause the new rotor to rust.

The brake wear sensors are going to have a tough time with the heat of real braking. Same for painting the calipers.

Your front rotors and pads made it thru 2 seasons? If I had to guesstimate an average replacement cycle for front pads and rotors, I’d say 8hrs for pads and 12hrs for rotors. Varies a lot with the track tho.

#4

http://www.autopartswarehouse.com/sku/BMW/325i/Replacement/Brake_Disc/1989/Base/6_Cyl_2-dot-5L/REPB271107.html?loc=Front&tlc=Brakes%2C+Suspension+%26+Steering

Nuf said. :wink:

#5

spend as little as you can on rotors. the expensive rotors don’t last any longer than the cheap ones. The same logic does not apply to pads…

#6

Wow! I am impressed. I knew that I could get the rotors inexpensively, but the AutoParts link was incredible. Thank you for the information.

Roddy

#7

Jealous of you guys and your cheap rotors!

And I’ve just got DBA to commit to making a test batch of 4000 series rotors for the E30 front - and they’re cheap at A$175 each (approx US$165 at current exchange, but that’s before you get the “We’ve got over 250 million consumers” discount).

#8

mcmmotorsports wrote:

[quote]http://www.autopartswarehouse.com/sku/BMW/325i/Replacement/Brake_Disc/1989/Base/6_Cyl_2-dot-5L/REPB271107.html?loc=Front&tlc=Brakes%2C+Suspension+%26+Steering

Nuf said. ;)[/quote]

this

#9

So I have surface cracks that I can catch my fingernail on, but the cracks are still a half inch or so from reaching the outer edge of the rotor… Scott, I guess what you’re saying is I can keep abusing them until some of the cracks actually extend out to the edge of the rotor…?

**** I need new front pads soon, and I am pretty sure I changed the rotors with the pads last time (PFC 01 or 06, I cant remember)… I was considering just changing the rotors also (they are sooo cheap, maybe the best practice is to just change both at once, while I’m in there working…), but if the rotors still have some life left in them, I’ll happily abuse them some more. Does anyone just change the rotors whenever changing to new pads?

#10

Gilles wrote:

[quote]So I have surface cracks that I can catch my fingernail on, but the cracks are still a half inch or so from reaching the outer edge of the rotor… Scott, I guess what you’re saying is I can keep abusing them until some of the cracks actually extend out to the edge of the rotor…?

**** I need new front pads soon, and I am pretty sure I changed the rotors with the pads last time (PFC 01 or 06, I cant remember)… I was considering just changing the rotors also (they are sooo cheap, maybe the best practice is to just change both at once, while I’m in there working…), but if the rotors still have some life left in them, I’ll happily abuse them some more. Does anyone just change the rotors whenever changing to new pads?[/quote]

yup, by the time my pfc06 pads are worn out the rotors are toast too

#11

Gilles wrote:

[quote]So I have surface cracks that I can catch my fingernail on, but the cracks are still a half inch or so from reaching the outer edge of the rotor… Scott, I guess what you’re saying is I can keep abusing them until some of the cracks actually extend out to the edge of the rotor…?

**** I need new front pads soon, and I am pretty sure I changed the rotors with the pads last time (PFC 01 or 06, I cant remember)… I was considering just changing the rotors also (they are sooo cheap, maybe the best practice is to just change both at once, while I’m in there working…), but if the rotors still have some life left in them, I’ll happily abuse them some more. Does anyone just change the rotors whenever changing to new pads?[/quote]
Unless it’s an important race, run the rotor until the crack goes to the outside edge. Don’t replace rotors just because you’re changing pads, you changed the mate on the other side, or it was in your horoscope. Change them when they fail.

#12

Change your rotors if you can catch a finger on a crack. You may be comfortable risking catastrophic failure to save the last $5 worth of wear, but I would prefer you not have that failure when I am on track. If you can’t afford new $20 or $30 or $40 rotors frequently, you can’t afford tracking a car. Thick rotors stop better anyway.

#13

Steve D wrote:

+1

#14

I just wanted to thank everyone for their input. I have also spoken to a local shop that supports me and they are in agreement with everyone else. I will be purchasing new rotors and since they are short lived, I am not worrying about the surface rust. It bugs me, but I will get over it. I will also be rebuilding my Girling calipers with new new seals and bleed valves. I’ll take pictures and post them for others.

On a separate note, nice paint job Steve D. Is that your shop or a shop that does your work?
Roddy

#15

ActionJunky wrote:

[quote]On a separate note, nice paint job Steve D. Is that your shop or a shop that does your work?
[/quote]
Thanks, Roddy. After a couple years, it doesn’t look quite so fresh but I am planning to refresh it over the winter.

OPM Autosports in Atlanta built the car for me. They have a couple outside shops that do their body and paint work. Damn near street car quality.

#16

A few points, from years of racing in Spec E30…

  1. Check your rotors after each session. I am a big believer in getting the car ready for the next session, right after this session. At VIR last year, I didn’t check the rotors and as I was driving across the paddock, to the grid for the race, I felt the bump, bump, bump of a cracked rotor. I did the 1-hour race anyway (and got a win!), because I was told that the rotor will heat-up and close the crack. It did, and the car did fine but I would not recommend anyone do this. And I didn’t feel any bumping after the previous session. It was as if it had cracked while sitting in the paddock between qualifying and the race.

  2. Have at least two sets of spare front rotors in the truck/trailer. New are best of course, but we usually have one set of new rotors, and a couple of used rotors that can get us through a session or two. I have the BimmerWorld front ducting kit and run the Hawk DTS 60 pads and have cracked a rotor after two sessions, although they usually go about two weekends. I bought the rotors at Autozone so it’s not like I bought them off the back of a truck that had just pulled into town.

  3. Steve is right about the $5.00 of wear that you might save, to get more life from a cheap rotor. Now - if mine develop any visible cracks at all, I toss them.

#17

Save up all your used rotors and take them to a metal recycler and you’ll get your $5 back :slight_smile: