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Rear axle help, drum won't rotate, chain slap also

Discussion in 'The Garage' started by kawabunga, Jul 27, 2020.

  1. kawabunga

    kawabunga XS650 Addict

    I’ve reached a stumbling block that I cannot sort out. Hoping to find some help from those wiser than I...
    (notice - the explanation is lengthy but I tried to be thorough)

    I cannot properly tighten the rear axle on my bobber and I’m at a loss. One of two things happens. 1. I use a thicker spacer behind the chain adjuster plate closest to the nut and I'm able to get more torque on the axle nut, but then the drum will not rotate freely. 2. I use a thinner spacer and then the chain adjuster bottoms out on the axle and I can barely apply any torque to the axle nut before it wants to pull the chain adjuster over but the drum spins more freely.

    Also, a symptom that may or may not be related but I'm also dealing with, is very, very excessive chain slap. Like...violent. The upper rung of the chain shakes so hard that it vibrates the entire chassis. It only seems to be present at small throttle openings to maintain speed or during light acceleration. Heavy acceleration does not seem to induce the same chain slap.

    *Important background on the bike before getting any further into it. My bike is far from stock with a custom made swingarm. I took a TC Bros hardtail kit and created my own "softail", essentially recreating my own Triumph Bonneville Bobber. So, the swingarm is completely custom, however, the rear axle plates are exactly as created by TC Bros. I know people have experience with those, which will hopefully come in handy.

    A couple of photos:
    [​IMG]

    [​IMG]

    I'll try to summarize this so it's not too drawn out but some of the things that lead me to this point may help.

    I initially had trouble getting the stock chain adjusters to fit properly, they're too wide for the TC Bros. axle plates. I reached out to TC Bros. regarding this, they suggested large washers as spacers to fill the gaps. I did that, it seemed to solve that issue.

    When I was building the swingarm, I used a threaded rod with washers and nuts as a jig to maintain the proper spacing between the axle plates while I was cutting and welding.

    I believe all of the OEM spacers are present. I have referenced other threads and parts diagrams searching for a possible missing spacer. I do not think that I'm missing any parts. However, that doesn't mean that I'm not...

    To address the excessive chain slap, I was not sure if it was axle related or potentially something wrong with the clutch cush drive. The six springs used to dampen the clutch are in tact with no visible signs of damage. However, I did find a warped steel plate and grooves worn in the push rod. I replaced the push rod and all new steels and fibers. The clutch feels a lot better but there has been no change in the chain slapping.

    Whether the drum not rotating freely when the axle is tightened down, or the axle being too loose, or something being funky to cause the chain to slap violently is all related or if they're separate issues, I'm not sure. And I'm running out of ideas. Obviously there's a really big potential that I created a really unique problem for myself here by hacking the bike apart and building all custom components, I realize that. But, there has to be some way to sort out both the axle/drum issue and the chain flailing around like crazy issue. I'm open to ideas! Anyone got anything??

    Thanks!
     
  2. bikefreakjon

    bikefreakjon XS650 Addict

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    I have seen the threads on the axle we cut poorly and full of crap from the factory to where they were stuck really tight.

    Verify that your axle nut is good and the threads are clean then stick a number 2 Phillips screwdriver through the hole in the right hand side of the axle so you can tighten it down.

    Also you might take the left side cover off the engine with the bike jacked up spin the wheel around and make sure there's no highspots on either of the sprockets that they are both round and center correctly.

    it almost sounds like you have the chain on too tight what can cause strange vibrations especially in a brand new chain
     
  3. lakeview

    lakeview XS650 Guru XS650.com Supporter Top Contributor

    Check to see if the drum side oil seal is in place. The backing plate should not be pulling tight against the drum/hub.
     
    GLJ likes this.
  4. 5twins

    5twins XS650 Guru Top Contributor

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    The oil seal shouldn't make any difference. Yes, you want it in there to seal around the bearing, but it doesn't have anything to do with spacing. It might be an issue if you didn't install it deep enough, then it might rub on the brake plate as you tighten the axle up. But, that seal install is pretty straight forward, you just make it flush with the hub.

    There is a steel spacer sleeve built into the brake plate. This contacts the inner race of the right bearing and should space the brake plate out enough so it doesn't bind or rub against anything, no matter how tight you make the axle .....

