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Thread: 1980 R100 front brake free play

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    1980 R100 front brake free play

    I am completing a frame on restoration of a 1980 R100. I am having trouble with the front brake free play. The front wheel turn with just a little drag, as does my 1984 R100. The master cylinder cable has what I believe is the correct free play, yet I have almost no free play at the lever. The only way I can accomplish free play at the lever is to loosen the cable to the mc too much, as in the cylinder at the end of the cable isn't even touching the master cylinder lever that pushes the plunger. The mc seems to be working right as fluids exiting and returning are evident when I take off the cap and look into the reservoir. Anybody have any ideas?

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    Sir Darby Darryl Cainey's Avatar
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    Going back from memory, there is a special feeler guage from BMW to set the proper gap so I don't think it's meant to touch.

    Hope this helps!
    Ambassador BMW MOA Ontario Canada
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    Administrator 20774's Avatar
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    I'm not sure if the '80 model had the under-tank M/C. If so, then as Darryl suggests, there's an adjustment at the back of the M/C to ensure that the internal piston is in the right spot. Shown here on a /6 owner's manual:

    http://www.pbase.com/dwerbil/image/74356089
    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!

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    Registered User lmo1131's Avatar
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    Ref., 1.20mm = 0.047"



    Being a /5 kinda guy I don't have a master cylinder. It's hard to tell from that old B&W manual photo; mechanically what's going on here, does the "fork" fit around the machined groove (holding it in place), and the "slack" is taken up/let out with the ferrule?

    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
    1973 R75/5 - original owner

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    Administrator 20774's Avatar
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    My Haynes says:

    "Slacken the cable adjuster locknet and insert the forked feeler gage into the groove in the master cylinder piston. [Note: the feeler gage is 1.2mm thick.] Adjustment is correct when the feeler gage is just freee to move against the master cylinder body."

    So, if there's too much tension on the cable, it pushes the small cylindrical shaft which pushes the piston farther into the m/c body and the groove moves with it, eventually disappearing inside the m/c body. Too little tension, and the groove comes too far out. So, the free play/tension has to be just right so that the groove is near the m/c body but just near enough to fit the feeler gage into the groove.
    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!

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    Registered User lmo1131's Avatar
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    I can see how that would be p-r-e-t-t-y hard to do without the special "feeler gauge".

    Thx Kurt.
    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
    1973 R75/5 - original owner

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    Thank you all for your replies. The problem, for some reason, is not with the piston position. Even if I slacken the cable so the barrel end is not touching the master, I still don't have enough free play. The only way I can accomplish free play is to loosen the cable so much that the piston can actually fall out. This leads me to believe the problem may be related to the calipers, but I can't identify what that might be.

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    The piston should not be able to fall out of the master cylinder unless the snap ring at the rear of the cylinder, as shown in the picture, is missing from yours. If the snap ring is there the piston will stop at the back of the cylinder and loosening the cable a bit more will only introduce a bit of free play in the system. If there's too much freeplay there is a danger that the cable will disconnect from the lever.

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    Administrator 20774's Avatar
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    He might not be talking about the piston...probably the oblong shaft that is between the external lever and the internal piston. That's the gold cylinder object shown in Lew's picture.
    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!

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    Kurt is correct

    Yes Kurt, you are correct. The piston is in place with the snap ring. If I back off the cable far enough to get free play then the piston plunger is in danger of falling out. Still perplexed, and missing some really nice California riding weather

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    Registered User lmo1131's Avatar
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    The only way I can accomplish free play at the lever is to loosen the cable to the mc too much, as in the cylinder at the end of the cable isn't even touching the master cylinder lever that pushes the plunger.
    Just throwing this out on the table...

    A part number search for the rod ( 34 31 1 233 309 ) shows it's the same back to the /6 "to" 09/80, but it also shows up in '84 and '85 model years. So it's probably not the "wrong" part.

    - Maybe you'se gots an aftermarket brake cable that's a tad too short?

    - Short of that (ooops, sorry for the pun) is there any crud in the depression in of activator arm that might be taking up space (in effect "lengthening" the rod)?

    - Is your brake lever solidly mounted, i.e. no slop (as a result of the bushing (#5)) being shot?

    - The control perch ferrule is screwed all the way in?

