This is regarding warped brake rotors on a '93 944T. I've owned the car about three years, and for the entire duration, I've had warped front rotors. Pads have about 60% remaining. Basically, the only symptom they're causing is the steering wheel wobbles a good deal during normal braking, less so during hard applications. Question is, in an emergency, will my safety be sacrificed, or is this something I can live with for a while until my pads wear down a bit more to save a buck? The PO obviously didn't want to spend the money on rotors, so I got a car with great pads and garbage rotors :/ . I've been contemplating IPD's Zimmerman cross-drilled ones. Anyone have these? Are they worth the extra $$? Should I pull the trigger soon?

"Warped rotors" are a misnomer and have no real basis in fact. If you have the tools, measure the runout and I suspect it will be within spec. What happens is an overheated pad remaining in contact with a rotor (usually a result of a sticky caliper) will deposit bits of itself on the rotor's surface resulting in uneven friction when the brakes are applied again.

"...every case of "warped brake disc" that I have investigated, whether on a racing car or a street car, has turned out to be friction pad material transferred unevenly to the surface of the disc."
(http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml)
(http://reviews.ebay.com/What-causes-rotor-warping_W0QQugidZ10000000005242298)
(http://www.raceshopper.com/tech.shtml#warped_rotors)

Any braking "shudder" will be magnified if the strut bushings are worn.

Once the uneven transfer of material has taken place the only cure is to turn the rotor AND REPAIR THE STICKY CALIPER(s). If all you do is turn the rotor, the shudder will most likely return as the root cause of the material transfer that caused the shudder has not been addressed.

Replacing the strut bushings, if worn, will show a marked improvement especially if the offending rotor surface transfer was small to begin with but it will still be there.

This is a perfect example of how integrated a vehicle's systems are and how a minor problem in one can affect (and even seemed to be cured by) changes in another.

i would say so you are not getting the full advantage of stopping definately replace them

The safety question is a matter of degree, (how much shaking can you overcome with pure muscle?)And then there is the annoyance factor...

What I'd do, is have the rotors you currently have turned, about $15 per at any machine shop) as long as there is enough there, 20mm minimum thickness. Put the same pads back on and wait till it's time for new brakes.

I'll second Lucid's comments. You'd be surprised how warped rotors can be before the shuddering gets bad enough to complain. Shuddering brakes are usually sticky calipers or bad suspension bits.

Check ball joints and cone bushings. Cone bushings are the only bushings that seems to need replaced in the front end. Go with Boge rubber or SuperPro Poly.

Unless you're racing around, there's no need to get fancy rotors. Plain ol' Brembo's will do the trick otherwise.

-Ryan


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Athens, Ohio
1987 245 DL 324k, Dog-mobile, E-codes
1990 245 DL 137k M47, E-codes, GT Sways/Braces, Dracos, A-cam
1990 744GLE 189K 16-valve project
1991 745 GL 304k, Regina, 23/21mm Turbo Sway Bars

See THIS LINK

My '93 Regina braking shudder was cured 100% by replacing the worn strut rod "cone bushings" with IPD's˜ blue poly versions (below). Still smooth braking 50K miles later.

More recently the right front caliper (Girling Jumbo) siezed, causing such intense heat that the edges of the pads turned a crispy gray color. I replaced the caliper & pads and the braking is still as smooth as ever. Actually, it didn't shudder even when hot.

IPD part #8K0058 $22.95 per side Details Here



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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Lucid - I appreciate the tip, but funny you mention the IPD bushings - I had those exact ones installed about 4 months ago. Slight improvement. But my mechanic - who's among the best (and two others before I found him) has diagnosed my front rotors as warped. Apparently it's more of an annoyance at this point, but I'm curious if anyone on here has some more in-depth knowledge as to whether safety is being compromised by leaving them in for a while.

Theoretically when the pads are over the low spots you are not recieving the full benefit of force applied to the pads and therefore rotors. So is your braking force compromised, yes, does that reduction in force make a meaningful difference in stopping distance, perhaps. I have driven with slightly warped rotors on a Toyota for months...until the shaking of steering wheel pissed me off.

If your mechanic has diagnosed rotors as warped (by measuring run out with a dial indicator), then get new rotors as soon as money allows.

-Ryan
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Athens, Ohio
1987 245 DL 324k, Dog-mobile, E-codes
1990 245 DL 137k M47, E-codes, GT Sways/Braces, Dracos, A-cam
1990 744GLE 189K 16-valve project
1991 745 GL 304k, Regina, 23/21mm Turbo Sway Bars