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Old 04-24-2008, 02:56 PM   #1
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warped rotor?

I replaced my original rotors last month with Zimmermann cross-drilled rotors.

My braking was fine until a couple of weeks ago. Now, when I am forced to do hard braking at freeway speeds, the steering wheel shakes like nobody's business all the way down to about 20 miles per hour.

I am also noticing a new vibration in the wheel and body of the car at freeway speeds I didn't have before. I thought this was a wheel out of balance, but now I'm wondering if I have a warped rotor.

1. How can I check to see which rotor may be warped? A visual inspection (wheel on the car still) yielded nothing out of the ordinary...

2. Are there any other sources for this problem, such as ABS sensors?

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Old 04-24-2008, 07:54 PM   #2
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Thread bump.
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Old 04-24-2008, 08:50 PM   #3
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Thread bump after only 5 hours?

So vibration at while braking from high speeds and also high way speed vibrations?

What makes you think it's not a wheel balance issue? If it started suddenly, it seems like it'd be a balance issue, no? ...As if one of your lead weights fell off. Did you inspect the inside of your rims for that?
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Old 04-24-2008, 10:54 PM   #4
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The optimal way is to use a Dial Gauge on a fixed base or attached to the Caliper, though fixed and set against the rotor. Zero out the gauge and turn the wheel/rotor noting any variance in the gauge. I say optimal because a certain amount of runout (warpage) is to be expected and there is a tolerance - The permissible lateral runout for the installed brake disc is max. 0.06 mm.

Now, you can also check by taking an absolute straight edge and holding it against the rotor face at several points and look to see if the straight edge is touching the rotor for it's entire length, if not, you have some runout.

Another way is to take a board, drive a nail through it. Stand the board upright so the nail is touching the rotor and fix it firmly in place. Rotate as before and see if the nail comes off the surface of the rotor.

These last 2 will tell you if there is any runout, but not the value of it, and 0.06mm is a very small dimension, hard to determine w/o a gauge, though you could use a 0.06mm Feeler gauge and see if it will slip under the t=straight edge or the nail.

I have heard several reports that the aftermarket Zimmermans are prone to cracking and warping. They are not the same spec as the OEM ones supplied to Porsche. Probably a cheaper generic which is then drilled and tapped in the Porsche 5-bolt pattern (or any pattern really depending upon the application).
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Old 04-25-2008, 05:54 AM   #5
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Quote:
Originally Posted by Jeph
Thread bump after only 5 hours?

So vibration at while braking from high speeds and also high way speed vibrations?

What makes you think it's not a wheel balance issue? If it started suddenly, it seems like it'd be a balance issue, no? ...As if one of your lead weights fell off. Did you inspect the inside of your rims for that?
Jeph, folks here usually give advice within an hour. I'm quite concerned about this problem so I bumped it... and you took notice, so it worked!

I inspected my wheel weights and didn't see any missing. Doesn't mean a wheel isn't out of balance, but I did inspect them.

I have never had a violent shaking issue while braking from a wheel out of balance, but then again, every issue I've encountered with this car has been a first for me.

I'll take it in and get the wheels balanced asap and report back. Could be a wheel bearing or a worn suspension part now that I think about it.

I don't know why I dread a warped rotor... possibly because I put zimmermans all the way around and I don't want to swap all four out for solid OEM ones.
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Old 04-25-2008, 07:55 AM   #6
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Yep,
Sounds like warped rotors. Use the straight edge method to check for gaps. These are brand new rotors??? Did they come with a warranty? If not they can be turned but will likely warp again. Remember Randall, you and I have the old underpowered 2.5's. We don't really need that middle pedal anyways .
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Old 04-25-2008, 02:28 PM   #7
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Mark (Houston_C4S) came over and drove my car today.

Back and front left side rotors are very smooth and still have some of the machine marks on them. Slight use.

The front right side rotor has a lot of wear on it and slight ridges in the rotor and looks as if I repeatedly stood on the brakes at the track for a half day compared to the other three. Definitely warped according to Mark when he braked hard.

