Recently my car has been overheating and warping the front rotors on my car. I am perplexed because I had put 30,000 hard driving miles without a problem, and now in a coupe of thousand miles it WILL overheat the fronts.

I need to know from you volvo experts if these cars have any kind of proportioning valve that adjusts brake bias related to height. I had a VW GTI in the 80's that had such a device to impede rear lockup, as you braked and the rear got lighter, and therefore higher the brake system sent less pressure to the back. The reason I ask is because I recently changed the rear springs from stock to OEM and the back is about 1.5 inches higher and thought this could be related.

In the absence of that does anyone have any information that may help me, malfunctioning hydraulic system, etc, etc. The front calipers are not sticking. The dealer has looked at the car, but just says to replace the rotors.

Thanks very much.

Andrew Levy

If wheels aren't torqued properly to manufacter's specs, rotors will warp.

Andrew,

I can't help with the proportioning valve question but a couple of points about using any brakes hard and warped rotors. Overheating, in and of itself, will not warp the rotors. I run my 850 on a road track and brake right to the threshold at least two times per 1.7 mile lap with moderate braking at three other corners. I've brought it back to the pits and you can't touch the wheels with your bare hands.

You can, however, warp the rotors by heating them up and then holding the brake pads on the rotor with the brake pedal at a stop light or by setting the emergency brake when you park. The rotor cools unevenly and warps.

Once warped the problem just worsens. The recommendation is to replace, rather than turn, the rotors.

I have an automatic transmission and I use my parking brake all of the time. This is the first I've heard of potential warping due to that practice. Would this recommendation to not use the parking break only apply when the car is parked after hard breaking and the rotors are still potentially hot? Any other considerations?

How about waiting for a light after hard breaking? I frequently set the parking break and release the pedal explicitly to avoid warping (I was under the impression that the parking break was a rear drum and thus would provide more uniform contact than a break pad).

Any consensus?

DaveK

Dave,

Like you, I religiously set my parking brake. The advice not to do so was presented in a high performance driving class and was specifically in the context of what to do after coming off the track. As you can imagine, the brakes in this situation are used pretty aggressively and get very hot. Their advice was to not set your parking brake or idle in gear with your foot on the brake while the rotors are hot.

I would think it would take some very aggressive driving to reach the same temperature state in street driving but it probably can be done. If you know you've gotten the rotors real hot (downhill mountain driving requiring extended periods of braking, for example) then allow for that and avoid the parking brake or sitting at idle with the brakes applied.

Another occasion where you want to avoid the parking brake may happen in the winter. A guest once drove to our cabin (which involved some wet, slushy roads) and set their parking brake. The next morning we were unable to get the brake to release because they'd frozen!

Yes, that can happen in winter esp. if you go through slush or a puddle and then stop and the water freezes in the cable housing.