By on December 22, 2010

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?

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40 Comments on “Piston Slap: A Decided Pulsation, A Tough Decision...”


  • avatar
    ash78

    Ditto Sajeev–disc brakes are way too cheap and easy (and important). Just replace them.
     
    (Heck, I’ve even replaced rear discs that had 40k+ remaining on them because I wanted lower dust pads so I wouldn’t have to wash the car so often.)

  • avatar
    gslippy

    Yes, it’s rotors.
     
    And I now install only ceramic pads if I can get them – they do better with heavy braking heat, and I don’t care how much they wear out the rotors.  I want my cars to stop when I say so.

  • avatar
    grzydj

    I’ve driven through the Rockies and other mountain ranges quite a few times and unless I had to slam on my brakes to avoid a vehicle cutting me off, I used little to no brakes at all and never got my brakes hot once. This is possible with smart downshifting, like Steve advises he does, but timing also helps.
     
    Last time I drove through the Rockies, I saw people with their binders on all the way down the descent. The warping happens when you come to a stop and leave the pads applied to the rotors, as the rotors cool, they deform around the pads. One way to avoid this scenario is to leave a gap in front of the vehicle in front of you if you find your binders cooking and let off the brakes and roll forward a few times to avoid warping a spot on your rotors. YRMV.
     
    Barring that, you’re still going to go through a lot of pads and rotors living in the mountains, so freshen up on changing both as they’re reasonably easy to do with basic tools. As far as buying rotors is concerned, you could probably get by with some Chinese specials, but I’d opt for some decent Wagner pads and rotors. I think it’s worth the extra few bucks as the quality is excellent.

    • 0 avatar
      SimonAlberta

      Good post. I agree with all you say and have similar experiences of rocky Mountain driving.
       
      One thing to add though. I got fed up with having to turn or replace rotors on my 6500 lb camping van after almost every trip. I started to think the rotors were poor quality or something.
       
      So I did some internet research and found some interesting information about brakes. One thing I learned is the importance of a proper bedding-in procedure for new brakes. I had thought just normal but gentle use was enough but no, there is a definite procedure involving about 10 stops of increasing intensity to coat the rotors with brake pad material. This is what actually gives the brakes their “bite”.
       
      This leads on to the juddering problem mentioned in the article above. Sometimes a hard stop, especially when the pads remain pressed against the disc after stopping, can cause disturbance of this friction coating and can cause similar symptoms to a warped rotor.
       
      After years of problems and probably over $2000 of expenses, I have been able to cure my most recent problems by re-bedding in the brakes to restore the friction material to the rotors. Voila! Smooth braking again.
       
      Of course, the shop won’t tell you this because they’d rather take your money.

    • 0 avatar
      sastexan

      Brakes are far cheaper than transmissions.  Depending on what you are driving, all that manual shifting of the auto trans in high-stress conditions is bound to wear out the tranny in a much shorter period of time.  If you are driving manual, not quite the case unless you are riding the clutch – then risk burning that up (again, much more expensive than replacing brakes).

  • avatar
    jaybird124

    I’m going to throw a slight possibility out there:
     
    When I worked for BMW, we would occasionally have this problem with our cars. The rotors weren’t warped, but they would vibrate if they had either been sitting for a while or weren’t being driven very much. Everyone naturally focused on the rotors, but it was actually the pads in some case.
    Now with your mountain roads and such, I’m sure you’re driving plenty, but it’s worth trying this out:
    go to a clear smooth road and do a few 60-0 runs standing on the brakes. This has a slight chance of mitigating the issue. If it doesn’t work, make sure that you consider the pads as you look to replacing the rotors.

  • avatar
    jaybird124

    I think it would make the most sense to put an oily rag in the gas filler. Light it on fire till the car burns to the ground. Then go get a new X3. That should solve the braking problem…
     
     
    I keed. :o)

  • avatar
    MrWhopee

    I used to have a Mitsu Galant that has chronic front disc warping problem. It seems like one moderately hard stop from highway speed is all it takes for the rotor to warp. I ended up replacing it practically every year. The fact that I autocrossed the thing might not help, but it’s always the high speed stop that warped the rotor.
    I agree that sometimes braking hard a few times could ‘cure’ the problem, at least for a short while. Check your rear while you’re doing that, mind! :)

  • avatar
    psarhjinian

    Maybe I’m just being conservative, but Sajeev is right: rotors are cheap, pads are cheap, your engine and transmission decidedly are not.  Again, maybe I’m a coward, but I’m also a coward who owned a car that would throw a transmission fault code and browned the fluid regularly.
     