    [​IMG]

    Maybe yours got worn shorter somehow? I have several extra brake plates laying around and could check that built-in spacer length if you like. Or, have you replaced that right side bearing and possibly used one thinner than stock? That would allow the brake plate to pull in more, and most likely rub on something.

    As you've discovered, wheel spacing is very important and must be correct for the axle to tighten up enough. Not enough spacing and you run out of threads for the axle nut before the wheel is tight. There can also be an issue with the stock chain adjusters. The left one has a smaller hole on the outside. It lets the smaller diameter threaded portion of the axle through but not the larger diameter axle itself.

    [​IMG]

    [​IMG]

    So, it seems something is off with your internal wheel spacing because, like I said, no matter how tight you make the axle, it shouldn't cause any internal binding or rubbing like your brake plate is doing. Another possibility is with the assembly of the left wheel bearing. It has a tophat shaped spacer that fits into it (#20 below). The lip on that spacer must be on the inside. It is several MM thick and combines with the tube spacer (#7) to properly space the bearings apart. Without it, the inner races of the bearings would get pinched in too tight and bind up the wheel when you tightened the axle .....

    [​IMG]
     
    Boog, kawabunga and bikefreakjon like this.
  5. 5twins

    5twins XS650 Guru Top Contributor

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    Here's the proper right rear wheel bearing. It should be 15mm thick .....

    [​IMG]
     
    kawabunga and timbeck like this.
  6. kawabunga

    kawabunga XS650 Addict

    bikefreak, threads are in great condition. Nut spins freely on the axle.

    Chain isn't too tight, in fact, it loosens as it goes through the shock travel because of where my swingarm pivot ended up. I have suspicions that the extra slack is contributing to the excessive chain slap, but I can only go so tight when the shock is fully extended.

    I wasn't able to verify the high spot suspicion since I have everything torn apart at the moment.

    lakeview, I'm not sure what you're referring to concerning the "oil seal".

    5t, there is a bit of a lip worn into the steel sleeve. It measures anywhere between 7.0 - 7.3mm. If you could measure some that you have, I would appreciate it.

    Picture of my steel sleeve:
    [​IMG]


    Bearings were replaced with brand new All Balls bearings. I measured the right side bearing and the specs are identical to the photo you provided.

    My #20 is a bit beat up, but it was properly in place with the top hat part to the inside of the wheel.

    [​IMG]

    My #24 is also showing signs of wear with a raised edge of about .007"

    [​IMG]

    [​IMG]

    I tore out all the wheel innards. Here is the exact order that everything came out, left to right.

    [​IMG]

    I'm confused by #23 in that diagram. Is it a separate piece from #24? Or do they press together. Here's what my #24 looks like from the side.

    [​IMG]

    I have the chain slack adjuster plates properly oriented, where the smaller I.D. sets up against the axle nut. I can't get the axle in with it set any other way. The thing that determines whether or not I run out of threads while tightening the nuts is how thick of spacers I use inside the chain slack adjusters. However, if I use thick enough ones to tighten the axle to proper torque (60-70 lb/ft), the drum won't spin.

    But, if it's not possible to over tighten the axle to the point that the drum won't spin unless something isn't right...well...something must not be right...
     
    Boog likes this.
  7. kawabunga

    kawabunga XS650 Addict

    I had no idea these were two separate pieces...

    [​IMG]
     
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  8. 5twins

    5twins XS650 Guru Top Contributor

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    Yes, but I've never found them separated, or had the need to separate them. I suppose if #24, the tin dust shield, was all bent up, you might want to remove and replace it.
     
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  9. kawabunga

    kawabunga XS650 Addict

    I had no idea. What about my other findings? Anything look off?
     
    gggGary likes this.
  10. stinky78

    stinky78 XS650 Enthusiast

    I’m thinking the chain slap is caused by a combination of what looks like a pretty long chain length and the design of your suspension, sounds like a harmonic thing with the power stroke of the pistons, mountain bike designers go to a lot of trouble to get rid of peddle induced bob, which is what yours sounds like, a shock with adjustable compression damping might help you to tune some of it out, but you might want to also look at some sort of spring mounted chain roller, I’ve seen them on various chopper websites but you could also build one from MX bike parts.
     
