Should I allow my Lexus RX300 automatic's brakes to cool before using them to hold the car stationary at traffic lights etc?

I have just bought an automatic Lexus RX 300 (2003, facelift, 5-speed auto). In many ways a silly concept, I am delighted with it, because the large number of speedbumps on our road (I live opposite a school) destroyed the wishbone suspension bushes on my previous car (which cost me £450 to replace). I have a crippled left foot, and while I understand your logic about using both feet with autos, the fact that I can drive without using a clutch means a lot less pain for me and I have - so far - never had a problem with this.

The Lexus has had new discs and pads (grooved ''racing'' discs) fitted by the previous owner, and while it brakes very well, it does so with a lot of juddering. My mechanic says the previous owner applied the brakes for too long, probably while they were hot, which has left a deposit on the discs. This may wear off with hard braking, or the discs may need to be skimmed (at an acceptable price). My question regards using the brakes on the car to avoid this happening again in future.

With automatics, I have always put it in neutral while waiting at traffic lights or similar obstructions, on the basis that it appears pointless to have the engine fighting the brakes when I am in any case not going anywhere. I take it this is a sensible thing to do to avoid this problem? And what about the foot-operated parking brake? Does this operate on the discs, and should I use it when parked (at home it is parked on level ground)? Should I wait while the discs cool down before applying them? Is it safe to rely only on the parking position on the auto box when parking to avoid this? Ever, or only on level ground?

As a final question, could I fit the 16-inch wheels with the bigger tyres of the pre-facelift model to improve the ride quality further? Even though it currently deals with the speed bumps very well, my wife is pregnant and I know she would appreciate this. The speed bumps make her life miserable. Again, many thanks. You have saved me considerable grief over the years.

Asked on 10 February 2011 by LN, Hastings

Answered by Honest John
What warps discs is a long brake, for example from 70mph into a dual carriageway roundabout, then sitting on the brakes. That means that the section of disc clamped by the pads cannot cool at the same rate as the rest of the disc and warps. Similarly, when track-driving ordinary cars on a circuit, you heat up the brakes so much that when you get back to the pits you must not apply the parking brake for the same reason. Just driving in town won't heat up the discs to the extent you have to worry. Have them skimmed in situ on the car and that should sort them out. And carry on driving as you wrote. Into neutral at traffic lights and parking brake on, just as long as you have not had a long hard brake into the stoppage immediately beforehand.
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