Author Topic: Shift pawl spring  (Read 394 times)

Offline Luca

  • Posts: 27
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Shift pawl spring
« on: August 11, 2020, 08:34:20 PM »
Well, it finally happened at a meager 28k miles.  Bike got stuck in second gear and the shift linkages are all good and tight. I suspect the dreaded shift pawl spring.

I'm going to pull the trans and crack it open.  I'm sure Snobum has a full length treatise on the issue, but before I delve into his quagmire of verbosity has anybody else replaced their pawl spring?

My main concern is making sure I have any special tools required for the job; it's been a while since I've brushed up on my airhead lore.

Offline Carott

  • Posts: 18
  • 1980 R45/N
Re: Shift pawl spring
« Reply #1 on: August 12, 2020, 10:52:01 AM »
Luca,
Snowbum doesn't go into any detail on doing gearbox work, he says send it to an expert.
Brook Reams has excellent documentation on doing this yourself and it was his write-up and videos that gave me the courage to dive into my gearboxes.
https://brook.reams.me/category/mc-rebuilds/
Several other good YouTube videos are out there but they are not all equal.
YRMV
Brett
« Last Edit: August 12, 2020, 10:55:21 AM by Carott »

Offline Barry

  • Posts: 5014
Re: Shift pawl spring
« Reply #2 on: August 12, 2020, 11:32:04 AM »
I've never needed to go inside the gearbox but I have this on file from someone withe the same pawl spring problem.

Barry Cheshire, England 79 R45

Offline jp9094

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Re: Shift pawl spring
« Reply #3 on: August 13, 2020, 12:28:13 PM »
Boxer 2 valve recently had 2 videos on reconditioning the gearbox  that I found very informative. They can be found here on YouTube:

 https://www.youtube.com/watch?v=fewJAc42Ffk

Hope this helps. Regards to all.
"It's what you learn, after you know it all, that counts"

Offline Tony Smith

  • Posts: 2274
  • Graduate, Wallace and Gromit School of Engineering
Re: Shift pawl spring
« Reply #4 on: August 13, 2020, 01:55:45 PM »
I think the only special tool needed is a puller to remove the output flange from its taper. These are TIGHT!

Once the flange is off a bit of heat is required to ease the rear cover's removal.

Once inside, removal of the shift cassette is easy (putting it back in is "fun" though).

Whilst the cassette is out polish the "wheels" and replace the little plastic wheel with a ball bearing. The buttery shifts that result for m these simple modifications is well worth it.

Make sure all the shims go back where they were and replace front and rear seals.

Please use new bolts on the output flange to driveshaft connection. Ignore any wise comments that suggest reuse, these bolts are stretched in the torquing down process and you risk them breaking if you torque them to spec. Under torque and you risk them undoing. Ask me how I know.......

If you cannot get a torque wrench adaptor for the bolts use a ring spanner. The uncalibrated torque standard is the Australian " F'cking tight". Even tension is more important than the actual torque number.

The output flange goes on "clean and dry" achieved by vigorous polishing with a clean, lint free rag. I have never understood why BMW chose to use a Morse taper for the drain be flange. I suppose they felt it was too hard to lubricate splines which does not make too much sense given the long life of the input shaft splines.

Not a difficult job aside from retiming the shift forks (three hands would make the job a snap). But it is a long one and there is a long list of parts you might need that you will not know till you are in there.
1978 R100RS| 1981 R100RS (JPS) | 1984 R65 | 1992 KLE500 | 2002 R1150GSA |

Offline Luca

  • Posts: 27
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Re: Shift pawl spring
« Reply #5 on: August 13, 2020, 08:36:26 PM »
Thanks for all the replies.  At 28k miles I reckon the rest of the gearbox is in good shape, or at least serviceable.  The mission is really to get in there, fix what's broken, and get it back together asap.  I'll give it a good inspection, but unless something is urgent I'm going to try to get this done in a day or maybe two and save a true overhaul as a winter project.

I now work as a wrench at a well equipped (GASP!) Harley dealership, and the spring broke about 5 blocks from work, so that is where I parked it.  Having the bike on an air lift table with a wheel chock and magnificent lighting should help things go along more smoothly.  I can also call in an extra set of skilled hands when needed.  We have an oven, too, that I can use to heat the rear cover for reassembly without facing domestic wrath.

I figure I can make a flange puller easily enough from a nice thick piece of plate steel and some high grade hardware.  I might even go with acme threads for the jack bolt.

The improved shift kit from motobins (also offered by BMW at one point) is around $500US!  I think I'll just go with the K bike bearing to replace the roller and polish the cam gears as Tony suggested.

Thanks for the information and advice.  I'll let you know how I make out

Offline georgesgiralt

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Re: Shift pawl spring
« Reply #6 on: August 14, 2020, 02:42:03 AM »
Hello,
Do not overlook the set of new lip seals and cover gasket for the gearbox.
Removing it, opening it and putting it back on the bike is a job you won't want to do again soon... And those old leap seals will suffer from movement of the parts they run on during processing...
Just my 2 ...

Offline tunnelrider

  • Posts: 321
Re: Shift pawl spring
« Reply #7 on: August 14, 2020, 05:47:35 AM »
Hi Luca,
Good on you having a job as a motorbike wrench, doesn't matter about the Harley aspect, two wheels good four wheels bad!
Could I ask if you noticed a change in the shift feeling or action before getting stuck in second gear? I ask this 'cause I've noticed my shift action seems to be getting less affirmative (less clunky?) clicking into gear than it used to be and i wonder if the pawl spring is on it's way out.

