k75 transmission problems

[Noel001]

HI, new to site hope I am posting in right area.  Looking for info on k75 transmission problems.  I am the original owner of my bike.  During the first couple of years I had transmission issues on 4 different occasions.  I was doing lots of miles in the first few years.  Each time the repair was done under warranty. The input shaft had failed 3 times, and the fourth time it was replaced before it failed. 
At the time the dealer did not know why this was happening and BMW also did not know.  The first theory was that the input shafts had poor plating on them, and then they thought some were made too short. Then it was thought that the bell housing may have been distorted. These reasons were never officially acknowledged as the cause of the problem.  In the early 90's I had the bell housing replaced as this was what most people felt the problem was. 
Over the years had the bike stored for long periods of time.  But I really like this bike so did not want to sell it.  I put it back on the road last year and have been riding it , but not a lot of miles.In the back of my mind I was waiting for the input shaft to fail.  And now it has again.  I have started to research to see what the actual cause of this is. As far as I know, BMW has never come out and acknowledged there was a problem.  They seemed to put the cause on poor maintenance, and stressed the proper lubrication of the input shaft.  This was always done, my bike was always dealer serviced while this was happening.
Can anyone let me know any information about this problem.  I want to fix my bike,but I want to be sure that it is truly fixed so I can ride with confidence. Let me know any info that you may have.  Thanks

[Laitch]

Welcome to the site, Noel. Describe the "failure" and "issues." Was the input shaft seizing or rattling; were the splines on the input shaft eroding; were the clutch hub splines eroding; was it howling or crying during the failure?

[Noel001]

HI,  the first 3 times it happened there was a slight noise, but nothing too serious sounding.  The next time I shifted gears the power would cease to the rear wheel. The fourth time it was replaced I brought it to the dealership before it went as I thought it was going to happen again.  They replaced the shaft. At this time I was told that they thought some input shafts were made too short.  At the time it was happening, I was told that I was the only one in North America this was happening to. A couple years after that I had the bell housing replaced.  I think the input shaft was replaced again at that time.  I will have to check my records.  The latest time was a couple of weeks ago and this time I was riding along in 3rd gear and the power to the rear wheel just stopped and I was coasting.  There was no noise.  I was able to shift through the gears.  I have not taken it apart yet as I have not had time,  but I'm assuming it's the input shaft again. 
I am trying to find out what the real reason for this happening is.  I would like to have it fixed properly so it doesn't happen again.  I hope to be riding the bike a lot more in the future than I have over the last 20 years.,

[The Mighty Gryphon]

If it were my bike, I would just replace the transmission.  There are a lot of bikes being parted out and transmissions are pretty common.  eBay is a good place to look. 

[Laitch]

At the time it was happening, I was told that I was the only one in North America this was happening to.

Your story of repeated failure is unique in the eight years or so that I've been reading this forum and the K100-forum. The only service bulletin that I've found that might be pertinent is this one indicates misalignment of transmission input shaft caused by lack of alignment dowels. Clutch hub spline wear seemed to be the major problem but perhaps transmission input spline wear was in the mix, too. Do you recall these dowels being present or being mentioned at service?

[Noel001]

Where did you come across this document?  I do have the dowels on my bike.  I notice that it says on it for the US only. So this would not have been released to the dealers in Canada then I assume.  I do know that at the time the clutch centering tool was not used on my bike.  The mechanic at the dealer I dealt with told me that years later.  The tool was not around at the time.  I got the clutch centering tool in the 90's.  I guess BMW  made a couple of arms that mounted on the locating dowels and then held the clutch centering tool in place, put I have not come across any of these over the years.
I was probably on my 2nd repair by the time this bulletin came out.  I will check out my documents later today and see.  Thanks for the bulletin. 

[Laitch]

Where did you come across this document?   

There are a couple of online repositories for these bulletins and many have been posted online in various Brick-centric forums, including this one. If these repeated breakdowns have happened on the same transmission and that transmission hasn't been replaced, follow Mighty Gryphon's suggestion and replace the transmission with a used one—perhaps one from as late a model as you can find. Your choice can be from either a K100, a K75, or a K1100 model. It's a nuts and bolts procedure. You can make a BMW-like centering tool using steel flat bar stock, a hacksaw and a drill but sequential tightening of the pressure plate while checking the centering tool for rotation in the following manner will be sufficient. Start at 4:13.

