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Thread: All neutrals after deceleration

  1. #1
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    All neutrals after deceleration

    My '94 R100R with 15K miles suddenly after decelerating from highway speed went into neutral and wouldn't engage any gear. The clutch pull became abnormally light. The clutch cable and external linkage all appear intact. After rotating the the rear wheel back and forth with the bike on the centerstand, shifting gears and jogging the engine with the starter motor, the transmission and engine became engaged again. I made it home (~20 miles) but the trans went into all neutrals 2 more times, both times after a deceleration to a stop. I was able to engage it both times after jogging the engine and rotating the rear wheel. I am the 3rd owner and am unaware of the circlip status. Any suggestions as to the root cause would be appreciated.

  2. #2
    Registered User GTRider's Avatar
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    That sounds more like a sticking clutch throwout piston on the back of the transmission—did you only roll off the throttle to decelerate, or did you roll off and also pull the clutch to downshift? Some variants of the throwout piston were known to swell and stick, so before worrying about the tranny I’d pull that piston and check it. The tip-off is your statement that the clutch pull got very light.

    IMHO, of course.

    Best,
    DeVern
    DGerber
    1983 R80ST — 1984 R80 G/S-PD — 2004 K1200GT w/Hannigan S/C — 2010 K1300GT — 2018 R1200GS
    BMWMOA#52184, AMA#271542, IBA#138

  3. #3
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    I agree with GTRider plus perhaps dried splines, which may need serviced, hanging up the clutch as well.[ATTACH=CONFIG]83236
    Attached Images Attached Images
    Dave Hutton '78 R100S (mfg 7/77)

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    Quote Originally Posted by GTRider View Post
    That sounds more like a sticking clutch throwout piston on the back of the transmission—did you only roll off the throttle to decelerate, or did you roll off and also pull the clutch to downshift? Some variants of the throwout piston were known to swell and stick, so before worrying about the tranny I’d pull that piston and check it. The tip-off is your statement that the clutch pull got very light.

    IMHO, of course.

    Best,
    DeVern
    Yes I pulled in the clutch to downshift during decelerations. Can the throwout piston be accessed without removing the transmission?

  5. #5
    Liaison 20774's Avatar
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    Quote Originally Posted by murty View Post
    Can the throwout piston be accessed without removing the transmission?
    Yes, look at the fiche drawing and remove the items that are outside the transmission. Do not try and remove the long pushrod that goes through the middle of the transmission.
    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
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    Quote Originally Posted by 20774 View Post
    Yes, look at the fiche drawing and remove the items that are outside the transmission. Do not try and remove the long pushrod that goes through the middle of the transmission.
    20210420_162009.jpg20210420_161958.jpg20210420_162100.jpg

    Thanks for your help on this.

    I removed the parts and and the piston was well-lubricated and slid out easily. The boot and other parts seem to be in good shape.

    Should I replace the piston? Or something else?

    Best regards,
    Paul

  7. #7
    Liaison 20774's Avatar
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    There was a period of time when that piston was prone to swelling due to heat and then jamming in the bore of the transmission. Don't know which period that was though! Snowbum mentions the "sticky hot piston" on this page:

    https://bmwmotorcycletech.info/clutch.htm

    He says the replacement piston is part 23-13-1-464-167 which likely your bike already has.

    Question...where's the bearing in this setup? Is it built into the piston?
    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!

  8. #8
    Registered User GTRider's Avatar
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    Quote Originally Posted by murty View Post
    Thanks for your help on this.

    I removed the parts and and the piston was well-lubricated and slid out easily. The boot and other parts seem to be in good shape.

    Should I replace the piston? Or something else?

    Best regards,
    Paul
    The throwout bearing may not stick until it and the transmission case are warmed up. And that is a $90 part, so before buying any parts I’d suggest going to https://bmwmotorcycletech.info/transmission.htm and scroll down to the section on throwout bearings. That may give you some checks and measurements that will help in determining if you need a new part.

    Best,
    DeVern
    DGerber
    1983 R80ST — 1984 R80 G/S-PD — 2004 K1200GT w/Hannigan S/C — 2010 K1300GT — 2018 R1200GS
    BMWMOA#52184, AMA#271542, IBA#138

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    Quote Originally Posted by 20774 View Post
    There was a period of time when that piston was prone to swelling due to heat and then jamming in the bore of the transmission. Don't know which period that was though! Snowbum mentions the "sticky not piston" on this page:

    https://bmwmotorcycletech.info/clutch.htm

    He says the replacement piston is part 23-13-1-464-167 which likely your bike already has.

