I was riding home from putting fuel in it and pushing pretty hard (for me) when my 1985 K100 RS suddenly downshifted to 4th HARD and stayed there. Hard defined as the rear wheel locked up momentarily until the engine speed caught up. I limped home a few miles away. I was able to downshift to first one time at a stop sign. Running back up the gears seemed normal, but it wouldn't engage 5th and then was stuck in 4th until I got home. today is the first day I've had a chance to look at it. Clutch is working normally, it will disengage the engine from the transmission every time. Checked the trans oil level and it was low, but still above the minimum mark on the shock adjuster tool and looked relatively normal for gear oil. When I drained the oil, however, I discovered the following:




The oil looks like it has finely divided metal dust suspended in it to my eye, but I've no experience with trans oil-other than checking the level-on any vehicle I've owned. I can't feel any shavings or granularity when I rub a sample between my fingers. Definitely metal shavings on the drain plug though. No chunks of metal came out with the oil. There's also a lot of accumulated oil under the engine oil pan-also new since December-that I am assuming was where the missing trans oil went since the oil was at the full mark at the same December check. The bike has 53,000 miles on it and I've put the last 7,000 miles on it. No major issues until now, but my commute went from 16 miles round trip, to 140 round trip at the beginning of the year, so I've put a lot of miles on it in the last three months. Am I looking at a rebuild/find a used one, or is this something a little less drastic?

Hi Tom
If you can feel the grit in the residue then there is trouble brewing. The stuck in gear is most likely the tapered grub screw in the selector mechanism and unfortunately it means transmission has to come out.
Don't go jumping in right away as there will be other opinions coming but that is the likely explanation.

Is the shifter flopping around with little or no resistance, and not changeing gears?  If so, it's the grub screw in the transmission.   A not uncommon problem.  With some of the crazy places BMW put red LocTite, and they didn't use any there...

Keep your fingers crossed that's what it is..  If you can swing a wrench it is a pretty inexpensive if time-consuming repair.  I had to do mine on a K75 as the very first thing when I bought it.  With my son helping, I did the whole job start to finish in about 7 hours of steady work.  It was a good opportunity to do a lot of other nice things for the bike like lubing the clutch splines, drive shaft and swing arm bearings.

Thanks guys, appreciate the help.

The shifter is moving but doesn't have full travel in the upward direction, otherwise normal feel. Fortunately, I have some facility with a wrench-although I don't own air tools-and the Clymer shop manual. I read the section on removal last night and while it looks time-consuming, it doesn't look like it requires any special tools other than a stand of some sort to support the motorcycle. 

Point-Seven-Five, your comments regarding the opportunity to do all that extra stuff was the silver lining in my otherwise gloomy cloud of trans removal contemplation.

Lets hope that when the grub screw let go the shifter stroke was curtailed when the linkage it holds moved out of position.  From what I recall of the internals, i think that is what you have.  Figure on a weekend of quality time with your bike. 

As far as a stand, a pile of 2x8 cutoffs under the engine is what I use.  Then a sawhorse under the rear loop of the frame.  Do a search here on spline lube threads and you'll see a number of photos.

Sawhorse I gots, and I can probably cobble something together with the 2x4s screwed together that I DO have to stash under the engine. Beats spending money on a lift! The goal is to support the bike at those two points, making the front fork/tire irrelevant?

Update: I got the trans pulled and cleaned up enough to start disassembly. The clutch control lever boot was torn, so the rear of the trans was filthy. After cleaning today, I cracked the top cover and found large bits of stuff in the bottom. Turns out the 5th gear shift fork is toast, the intermediate shaft has a broken gear on it, and 3rd gear on the output shaft is broken as well. Shifter assy. is in good working order and none of the other trans components have suffered any damage. Found replacements on Ebay that look in good shape so they should arrive in time for reassembly next week. 

Update:  Replaced the leaking rear engine seal,  both input and output shaft seals on the trans and put the trans back together. Question: after putting the trans cover on, I was testing everything for free movement and while the shafts all rotate easily,  shifting seems to be problematic. The shift drum and forks have a light coating of gear oil on them and the intermediate and output shaft were sprayed with WD-40 after a solvent scrub. I can't tell if my probkem is the shift mechanism or the lack of a transmission case full of oil. I don't want to put it all back together onlyto have to take it all apart again. Or worse, break something again figuring it out. 

So for those that have been to this rodeo before,  is this normal and once it's installed and full of oil and being used normally it'll be fine, or am I looking another issue since it's not shifting smoothly on the bench? 