[Noel001]

HI, I am considering the used transmission.  And yes I would look for one from a later model as it seems that there was not the problem with them.  But that is what I am trying to figure out.  I am trying to get as much info as possible about the problem so that when I do this repair, it will be fixed.  I have been told by someone else that apparently some of the holes for the dowels were not drilled to the proper depth.  This caused the dowel to not allow the transmission to line up perfectly with the bell housing. This misalignment would cause the input shaft to wear prematurely.
Are you able to let me know what sites have the technical bulletins so I can check them out?
I purchased my bike in Feb 1987.  The first failure was in April 1987, at 7000 km.  There were another 2 failures in 1987, and then the fourth replacement was in early 1988. 
Since the technical bulletin was for the USA only, I don't think I ever had the dowels checked by the dealer. 

[Laitch]

HI, I am considering the used transmission.  And yes I would look for one from a later model as it seems that there was not the problem with them.  But that is what I am trying to figure out. I have been told by someone else that apparently some of the holes for the dowels were not drilled to the proper depth. I am trying to get as much info as possible about the problem so that when I do this repair, i
Are you able to let me know what sites have the technical bulletins so I can check them out?

Your problem with multiple failures of the same transmission is unique. The depth of the dowels isn't as relevant as their alignment location. You've read the only technical bulletin I've found so far that is remotely close to describing what happens when there is a misalignment and the effect it describes seems to be mainly on the clutch disc hub splines.

If anybody else here has read about or experienced multiple failures of the input splines on a single transmission, now is the time they should chime in; otherwise, I think you're squeezing a dried lemon expecting juice to flow from it and missing some good riding time with a replacement transmission. Furthermore, riding a 34-year old bike is always a ride into the frontiers of reliability. We fix this condition, there's reasonable probability of another disappointing us. That's why Mighty Gryphon has a box full of spare parts waiting at home to be shipped to him when he's on the road if fate comes calling, and that's why our old Bricks should be considered adventure motorcycles.

For my own peace of mind, I've successfully coupled denial with regular maintenance as a riding strategy. 

[Noel001]

I do agree.  I will not have the time to do assess the damage and do any repairs for at least a couple of months.  Work gets in the way.  That's why I'm trying to find out what I can with regards to the true nature of the problem.  I appreciate any information that comes my way.  And as I mentioned to Gryphon, there are a lot more used parts in the US than Canada.   And until the border reopens it is not possible to do a quick day trip across the line and pick up.  Thanks for your help and if anyone else has any information on this matter I would like to hear from you.

[Laitch]

At risk of beating a dry lemon into a dead horse, I believe the true nature of your problem is a transmission that is a lemon and a dealership that fails to grasp or acknowledge that for some reason or other. That's why many of us here depend upon ourselves, multiple workshop reference manuals and the experience of others to guide us rather than submit to the cost and/or frustration of dancing with dealerships.

So, here we are. 

[daveson]

A couple of thoughts that are too stupid to mention, which is probably why they haven't been mentioned yet, but someone has to ask.

I spose the pilot bushing was checked, was it? Could it be worn or even missing? You haven't mentioned if the bell housing looks good on both sides and to make sure there's no gap on either end.

Could it be a missing locating dowel on the lower crankcase half? Or not fully closed? Or axial play in the output shaft? Does the lower crankcase half contact  look good? But I'm also thinking another gear box is the best bet.

[Noel001]

HI, there are not stupid thoughts.  Thanks for the input. I will check out the dowels when I do disassemble.  The maintenance done on it in the fir st few years was at the dealership so all of that should have been done properly.  When I have taken it apart since, I have been careful to follow the instructions and replace what parts were needed. 
The service bulletin that was sent to me on this site is something new.  I will definitely check out the dowels.  There are pretty tight tolerances, .25mm.  Something I would not notice.  As far as I can tell everything fits together as it should.
Thanks for the input.

[frankenduck]

A slightly bent bellhousing (a.k.a. intermediate housing) can cause the splines to be out of alignment which induces abnormal wear.

One urban legend concerning this is that some dealers uncrated the early Ks improperly and caused this problem. It surprises me that if you had this issue corrected multiple times at a dealer that the dealer never replaced the bellhousing.

If it were me I would replace the bellhousing.

When I stripped the splines on my K75RT I replaced both the transmission AND the bellhousing.  (Although I think I may have tweaked the bellhousing myself when I bottomed out riding an ATV trail up in Alaska. But I did catch a nice 18" rainbow trout for my efforts.)

[rbm]

I agree with Duck 100%. The intermediate housing and possibly transmission needs to be replaced.  If you're clever and lucky, you might be able to find a complete engine and drivetrain for cheap, replacing everything.  Or if you want a great performance improvement, find a used K1004V or K1100 rear end and change from Monolever to Paralever.