    Question...where's the bearing in this setup? Is it built into the piston?
    Apparently the bearing is integral with the piston. My piston looks exactly like the one pictured on the Max BMW online parts catalog for the above part number.

  10. #10
    Registered User GTRider's Avatar
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    I think it’s time to measure the OD of your piston in a couple of places along its length, and get a handle on the size and checking for any ovality. If it is close to the upper limit mentioned by Snowbum then sand it as he describes, clean everything thoroughly, assemble with a light grease, adjust the clutch using Snowbum’s procedure and a 201mm length of coat hangar wore, and go for a test ride. Be sure to grease the pivot pin and bushing so there’s no binding of the actuating arm.

    Best,
    DeVern
    DGerber
    1983 R80ST — 1984 R80 G/S-PD — 2004 K1200GT w/Hannigan S/C — 2010 K1300GT — 2018 R1200GS
    BMWMOA#52184, AMA#271542, IBA#138

  11. #11
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    Update 2

    Quote Originally Posted by GTRider View Post
    I think it’s time to measure the OD of your piston in a couple of places along its length, and get a handle on the size and checking for any ovality. If it is close to the upper limit mentioned by Snowbum then sand it as he describes, clean everything thoroughly, assemble with a light grease, adjust the clutch using Snowbum’s procedure and a 201mm length of coat hangar wore, and go for a test ride. Be sure to grease the pivot pin and bushing so there’s no binding of the actuating arm.

    Best,
    DeVern
    The existing piston is 28.95mm vs. the limit published in the article of 28.7. I know the suggestion is to sand it down but I was able to get a new one locally so I replaced it. The new piston measured 28.65.

    I reassembled everthing but I haven't adjusted it yet. I need to read the instructions again, i'm not clear on where to measure the 201mm length.

    Thanks,
    Paul

  12. #12
    Registered User GTRider's Avatar
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    Quote Originally Posted by murty View Post
    The existing piston is 28.95mm vs. the limit published in the article of 28.7. I know the suggestion is to sand it down but I was able to get a new one locally so I replaced it. The new piston measured 28.65.

    I reassembled everthing but I haven't adjusted it yet. I need to read the instructions again, i'm not clear on where to measure the 201mm length.

    Thanks,
    Paul
    Thanks for the numerical data--that makes the sizing issue clear. On the free play adjustment, the diagram below from the Clymer manual might help:

    length.jpg

    "A" is the locknut, "B" is the adjusting screw, and dimension "A" should be 201-203mm from the rear face of the boss that holds the clutch cable to the front of the barrel at the actuating arm.

    HTH,

    DeVern
    DGerber
    1983 R80ST — 1984 R80 G/S-PD — 2004 K1200GT w/Hannigan S/C — 2010 K1300GT — 2018 R1200GS
    BMWMOA#52184, AMA#271542, IBA#138

  13. #13
    Registered User PAS's Avatar
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    At some point they went from a metal piston to the plastic/nylon one. My 81 has the metal and it's never been an issue.
    throwout piston.jpg

  14. #14
    Registered User STEVENRANKIN's Avatar
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    Metal to nylon

    Yep, BMW saved some money, and passed the savings onto us customers, LOL, NOT!

    I have been reading this from the sidelines and to be honest have never encountered this problem of the piston swelling or sticking. Pictures of the offending parts bring to my question what was BMW thinking when they redesigned a long time working design for the new system?

    Nylon replacing metal? In some cases NEVER a good idea for the user, great idea for the company. Cheaper to mold rather than machine, cheaper material and it wears out faster meaning more money from replacement parts and repair costs at dealerships. a win for BMW, a loss for us who buy them.

    Design them to be built cheap, and assembled fast then charge the highest price for the BMW name. Yugo quality at BMW price, well maybe not that bad but bad enough, lucky us who buy them and repair them rather than ride them three years and trade them in.

    Oh by the way, it is raining this morning and I am grumpy hence the dig at BMW. Praise to those who have been answering this post and providing answers or solutions. St.

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    Nick Kennedy
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