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Thread: Bump Stops on Struts

  1. #1
    Registered Member Kirbert's Avatar


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    Bump Stops on Struts

    One of my rear struts was making racket, so I'm in the process of replacing it. When I slid the (fake) boot off the old strut, the bump stop came out in crumbs. The biggest piece was a half inch. My car is pampered, garaged, has only 85K miles; if my bump stops have crumbled, y'all's are surely long gone by now.

    Not the biggest deal I guess, especially if you never drive it hard enough to hit the limit of suspension travel. If you do, though, you could cause damage to more expensive parts. Note that there are 4 bump stops on a Protegé5, one each corner. You can look at them easily; just jam a ruler through the coil spring and slide that fake boot up until you can see the strut shaft. The bump stop should be right there within the bottom of the fake boot.

    Easy to replace, but it does require a spring compressor. You can borrow a spring compressor from AutoZone for free.

    The hard part is finding replacement bump stops. My policy is: If the OEM part failed for no good reason, I'll be looking to aftermarket for a replacement. So far, the best option seems to be ProThane 6-1302. These poly items are 50mm diameter and 50mm tall with a 17mm hole in the base. That hole is too small, needs to be a loose fit on a 20mm strut shaft, but it proved pretty easy to ream it out with a Dremel.

    My only concern is that these poly bump stops are really hard, harder than I think they should be. Better than no bump stops at all, surely, but hard enough that I kinda doubt they'll compress much at all when hit.
    -- Kirbert | If anything is to be
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  2. #2
    Registered Member Corphish's Avatar

    83 RX-7 Gsl, 2000 Mazda Protege LX, 2011 Mazda3 Sport i

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    Quote Originally Posted by Kirbert View Post
    One of my rear struts was making racket, so I'm in the process of replacing it. When I slid the (fake) boot off the old strut, the bump stop came out in crumbs. The biggest piece was a half inch. My car is pampered, garaged, has only 85K miles; if my bump stops have crumbled, y'all's are surely long gone by now.

    Not the biggest deal I guess, especially if you never drive it hard enough to hit the limit of suspension travel. If you do, though, you could cause damage to more expensive parts. Note that there are 4 bump stops on a Protegé5, one each corner. You can look at them easily; just jam a ruler through the coil spring and slide that fake boot up until you can see the strut shaft. The bump stop should be right there within the bottom of the fake boot.

    Easy to replace, but it does require a spring compressor. You can borrow a spring compressor from AutoZone for free.

    The hard part is finding replacement bump stops. My policy is: If the OEM part failed for no good reason, I'll be looking to aftermarket for a replacement. So far, the best option seems to be ProThane 6-1302. These poly items are 50mm diameter and 50mm tall with a 17mm hole in the base. That hole is too small, needs to be a loose fit on a 20mm strut shaft, but it proved pretty easy to ream it out with a Dremel.

    My only concern is that these poly bump stops are really hard, harder than I think they should be. Better than no bump stops at all, surely, but hard enough that I kinda doubt they'll compress much at all when hit.
    Well so I'm not a 100% sure but I was told that the stock bump stops would feel the most comfortable. Now I was told this by an older mechanic at my shop so I'm not really sure on how true any of this is.

  3. #3
    The Diagram Dude pcb's Avatar

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    Quick Struts... Everything is included and you don't need a spring compressor.

    PS... Those aren't fake boots... They help keep dust and water from getting on the strut shaft and wrecking the seals.

    Last edited by pcb; 08-02-2017 at 11:44 PM.
    The Diagram Dude

  4. #4
    The Diagram Dude pcb's Avatar

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    Quote Originally Posted by Kirbert View Post
    One of my rear struts was making racket, ....
    Mine Too !!!
    Big Ole' Clunky Noise Right ??!

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  5. #5
    The Diagram Dude pcb's Avatar

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    Quote Originally Posted by Corphish View Post
    Well so I'm not a 100% sure but I was told that the stock bump stops would feel the most comfortable. Now I was told this by an older mechanic at my shop so I'm not really sure on how true any of this is.
    That old mechanic probably needs some Poly...
    Both for his dentures and his bumpers...

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  6. #6
    Registered Member Corphish's Avatar

    83 RX-7 Gsl, 2000 Mazda Protege LX, 2011 Mazda3 Sport i

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    Quote Originally Posted by pcb View Post
    That old mechanic probably needs some Poly...
    Both for his dentures and his bumpers...

    lol well I did say he was older

  7. #7
    Registered Member Kirbert's Avatar


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    Smooth Ride at Suspension Bottom?

