My '88 K75 rear splines

I bought a high-mileage 1988 K75C from the original owner. It now has 174K on it. The owner told me that the rear end was rebuilt at 145k. He doesn't think the splines or shaft were replaced/rebuilt though. Only recently after watching a mechanic do K75 splines did it dawn on me: "Hey, I can do this!" So I got some Honda M77 moly paste from the local Honda shop and my cat and I relubed the splines in the driveway in about 2 hours.

You can offer what observations you want. I cleaned them and lubed them and reassembled without incident. Next project will be to elicit the help of the mechanic to help me relube the clutch spline and replace the main seal, as the bike has leaked oil since I've had it and probably half of its life.

Thank you.

From experience, I'd suggest looking for a good used replacement driveshaft and final drive because the one your cat is displaying in the photo isn't long for this world. The splines should have a lot more meat on them. Attached are a couple photos of mine when it failed.



I had just dropped a gear and pulled out to pass when it failed. We were doing so well, 500 miles behind us with 120 to go to reach home. Anyway, it would be good to have the parts on the shelf. Good luck and have a good riding season.

Yup. Time to get a new driveshaft and rebuilt final drive. Those spines are shot.

Longevity

I see what you're saying and so far the consensus is they need replacing, and I don't disagree. I guess my thought is that a bike with this many miles on it may not be worth the investment in shaft and final drive. If I can get 15-20 K more out of these worn splines either the bike or I will be hanging up the keys and be thankful for the time together.

I can't say how many miles she'll take you but I found a used shaft and final drive with very good splines for a total of $350. You have time to start searching for these. The main thing is that they each have the same number of splines because BMW changed them along the way so make sure to match those numbers. Also matching the fd ratio with what you currently have, and some of the K75s have ABS, some don't. That may be a selection factor or have no bearing. If you find a shaft and final drive, ask for high res photos to confirm condition. The market place on this site, IBMWR or ebay may be good sources. Occasionally a dealer may have what you need in the form of used parts. Good luck.
gp

K75solo said:

I see what you're saying and so far the consensus is they need replacing, and I don't disagree. I guess my thought is that a bike with this many miles on it may not be worth the investment in shaft and final drive. If I can get 15-20 K more out of these worn splines either the bike or I will be hanging up the keys and be thankful for the time together.

Click to expand...

15-20k? LOL! I wouldn't trust those for 50miles.

Plans

Wow, tough crowd. In truth, I suppose you are telling me what I don't want to hear. I rode 40 miles round trip to work today, so I have around 10 left! I scanned the net today and didn't find anything (the $350 find above sounds tempting. Where was that?). I will keep looking around and maybe commit to keeping it going, particularly if I go through the effort to change the main seal and do other things to it. I suppose I should be happy to at least be a Platinum Roadside Assistance enrollee

Actually, the final drive splines MIGHT be ok. It would be easier to tell if they didn't have all that old grease on them. What you want to look for is a fairly consistant flat along the top of the spline between about .060" (like new) to about .040" (worn but serviceable). Your final drive looks like it could be within that.

Your driveshaft, on the other hand has worn to the point where there is little to no flat remaining at the tops of each spline and has the distinctive jagged saw tooth pattern of a very worn shaft. The splines wear on one side (the side that is pushed towards the mateing spline during acceleration and cruise). That side will develop a step that is wide at the base than steps down part way towards the narrowing tip. The driveshaft splines tend to wear faster than the final drive splines due to different hardnesses. Decent used driveshafts are getting VERY hard to find.

If your final drive has spline top flat within the above widths and there is very little step in the spline sides, you might consider a new shaft ($360) and religiously lube it every 3000 miles. You'll probably have no further problems with it.

As far as lube goes, Honda Moly 60 (or Guard Dog Moly) USED to be the go to spline lube. Honda discontinued Moly 60 a few years ago and Guard Dog closed up shop around the same time. Honda superceded Moly 60 with 77. Moly 60 is labeled 60% molybdenum disulfide. It is labeled for driveshaft splines. It is labeled for 1500 degrees. There is no moly content spec. for 77 anywhere that I've been able to find (internet search, package, Honda). The only application that Honda specifies 77 for is brake caliper sliding parts. The temprature rating on the packaging is SEVERAL hundred degrees lower that 60. I would question whether 77 is appropriate for our driveshafts. I stll use 60 (with some additives) because when I learned that they were discontinueing it, I bought out the leftover inventory of 4 Honda dealerships (I have 6 K75Ss and work on many others).

