By on April 26, 2016

 

auto parts. shutterstock user FabrikaSimf

David writes:

Over the last few years, I’ve had work done on my ’99 Ford F-150 at various places near my work. It seems that when a wear item goes (like ball joints), the mechanic wants to replace absolutely everything in the system — tie rods, pitman arm, trailing arm, etc. Or when the left side brake caliper goes bad, they want to replace the right one, too. Or give me all new hoses when I replace my radiator.

The reason the mechanic gives is always, “Well they are the same age, and if the left one is bad, the right one is not far behind.”

This gets really expensive really quick. Is this worth it? Why do mechanics always want to replace everything in the system, if only one part is bad? Is this strategy only to boost profit? Or is there some truth in their reasoning?

Sajeev answers:

Do you think that if one 17-year-old moving part goes bad, the other 17-year-old bit is not going to fail in the next few months? Or, being generous, the next year?

You didn’t mention a problem with tires being replaced in pairs. So apply the same logic to any other chassis bit (i.e. not seats, floormats, etc) and you’ll be set. A new tire can be shaved to match the tread of the other three, but a new shock/spring/brake item could upset the balance created by a matched set of worn items. It’s much like replacing only one headlight bulb only to realize the other is so dim you regret not replacing both at the same time.

Replacing parts for one side only works if you drive on two wheels and never let it drop back on all fours without cushioning the fall.

So what if a mechanic recommended replacing late-model, low mileage suspension bits in pairs? That might raise a red flag, unless a big pothole did a suspension component in.

Finally, with the radiator hoses in mind, why not get it all done while the mechanic is in there? You are saving labor (easier to reach with the radiator gone, you only add/burp coolant once) and rubber parts are notorious for weathering after 10+ years on the road. Such is the life of owning an older vehicle, my friend.

[Image: Shutterstock user FabrikaSimf]

Send your queries to [email protected]com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

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59 Comments on “Piston Slap: Why Replace Parts In Pairs?...”


  • avatar

    For these newer vehicles where you have to have sections of the car removed in order to access things such as LED lightbulbs you might as well replace two at the same time.

    I totally agree when it comes to replacing suspension components, tires, brakes and other moving parts in pairs.

  • avatar
    -Nate

    An honest Mechanic and he still gets complaints .

    Sigh .

    -Nate

  • avatar
    Jacob

    This car mechanic is a wise man. I have driven cars which after having work done only on one side of suspension would never drive straight again, no matter how many times you adjust the wheel alignment.

  • avatar
    Kenmore

    Hope my ortho surgeon doesn’t see this.

    Right now, I’m only scheduled for one hip.

  • avatar
    Shortest Circuit

    Father?
    (My old man is like this, bitching up and down at everybody that they changed _both_ his shocks when only the left tested below 29%, brake discs in pairs – why? Only one was warped! etc etc. I’m pretty much the opposite, I suppose my kid will be the ‘save a penny’-type too.)

    • 0 avatar
      jkk6

      Sometimes it is hard to justify double the spending when the car is nearing the end of it’s product life cycle.

      • 0 avatar
        redmondjp

        Bingo.

        I replaced a single ball joint on a 1997 Taurus with over 200K miles on it. Only one side was loose. The car’s owner was a young female friend of the family with a minimum-wage job.

        [non-related, but interesting story continuation . . . ]

        Later on, I replaced her water pump, accessory belt and idler, did a complete tuneup, polished the headlamps, changed the transmission fluid, and topped off the R134A. The car was running better than it had in years.

        She rear-ended somebody and totalled the car the very next day after getting the car back.

        D’op!

        I hope somebody at least harvested some of the new parts after the car ended up at pick-n-pull.

        • 0 avatar
          jkk6

          My father and I has a similar experience. $300 dollars for a fresh set of tires on a $500 dollar car that gets totaled the following week.
          I’m suspecting the increased/renewed performance increasing the confidence of the driver correlates to the likeliness of an accident. It’s my own silly superstition.

  • avatar
    Zackman

    Not only have I always replaced things in pairs, but as cars have gotten more complex, it’s much cheaper in the long run.

    For example: Last December, I took my car in for an oil change, front rotors (warped) and other maintenance services according to my mileage at the time (80,000). Shortly after I dropped the car off, the service manager called me and told me they were keeping the car. A previously-known occasional oil drip was finally found and it was coming from the front engine cover.

    Apparently this is a known issue by GM on the 3.6L motor, and they would pay for it, even throwing in a new water pump. He did warn me about replacing the timing chain assembly as well, though it wasn’t covered. A little over $200.00. I went ahead and had them include it as well, because if that went bad, it would have been a $1300.00 bill later on!

