Rotor Whoa's... Need some advice - 986 Forum - The Community for Porsche Boxster & Cayman Owners

CJ_Boxster · 06-13-2007, 12:00 PM

Ok, In late Feb I purchased a Front & Rear set of Zimmerman Cross-Drilled & Slotted rotors from ebay. About 3 weeks ago I noticed a tad bit of wobble under braking and 1 week ago it had gotten alot worse and more obvious that the rotors were the cause of the wobble.

Now they wobble like a mofo when braking at speeds higher than 60mph. Emailed the Seller and told him if they can replace them, since i see a similar auction on ebay for the same rotors but with a 6 month warranty.

They replied with "rotors come with 30 day warranty". So that avenue is no good for me. Rather than Replace the rotors all over again, Is there anyway I can have them cut/straightened?

I heard that not all Rotor cutting machines can do Cross-Drilled/Slotted rotors but some can... Is this true? if so, where might I find a shop with this type of machine in the Los Angeles area?

Any advise or ideas welcome.

der Geist · 06-13-2007, 12:18 PM

Carlos:

You can't turn slotted or drilled rotors as far as I know. You may want to check everything to make sure it is all tight and that your pads are in good shape. Slotted or drilled rotors shouldn't warp with normal street driving in less than 6 months. Pull the rotors off and have them checked to see if maybe only one is warped. No sense in replacing all 4 if you don't have to.

Good luck

CJ_Boxster · 06-13-2007, 12:25 PM

I did a brake check 1 week ago when I removed my Wheels to wash the brake dust off the inner parts of the wheel. All the pads on all 4 brake assemblies still look pretty new.

Guess I'll have to inspect each rotor for warping, Can you or anyone tell me why cross-drilled/slotted rotors cannot be machined?

der Geist · 06-13-2007, 12:33 PM

Carlos:

They turn them on a lathe. The tool bit would get caught on the holes and slots and make a mess of the rotor or ruin the tool or both. At least I am pretty darn sure but someone please correct me if I am mistaken.

Great looking car BTW. What did that respray set you bac? I am thinking of doing the same to mine this winter.

Pat · 06-13-2007, 12:37 PM

You said, "....obvious that the rotors were the cause of the wobble." Although it may happen under braking, the rotors may be in good shape. There's a decent chance their are pad deposits on the rotors, causing unequal friction as the disc rotates along the pad. Try re-bedding the pads an see if that cleans it up. To do this, threshold brake 5-7 times from 80 mph to 20 mph or so. This will heat up the rotors and clean off any potential deposits. Your brakes may smoke after this, but don't worry about it if they do. Try driving without using the brakes at all for about five minutes after doing this to allow the brakes to cool evenly.
Also, what kind of pads are you using?
Be sure not to use the parking brake when the rotors are very hot.
Disclaimer: I'm new to the Boxster scene, so my comments are based on Audi experience, which is significant.

CJ_Boxster · 06-13-2007, 12:38 PM

Yeah i figure it has to do with catching the holes. I wonder if it can be safely done by having it cut very lightly into the rotor rather than the average depth.

The paint set me back $1800 but normally would have been 3k but i paid just the shops overhead costs like the hourly wage for the bodywork and painters and some supplies.

CJ_Boxster · 06-13-2007, 12:41 PM

Quote:

Originally Posted by Pat

You said, "....obvious that the rotors were the cause of the wobble." Although it may happen under braking, the rotors may be in good shape. There's a decent chance their are pad deposits on the rotors, causing unequal friction as the disc rotates along the pad. Try re-bedding the pads an see if that cleans it up. To do this, threshold brake 5-7 times from 80 mph to 20 mph or so. This will heat up the rotors and clean off any potential deposits. Your brakes may smoke after this, but don't worry about it if they do. Try driving without using the brakes at all for about five minutes after doing this to allow the brakes to cool evenly.
Also, what kind of pads are you using?
Be sure not to use the parking brake when the rotors are very hot.
Disclaimer: I'm new to the Boxster scene, so my comments are based on Audi experience, which is significant.

Im using the OEM porsche pads, Ill give that a try if there isnt much traffic on the freeway but I dont think I could safely get that done in city fwy's.

Pat · 06-13-2007, 12:48 PM

Like I said, I don't have experience with Boxsters, but have many hard track laps on my A4 that have taught me a bit about hard brake use. I'd be surprised if there was a problem with the rotors themselves. It is certainly possible, just not what I would look into first. For what it's worth, I've been using Zimm x-drilled rotors for five or so years, in conjunction with Pagid Blue and Ferodo DS2500 pads and have had zero problems with the rotors.
I know it can be hard to find a place to safely bed brakes, but before you spend any money or start taking the car apart, it would be wise to re-bed as a first step.