I found the gearbox shaft and shift fork re-assembly reasonably easy with the Clymer manual for reference, as you know the rear cover has to be heated (hot to touch) and put the shafts in the freezer overnight as an extra help. As far as I recall, I placed the intermediate and output shafts, along with the rear and mid shift forks in together first as an assembly, you'll hear the shafts drop into place in the bearing receptacles.

I have to admit I farmed out the output flange removal which I'm glad of as the previous ham fisted assembler jammed the flange nut by using no washer with the nut. I didn't know this before I farmed it out, the BM trained mechanic wasn't impressed and it took him half a day to get it off, most of it fabricating a removal tool. In my more novice state I was glad I didn't attempt it in my garage...

As George and Tony say, buy all the lip seals (input, output, selector shaft and clutch push rod), I bought a new clutch thrust bearing and clutch arm rubber boot) and lube the input shaft splines with high moly paste. Remove the neutral switch otherwise it'll get knocked and start leaking (don't ask me how I know)

Have fun, all will be good.
« Last Edit: August 14, 2020, 06:36:40 AM by tunnelrider »
'85 Black R65 / '74 GT185 / '83 Pantah 500 / '90 Super Tenere 750  / '01 DRZ400 dirt only

Offline mrclubike

  • Posts: 1437
  • Jungheinrich Master Tech
Re: Shift pawl spring
« Reply #8 on: August 15, 2020, 12:06:54 AM »
Here is a picture of my sorta home made puller

The disc with the holes is a Snap-On adapter plate
« Last Edit: August 15, 2020, 12:08:15 AM by mrclubike »
1982 R65 running tubeless Snowflakes
2004 R1150R

Offline Luca

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Re: Shift pawl spring
« Reply #9 on: August 15, 2020, 05:29:30 PM »
Tunnelrider, the only difference I might have noticed in shifting was I went through second gear into a 2nd/3rd false neutral a couple times this year.  That has never happened before this season.  I always preload the lever, work the clutch, and maintain lever pressure until the clutch is re-engaged. It was starting to get a little notchy, too, but I'm due for a spline lube.  I'll have a much better idea of how the mechanism works when it's in my hand, but from my initial impression your vague shifting feeling might be from a worn nylon roller and its corresponding spring.  The improved shift kit has bigger lumps on the cam gear for a more positive feel/action, but I'm not dropping $500 on a set of gears that still probably work just fine.  The ball bearing replacement for the nylon roller should yield a good improvement.

I've ordered a full seal set, driveshaft bolts, and shift overhaul kit from motobins, along with some other rubber bits and some fresh roundels (great prices from motobins right now).  Unfortunately they are sold out of the clutch boot so I'll have to suck it up and pay US dealer prices for that.  Mine got the silicone treatment the last time I had it off and needs to be replaced.

Mrclubike, that's pretty much what I envisioned for a puller.  I'll make sure I have some sort of swivel or sacrificial washer to prevent the jackscrew from turning directly on the output shaft.  Any chance you could get me dimensions on the tool?  I'm interested in the OD of the plate and the hole pattern for the flange bolts.

Offline Luca

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Re: Shift pawl spring
« Reply #10 on: August 16, 2020, 10:48:37 AM »
Quote
The output flange goes on "clean and dry" achieved by vigorous polishing with a clean, lint free rag. I have never understood why BMW chose to use a Morse taper for the drain be flange. I suppose they felt it was too hard to lubricate splines which does not make too much sense given the long life of the input shaft splines.

I suspect the morse taper does a better job of spreading the clamping load between the flange and shaft rather than place all that load on a small shoulder and doesn't require the use of a sealant under the washer.  Tapered connections can also persist if the fastener loosens.  Splines are needed on the input so that the clutch parts can slide.  Splines would have probably worked just fine on the output, but with no bearing preload or sliding parts to worry about it might be a case of; teutonic technical superiority

Offline tunnelrider

  • Posts: 321
Re: Shift pawl spring
« Reply #11 on: August 17, 2020, 05:04:42 AM »
Thanks for the description of how it went out and what a vague feeling shift might be caused by, it's kinda funny 'cause I got a shift overhaul kit when I went in and replaced the g'box bearings but ran out of time to do the shift cassette, hastily inspected the cassette springs and roller, decided they look good and it's not broke so don't fix it, who knows how long before I rue that decision, hopefully a while yet  ;D . It's definitely not a quick job as mentioned by others if you're going to to clean all the parts that have to come off before putting back together. Another job that can be done while you're there is measuring the clutch plate thickness for peace of mind and at your low mileage it's probably not necessary to do anything further clutch wise.
'85 Black R65 / '74 GT185 / '83 Pantah 500 / '90 Super Tenere 750  / '01 DRZ400 dirt only

Offline tunnelrider

  • Posts: 321
Re: Shift pawl spring
« Reply #12 on: August 18, 2020, 03:22:26 AM »
Another part readily accessible with the gearbox removed is the flywheel / clutch carrier - some choose to paint the timing marks so they're easier to see when checking the timing.
'85 Black R65 / '74 GT185 / '83 Pantah 500 / '90 Super Tenere 750  / '01 DRZ400 dirt only

Offline Luca

  • Posts: 27
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Re: Shift pawl spring
« Reply #13 on: August 18, 2020, 07:23:16 AM »
Thanks for the suggestions.  Once I'm ready to re-assemble I'll see how much time I have for some of the little extra details.  If I'm not done by the end of the day it will be a minor fiasco to make my space workable for another week.

Any chance somebody could measure their flange puller/holder?  I'm going to make one but I don't know the maximum OD that's allowed to fit inside the trans boss or the driveshaft bolt spacing.