    The bill was almost $800.00 for everything, but I felt it was money well spent considering my long commute and the car is a great highway-runner.

    Upside: I got to drive a brand-new Impala for 4 days! Sweet!

    Conclusion to this account? Yes, ALWAYS replace everything in pairs!

    • 0 avatar
      andyinatl

      Wait, timing chain replacement at 80K? I thought the benefit of the timing chain was that you don’t have to replace it, as opposed to timing belts. But even the timing belt on Volvos has 105K interval…

      • 0 avatar
        Kenmore

        This. Wassup wit dat 80K *chain*?

      • 0 avatar
        Zackman

        I didn’t have to replace it if I didn’t plan on keeping the car, but I took a gamble and went ahead with it because it is my intention to keep this car long after retirement in 11 months. I really like my Impala and figure it’s worth it unless it suddenly goes south on me, so stay tuned!

      • 0 avatar
        EAF

        Take a look at pictures of that GM 3.6vvt timing chain arrangement, it is destined to fail. I prefer timing belts. They do require maintenance but if the service interval is observed they are less failure prone. They are also less audible and do not shear oil down as much. Each link in the chain is a moving part.

        As for replacing items in pairs, my answer is, it depends! Example; a power steering leak prematurely wears a lower control arm bushing. The vehicle has 30k miles. Replace the entire front end? Absolutely not, you’re throwing money away!

        I can think of countless examples, the only item I will always replace in pairs are brake discs and obviously brake pads.

    • 0 avatar

      I agree. Many times the frugal solution is the one which costs more to begin with, but saves money, time, frustration over the long run.

    • 0 avatar
      Gardiner Westbound

      In 2012, GM performed a Technical Service Bulletin (TSB) on 2007- 2009 HFV6 engine vehicles to shorten Oil Life Monitor (OLM) change intervals. Excessive timing chain wear due to lubrication failure was resulting in a high incidence of warranty claims.

  • avatar
    dude500

    Counterpoint: I find frequently that time savings don’t translate to cost savings to the customer.

    For example: getting 4 brake pads and rotors changed, the mechanic will also suggest to bleed the brake fluid since “he’s there anyway and it saves time”. Great, how much does it cost? 1.5hrs labor… Uh how much would it be if I just did it separately? 1.5hrs labor.

    I’ve heard the same sell for coolant changes while doing timing belts, it still costs 2hrs labor even the the mechanic “saves” 1hr by already doing the belt. So the OP’s question is unsurprising.

    • 0 avatar
      heavy handle

      Try a different shop. No honest licensed tech will do a brake job without bleeding the fluid.

    • 0 avatar
      Jacob

      You are insane if you don’t believe your mechanic that the brake fluid must be flushed every time you do work on your brake parks. In theory, brake fluid lasts about 2-3 years. After that it starts absorbing water, which is bad in many ways. In reality, most brake pads and rotors last more than 2-3 years, so you should definitely not just bleed, but FLUSH your entire brake fluid system every time you replace the brake pads and the rotor (and I hope you do understand that you also MUST either replace or resurface the rotor every time you replace the brake pads). Yes, your mechanic didn’t articulate himself correctly, but trust me, the brake fluid should last a lot less time at its peak performance than either your brake pad or rotor. Flush ALL of brake fluid at every opportunity.

      • 0 avatar
        turf3

        I agree about brake fluid, but it is not true that you MUST replace or turn the brake rotors every time you change pads. This is a way to sell more rotors. I drove my Mazda 626 175,000 miles, never turned or replaced the rotors.

        If you have real aggressive pads, or thin rotors that warp easily, they may need turning. The presence of grooves just means that the pads will bed into the grooved surface rather than a new flat surface.

        Also, if you drive your car till the pad material is gone and you hear a loud scraping grinding noise, you will need to turn the rotors. I don’t do that.

        • 0 avatar
          Sigivald

          Yeah, I went a decade on my Mercedes without replacing the rotors, because they remained flat and above spec width.

          If they’re not warped or below spec they do not need to be replaced.

        • 0 avatar
          JMII

          I track my car thus I go thru brakes like most people go thru socks. Brakes pads last about 4 track days – that is it, but the rotors last MUCH longer, not sure yet but I’m guessing 3 to 4X the life of the pads. I don’t resurface them or anything, I just put in some new pads, bed them in and go (or should I stay STOP).

