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Thread: Front brake binding on '76 R90/6

  1. #1
    Registered User ezwicky's Avatar
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    Front brake binding on '76 R90/6

    howdy all,

    i have a new-to-me '76 R90/6 and the front wheel is difficult to roll because the brake is sticking or binding.

    i tried adjusting the cam pin in the caliper and that helped a little but it's still not right. sometimes it's hard to turn the front wheel, sometimes it's almost impossible. there's no free play in the hand lever, no sponginess.

    i think i am looking at a caliper rebuild, what do you all think? this was a tampa-area bike and maybe the salt air has hastened corrosion?

    a rebuild kit is about $120 and i am wondering if i should also just go ahead and rebuild the master cylinder as well for another $75 or so?

    thanks in advance for any advice.

    -eric
    BMWMOA #182796

    '76 R90/6

  2. #2
    Administrator 20774's Avatar
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    Your rebuild kit probably includes a new piston. IIRC kits can be found for cheaper w/o the piston.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  3. #3
    Registered User jad01's Avatar
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    Quote Originally Posted by 20774 View Post
    Your rebuild kit probably includes a new piston. IIRC kits can be found for cheaper w/o the piston.
    When I rebuilt mine as I was doing my dual disc conversion, I found one piston was rust-pitted pretty badly, and one was OK... If you proceed with a caliper rebuild, I would recommend disassembling the caliper before you order the parts so that you will know which kit you need (w/ piston or not).
    Jim
    '78 R80/7 and '84 R100RS (Blues Brothers), '86 K75C (Icy Hot)
    '90 and '93 Mazda Miatas (Jelly Bean and Red Hot), '02 325ci (Blue Streak)
    '96 Giant Upland (big Kendas & freshly greased bearings!)

  4. #4
    #4869 DennisDarrow's Avatar
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    Have you tried to change out the brake fluid?......This needs to be done at least every couple of years........Have you adjusted the brake cable at the master cylinder?.....The "tool" to do this is part of your tool kit with the feeler guages. For me, I would do a flush and adjust of the system before tearing it apart.

    Has this just begun to do this or did you get the bike in this condition? Could very well be lousy maintenance by the previous owner and just needs cleaning and adjusting............God bless.......Dennis

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    There should be some free play in the hand lever, ~1-2mm IIRC. The cable adjustment is at the master cylinder though, which requires the tank be removed for access. Before tearing the caliper apart, I would do a fluid flush once or twice, spray brake parts cleaner on the pads while turning the wheel, and adjust the cable for some free play at the hand lever. The fluid flush can be done at the same time the cable is adjusted because the tank must be removed for both.

    I found attaching a small length of clear PVC tubing on the bleed nipple allows gravity draining brake fluid with minimal mess. A timer or some other reminder is needed so you don't forget to check the master cylinder while fluid is dripping out the caliper and run out of fluid. Otherwise, a mechanical pump/syringe can be used to extract the brake fluid. If the brakes are not permanently locked, fresh fluid and cleaning the pads/piston seals with spray brake cleaner may be all that is required. I had a similar situation with my single rotor ATE caliper and that fixed the problem. Good luck!
    Stan

    AH# 13238

  6. #6
    Registered User ezwicky's Avatar
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    this is a great forum! thanks for all the advice, and i will start in as soon as possible. barron williams also gave me similar advice.

    will break out the clymer's and get to work. i'll keep you all posted.

    thanks everybody,

    -eric
    BMWMOA #182796

    '76 R90/6

  7. #7
    Registered User lkchris's Avatar
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    Might get a new brake hose, too.
    Kent Christensen
    21482
    '12 R1200RT, '02 R1100S, '84 R80G/S

  8. #8
    Registered User ezwicky's Avatar
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    hey all,

    i have been getting a TON of really useful information from forum denizen barron williams via emails, and i wanted to send an update to the forum of what i have found so far with my front brake situation. here's a condensed version of what i emailed to barron just now:

    today i removed the pads and cleaned everything as much as possible. the braking surfaces have a lot of wear left and look to be in good shape. the other sides are rusty but i wire-brushed them and they should be functional enough. there were no little O-rings around the pad posts though.

    i also sprayed brake cleaner in among the piston. i compressed it with a C-clamp and it moved, but it was hard to tell how much i should have been looking for.

    i put it all back together, adjusted the cam pin for the sweet spot but still it was binding.

    so then i flushed completely the brake line and in so doing effectively changed the brake fluid. still no luck. the old brake fluid did not look too funky. a bit cloudy but that was all.

    so i drained the brake line, removed the caliper and dis-assembled it. the piston would not move. i had to grasp it with a pair of channel-locks and wiggle it out. the piston is pitted and rusted in spots around the sides near the top (nearest the seals) but the main part of the body is clean and smooth.

    however, it will NOT go back in without a lot of pressure. and the weird part is that the inside of the caliper looks like it's been painted or something. i would have expected a smooth shiny surface but it's not. the cylinder where the piston moves.

    so i think it would be a good idea since the piston is pitted and i have to get new seals anyway, that i go ahead and get a rebuild kit (piston and seals).

    but i am still nervous about the inside of the caliper. it jjust does not look right. why would it be black and not shiny metal?
    BMWMOA #182796

    '76 R90/6

  9. #9
    Rally Rat
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    Also check the master cylinder reservoir and the very small brake fluid return hole.