    Quote Originally Posted by Corphish View Post
    ...I was told that the stock bump stops would feel the most comfortable.
    Well, that's probably true. If the comfort of the ride when you're bottoming the suspension is important to you, the OEM bump stops are the way to go. I'd plan on replacing them every five years or so, though, based on the condition of my 15-year-old bump stops. When they're crumbling, they do no good at all, and hitting bottom would yield not only a very uncomfortable clunk indeed but it'd probably damage something.

    Sorry I didn't get back sooner. I was expecting notifications, didn't get any, just came back to see why not.

    I finished the job on the rear. The other bump stop was in only slightly better condition, came out in two large pieces that clearly were good for nothing. And replacing the rear struts did clear up the faint "clicking" I was hearing back there. I'm pretty sure my RR strut was defective from the factory, had been clicking all along. It was faint, only noticeable when barely moving, but I think it had been there since new.
    Last edited by Kirbert; 08-09-2017 at 08:47 PM.
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  8. #8
    Registered Member Kirbert's Avatar


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    Quote Originally Posted by pcb View Post
    Quick Struts... Everything is included and you don't need a spring compressor.

    PS... Those aren't fake boots... They help keep dust and water from getting on the strut shaft and wrecking the seals.
    Yeah, I saw those preassembled strut/spring combos. So, I coulda paid $260 or so and avoided having to borrow a spring compressor for free. My preference, though, was to pay only $54 for the PAIR of struts plus $13 for a pair of bump stops that'll still be on the job the next time I look at them.

    And, yeah, perhaps those fake boots might deflect a bit of mud. They're still fake; not sealed at the top, not sealed at the bottom, and plastic rather than rubber so they really can't flex very well. They are incapable of flexing enough to handle the range of suspension travel here; they basically just sit motionless while the strut works.

    I am seeing an oddity in the assembly. Some photos of new parts, such as the photos of the strut/coil assemblies above, appear to show the bump stop as visible above the boot. Such was not the case with my rears; the bump stop fit inside the boot and was therefore not visible through the coils unless you lifted the boot up over it. The repair manual appears to confirm this. Perhaps the photos show an aftermarket upgrade to real boots? Perhaps the fronts are different than the rears? I'll be getting to the fronts next, as my second set of poly bump stops is scheduled to arrive today.
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  9. #9
    Registered Member Kirbert's Avatar


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    OK, I got the LF strut out this afternoon. It has no gas pressure, so a new pair of front struts are now on order. It also had a bit of slop to it, not a lot, but I'm not used to seeing any.

    Of interest: The rubber boot on the front struts is really rubber! As opposed to the plastic ones on the rear. Whassup wit dat? These are also long enough for the full stroke of the front struts (which have a shorter stroke than the rears). They're still fake, in that they don't seal at either end, dirt and water can wander freely in and out. In fact, there was a goodly amount of sand and grit right on the shaft when I got it apart.

    And most surprising: The bump stop was actually in good shape! It was a little frazzled on one corner, but if I had done this end of the car first it wouldn't have occurred to me that it needed replacing. I'm going to replace them anyway since I already ordered and received a ProThane pair.

    And again, the bump stop was inside the boot, not on top of it as several photos have shown. I dunno what's the discrepancy there.
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  10. #10
    Registered Member Kirbert's Avatar


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    For use at the front end of a Mazda Protegé5, the ProThane 6-1302 bump stops require two modifications. First, the hole in the base needs to be enlarged from 17mm to a snug fit on a 20mm shaft (as opposed to the loose fit needed at the rear). Second, a bevel must be cut on the outside corner of the base, which is a very crisp corner indeed on the ProThane item.

    The OEM bump stops have another feature, a pair of grooves in the sides of the hole in the base which form a vent so that dirt and water can be funneled directly to the upper seal on the strut. I chose not to reproduce these grooves, opting instead to leave the ProThane bump stops snug around the shaft so that mud can't get through, it'd have to go around. If you choose, though, it certainly wouldn't be difficult to cut a pair of grooves.
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  11. #11
    Registered Member katapaltes's Avatar

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    As far as "comfort," from what I remember reading on Miata.net, Miatas actually "use" the bump stops more in day to day driving than a P5 ever would. Don't quote me on that.

    Yes, the stock bump stops on our cars are concealed by the stock rubbery boots on all four corners. The KYB bump stops I bought sit above the KYB boots and "lock" into a lip in the boot. I kept all my stock rubbery boots and will probably go back to them in 10 years.

    Funny, I've had clicking -since- I replaced my rear struts. Every time I go over on of those small reflectors in the road I get a clicking from the rear. I torqued the top bolts and all other properly, so it may be my end links? Anyone want to guess? I know the grease seals are split on all of them, but they still seem to work fine.
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