Bleeder screw for motorcycle caliper
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  1. #1
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    Default Bleeder screw for motorcycle caliper

    Hello..
    I have a caliper with a stripped bleeder screw(screw is 1/4-28).
    I attempted to repair the existing hole and the end results was a bleeder screw that would not hold pressure. The bleeder screw shoulder would not seat in the pocket I attempted to repair.
    Drilling a new hole seems like the way to go.
    The question I have is about creating the pocket that the bleeder screw tightens down onto...allowing the brake system to pressurize(and not leak). Here is a picture of the bleeder screw.

    Any thoughts would be much appreciated..

    Thank you

    Butch C
    Attached Thumbnails Attached Thumbnails 20200405_163456.jpg  

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    I don't like using "iffy" brake calipers on my motorcycle. Can I suggest you bite the bullet and find an new caliper?

    JMHO

    -Ron

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    That seat and the bleeder have to match real well or it's a thin band doing all the sealing. It not only has to seal under repeated braking cycles but the bleeder has to "bite" enough to remain in place without backing out a little at a time, unnoticed by you while riding. I own several motorcycles and I'm also prone to trying to repair things and if this was a rider mower or some low speed/low risk application I'd be inclined to repair/experiment. Approaching the apex (and guardrail) of a turn at 60 mph is not where/when I want to be wondering just how effective my repair was and whether it's still holding up. I agree with the above post about "iffy" brakes, your life should be worth more than the $100 for caliper replacement. What if you survive the crash and wish you hadn't? That's a very real possibility it could happen, I knew a few this happened to.

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    1) if you re-machine a new bleeder screw fitting on the caliper, the old one is still open. No way to plug that.

    2) if you tap a larger diameter thread in the existing one you need to find the correct bleeder screw for that.
    The seat will still be off though.

    3) unless this is an unobtainium part made for a very expensive motorbike that is display only and will never
    be riddent, I stand in the line of folks who say: bite the bullet and buy a new caliper. Make sure to put a dab
    of molycoat on the threads and have the protective cover on the open fitting.

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    I agree with the others who say that this is a critical safety device and should probably be replaced. If that is not possible for some reason then I think your best bet would be to use a helicoil or time-sert to replace the damaged threads. This would eliminate the need to cut a new seat (dicey at best). I would probably trust an insert but do you really want to take a chance?

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    Quote Originally Posted by butchdsd View Post
    I have a caliper with a stripped bleeder screw(screw is 1/4-28).
    I attempted to repair the existing hole and the end results was a bleeder screw that would not hold pressure.
    A stripped bleeder screw and you attempted to repair the hole. What was wrong with replacing the stripped screw first?
    Or was the hole stripped and the text should read as "stripped bleeder screw hole" ?

    Picture of the caliper?

    Not a fan of under 100% functioning brake parts.

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    Quote Originally Posted by rons View Post
    Not a fan of under 100% functioning brake parts.
    LOL well the bike does have two sets of brakes. I think the bleeder screw
    itself looked pretty good. Probably the threads in the caliper stripped out, yes?

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    Quote Originally Posted by jim rozen View Post
    LOL well the bike does have two sets of brakes. I think the bleeder screw
    itself looked pretty good. Probably the threads in the caliper stripped out, yes?
    Yes. A steel plated screw going up and down in a aluminium caliper hole over the years. Steel always wins. Especially when strong-arm tactics are used.

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    Quote Originally Posted by AD Design View Post
    Approaching the apex (and guardrail) of a turn at 60 mph is not where/when I want to be wondering just how effective my repair was
    If you are running out of road you don't want to be on the brakes. More gas is the correct answer.

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    IF there's enough "meat" in the area you could drill & tap it for a larger bleeder (assuming the internal threads are boogered). As for getting it to seal - I've seen a couple common issues. One - an over tightened bleeder can sometimes partially crush the sealing surface - this can be identified by the crosshole no longer being round - they tend to flatten out some if they are drilled too close to the end. If this has happened you need to find a replacement bleeder and go from there. Next of course is the seat as you suspect. You may want to try bluing it to see how the contact surface is mating. If it IS "off" some you can try working it in. Add some lube to the seat&threads and tighten/loosen it multiple times. The idea here is to burnish the sealing surfaces together. Tightening (or overtightneing) is NOT the way to do this - repetitive loosenign/tightening is FAR better than trying to do it with fewer attempts using more force. Reminds me of some some pipe threads at work once. The machinist had goofed and made the parts with a TRUNCATED thread form. As a result the threads wouldn't seal very well. Some "sealants" are more lubricant than sealant and in our case the sealant would eventually leak over time. We needed a "quick fix" until replacement parts could arrive (months later) - we found that one could tighten the fittings multiple times and get the threads to "mate" resulting in a perfect seal. Doing this many times resulted in actually reforming the threads - we also noted that you could NOT accomplish this by doing it one or two times - you could NOT get enough force - you'd break the fitting first. The key was repetition. I remember the idiots complaining that this was a BS way to "fix" the problem - I said, "I wholeheartedly AGREE" - if you go get some parts that were actually to print - we wouldn't be talking. I digress. And of course you could always brunish the seat with a special made tool. Not being there to inspect parts first hand makes it very difficult to determine if your repair is sound or not, but regardless of your repair or even replacement - something critical like this would warrant some "panic" type testing BEFORE you ever get on the bike and ride. Whatever route you decide - make sure it's "right".

