Piston Slap: A Decided Pulsation, A Tough Decision

Sajeev Mehta
by Sajeev Mehta

Steve writes:

My wife’s beloved ’04 Lexus RX330 has a decided pulsation when the brakes are applied at highway speed coming down from the mountains. Do understand that I try not to overuse the brakes in mountain driving– I will downshift the 5-sp AT whenever it will help. I figured it has warped rotors. It did this at about 30k and they replaced the rotors under warranty. I’ve not noticed this on flat ground, but given the car I’m not into aggressive driving with this vehicle.

She took it to the dealer and they checked it out and said the brakes are fine. Of course where we live the mountains are 50 miles away, while I don’t know their test procedures I doubt a 100 mile round trip is taken. Their restraint is amazing, considering the shop talked her into doing the 100k mile service at 60k. The car currently has 76k.

My questions are: Since the braking effect seems unaffected, is this dangerous? It’s not like the pulsation rips the wheel out of my hands. Secondly, can they really tell if the rotors are warped without driving it in the conditions that brings out the problem?

Sajeev answers:

How generous of the Lexus dealer to perform a 100k service at 60k! That’s fantastic.

Okay, seriously: brake rotor faults are sometimes hard to spot, especially if the dealer doesn’t drive in your conditions. But if the steering wheel vibrates under braking, the rotors are indeed warped. Sometimes tire and suspension bits can be out of whack, but those resulting vibrations are present at highway cruising. So, yes, you are looking in the right place.

My advice? Deal with it until it gets worse. Just a little worse! The vibration will get bad enough for anyone to spot, not just an owner intimately familiar with their ride. Hell, even my trusty mechanic often can’t duplicate the problems I notice, forcing me to deal with it until they suggest a fix. Honestly, this is how you enjoy the financial benefits of an older car: only throw money at it when someone can fix it!

Or not? Rotors are cheap. Matter of fact, they are stupid cheap, thanks to Chinese production (which is more than acceptable if you stick with OEM-spec rotors, not the ricey drilled or slotted junk). And they are stupid easy to replace on almost every modern vehicle. So if it’s really driving you nuts, $100-150 spent at RockAuto.com gets you decent replacement front brakes, and anyone (including yourself) can install them in a couple of hours.

Tough call. What say you, Best and Brightest?

Send your queries to mehta@ttac.com. Spare no details and ask for a speedy resolution if you’re in a hurry.

Sajeev Mehta
Sajeev Mehta

More by Sajeev Mehta

Comments
Join the conversation
4 of 40 comments
  • Highrpm Highrpm on Dec 23, 2010

    There is something more to this story on your particular car. We used to have an 04 RX330. The brakes would normally not pulsate at all. Sometimes after a long highway ride, when I hit the brakes I would get a pretty hard pulsation. If I released the brake pedal and hit the brakes again, the pulsation would be gone. There was some issue with the master cylinder I think. I found it on ClubLexus.com at the time, although I sold our RX before I had it remedied. There may have been a TSB for it. So if you are normally not getting a pulsation except after a long high-speed run, your issue is probably not the rotors or pads.

  • Brandloyalty Brandloyalty on Dec 23, 2010

    The mention of over-torqued lug nuts spurred me to go check them on our car, because I just had new tires put on. Some of the nuts were around 250ft/lb, while they're supposed to be 95. I would never have been able to get them undone in the event of a flat away from home. Not to mention possibly stretching or breaking the studs. How can garages be so incompetent?

    • See 1 previous
    • Brandloyalty Brandloyalty on Dec 25, 2010

      Indeed. This has happened every time I've had wheels removed for rotation, flat repair or tire replacement the last 4 of such events. Including our normally fully trusted independent mechanic. I can only get them undone with my 250ft/lb reversible torque wrench, which I screw all the way out to the highest setting. Whereas if they're at the correct torque, I can budge them using an X-lug nut wrench. Just to make it more serious, we regularly drive on backroads beyond cell service or other traffic.

  • MaintenanceCosts It's not a Benz or a Jag / it's a 5-0 with a rag /And I don't wanna brag / but I could never be stag
  • 3-On-The-Tree Son has a 2016 Mustang GT 5.0 and I have a 2009 C6 Corvette LS3 6spd. And on paper they are pretty close.
  • 3-On-The-Tree Same as the Land Cruiser, emissions. I have a 1985 FJ60 Land Cruiser and it’s a beast off-roading.
  • CanadaCraig I would like for this anniversary special to be a bare-bones Plain-Jane model offered in Dynasty Green and Vintage Burgundy.
  • ToolGuy Ford is good at drifting all right... 😉
Next