          Fluid as mentioned should be changed more often. In fact I’d bet most people getting a brake job feel a firmer pedal due to the fluid change more so then the new pads (or rotors) themselves. Using a power bleeder (like Motive) makes bleeding brakes an easy one person job.

          Also don’t buy fancy rotors that are drilled (aka cooling holes) as that removes material and actually weakens the disc. Google images on cracked rotors, they almost always the drilled kind. If want to cool your brakes (good idea) you need brake ducts. I run slotted rotors because they kind of self clean, but do seem to create a slight vibration at max application. After my current set of slots are worn I’m going back to regular blanks to see if that cures the vibrations. It might be cause by pad deposits from not doing proper cool down laps, however so the jury is still out on this.

      • 0 avatar
        dude500

        Of course I bleed the brakes every 2yrs, that’s not my point. My point is that with everything already accessible (wheels off, pads/calipers/bracket out of the way), it should take at most 30 more minutes for a shop to do a brake bleed. Hell it takes me 2hrs on a bad day to do it myself, from jacking the car up to tightening the last lug nut.

    • 0 avatar
      DenverMike

      Ask for a discount on labor, since the mechanic is ‘in there’/’under there’ already, with the same tools, fluids, parts suppliers, etc. If they’re already removing a specific part to get at something else, that part’s “labor” should be free if you chose to replace it.

    • 0 avatar
      Sigivald

      1.5 hours for a bleed (or flush)?

      Burn his shop down.

      I can’t think of any car that should require that kind of labor to flush brake fluid.

  • avatar
    87 Morgan

    Perhaps the OP should consider a lease. This way worrying about whether replacing both front struts simultaneously is a rip off or not will no longer be a concern.

    Seriously. You get to do one or the other. Option A: Have a new car, with new car payment OR up front expense if paying cash. Option B: Drive an older car (2008 or older is what I consider to be aging at this point) and know that repairs will be necessary AND every now and again they may be pricey, as in $500 or better. Consider it one month’s payment for option A.

    If the plan is be a cheapskate and only fix what has failed you will add mountains of brain damage later when the rest of the ‘eco’ system is upset by adding a new part to it, which the rest can’t handle.

    • 0 avatar
      rehposolihp

      I think the word ‘cheapskate’ may be where some of the comments are missing the boat. Someone asking a question about a practice that appears to be costing them money is not necessarily a greedy, penny-pinching fool. Its a valid question and honestly there are several practices that mechanics advocate that are of questionable value (transmission flush, 3k oil change interval, etc).

  • avatar
    DenverMike

    With ball joints, brakes, steering, suspension, etc, the mechanic/shop is more concerned with covering their own A$$, than a few extra dollars.

  • avatar
    brettc

    I replaced a single rotor on my wife’s 94 Cavalier many years ago. The guy at Autozone recommended doing both, but we were poor and only one was warped at the time. Not my finest moment in car repair. Always replace in pairs whenever possible.

    I see so many cars on the road with one bright headlight and one dim headlight. If people are only replacing one bulb at a time, what else are they cheaping out on? Kind of scary to be sharing the road with “one side at a time” car owners.

  • avatar
    JimZ

    when you’re a wrench, situations like this are damned if you do, damned if you don’t.

    if you recommend replacing other parts which are likely to be worn, you get accused of trying to rip people off. If you don’t, and they come back a short time later after the other part(s) have failed, you get accused of being incompetent.

    • 0 avatar
      tedward

      I agree. I’m a hobbyist so I can’t really relate, but I find myself sticking up for indie mechanics all the time on this subject. My advice is often, “go back and apologize” then agree to the comprehensive service that week save you time and money.

      I usually keep my mouth shut if it’s a dealer. I’ve seen more than a few people charged individual job time rates on related work in that business model.

  • avatar
    tedward

    I’d say go beyond pairs when it comes to suspension wear items. Seriously, if your control arm bushings are showing wear you will have clean access to your tie rod and sway bar endlinks and they are getting older too. It’s almost the same job, just do it. These are also the simplest of DIY jobs. Fixed isn’t enough, like new should be the standard (money and love of car allowing).

    Likewise dampers and springs. One is worn? Do all 4 (rears are usually stupid easy), might as well look at wheel bearings and any original suspension rubber while in there. Never re use top mounts etc…

  • avatar
    Dan

    My natural inclination as a skinflint is to always spend the bare minimum today but I’ve never yet managed to have the car totaled, stolen, or engine seized in time to come out ahead by doing so. You’ll be back for the rest of the repairs later anyway, you won’t save any money, you’ll drive a car that much creakier in the mean time, and you’ll get a second bill to put the cost front and center in your brain all over again.