Mark thinks that one of the caliper pistons on that wheel might have gotten stuck. I did not know to clean the inside of the calipers and the rings before I put them back on the car after the disc and pad replacement.

So, I ordered a new rotor.

Mark and I will remove the caliper and clean it good and clean each piston as well. Then, we'll put it back on, drive the car a while, and use a laser thermometer to measure the heat from both rotors up front and see if one we worked on is hotter or the same temp. This will help us see if we fixed the problem or if the caliper needs to be rebuilt.

If we fixed the problem, I'll install the new rotor and call it a day.

What a pain in the arse. These 11 year old boxsters are one problem after another.

I'd trade it on a much newer one, but I don't have an extra $25k lying around to spend on a weekend vehicle.
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Old 04-25-2008, 04:40 PM   #8
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Look for uneven wear/thickness of the inboard and outboard pads on the suspect caliper.

It also seems somewhat odd that you still have machining grooves on the other calipers, these disappear rather quickly - how many miles on the Pads/Rotors? On the car?

Odd for a single caliper to warp, this will usually occur in pairs - axle mates - did you properly torque the wheel bolts? That's usually the only way a single caliper will warp, except of course a hanging piston/pad.

If you're removing the caliper, bleeding the brakes, etc, it's easiest to just rebuild the caliper while your in there - takes about an extra 10 min. and parts are usually cheap.
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Last edited by Lil bastard; 04-25-2008 at 04:42 PM.
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Old 04-25-2008, 04:41 PM   #9
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Quote:
Originally Posted by RandallNeighbour
Then, we'll put it back on, drive the car a while, and use a laser thermometer to measure the heat from both rotors up front and see if one we worked on is hotter or the same temp.
Actually, it's a laser guided infrared thermometer...
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Old 04-26-2008, 05:16 AM   #10
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Sorry Mr. Flashlight. I got that wrong. Infrared! Sheesh

Anyone know where I can find the parts to rebuild the caliper? I have yet to find them anywhere.
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Old 04-26-2008, 09:39 AM   #11
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Any dealer should have it or can order it. PN# 951.352.917.00 (36mm) or 951.352.917.01 (40mm) - I believe you will need the .00 part, but double check.

The typical Caliper rebuild kit consists of a rubber piston seal, dust boot and retaining clip.

But these caliper intergrate the seal and dust boot and don't require a retaining clip, so it's really just a single part. They're priced around $20.

You'll need a compressed air supply, a thin piece of wood and some fresh Brake Fluid.

Using about 8-10PSI pressure, place the piece of wood between the pistons where the pads usually sit - this is to prevent the piston from being damaged when it is pushed out of the caliper bore.

Remove a bleeder valve and while holding your thumb over the Brake line hole, add compressed air into the hole for the Bleeder Valve and the piston on that side will 'pop' out. It can make a pretty loud POP, but that's normal.

Remove the piston and seal/dust cover. Repeat for the other side.

Then, clean up both pistons with Brake Cleaner and then Brake Fluid, being sure not to scratch them (also a good idea to identify which side each came from and replace them the same way). If there is some scoring or a ridge where the seal was, lightly scour this area with 00 Steel Wool. Then, clean the calipwer where the seal seats and add the new Seal/Dust Cover to the caliper and press the piston back in on both sides. Replace the Bleeder Valves and that's it.
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Old 04-26-2008, 09:46 AM   #12
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true warped rotors are rare; usually runout difference is the result of pad material build-up and hot spots. if your rotors are fairly new, this shouldn't be a problem. i'd be looking at wheel bearings and tie rods.
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Old 04-26-2008, 09:50 AM   #13
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to answer the caliper rebuild stuff: when the inner seals go bad, they get soft. the inner seals actually retrac the pistons when you release the pedal. if they get soft, the pads don't retract and ride on the disks. this causes heat build-up and fade. i doubt if this is your problem. at any rate, if you want to rebuild the calipers, the dealers will NOT sell you the inner seals, only the outer dust boots. the best place to get seals AND dust boots is here:

http://www.zeckhausen.com/Brembo/Consumables.htm#Rebuild

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