Here's everything installed just prior to putting the cover on:

Tom: if you could describe 'shifting seems to be problematic', it might help?

Where do people get the idea that WD-40 is a lubricant?  It is not that different from water in that as soon as it evaporates, the fish oil lubricant, what there is of it, is gone. 

When you put the transmission together you need to use a a thin film of molybdenum assembly paste on all the surfaces that come in contact with each other.  This is critical in helping everything settle into where it finally needs to be in order to work properly.   Especially important is where the shift forks ride on their shafts and the rollers in the shift drum grooves.  I even add a couple tablespoons of molybdenum disulfide powder with the gear lube to keep things moving smoothly.

Beyond that, did you drop any of the rollers that go on the end of the shift fork where it follows the groove in the shift drum?  I know I dropped mine at least three times assembling my transmission when I did my grub screw.  Without those rollers, shifting can be pretty hard.

+1 The WD in the name WD40 stands for water dispersant. It was designed to remove water from old point style ignition systems and other parts and things that had been subjected to water. As a lubricant it is temporary at best.
Regards Martin.

Now that I have access to a computer and not just my smartphone, let me clarify: I use WD-40 for it's intended purpose as a water displacer and rust inhibitor as a matter of course after cleaning steel parts using the water-based solvents which are the only thing available in CA. Even using an air compressor to get most of the water off, all the nooks and crannies in the shafts mean plenty remains. I don't use it as a lubricant even though it has some lubricating properties. I followed the Clymer manual instructions regarding the liberal use of gear oil to lubricate the parts during the reinstall. I also use an assembly lube when i think it's necessary, such as keeping the rollers on the shift forks. This isn't my first rodeo, just my first MC transmission.

My question was whether it was normal to have trouble shifting gears while hand-rotating the input shaft because of how much slower that is vs. actual riding, or am I looking at another problem? Based on the response I got, I went back and lubed the shift drum channels with the assembly lube. None of the rollers had fallen off the shift forks. Everything was well coated with gear oil already. All the gears slid freely when moved by hand. 

After bench testing a second time, I've come to the conclusion that I need to replace the shift drum and look closely at the shifter mechanism. I'm not sure which is causing things to hang up, but the shifter pawl isn't consistently grabbing the next roll pin. Either it's not rotating the drum far enough or it's not returning all the way in order to engage the next roll pin. Difficult to tell, since keeping the drum in the right spot with the cover off isn't easy and the shifter can throw it off axis, causing the symptom, and with the cover on, I can't see what's going on but the symptom is still there. First, Neutral and Second gear shifts seem ok, but the consistency drops off after that. Downshifts seem to be good.

Right - I think I gotcha! There's a spring on the cover that helps with the selector fork (I recall there's some funny way of loading it before putting the cover on but I'm too lazy to walk out to the garage to get the manual). That's most likely your 'problem'. Put the cover on and try again.

basically a bolt is inserted through the front cover , to hold the cam follower pawl out of the way , during reassembly

once fitted up correctly the bolt is removed allowing the cam follower to relax under tension onto the selector drum cam

hope that helps

charlie99 wrote:basically a bolt is inserted through the front cover , to hold the cam follower pawl out of the way , during reassembly

once fitted up correctly the bolt is removed allowing the cam follower to relax under tension onto the selector drum cam

hope that helps

Way ahead of you. I almost missed that but that step in the manual caught my attention before I put the cover on the first time. The spring for that lever is strong enough that I made a mental note not to get my finger between it and anything else just in case I slipped and released it while setting the drift in the hole-that would smart! You would think that any deficiency in the shifter would be corrected by this spring as it forces rotation in order to sit in the valleys of the cam, but I'm at a loss at this point as to why I can't get consistent shifting whilst sitting on the bench. When it's in gear, everything moves freely and with little effort. It's just getting it into gear consistently is the final issue.

"After bench testing a second time, I've come to the conclusion that I need to replace the shift drum and look closely at the shifter mechanism. I'm not sure which is causing things to hang up, but the shifter pawl isn't consistently grabbing the next roll pin. Either it's not rotating the drum far enough or it's not returning all the way in order to engage the next roll pin. Difficult to tell, since keeping the drum in the right spot with the cover off isn't easy and the shifter can throw it off axis, causing the symptom, and with the cover on, I can't see what's going on but the symptom is still there. First, Neutral and Second gear shifts seem ok, but the consistency drops off after that. Downshifts seem to be good."


Tom, I have found that many transmissions feel that way when working them on the bench but I have never split a K-bike box. I wish I could be more helpful.