    Side note: this environment is one where hybrids do really well.  I rented an Escape for a trip through Vermont and the regen-braking system does really well on mountain declines without invoking the brakes at all.
     

  • avatar
    George B

    Just buy new rotors and pads when the vibration gets annoying.  Relatively easy DIY job that probably costs less time and money than any trip to the Lexus dealer.  Replacing rotors every 6 years isn’t unreasonable maintenance considering their hard use in the mountains.

  • avatar
    philadlj

    I can’t believe I just read “RX” and a variant of “pulse” in the same sentence!

  • avatar
    twotone

    My 300ZX shared front brake issues noted by many other owners of that car. It was very difficult to get the rotors, pad and calipers to talk nice to each other. My independent specialist solved the problem by truing the rotors after mounting them on the hubs. Not sure exactly how he did it, but it solved the pulsing front brake issue after many failed attempts.

  • avatar
    geozinger

    The OP doesn’t mention how the vibration manifests itself; is it felt throughout the car, only in the steering wheel, etc. I’ve been fooled by warped rotors occasionally. Our G6 had a vibration issue (felt through the steering wheel) I attributed to front rotors, when the techs inspected them, they were within tolerance. The rears, however were not. Once the rear rotors were trued, no problems since then.
     
    Two things to keep in mind, cars act differently when they’re truly warmed up and usually the cheapest part is the first to fail. So the course of action should be this: With the car & tires & brakes warmed up; Check torque specs on the wheels, check the wheels themselves, see if the tires are OK, and then check the rotors for out of true condition.
     
    It sounds like a rotor issue, and if it is, they’re so inexpensive (these days) just replace the pads and rotors all the way around. Why risk it?

  • avatar
    jpcavanaugh

    This reminds me of one of my greatest auto service mysteries.  When I married my wife, she had a late model 88 Honda Accord.  It needed brakes, and I took it to my favorite (at the time) independent shop.  Shortly after, the brake pedal pulsated on moderate or heavier braking.  Warped rotors, I figured.  I lived with it for awhile.
    Later, my wife wanted some Genuine Honda service done, and I mentioned the brake pulsation.  The service advisor said “you used non-Honda pads, didn’t you?”  The dealer replaced the pads (and not the rotors) and the pulsation was gone.  I never figured this out, but my current favorite independent shop puts Honda pads on Hondas.  Could this apply to Lexus?  I have no idea.

  • avatar
    monomille

    @psarhjinian – hybrids do well as long as the hill isn’t too long – experience with Prius shows that regen slows beautifully on hills until the battery is full – then you hear the gas engine spin up to provide classic “engine braking” which you need to augment with friction braking so it doesn’t rev too high – workable, just different.

    • 0 avatar
      j_slez

      My understainding of this is that it’s not really engine braking, it’s that the battery is over-charged relative to its ideal range.  The battery management system then uses the battery to spin the engine and “burn off” the excess charge.  An OBD scanner would verify this, but I believe the injectors are shut off, so no fuel is being burned.

      Unless you shifted into low, or “B” in a Prius, the hybrid system doesn’t provide “engine braking” and just lets you coast.  In low, with the battery over-charged, I don’t know if the engine is doing much to slow the car or if it’s just using the electricity as it’s generated.

    • 0 avatar
      monomille

      @j_slez
      oops, I forgot to state that the normal setting for going downhill is to use the B mode.  But when the battery is full, energy has to be dissipated somehow – the excerpt from this wiki article describes how engine braking is invoked.  You definitely need both “engine braking” and friction braking on those long, steep Colorado mtns.
      http://en.wikipedia.org/wiki/Hybrid_Synergy_Drive

      Compression braking: The HSD system has a special transmission setting labelled ‘B’ (for Brake), that takes the place of a conventional automatic transmission‘s ‘L’ setting, providing engine braking on hills. This can be manually selected in place of regenerative braking. During braking when the battery is approaching potentially damaging high charge levels, the electronic control system automatically switches to conventional compression braking, drawing power from MG2 and shunting it to MG1, speeding the engine with throttle closed to absorb energy and decelerate the vehicle.

      btw, I’ve got 110k miles on the initial pads/shoes and am still stopping strong – regen really lightens the load on them

  • avatar
    colin42

    Some say disc rotor on road cars don’t warp

    http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml

  • avatar
    brandloyalty

    If it’s the rotors, it should show up sometimes and not other times.  That’s because if the ‘grabby” bits are out of sync, they will cancel each other out; whereas if they’re lined up on the two sides, you’ll feel the grabbing.
    I’ve driven standard cars, heavily loaded, up and down mountain logging roads for decades.  This included a huge amount of using the automatic transmissions to help keep brakes from overheating.  I never had a transmission problem that could be attributed to the engine braking. That’s not what I’d expect, but that’s what the outcome was.
     
