jford

Replaced my front rotors one year ago with zimmerman rotors. The old rotors were in good shape but were developing a bit of a lip so, as I needed new front pads anyway, I changed the rotors as well. Recentley I started getting a steady vibration through the steering wheel.... at the same time I noticed hairline cracks spreeding out from every cross drilled hole (in the front rotors) extending about 1/8th to 1/4 inch....two thin lines from each hole.

At the time I didn't think the cracks were causing the vibration, but that maybe I had a tire or tires out of balance. Well, I got new track tires in prep for a DE this weekend and thought that maybe the vibration would go away with the freshley mounted and balanced tires. Before I tried them out I thought I'd put the old rotors back on and take a run with the street tires as some sort of control. They old rotors were OEM (with only 2 track days on them and not sure how many street miles). Well the vibration is gone and the car feels great. So the tiny craks in the zimmerman rotors caused the vibration.

Now I would like to know how to avoid this from happening or at least happening so quickley. The new rotors had 10 track days on them and maybe 1500 street miles. I used padgid dark blue and padgid orange pads with about 5 days for each. All track days were at Summit Point and the Glen so there was quite a bit of heavy braking. I have no aftermarket brake cooling set up. ATE blue brake fluid was used and flushed and bled just before last track season.

Is it the rotors? Do I need to add brake cooling ducts? Do the pads have anything to do with it? Any thoughts or comments appreciated.

Thanks.
Jamie

Fishey

Crappy Rotors...

jford

You don't say....lol.

Greg Fishman

Don't use zimmerman rotors. Pagid Oranges, if not bedded in properly, could cause a problem. I have used Hawk Blues with no issues. Cooling ducts would help as well.

BTW, small cracks are normal after track use.

Eric in Chicago

Hey Jamie,
nice to see your still around! You could have left deposits on the rotors from your hard track days (what some call warping is really pad deposit left behind) Agreed Zimmerman rotors have a pretty short life before the cracks start joining each other. When bedding in rotors and pads, make sure you dont have new pads going on new rotors. Use old pads with new rotors and new pads with used rotors. I forget where that advice came from (stoptech or pagid) but it has something to do with the transfer of material from one part to the other.
did you add another car to the fleet?? I see a 81SC. How is your Brothers 944 T doing?

jford

Greg..I'll probably go with OEM next time out and look to add the ducts. Glad to hear the cracks are normal though. Now at least I won't panic when next I see them.

Eric,
Thanks for the advice. I did indeed get another car. Not sure what my intentions with it are...perhaps a stripped out dedicated track car ala Edward's project. I let my buddy take the SC to the Glen he had a blast...perhaps I'll use it just to get freinds hooked. Doug's car is in pieces and we are off to Summit Pt. tommorow. He cracked the housing at the rear of the torque tube when backing out of his driveway. Well, you have to drop the entire rear to get the torque tube out. Of course its a good time for new clutch and LWF....you know how this story ends up. Along the way while moving the tranny around we broke the tranny fluid cooling line...thats arrives in the AM. Car is almost back together (new starter and clutch slave too..lol) wish us luck!

I'll be at mid-ohio for three days with Potomac region at the end of April....any interest? Well I'm sure there's interest but can you make it? Nice to hear from you!

Jamie

PedroNole

I've got Zimmerman's on my front end and haven't had any cracks (4 DE's and a few AX's on them so far) yet. That said, I've seen plenty of the Zimmerman's with the cracks but really didn't think there was enough separation to come into contact with the pads to cause the vibration although your test seemed to prove it out. Interesting post.

jford

Pedronole,
I may clean the zimmermans up and put them back on to see if there was buildup as Eric suggested. I didnt' see any noticable buildup (even the holes were clear of dust). Since both Eric and Greg indicate that the cracking is normal (and now you actually) I feel better about running with them...assuming, of course, that I dont' continue to get the vibration. I will tell you this, my the holes on my old rotors (the ones I put back on) were packed with dust..I did poke the dust free before re-installing but didn't do anything to the actaul surffice. Still some experimenting to go it seems. Another thought...I bedded new pads to the new zimmermans when I did the install....Eric indicated that you should use old pads to new rotors and vie versa....maybe this contributed. I'm confusing myself....lol.

Jamie

Mark in Baltimore

Jamie,

I've never been too happy with the pad deposit the Pagids leave on rotors. I almost threw out a set of rotors after a bad vibration that I thought was from warpage. Late this winter, I put the "warped" rotors back on and cleaned them off with the Hawk Blues I now run. After a few heavy braking sessions, the rotors felt like new.

1999Porsche911

Try as much as possible NOT to apply the brakes when the car is stationary after a hard track run. Pad material build up only occurs when the car is not moving, the rotors are hot and the brakes are applied.

jford

Mark,
Nice to see you. That's two votes for the Hawk Blues. I'm sold. I won't throw the zimmermans out just yet, seems they may be salvagable.

1999,
I'll try to brake as little as possible when I get back to the paddock this weekend. Thanks.

Jamie

MrRoboto

So while we're on the topic of rotors, are there any good alternatives to the OEM ones? Any lighter aftermarket 2 piece rotors that will work with the stock calipers?

viperbob

Not quite yet

MrRoboto

Tell me more...

George A

Bob, tell me more too.....

I'm dying to find some non-cross drilled rotors. I seem to get cracks in them way before I even get a lip.

George