    If it is plugged, brake behavior like you noted will occur.

    You can see the hole by removing the cover and with a flashlight, see it at the bottom, towards the port side of the reservoir. I might have a photo, if you need it for reference.

    Regarding the operation of the pistons, they will be difficult to move. I never had a piston that I could remove without compressed air. I think what you are seeing is a hard anodize plating for wear.

  10. #10
    Registered User ezwicky's Avatar
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    will check the master cylinder hole tomorrow, thanks for that tip.

    replacing the piston in the caliper bore: clymer's says just put it back in there, makes it sound simple. but this one feels like it would need to be pressed in with a bearing press and that does not seem right.

    i have a caliper rebuild kit on the way from max's. since the piston is pitted and the seals are ficklified i decided to do a rebuild. we'll see where we stand after that. hopefully i will have this caliper bore tightness figured out.

    thanks,

    -eric
    BMWMOA #182796

    '76 R90/6

  11. #11
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    Same issue with K1200LT

    I had this same problem with my 2000 K1200LT. I live in Newfoundland and when I took the bike to the dealer, they found that the guide pins the shoes slide on were corroded (presumably from the salt air). Since the calipers on the bike have inner stainless components, a rebuild was unnecessary. These pins were replaced, brakes bled and no more issues. Breaks felt like new. My clue was spraying them with silicon freed them up (but had a negative impact on breaking). Hope this helps.

  12. #12
    Registered User jad01's Avatar
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    Quote Originally Posted by ezwicky View Post
    will check the master cylinder hole tomorrow, thanks for that tip.

    replacing the piston in the caliper bore: clymer's says just put it back in there, makes it sound simple. but this one feels like it would need to be pressed in with a bearing press and that does not seem right.

    i have a caliper rebuild kit on the way from max's. since the piston is pitted and the seals are ficklified i decided to do a rebuild. we'll see where we stand after that. hopefully i will have this caliper bore tightness figured out.

    thanks,

    -eric
    Placing the new piston and seal into the caliper is easier than you might think. If I remember correctly, once everything is cleaned up nicely, just a thin film of clean brake fluid on the piston seal and carefully press into place. I was able to do mine with my hands. Dust seal presses in lightly after the piston is seated.

    One important thing is to press the piston in straight- don't let it cock from one side to the other. Based on my experience with my ATEs, I would advise against using a press, vice, c-clamp, or pliers- firm, gentle pressure by hand (thumbs pressing on the piston) should get it done if everything is right. The piston with the old rubber seal is much more resistant to remove than the new one will be to install.

    I was having an issue similar to yours (brake drag)- rebuilding the caliper made a huge improvement. I think the rubber seal gets old and stiff, and no longer allows the piston to retract correctly. Be sure to flush the system annually and the rebuild should last a long time.
    Jim
    '78 R80/7 and '84 R100RS (Blues Brothers), '86 K75C (Icy Hot)
    '90 and '93 Mazda Miatas (Jelly Bean and Red Hot), '02 325ci (Blue Streak)
    '96 Giant Upland (big Kendas & freshly greased bearings!)

  13. #13
    Registered User ezwicky's Avatar
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    Quote Originally Posted by rozemab View Post
    Also check the master cylinder reservoir and the very small brake fluid return hole.

    If it is plugged, brake behavior like you noted will occur.

    You can see the hole by removing the cover and with a flashlight, see it at the bottom, towards the port side of the reservoir. I might have a photo, if you need it for reference.
    on my '76 R90/6 master cylinder reservoir, there is only one hole, right underneath the cap. i can't see any other orifices in there.

    but i blew into the other end of the brake line and the air came out the hole in the master cylinder reservoir so i think that means the brake line and orifices are clear, right?
    Last edited by ezwicky; 11-23-2012 at 05:25 PM.
    BMWMOA #182796

    '76 R90/6

  14. #14
    Rally Rat
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    See the small orfice marked ? It is required for a return path for the system to work.
    Attached Images Attached Images

  15. #15
    Registered User ezwicky's Avatar
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    ahhh, ok got it. i was looking in the reservoir, not the cylinder itself, thanks for the pic. i'm a "visual thinker" as they say.

    the fact that i was abl to blow air through the hose should be a good sign though, right?

    i have a caliper rebuild kit, new pads and a brake hose on the way. all that would remain is master cylinder rebuild, but i don't see any indications that i need to do that yet.

    thankfor the good advice,

    -eric
    BMWMOA #182796

    '76 R90/6

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