    Buy once cry once.

  • avatar
    55_wrench

    With brakes and tires, it’s always replace in pairs. It’s worth the peace of mind.

    I recently had a seized caliper on my 31YO F-250 that has been doing some really heavy hauling in the last year. While I was at it, I got new hoses and flushed the entire system.

    If old fluid had caused the first caliper to seize, the second one might not be far off. While in it I was able to pack the front wheel bearings. A couple of hours later it’s all good for another few years.

    Ditto for shocks and struts. Why end up with assymetrical suspension dynamics / brake life, only to have to deal with the other side sooner than later?

  • avatar
    APaGttH

    …Finally, with the radiator hoses in mind, why not get it all done while the mechanic is in there? You are saving labor (easier to reach with the radiator gone, you only add/burp coolant once) and rubber parts are notorious for weathering after 10+ years on the road. Such is the life of owning an older vehicle, my friend…

    Exactly this. If I’m doing a timing belt, I’m doing the water pump, just because.

    If I’m doing a clutch, I’m doing a throw out bearing, just because.

    If I’m doing a radiator, darn straight I’m doing the hoses, at least the lower one at the minimum.

    If my mechanic is going somewhere under the hood to fix X that is deep in the bowels of my vehicle, and I have a service item in there that will be need to be done in 10K or 20K miles, darn straight I’ll do it early while things are apart.

    • 0 avatar
      Jagboi

      ” If I’m doing a timing belt, I’m doing the water pump, just because.”

      That’s cost me a fair bit of time and money, as well as a tow and stranded other half. We have a Saab 9-5 V6, and while I was doing the timing belt I did the water pump, since I was there. It’s a fair bit of work to get to the pump, so I changed it. There was nothing wrong with the OE pump though.

      I bought a Gates pump (good name I thought, but it was made in China) and it lasted about 10,000 km. The shaft seal leaked, and rusted and seized the bearing of the WP. Of course it’s behind the plastic cover for the timing belt, so I can’t even see the WP.

      Fails when the better half is visiting friends 300 km away, so I had to borrow a trailer and drive up and collect the car and driver and bring them home and then do the job over. Car was down for about a week in total. I should have left it alone!

  • avatar

    So here’s a question. A pair of tires or all four? Assume normal wear and not road damage to just one tire.

    • 0 avatar
      Zackman

      Answer:

      If you regularly rotate your tires, you replace all of them. If you don’t, the fronts will require replacement before the rears.

      • 0 avatar
        turf3

        On front wheel drive cars, I like to replace the fronts when worn, and replace the rears when worn. Obviously I am replacing fronts more often. But I don’t rotate on front wheel drive cars.

        On four wheel drive cars, I rotate, and replace in fours, since a discrepancy in tire diameter whether side to side or front to rear will cause added wear to the differential mechanisms (the spider only rotates when the two sides of the differential are rotating at different speeds, and it is designed for that, not for constant spinning).

        I don’t know what I would do for a rear drive car since it’s been so long since I had one.

  • avatar
    DougD

    Although I do most of my repair work myself these days, I’ve found that if you replace as much as possible while you’re in there it saves hassle in the long run. When we got a new clutch put in the car I had them do the water pump, should have also had them do the rad hoses and alternator.

    We had a mechanic for a while who tried to save money by only replacing the part that was worn out. It probably saved a bit of money but the car had to go to the shop twice as often, which got irritating. I’d rather spend a bit more money for a lot less hassle.

    • 0 avatar
      turf3

      I don’t really understand doing a water pump and alternator at the same time as the clutch, they are on different ends. Certainly if you replace a water pump you ought to do the timing belt at the same time (for those where the timing belt drives the water pump).

      • 0 avatar
        DougD

        Good point, actually yes I had them do the timing belt at the same time as well. These were jobs that were much easier with the engine out, and since it had over 100,000 miles on it I figured it would pay in the long run.

        The alternator was just hindsight and specific to my car (MK1 Ford Focus). It crapped out the next year and it was a miserable job to get it out from where it sits behind the engine.

  • avatar
    jacob_coulter

    Usually it makes sense to replace in pairs, also take in mind that when you replace many suspension parts it requires an alignment after everything is installed, so not having to do that twice is a money saver.

    I will say though some mechanics can over shoot on the “might as well” type repairs in order to simply drum up business, like trying to sell both front and rear brake jobs at the same time. That’s a really common one, when the reality is for most cars, rear pads last twice as long as front ones.

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