  11. kawabunga

    kawabunga XS650 Addict

    I think you may be right regarding the chain slap. The rear is stretched a bit and I did move the swingarm pivot from the stock location. The chain slap might just be the nature of my set up. I may end up adding a second tensioner to the upper chain rung to quell the movement.
     
    Paul Sutton likes this.
  12. kawabunga

    kawabunga XS650 Addict

    Also, can someone confirm for me, when the rear axle is fully tightened, is the drum supposed to spin freely or not?
     
  13. bikefreakjon

    bikefreakjon XS650 Addict

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    Maybe I misunderstood you, the drum shouldn't spin. It still needs a torque arm to keep it located against the brake forces though.
     
    kawabunga likes this.
  14. bosco659

    bosco659 XS650 Addict XS650.com Supporter

    If you come up with a chain tensioner, pls post up what you have come up with. Wouldn’t you put the tensioner on the bottom which is where the slack would be? I have a problem of the chain rubbing on my reinforced swing arm and a tensioner would help eliminate this. Haven’t looked into it in any depth yet.
     
  15. joebgd

    joebgd XS650 Addict

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    I see that is the case of having the what I guess is the drum anchored.
    I have a disk so I don't know how shoe mc brakes work. What do the shoes press against to stop?
    Edit- I did a search, I see they stop the hub it looks like.
     
  16. kawabunga

    kawabunga XS650 Addict

    I understand that the drum is held in place with a brake stay and should not/can not rotate once fully installed.

    What I’m wondering is whether or not the drum should be able to rotate freely without the brake stay in place. The rear drum spins freely on my CB550 when the axle is torqued, without the stay installed. Should the XS drum act the same?

    (edit - I was using the incorrect terminology above, by drum I meant brake plate, and I tested my CB550, and that does not spin freely when the axle is torqued.)
     
    Last edited: Jul 30, 2020
  17. chewblanca

    chewblanca Jack of Few Trades

    So the brake backing plate that holds the shoes is anchored to the frame. The drum, wheel hub and tire should spin freely. Is your brake actuator arm to tight the linkage that goes to the pedal? Reassemble leave the axle loose and the actuator arm off. With the bike jacked up you should be able to spin the tire around. Then try it with the axle tight. If it still works try it with the brake actuator arm on and adjust till you can barely feel them drag.
     
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  18. bikefreakjon

    bikefreakjon XS650 Addict

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    The backing plate does not have a bearing in it so between it, the inner bearing races, and the center spacer tube it actually a solid steel bar all the way out to the swing arm and therefore should not turn when tightened down
     
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  19. timbeck

    timbeck XS650 Junkie XS650.com Supporter

    I have encountered rear brake shoes that are perhaps 3/8 of an inch wider than normal being sold for the XS's. I installed them not paying attention to the width. To my surprise the rear wheel would turn but with a lot of effort. Taking things apart it was obvious the brake shoes were tight against the inner drum causing a huge drag.....

    tim
     
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  20. 5twins

    5twins XS650 Guru Top Contributor

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    Yes, the brake plate won't turn freely once the axle is tight, but it needs to be anchored or braking force could/would turn it. Your terminology is confusing. The brake drum is part of the hub, the backing plate that the shoes mount on is the part I'm pretty sure you mean. Speaking of which, I measured that built-in spacer in three I have, a '77, '78, and an '80-'83 one. They all measure pretty much the same and seem to match what you found on yours. The spacer sticks out on the inside about 6.5 to just over 7mm, and the overall length of the spacer from the inside edge to the outer face is about 32mm. So, I don't think it's your brake plate rubbing when you tighten the axle, I think the internal spacing on the bearing stack may be off.

    That area on the inside face of your tophat spacer around it's I.D. looks pretty beat up. That's the area that contacts the long tube spacer and actually does the spacing. If it's bashed in, making the spacer not as wide as it used to be, that could be the issue. I'd put the bearings and spacers back in the hub then cut up some pipe spacers to take the place of all the external spacers, brake plate, swingarm, and chain adjusters. Basically, make spacers so you can just stick the axle in and tighten it up. See if it spins once tight, it should. If it doesn't, the bearing spacing is off (too little). The bearings are being pinched together too much which is binding them up.
     
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