    - What's up with the "sleeve" (#20)? I don't know what it's supposed to do, but if it's sticking out too much it looks like the effect would be to "shorten" the cable

    Logic check...

    With the circlip in place the piston can't come out any further, correct?

    You could tune the length of the actuator rod to shorten it a tad.. . .. . at your own risk of course. Personally, I'd want to know "why" the set-up isn't working correctly.



    Any crud built up inside the adjuster?

    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
    1973 R75/5 - original owner

  12. #12
    Monza Blue 1974 R90/6
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    In your first post, you made it seem like your calipers were adjusted correctly, that is, not dragging to any extent on the disk. Is that correct, are the calipers adjusted?

    If so, and the problem is really not enough free play in the cable, Like yourself, I'm having a hard time imagining what is causing it.

    The front brake isn't like the clutch, where you have two adjustments. The adapter sleeve on the brake hand grip doesn't have any threads, so no adjustment at the lever. The only threaded adjustment is on the master cylinder end of the cable.

    I've never experienced the front brake cable adjustment needing to be "too precise". Since the adjuster is right there at the MC, you can eyeball the groove in the piston if you don't have the feeler gauge. Pretty close seems to be ok.

    So, is it possible you have the wrong cable, like a short one for lower bars and you have high bars, so the lack of free play comes from the cable simply being too short?

    Or, could you have the barrel inside the lever (or at the MC end) reversed? If the barrel was backwards, the cable end wouldn't slide into the barrel and you would loose 3-5mm of cable length.

    Barron

  13. #13
    Registered User lmo1131's Avatar
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    The front brake isn't like the clutch, where you have two adjustments. The adapter sleeve on the brake hand grip doesn't have any threads, so no adjustment at the lever. The only threaded adjustment is on the master cylinder end of the cable.
    I'm not speaking with any authority on this Barron, but the parts fische (MAX) shows an adjuster at the handlebar end and the master cylinder end. Granted, it seems redundant and kinda silly. I can't find a clear shot on the net. Maybe it is the MASTER CYLINDER adjuster (shown with the control perch (?)) #!7

    Just looking through Hucky's collection of brake cables (there are a ton) between the R90 series and R100 they vary in length from 101cm to 112cm. It wouldn't be too much of leap to find out the OP's cable is incorrect. Typically, the amount of "free end" end between the ferrules is the same, regardless of overall length.
    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
    1973 R75/5 - original owner

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    Registered User jad01's Avatar
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    Quote Originally Posted by lmc3881 View Post
    Thank you all for your replies. The problem, for some reason, is not with the piston position. Even if I slacken the cable so the barrel end is not touching the master, I still don't have enough free play. The only way I can accomplish free play is to loosen the cable so much that the piston can actually fall out. This leads me to believe the problem may be related to the calipers, but I can't identify what that might be.
    Have the calipers ever been rebuilt? Are they Brembo calipers or ATE's? I had a similar issue with the ATE's on mine (single piston), but I had quite a bit of drag at the disks. Rebuilding the calipers with new rubber & pistons helped a lot. I think the Brembo calipers are two piston (each caliper), which would imply to me that they should have very little to no drag at the disk(s)/wheel. Maybe it's time to buy a couple of rebuild kits? Also, just to clarify, exactly how much free play do you have at the lever? Mine has about a centimeter...
    Jim
    '78 R80/7 and '84 R100RS (Blues Brothers)
    '90 and '93 Red Mazda Miatas ("Jelly Bean" and "Red Hot")
    '96 Giant Upland (big Kendas & freshly greased bearings!)

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    Kurt, Lmo1131 and Barron

    Thanks for sticking with this. To Kurt, the push rod is the same on both ends so no help there. My MC looks like one in Lmo1131 photo (without the rust). The only way for me to achieve free play is to slacken the cable so the cable end is not secure to the MC fork. (hopefully that makes sense) If I do so, then the brake lever is just free and doesn't spring back into the proper position against the lever housing. One thing I haven't considered, and am not sure why it would matter, is that I changed handle bars from stock. The stock bars are in a really silly position, somewhat like a beach cruising bicycle. The bars I put on are different, but not low bars. If anything that would make the cable too long. Is that possibly the problem? If so, how does one know what length it should be?

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