[frankenduck]

I agree with Duck 100%. The intermediate housing and possibly transmission needs to be replaced.  If you're clever and lucky, you might be able to find a complete engine and drivetrain for cheap, replacing everything.  Or if you want a great performance improvement, find a used K1004V or K1100 rear end and change from Monolever to Paralever.

Unless you replace the gearing in the para final drive you're giving up torque and LOSING performance.

The K75 has a stock 32:10 final drive. (3.2) The shortest "out-of-the-box" gearing you can get in a paralever K final drive is a 32:11 from an early K1100LT. (2.91) A K100RS4V is 31:11 (2.82) and has even less torque.

I have 32:11s on both my Frankenbrick and K75 turbo though.

[rbm]

You're right about the gearing and  loss of speed.  I was thinking suspension performance, and road feel.  The Paralever feels more planted on the road.  You can use wider wheels and radial tires. The advantages of changing to a Paralever outweigh those losses you mention.  I love my K75 with Paralever rear end and K1100 forks.

[frankenduck]

You're right about the gearing and  loss of speed.  I was thinking suspension performance, and road feel.  The Paralever feels more planted on the road.  You can use wider wheels and radial tires. The advantages of changing to a Paralever outweigh those losses you mention.  I love my K75 with Paralever rear end and K1100 forks.

Four of my six K75s are still mono. With good radials they ride fine. I ride them pretty hard and don't really notice the jacking effect.

For my recent 95 K75 purchase I installed a K1100 transmission in case I ever want to paralever it. Probably won't though.

The K1100 front end is good though. Better forks and much better brakes.

[The Mighty Gryphon]

"four of my six K75s are still mono. With good radials they ride fine. I ride them pretty hard and don't really notice the jacking effect."

+1 The only place I've ever seen rear end "jacking" is on a dyno where acceleration is on a stationary bike.  In the real world, weight transfer under acceleration actually causes the rear to squat.  Jacking, if anything just helps reduce that squat.  It's physics.

IMNSHO, jacking was just a marketing ploy to disguise the real reason for the Paralever which was to reduce the fore and aft drive shaft sliding at the final drive caused by the single u-joint MonoLever drive shaft, and the resulting spline wear which was a bad mark on the BMW brand.

[K1300S]

Four of my six K75s are still mono. With good radials they ride fine. I ride them pretty hard and don't really notice the jacking effect.

both of my K75S's are mono.  with modern bias tires like Michelin Pilot Activ's the ride/handling is OUTSTANDING!  on street and on a track. the need for radials on these bikes is grossly overrated.

[Noel001]

In the early 90's I replaced the bell housing with a new one.  That was the popular theory at the time that the bell housing became distorted in the shipping crate.  It didn't make much sense but I did that anyways.  BMW was not offering up any other explanation at the time for what was causing the problem. 
The first 4 times it was replaces under warranty, the dealership was really good about getting it repaired.  But they did not have a reason for why it was happening.  From that service bulletin that was sent in this feed it seems to indicate that BMW had an idea of what was causing the problem. Unfortunately it seems that it was only sent out to US dealerships. 
In the first year of owning the bike I put about 70,000km on it.  I had the input shaft fail 4 times.  Since the warranty was 3 years at that time, the dealer figured they would have the problem figured out before the warranty expired. I ended up working out of the country for the next year so the bike sat for awhile.  Before the warranty was up, I asked BMW to replace the transmission, but they said that since it was working they would not replace it.  They told me that they would deal with it when it happened again.  Well I have hung on to that letter for over 30 years and I am going to see if they will honour that and deal with it. 
It's a long shot, but I have time before I can get time to fix the bike.  Thanks for all the input.  As far as the monolever goes I have always been happy with the handling of the bike.  I did replace the standard shock with an Olins when it was about 4 years old and have been happy with that.
I have also picked up a spare engine along the way, 
How did the bike handle on the ATV trail?  I've had mine on a few dirt roads, but haven't bottomed it out,

[Laitch]

I still think your original transmission is a lemon and it is unlikely any dealership will do a forensic analysis of the internal defect that is causing its repeated failure; striving toward that outcome could be a new goal.    Riding seems secondary, anyway. 

[Noel001]

I agree.  The problem is probably with the dowel alignment that the service bulletin mentioned.  I have had another person tell me this a few weeks ago, without seeing the bulletin.  He was a machinist that had the same issue and made up a gauge to determine if the bell housing was out of alignment.  He discovered it was and that there were filings in the holes where the dowels go.  Meaning the a dowel was not sitting at the right depth and causing the misalignment.  I just wish that BMW NA had made the bulletin available to BMW Canada at the time.  That was 2 months before I bought my bike and I am sure the mechanics would have dealt with it at the time.
Since I have time before I repair it, I will see if my letter gets me anywhere with BMW Canada.