John V · 06-13-2007, 02:53 PM

I agree with the re-bedding idea. I'm guessing the brakes were not bedded-in properly after they were installed, and this led to a gradual deposition of uneven pad material onto the rotor.

You don't really need to go 80-20 - just go as fast as you safely can (50-60MPH will work just fine) and slow down quickly (nearly full braking force) to 5-15 MPH. The key here is to NOT STOP. Repeat several times. I would think you could do this in a large parking lot or a deserted road.

Dohertycm · 06-14-2007, 04:50 AM

What about tires and alignment? My car fell off of the jackstand right onto my zimmerman rotors and they were not damaged or warped. Seems odd to happen right off the bat like that.

uneven pressure in the pads will cause pulling, and surging... not a wobble.

To be honest the best thing you should do is remove the rotors and take them to a place that can tell you if they are warped...

Then buy a new one. I would not cut them if I am Autocrossing or DE'ing the car.
Cutting the rotor with off balance the rotor. Ok for everyday street driving, but not the best thing for high speed, hard brake DE's.

CJ_Boxster · 06-14-2007, 05:33 AM

I had a complete 4 wheel alignment done alittle more than a month ago and my tires are fairly new now, but were completely new at time of alignment. A kind german named Axel Peters from Zimmermann has responded issue and this weekend i will be pulling the wheels off to get the diameter codes from the rotor to give to him so that he could verify which model rotors i have in the first place. Ill have to see where we go from there.

Grizzly · 06-14-2007, 05:34 AM

CJ

Did you put the rotors on yourself or have somebody else do it? If you put them on yourself, (and any other times you had the wheels off for that matter) did you use a torque wrench to tighten the lugs? If the lugs are not equally tightened, or they're over tightened, the rotors will warp.

That's why you never, ever let a mechanic put your wheels on with an impact gun.

John V · 06-14-2007, 05:49 AM

Quote:

Originally Posted by Dohertycm

What about tires and alignment? My car fell off of the jackstand right onto my zimmerman rotors and they were not damaged or warped. Seems odd to happen right off the bat like that.

uneven pressure in the pads will cause pulling, and surging... not a wobble.

Uneven pad deposits will cause a really nasty wobble when braking. If his tires were imbalanced or the alignment were off, it would wobble regardless of whether he was braking or not.

JV

CJ_Boxster · 06-14-2007, 05:52 AM

Quote:

Originally Posted by Grizzly

CJ

Did you put the rotors on yourself or have somebody else do it? If you put them on yourself, (and any other times you had the wheels off for that matter) did you use a torque wrench to tighten the lugs? If the lugs are not equally tightened, or they're over tightened, the rotors will warp.

That's why you never, ever let a mechanic put your wheels on with an impact gun.

I put them on myself and i ALWAYS use a torque wrench.

Grizzly · 06-14-2007, 08:53 AM

Quote:

Originally Posted by CJ_Boxster

I put them on myself and i ALWAYS use a torque wrench.

Then I vote for the pad deposits as well. Go out and slam on the brakes.

CJ_Boxster · 06-14-2007, 08:55 AM

Ill do that today, i get off at 1pm today and the 47 is usually empty around this time so i should have enuff space to safely do this... How many times should i do this?

Pat · 06-14-2007, 10:50 AM

To do this, threshold brake 5-7 times from 80 mph to 20 mph or so. This will heat up the rotors and clean off any potential deposits. Your brakes may smoke after this, but don't worry about it if they do. Try driving without using the brakes at all for about five minutes after doing this to allow the brakes to cool evenly.
Also, try to avoid getting into the ABS.

Pat · 06-14-2007, 10:55 AM

Another good resource:
http://www.zeckhausen.com/bedding_in_brakes.htm

aussieboxy · 06-17-2007, 03:57 AM

Sorry guys but I think it's bull that u need to use a torque wrench. I have never experiences worped discs as a result of not using a torque wrench on wheel studs. I would try different pads before replacing the discs, perhaps they have not been bedded in peoperly.

Grizzly · 06-17-2007, 04:49 AM

Quote:

Originally Posted by aussieboxy

Sorry guys but I think it's bull that u need to use a torque wrench. I have never experiences worped discs as a result of not using a torque wrench on wheel studs.

I love it. Try typing "warped rotors overtorqued" into Google and you'll find pages and pages of references, because overtorquing is the most likely cause of warped rotors. Maybe you're not strong enough to overtorque yours

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