Staburags NBU 30 PTM is the factory specified grease. It's expensive and hard to come by, but there is a guy on ebay selling it. He's in Wisconsin and goes by Peanut something. He sells 10, 30, and 60 gram containers. 60 grams is a hair bigger than an old film container and goes for near $30. Yes, I have bought that too.



The leaking in the clutch area is probably the o-ring that is beneath the nut that holds the clutch housing to the output shaft. You have to change that when you do a rear main seal anyway.

BEFORE YOU REMOVE THE CLUTCH: mark the rotational relationship between the three clutch parts that are bolted together with the six clutch bolts. If they are not reassembled in the same rotational relationship to each other, you stand a good chance of creating a vibration. Each piece is only balanced to sort of close, then at the factory the align them so that the heavy spot on each of the three parts are indexed 120 apart giving the best total balance. If you end up putting all the heavy spots in the same spot, you will have a vibration. Factory balance marks are rarely still visable, so just mark their rotation BEFORE disassembly.

Is the Loctite 65% moly paste still [informally] approved? How about the Wurth SIG 3000, mixed 50/50 with the Honda moly (if you can find it) or similar?

I also recall somebody mentioning the Castrol Optimoly TA, same question...
EDIT - from the Castrol site: "For paste-specific applications - cannot replace oil or grease lubrication."

Pauls1150 said:

Is the Loctite 65% moly paste still [informally] approved? How about the Wurth SIG 3000, mixed 50/50 with the Honda moly (if you can find it) or similar?

I also recall somebody mentioning the Castrol Optimoly TA, same question...
EDIT - from the Castrol site: "For paste-specific applications - cannot replace oil or grease lubrication."

Click to expand...

A 65% moly paste will typically drow out more quickly than I like (as did Honda Moly 60 as far as I was concerned). So, I mixed it and Wurth Sig 3000 50-50, providing a really sticky 30% or so moly grease. If you get these two components go for it is my opinion.

More images

Thanks for the information Lee. I thought I would post a few more images of the splines cleaned up before I lubed them and reassembled. I like your idea of finding a shaft and hope the rear end is in better shape due to hardness of steel.

Also, as far as the Honda M77 paste, FWIW, I went back and forth a bit with the Honda dealership on the suitability of the M77 for my splines as a replacement for the Moly 60. He pulled out his catalog and all the descriptions for the discontinued Moly 60 were used in the description of M77, in other words, M77 superceded Moly 60 and is suitable, according to the dealer. I understand he may not have an intimate knowledge of the chemistry of the compound, and perhaps he was just interested in selling me a small tube for $22, but that's what I ended up using.

If I can find a decent and affordable shaft, I will proceed with the main seal replacement and begin to address the neglected maintenance in this old bike and see how far I can go, and how much my mechanic wishes to commit to the project.

Thank you.

The final drive doesn't look as good as I thought it might. There is a very pronounced step in the side of each spline and the top flat is pretty narrow about half way back. It probably would be a good plan to start hunting for both a good driveshaft and final drive.

Hurting

I am hunting for used shaft and rear now as I can't afford to invest too much. Will let you know how things develop. BTW, I sketched what I think the splines are currently, the green representing missing steel.

I read on one of the forums that someone tried Honda M77 and found that it had separated to liquid and solid in the tube. He tried it anyway and found wear at the next check.

I'm sure you've read this as I recently got to experience the same thing.
https://forums.bmwmoa.org/showthread.php?91472-2018-%96-The-Current-State-of-K75-K100-Driveshaft-and-Final-Drive-Splines-Repair


Side note: The final drive is currently at Hansen's BMW being worked on, I'll post an update when it comes back.

My biggest word of warning - look suuuuper hard at any final drive/shaft that you're going to buy online before you bid. In my experience, there are a lot of shady people trying to pass off half to fully worn driveshafts as in "good condition," just because the bike ran great before they tore it to pieces. Before I sent my FD off, I asked several eBayers to send me more pictures, one person never responded, the other one sent me super grainy pictures the first time (maybe trying to hide it?) and then finally a picture showing that the FD was shot.

spline wait

Yes, I did read your post and found it very informational. Looks like you went with the most cost effective option (Hansen) with the best upside. I've got Kbike parts hunting for a rear drive and shaft and will be looking closely at photos too.

Thanks for the help.

The best way to know what the splines SHOULD look like is look at the transmission end. The splines on the transmission end of the driveshaft are identical to what the final drive end of the driveshaft SHOULD look like. The splines on the transmission output shaft are what the splines on the input of the final drive SHOULD look like (except for the retaining ring groove). They are exactly the same size. The transmission end doesn't wear because the splines don't slide in and out on that end.