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Thread: Sticking front wheel

  1. #1
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    Sticking front wheel

    The bike is a recently acquired ‘76 R90S. I have not had a chance to actually ride the motorcycle, but I have managed to address a couple of minor issues. While rolling the bike around the garage this afternoon and checking tire pressure, I noticed the front wheel was extremely difficult to turn. No obvious cause. I have done nothing with the brakes. Any suggestions for where I should start?

    Rickt
    Last edited by r65lsk75c; 10-21-2018 at 02:25 AM.

  2. #2
    '99 '03 '06 National Co-Rally Chair Friedle's Avatar
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    Quote Originally Posted by r65lsk75c View Post
    The bike is a recently acquired 76 R90S. I have not had a chance to actually ride the motorcycle, but I have managed to address a couple of minor issues. While rolling the bike around the garage this afternoon and checking tire pressure, I noticed the front wheel was extremely to turn. No obvious cause. I have done nothing with the brakes. Any suggestions for where I should start?

    Rickt
    Hopefully there is a service history with the bike. When were the brakes last serviced, fluid changed, how old are the pads? Make sure the bike is properly sorted before you actually take it for a ride. If you are not familiar with the particulars of the bike, find somebody to help you. Have you joined the Airheads Beemer Club yet? www.airheads.org

    Friedle
    Ride fast safely

  3. #3
    Registered User lmo1131's Avatar
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    Could be a number of things brake related; stuck pad, corroded piston, contaminated brake fluid, etc. Unlikely, but wheel bearings might be knackered.

    ... pull the wheel and take a look.
    "It is what you discover, after you know it all, that counts." _ John Wooden
    Lew Morris
    1973 R75/5 - original owner
    1963 Dnepr

  4. #4

    stuck wheel

    Quote Originally Posted by r65lsk75c View Post
    The bike is a recently acquired 76 R90S. I have not had a chance to actually ride the motorcycle, but I have managed to address a couple of minor issues. While rolling the bike around the garage this afternoon and checking tire pressure, I noticed the front wheel was extremely to turn. No obvious cause. I have done nothing with the brakes. Any suggestions for where I should start?

    Rickt
    Best to put the bike on the centerstand and remove both calipers. That's an easy way to determine if the brakes or wheel bearings are the culprit.

    Worked on a R90s a few years ago that had the exact same problem. The caliper pistons were frozen.

    That's why it's best to flush brake fluid annually.

    RickR90s

  5. #5
    Liaison 20774's Avatar
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    Probably not the issue, but you might try cracking the bleeder(s) on the calipers to see if there's trapped pressure. Likely it would have dissipated over time. But if there's a blockage in the return hole in the master cylinder or the brake lines are original rubber, they could prevent fluid returning or artificially keep pressure applied to the pistons.
    Kurt -- Forum Liaison ---> 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!

  6. #6
    Quote Originally Posted by r65lsk75c View Post
    The bike is a recently acquired 76 R90S. I have not had a chance to actually ride the motorcycle, but I have managed to address a couple of minor issues. While rolling the bike around the garage this afternoon and checking tire pressure, I noticed the front wheel was extremely to turn. No obvious cause. I have done nothing with the brakes. Any suggestions for where I should start?

    Rickt
    Is the bolt that holds the caliper eccentric ? I recall that you rotate the bolt to adjust the angle of the caliper housing to the brake disk prior to securing the end cap on that bolt.

    If the angle is offset, then the pad(s) drag on the disk. It is even more pronounced with dual brakes.
    JWMcDonald
    2016 R1200RS (current)
    2003 R1150RS (prior) / 1978 R80/7 (prior) / 1966 R69S (prior) / 1972 R75/5 (prior)
    Windsor, California

  7. #7
    Registered User Anyname's Avatar
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    Brake master cylinders have a tiny return hole that allows the fluid to bleed back into the reservoir when the handle is released. If that is blocked, it can prevent the pressure in the calipers from releasing the pads. That having been said, I'd agree with the thought that it's likely that the calipers are seized.
    BMW R bike rider, horizontally opposed to everything...

  8. #8
    #4869 DennisDarrow's Avatar
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    Try rebuilding the master cylinder....Good luck

  9. #9
    To diagnose this, remove the calipers from the disc and pull them back holding up with a wire to keep tension off of the brake lines. Now roll the bike, if it rolls fine. The calipers more than likely need rebuilt. This is very typical on the disc brakes.

  10. #10
    John D'oh
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    (Please don't use dot 5 silicone based fluid in your rebuilt ATE system).

