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  1. #1
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    Default TECH: Rear Brake Lever Mount - Fab and Install

    Hi all - thought I'd do a tech article on my latest bit of fab work for my XS. It's a jap-rod but this is a fairly generic sort of job, mods feel free to move this though.

    First up, a bit of background: XS's mount their foot brake pivot in the section of the frame that gets cut off when hardtailing. Subsequently I needed a mount for it.

    I went to my local bike wrecker and found a brake lever and a splined shaft/crank to suit. The original ones off the bike were pretty thrashed.

    Basically I got my mate to turn up a boss that I can press a maintenance free bronze Plain Bearing into it. I found a FAG Permaglide plain bearing that fitted my 20mm shaft and then sketched on a bit of paper a boss to suit the plain bearing. It's fairly straight forward, just work out the ID of the boss, make sure you put chamfers for the bush radius and it's all good. Here's a snapshot of the dimensions of the plain bearing I used.



    It's a phosphor bronze bushing, "self lubricating". No grease required. It's got a teflon coating that's designed to wear and bed in after a bit of use.

    Websitehttp://www.fag.com/content.fag.de/en...permaglide.jsp

    Had my mate jimmy turn up two (always get two, never know what you might stuff up!) for a carton of beers. Here's the resulting part:



    The boss is about 28mm long, just a bit shorter than the running section of the brake shaft, including the thickness of the bearing flanges.

    The OD of the boss is slightly larger than the bearing flange, and make sure you get a chamfer on the hole so that the bearing sits flush. Otherwise the hole edge will interfere with the radius on the bearing
    Last edited by philbey; 01-10-2010 at 7:07 PM.

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    moving on...

    Once I got the boss home, I basically thought about how to mount to the frame. As it's at 90 degrees to the lower down tube, I basically "thought up" a couple of flat steel gussets. Using a piece of 3mm flat strip, I just marked out the profile and traced the radius of the boss on the flat.

    The strip was just slightly wider than the boss diameter, so I cut the angled faces to make it look a little more professional....?

    Here you can see my mark outs and the traced line, after it's been cut.



    To cut, I simply clamp a straight edged piece of wood, ~20mm thick, down on the marked line. I run along the edge gently with a very thin slitting disc on my 5 inch angle grinder. If you're careful this is a very effective way to cut steel.

    You can see that in order to do the radius, I cut a number of slits, not quite to the curve marked out on the steel. In a couple of minute you can get rid of most of the material very easily:



    After some light touch up with a grinding disc, and then some hand filing, I got a fairly nice fit to the curve:


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    and more:

    to get the gusset for the other side, I simply used the first part to pattern the next part. Take care when cutting the profile out using the steel part as a stencil, because you can damage it quite easily. If you're not confident, use the first part to replicate your markout lines on the workpiece and then use the clamped wood method again.

    Two parts clamped together in the vice, cutting the radius:



    Follow all the previous steps again to grind and file out the curve. Keep checking the two parts against one another, as long as they are the same, who cares what the intended shape looks like! There is a slight difference between my two, but it's so hard to tell anyway.

    Two gussets with the boss placed together:



    From here I tig'd them together on the inside edges, and also filled on the outside face and filed it all back smooth.

    I've since tacked the unit to the frame in the right location - ignore my shitty looking tacks, I had turned the gas off at the first attempt!


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    And almost done, I've slipped the brake lever and crank arm into place (although sitting on a block!) to see how it looks.

    I'll strip the bike down and finish the welds on the bench where access is a bit easier. until then I've left the bearings out of the boss.


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    And just to finish up, while I was on a roll with this fabrication, I decided to use the same method of marking out, clamping a straight edge, cutting, grinding and filing to create a tab for my rear brake stay:



    This is out of 6mm flat; I didn't get too scientific with the radiusing, I basically roughed it out with a grinding disc and hand filed till they looked the same radius!

    Good luck with your fab guys. All I can say is just give shit like this a shot, I'm no metalworker, but with a bit of thought, care and a few stuffed attempts, this stuff is easily acheiveable with basic workshop hand tools.

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    looks really tuff man! keep us posted

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    Very nice work man.

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    This is good stuff, the guys that are good at it know all this shit. We are still learning, and that's always fucking fun.

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    great job! lets see some more.

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    Looks great, nice engineering man! I have been brainstorming the same application for my BSA. Thanks!

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    Cheers for the words guys. I'd been mulling over this in my mind for a while, in the end I just thought F**K it, googled the plain bearings that would fit the shaft and the boss dimensions fell out from there.

    I'm a Mechanical Engineer and sometimes have to break out of my tendency to overdesign the shit out of things in my head...

    The old dude has a pile of steel around the place so I just started cutting the brackets out and next thing I know it's all falling together.

    I've got to make a brake rod and the stay strap, so once that's done I'll add them to the thread.

  12. #12
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    awesome tech, but im kinda confused as to why you would need tapers in the boss. is your bush shouldered? can you elaborate?

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    You might drill a hole for a gease zirk. Even the self lube bushings freeze up when they get dirt & road grime in them.

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    sickboi55, the bushes are shouldered so the chamfer on the edges of the bore is to accomodate the radius on the inside of the bush (plain bearing to use the correct name as per the IN/FAG catalogue)

    Afterhours, that is a good point. I originially planned to fit a grease nipple but with all the excitement I forgot all about it. It won't be too hard to do anyway, just drill and tap in at the top.

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    Oh just to note, I changed where I said taper in my first post to chamfer, that could get confusing. Sorry for that!

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    After a bit of thinking, I don't reckon I'll put a grease nipple on there, it's a 2 minute job to pull the bolt out and just pack some grease in there, and It'll keep the frame looking that little bit neater.

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    I'm building an XS too and its posts like this that keep me coming back here for more, THANKS.

  18. #18
    ARBY
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    That's a nice clean piece.

  19. #19
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    Default Fabrication

    Without experience, many of us seem to take the long way around- seeing someone else do it helps us all get better end results in less time.
    Last edited by EODrew; 07-17-2011 at 4:39 PM. Reason: missing word

  20. #20
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    nice job man looks good

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