K100 transmission woes - what to do? - K-Bikes.com - Excellence in Motion
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post #1 of 6 (permalink) Old Aug 16th, 2019, 7:12 pm Thread Starter
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K100 transmission woes - what to do?

I have an '88 K100LT that loves to kick itself out of second gear into neutral. I believe this is a relatively common problem, but the odometer only has 30k miles which seems early for it to be happening.

As I understand it, these are the available options:
  1. Rebuild gearbox
  2. Acquire a replacement K100 gearbox
  3. Acquire a replacement gearbox from a paralever bike and go through that upgrade at the same time

Having trouble deciding which one to do because I don't know the costs of each, I don't know where to source a confirmed-good used transmission, and I don't know who does K-bike transmission work in the Los Angeles area. Any advice from folks who have gone through this before? Thanks!
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post #2 of 6 (permalink) Old Aug 17th, 2019, 2:30 pm
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Location: Austin, Texas, USA
Posts: 190
I rebuilt my original gearbox for about $12-1300 maybe 20 years ago by doing it myself. The results were good. Shift drum, shift fork, 2nd gear, bearings and seals. Maybe a couple of other items. I spent the time using the factory template to set up the shimming of the shafts. The master tech advising me said I didn't have to do that, but I did it because the tools were handy.

Fast forward a decade and it needed it again (same problem- jumping out of second). This time I bought a used K1100 trans and installed it after I took it apart to inspect the internals and install new seals. Put it back together with the original swingarm and that is the way the bike sits today.

I would say that the cheapest option would be to get a used trans. But not knowing how it was used or abused, getting inside to inspect what you have can save you some headaches. Any K-bike five speed transmission from '85 to the mid 90's (pre-K12 6-speed) will fit without mods. The paralever types will have a lug on the underside to mount the torque arm that you don't have to use if you retain the original monolever.

Frank

'17 R1200RS, 2 yrs. 25,000 mi.
'16 R1200RS, 18 mo. 28,000 mi. (gone)
'03 R1100S Boxer Cup Replika 6/200
'85 K100/1100RS, 34 yrs. 326,000 mi.
'05 R1200ST, 8 yrs. 57,400 mi.-3rd deer killed it.
'11 R1200RT, 2 yrs. 30,000 mi. (gone)
'99 R1100S, 2 yrs. 15,000 mi. (gone)
'96 Ducati 900SS/SP, 12 yrs. (gone)
500,000+ BMW miles
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post #3 of 6 (permalink) Old Aug 18th, 2019, 3:36 am
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Quote:
Originally Posted by sp88k100 View Post
I have an '88 K100LT that loves to kick itself out of second gear into neutral. I believe this is a relatively common problem, but the odometer only has 30k miles which seems early for it to be happening.

As I understand it, these are the available options:
  1. Rebuild gearbox
  2. Acquire a replacement K100 gearbox
  3. Acquire a replacement gearbox from a paralever bike and go through that upgrade at the same time

Having trouble deciding which one to do because I don't know the costs of each, I don't know where to source a confirmed-good used transmission, and I don't know who does K-bike transmission work in the Los Angeles area. Any advice from folks who have gone through this before? Thanks!
My 1985 K100RS developed the problem at around 30,000-35,000 miles. Would jump out of second gear under power. Eventually under hardly any power. I rode it in that condition from Phoenix to San Diego and up the coast to Seattle, all without 2nd gear. There I had a mechanic do quite a bit of work on it, including replacing the transmission, Cost was about $1600 for the tranny, if I recall correctly. That was back in 2005 when the bike was already 20 years old.
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post #4 of 6 (permalink) Old Aug 18th, 2019, 9:58 am
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Join Date: Sep 2006
Location: Austin, Texas, USA
Posts: 190
What happens is the shift drum and shift fork for second gear wear enough that second does not fully engage and slips out of engagement. If you drain the gear oil you will see a bunch of glitter in it. Ride it for a while and the engagement dogs of second gear become rounded off and then that needs to be replaced. The drum and forks are made of an aluminum alloy with a protective coating and once that coating wears through, the aluminum underneath wears even quicker. If I remember correctly, I paid $6-700 for the K11 transmission 15(?) years ago.

Frank
Beech likes this.

'17 R1200RS, 2 yrs. 25,000 mi.
'16 R1200RS, 18 mo. 28,000 mi. (gone)
'03 R1100S Boxer Cup Replika 6/200
'85 K100/1100RS, 34 yrs. 326,000 mi.
'05 R1200ST, 8 yrs. 57,400 mi.-3rd deer killed it.
'11 R1200RT, 2 yrs. 30,000 mi. (gone)
'99 R1100S, 2 yrs. 15,000 mi. (gone)
'96 Ducati 900SS/SP, 12 yrs. (gone)
500,000+ BMW miles
duckbubbles is offline  
post #5 of 6 (permalink) Old Aug 18th, 2019, 11:36 pm Thread Starter
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Posts: 2
Quote:
Originally Posted by duckbubbles View Post
I rebuilt my original gearbox for about $12-1300 maybe 20 years ago by doing it myself. The results were good. Shift drum, shift fork, 2nd gear, bearings and seals. Maybe a couple of other items. I spent the time using the factory template to set up the shimming of the shafts. The master tech advising me said I didn't have to do that, but I did it because the tools were handy.

Fast forward a decade and it needed it again (same problem- jumping out of second). This time I bought a used K1100 trans and installed it after I took it apart to inspect the internals and install new seals. Put it back together with the original swingarm and that is the way the bike sits today.

I would say that the cheapest option would be to get a used trans. But not knowing how it was used or abused, getting inside to inspect what you have can save you some headaches. Any K-bike five speed transmission from '85 to the mid 90's (pre-K12 6-speed) will fit without mods. The paralever types will have a lug on the underside to mount the torque arm that you don't have to use if you retain the original monolever.

Frank
Where are good places/sites to source a K1100 gearbox?
sp88k100 is offline  
post #6 of 6 (permalink) Old Aug 19th, 2019, 8:08 am
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Join Date: Sep 2006
Location: Austin, Texas, USA
Posts: 190
I found mine at a BMW yard in Morganton, N.C. Also bought a K1100 engine, motronic, wiring harness, airbox, etc. I don't remember the name of the place- 10-15 years ago. Beemer Boneyard is a source sometimes. A web search might be the way to go. Look for BMW motorcycle dismantlers, salvage, junkyards, used parts, etc. Look for K-bike 5-speeds.

Good luck!

In the absolute worst situation, I still have my original transmission, rebuilt once. Problem is that it has well over 230,000 miles on the gears and such. It's been sitting for the last 10-15 years and I have no intention of re-using it. It DOES have a set of Luftmeister 7%-11% gears in it. 1st-4th is 7% taller and 5th is 11% taller. I've always felt that the K's were geared for stump pulling, hill climbing.

Frank

'17 R1200RS, 2 yrs. 25,000 mi.
'16 R1200RS, 18 mo. 28,000 mi. (gone)
'03 R1100S Boxer Cup Replika 6/200
'85 K100/1100RS, 34 yrs. 326,000 mi.
'05 R1200ST, 8 yrs. 57,400 mi.-3rd deer killed it.
'11 R1200RT, 2 yrs. 30,000 mi. (gone)
'99 R1100S, 2 yrs. 15,000 mi. (gone)
'96 Ducati 900SS/SP, 12 yrs. (gone)
500,000+ BMW miles
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