    ATE brake calipers and master cylinders suffer from lack of proper service more than most brake systems I've dealt with. They really need serviced yearly. Use only DOT 3 or 4 fluid and bleed the brakes at least once a year when you get them working again of course. The amount of money you are about to spend on a dual disc set up will ensure your attention to this service in the future - I always say :-) The commentary above by others has pretty much nailed the issues really. Sounds like they each know from experience. Water condenses and settles in low places causing rust pits to form in master cylinder bore and on the caliper piston. The resulting coarse surface destroys seals causing failures in the system one of which is a 'stuck piston' clamping a brake disc. Several folks in the US repair ATE master cylinders by replacing the damaged bore with stainless steel inserts which are then fit to your new M/C piston. The calipers themselves are probably fine but there may be damage to the pistons.
    I'd make it stop first. Then go. Start fresh with new BMW hoses and brake pads. You might even consider some contemporary modifications to improve the performance of the ATE system.
    John D'oh

  11. #11
    #4869 DennisDarrow's Avatar
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    Quote Originally Posted by Na Cl K9 View Post
    ATE brake calipers and master cylinders suffer from lack of proper service more than most brake systems I've dealt with. They really need serviced yearly. Use only DOT 3 or 4 fluid and bleed the brakes at least once a year when you get them working again of course. The amount of money you are about to spend on a dual disc set up will ensure your attention to this service in the future - I always say :-) The commentary above by others has pretty much nailed the issues really. Sounds like they each know from experience. Water condenses and settles in low places causing rust pits to form in master cylinder bore and on the caliper piston. The resulting coarse surface destroys seals causing failures in the system one of which is a 'stuck piston' clamping a brake disc. Several folks in the US repair ATE master cylinders by replacing the damaged bore with stainless steel inserts which are then fit to your new M/C piston. The calipers themselves are probably fine but there may be damage to the pistons.
    I'd make it stop first. Then go. Start fresh with new BMW hoses and brake pads. You might even consider some contemporary modifications to improve the performance of the ATE system.

  12. #12
    Ditto to all of the above. And even after I did everything listed above, my R90S always had a bit of brake drag on the stand. Not noticeable while riding.
    '61 Clubman's Gold Star, '13 690 Duke, '13 Daytona 675R, '18 Street Triple RS, 2020 R1250R (gone but not forgotten: '76 R75/6, '84 R100, '76 R90S)

  13. #13

    Sticking front wheel

    I had exactly the same problem with my R90S and R100S. The R90S sat for over 20 years, during which time brake fluid leaked front the right caliper down to the rim. The pads were frozen against the rotors on both sides. R100S was a little better but when I removed the wheel I saw that one rotor was actually blue from heat caused by a sticking caliper and the brake pads crumbled when I removed them. If your R90S was not properly maintained, I suggest you consider a complete brake rebuild starting with the master cylinder.Remove the gas tank and look for rust on the frame below the master cylinder. This is indicative of brake fluid leaking from the mc. If this is the case you will either have to buy a new mc or have the existing one bored and sleeved, then rebuilt. (Apple Hydraulics)

    Regarding the calipers, remove them from the bike and inspect the seals. if they appear wrinkled, this indicates that they have failed and contaminants may have gotten into the calipers.Even if they appear intact, plan on a rebuild. Remove the pistons with compressed air and inspect the bores and pistons. If the pistons are rusted and pitted, they will have to be replaced. The calipers on both my R90S and R100S had minor corrosion which I carefully removed with 600 wet or dry.The pistons were throwaways.

    At the end of the day, I installed a rebuilt master, new brake lines, brake pipes, brake cable, rebuilt calipers(new pistons and seals) and new rotors on the R100S. Essentially, the entire system is brand new. It wasn't cheap but considering the brake system was 40 years old and the bike still had the original rotors, I felt it was best way to go. Very high Peace of Mind Factor.

  14. #14
    Registered User harryhendo's Avatar
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    Take a Sharpie marker, and draw a line on the brake rotor from the outer edge to the inner edge on both sides of the rotor. Then rotate the wheel. You will see where the rotor is binding by how much of the mark is rubbed off. I did this on my '87 R80, and found that the outside of one of the caliper pistons was not retracting. I rebuilt the caliper (cheap kit from Brembo, only $30 or so... easy job), bled the system, and no more binding.

  15. #15
    Registered User beemeruss's Avatar
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    Sticking pistons

    Regarding the calipers, remove them from the bike and inspect the seals. if they appear wrinkled, this indicates that they have failed and contaminants may have gotten into the calipers.Even if they appear intact, plan on a rebuild. Remove the pistons with compressed air and inspect the bores and pistons. If the pistons are rusted and pitted, they will have to be replaced. The calipers on both my R90S and R100S had minor corrosion which I carefully removed with 600 wet or dry.The pistons were throwaways.

    At the end of the day, I installed a rebuilt master, new brake lines, brake pipes, brake cable, rebuilt calipers(new pistons and seals) and new rotors on the R100S. Essentially, the entire system is brand new. It wasn't cheap but considering the brake system was 40 years old and the bike still had the original rotors, I felt it was best way to go. Very high Peace of Mind Factor.[/QUOTE] ruzneb

    So much good information here. I would just offer a word of caution regarding the use of typical 120 +/- psi shop air. It is a good idea to put a rag between the piston and the caliper as a cushion. I find the ideal tool to use is a rubber tipped air pistol held to the caliper port. Just a tickle of air is often enough to dislodge a stubborn piston. Too much air and the piston will try to depart with amazing force. Keep your fingers clear!
    Russ
    Last edited by beemeruss; 01-19-2019 at 07:09 AM.

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