    It is also possible to get rotors warped to a point where they’re annoying in hard stops on long downhills, and they never get any worse.  For years.  I finally got tired of this going on with our car, which developed this problem every time it got new rotors.  So I bought some premium rotors (ATE), and they have not warped.

  • avatar
    Ian Anderson

    As long as the rotors aren’t the type that need ~10 tons of force to be pressed on/off, a front brake job should be an easy/cheap DIY. OEM spec rotors and some decent pads should do the trick.

    • 0 avatar

      ++
       
      The rotors on my Accord were “easy” to remove according to the Chiltons book, but I learned the hard way that my Accord was different, they were pressed on, and I spent many hours and many dollars learning that I could not remove them.

  • avatar

    I had this problem with my old ’93 Saturn. Rotors were one of the many things GM scrimped on. https://www.thetruthaboutcars.com/the-truth-about-saturn/ I learned to pump the brakes, and have been doing it ever since, even though I’m sure my accord is not particularly susceptible.

  • avatar
    dolo54

    I have heard that the greatest cause of warped rotors is using the airgun to put the wheel lugs back on instead of torquing them properly. I always use a torque wrench by hand to redo the lug nuts after getting new tires or anytime a shop has the wheels off the car. They are never torqued properly from the shop, any shop I’ve ever been to. I’ve actually found nuts that I could turn by hand after getting wheels put on.

  • avatar
    BMWfan

    I would not use Chinese rotors. Your life is worth more than the few bucks extra it costs to get name brand rotors. As mentioned, you should also use a torque wrench to install your wheels, and tighten in a cross pattern. Check to see if Brembo rotors are available for your vehicle.

  • avatar
    Daanii2

    Interesting discussion. My wife’s Acura MDX shows the same symptoms. Perhaps it has the same disease. My thought was tie rods, but warped rotors seems much more likely.

  • avatar
    willbodine

    One frequent cause of rotor warpage is improperly-torqued alloy wheels. When tires are changed or wheels rotated be sure to insist that they be tightened to mfr’s specs with a torque wrench and not a pneumatic impact wrench.

  • avatar
    golden2husky

    Something that may make that rotor job a bit more complicated are those cars with “captive” rotors.  Hondas had (have?) these and they are a pain in the butt.  Honda used to specify turning them on the car with a special rotor lathe.  Buy Brembos if available and for mountain use, upgraded pads are worth the dirty wheels.
     
    Rotor warpage may not show up in “normal” driving, but if you are moving and slam on the brakes, the warpage will be clear.

  • avatar
    LectroByte

    @Sajeev — I’m a little hesitant to tell anyone to change their own rotors.  I suspect if they had the skills to do it, they’d have already done it, and wouldn’t be asking for advice here.   Rotors are relatively inexpensive, and not that difficult to change, but I have seen folks turn something simple like an oil change or replacing spark plugs into major trauma…  Anyway, If it were me, I would live with the pulsation a while and see if it gets any worse, especially if it only seems to happen when the rotors are really hot, and they have had their brakes checked out.

    • 0 avatar

      I suspect if they had the skills to do it, they’d have already done it, and wouldn’t be asking for advice here.
      While I agree, I totally disagree from personal experience.  Aside from oil changes and cosmetic mop and glow stuff, I didn’t know squat about cars until I mustered the courage to ask questions on the car forums.  Questions that included doing brake work.
      10 years later, I do this Piston Slap thing to encourage more of it.

  • avatar
    rpn453

    If you’re feeling it through the steering wheel, it’s possible that it could be due to worn-out control arm bushings or ball joints.  Less common, but possible.

  • avatar
    Zackman

    The only weak link on my 2004 Impala is the rear rotors. I’m about to replace them again after 19 months. Warranty fixed the first couple of times.

    Do it – it makes your ride that much more comfortable and your car will love you for it – it may even run just a little better; you know, like when you drive a freshly-cleaned car, it just feels better!

  • avatar
    highrpm

    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.

  • avatar
    brandloyalty

    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?

    • 0 avatar
      BlueHighways

      +1   If there’s any chance that the shop removed a wheel, I always loosen the bolts, tighten in a star pattern, and torque.

      I had a flat on a rental car once, and could not bust the bolts loose … nor could a helpful Highway Patrolman.    AAA came to the rescue with air tools.
       
      I was late, dirty, and embarrassed for a job interview … and, I did not get the job.

    • 0 avatar
      brandloyalty

      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.

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