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    Don't let anyone convince you that a threaded insert is a good fix.

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    No way would I consider trying to fix threads in aluminum for a life critical thing like this. A brass plug might help the replacement last longer between failures.
    Bil lD

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    There are kits like this that replace all the original features with a plug that contains the seat. googling brake bleeder repair kit should turn up plenty of choices.
    21260012_rnb_13915_pri_larg.jpg

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    Quote Originally Posted by EmanuelGoldstein View Post
    If you are running out of road you don't want to be on the brakes. More gas is the correct answer.
    -Well no not really, pointing the bike and leaning over more is better than increasing velocity but let's not dilute the topic. My point was about reliability on a critical safety component and how it could be conspicuously absent at an inconvenient moment, not an instructional about riding technique. We can debate the merits of trail braking at the apex in another thread. Hope you're doing well.

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    Quote Originally Posted by Mud View Post
    There are kits like this that replace all the original features with a plug that contains the seat. googling brake bleeder repair kit should turn up plenty of choices.
    21260012_rnb_13915_pri_larg.jpg
    -Seen these used with good results and would be a far better/reliable/safer choice than machining another hole/seat if there's room for them. Good suggestion by Mud, I forgot about these.

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    Quote Originally Posted by AD Design View Post
    -Well no not really, pointing the bike and leaning over more is better than increasing velocity ...
    It's not about speed, it's vehicle dynamics. Get on the brakes and you stand the bike up and make it take a wider turn = run off the road. Get on the gas and it pushes the back end out and makes the turn tighter. Same idea as an early corvair or porsche, get off the gas in the middle of the turn and the thing spits you off.

    I can see why you'd ignore some dweeb on the internet but this came from Dick Mann, at a roadracing school he gave at Sears. Same advice from Mert Lawwill, both of them ex number-one AMA guys.

    If you've got the balls, it works. First time is a little nerve-wracking tho.

    Point was, grabbing the brakes is the wrong thing to do.

    If you're going way too fast, lay it down.

    highside.jpg

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    Quote Originally Posted by MetalCarnage View Post
    I don't like using "iffy" brake calipers on my motorcycle. Can I suggest you bite the bullet and find an new caliper?

    JMHO

    -Ron
    Or even good used calipers from a salvage yard plus an overhaul kit. If the bleeder screw leaks severely or blows out not only do you lose pressure but a slippery fluid is leaking near your tires.

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    Folk are overthinking this.

    Repair is easy but you have to be meticulous about setting up. Holding the caliper in the mill to be operated on is maybe the worst part. Time to haul out the two way tilt vice and long dowel pin so everything lines up with the port between bleed nipple and caliper bore proper. Once set-up to operate concentrically to and parallel to that port its all basic machining.

    The seat for the bleed screw cone is a simple flat with a hole in the middle. Cheap, crude, and good enough. Seal is made between the "sharp" edge and the cone on the bleed screw. Visible taper area in the seat usually means some lunatic has done it up too tight. Shop manual torque settings are almost scary low. Yet to find one that hasn't been seriously over torqued.

    Set it up on the mill absolutely vertical. Run a centre cutting end mill down to open up the parallel end of the new bleedscrew, not forgetting the clearance so fluid can reach the hole when the screw is loosened, going down just at touch further so the end is cleaned up. Run a sharp drill in to clean up the bleed hole. Drill, or better if you have the sze, end mill tapping size for the new thread. Tap with a good sharp tap. Preferably in the machine but serial is better by hand.

    Job done.

    If you look carefully at a factory or, worse, economical pattern part, one they frequently aren't all that good. Often evidence of the hole and bleed screw cone being a touch out of line. On a well used set-up it can be real crappy in there. Older Yamaha in particular tends to re-define disgusting.

    No reported issues on any I've done beyond "Yours works better than it did when new." Well of course it would! I'm really, really inspector meticulous with brakes.

    A Wurth Timesert type thread insert should in fact work because its effectively just an uber-thin bush with threads both sides. But getting everything aligned just so is a bitch. Time was Wurth actually suggested that Timserts could be used for this job. I wouldn't!

    Clive

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    Thank you all for taking the time to respond....plenty of valuable information.
    I welded up the origional bleeder hole and installed a banjo bolt with a built in bleeder....20200501_115313_007.jpg
    First ride of the year....about 200 miles...

    Thank you all again...

    Butch C
    Last edited by butchdsd; 05-02-2020 at 10:56 PM.

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    Quote Originally Posted by butchdsd View Post
    Thank you all for taking the time to respond....plenty.of valuable information.
    I welded up the origional bleeder hole and installed a banjo bolt with a built in bleeded....
    First ride of the year....about 200 miles...

    Thank you all again...

    Butch C
    Glad it is working for you.

    I wouldn't have had any qualms about machining up an insert, over boring and Loctite in place. Probably would be better and longer lasting than the original set up.


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