3k miles on shaft drive -- inspection time!

[moribundman]

As some of you may remember, my MTB has a shaft drive instead of a chain drive. After some experimenting with different greases, I have stuck with Red Line CV-2 grease spiked with a little Paratec tackifier added (Thanks, bruce381!) for the past 3k (2,9xx) miles. Last Saturday, with BITOG in shambles and looking for a therapeutic activity, I decided to break the shaft drive down for inspection and regreasing. First of all, so you have an idea of how the shaft drive works, look at this picture: Let's start in the rear with the rear transmission gear. I see essentially no wear, the lube still looks good: The above shown rear transmission gear meshes with the rear hub gear, which is connected to the rear wheel axle. This gear also looks fine. I believe it is sufficiently lubricated and I don't see any abnormal wear: On to the front transmission gear, which is the smallest gear and the one which suffers the most wear and tear. As you can see, the grease migrates, due to high rotational speed and centrifugal force, to a large degree off the gear and onto the shaft: Here is the same gear with most of the grease cleaned off. You can see surface imperfections (pinpoint pockets from casting) and maybe some galling? Please comment! I did not take a picture of the crank axle gear, which drives the front transmission gear, because it appeared in very good condition (similar to hub gear). The weak spot in the system appears to be the front transmission gear, mostly because it's such a small gear. All in all I'm happy with it's durability and performance. While I do see wear and tear on the gear contact points, the teeth have not lost any noticeable amount of thickness, the teeth edges are undamaged and the tranny still operates smoothly. Does anybody believe I could choose a more suitable lube for the front tranny and crank gears?

 

[JHZR2]

pics no workie

 

[AndyH]

Pics are working fine for me.

 

[moribundman]

Quote:

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pics no workie

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The new forum is pure evil. Or do you per chance use a Mac? They work fine on my end (on a Mac).

 

[Pablo]

Picts work fine. Can you clean the small gear some more (think sterility) and repost it. I don't like the looks of that thing.

 

[moribundman]

I'll take the drive apart again in another 3k miles, so you'll have to wait a few months for more pictures. The little gear is very small -- only about 1" in diameter. I'm pretty sure there's some fretting, rubbing, etc happening, especially under a high load when going uphill. I'm also not sure how much shock the gears suffer when I jump a little. After all, my full weight and inertia land on the crank axle. I believe the front gear box should be sealed and filled with gear oil. Alas, it's not been designed that way. I suppose gear oil changes would be counterproductive to one of the main selling points of the shaft drive, which is of course low maintenance. The gears are inexpensive and easily replaced components, and only the small one seems to be a wear item.

 

[moribundman]

Here, max magnification of the small gear. Click on the thumbnail for a larger version. As you can see, there are lots of tiny pits in the surface. I suppose it's a casting issue, but maybe it's some type of wear? To give you an idea of the scale, the screw head that holds the gear to the prop shaft is an Outer hex M6.

 

[huffmuds9320]

Yeah with a lot of steep hills in the city, your gears handled it well. Probably just breaking it in now. It looks like its setup like a car drivetrain sort of like a rear wheel drive. I don't see that many bikes with the shaft drive. Does your owners manaual recommend an interval for regreasing and type of grease to use? What you use to clean the gears? If the gearbox used gear oil thats not a bad idea except possibility of leaking. I usually use simple green or similar cleaner to clean my gears and chain.

 

[moribundman]

Someone recently told me that a bike shop in SF just started selling Danish shaftdrive bikes. Shaftdrive bikes have been popular in Asia and they have caught on in Europe. I expect to see more of them here, too. The owner's manual is pathetic, because it's been put together sloppily by the US importer of the bike. It says to relube every 6-12 months with any bearing or joint grease that's rated for use from -10F to 140 F. I tried a few greases and so far the Red Line CV-2 with a bit tackifier added has worked best. The place that sells the bike says they use Park Tool Polylube 1000, but that stuff doesn't seem right to me. Whatever was on the gears was some supper-sticky stuff like an open gear grease. There's no way to fill the gear box with oil, because the bottom bracket has covers without seals. Filling the bottom bracket up with a (thin) grease is possible, but it will add viscous drag and probably not improve lubrication a whole lot.

 

[Jim 5]

How about a shot of the mountain bike? I'd like to see how the shaft drive is integrated into the design of the bike. All you need now is a single sided swing-arm and a paralever front suspension and you've got a BMW GS mountain bike!

 

[moribundman]

It's an old Y-frame design from the mid/late '90s which is still in production. A Trek Y-frame rip-off, basically. It has the back then state of the art active unified suspension. With a good rear shock with lockout or SSV there isn't much bio-pacing. It's a heavy old cow of a bike, but I like the shaft drive, because I live by the ocean and have issues with corrosion and sand. The shaft drive is mated to a 8-speed internally geared Shimano Nexus hub with a gear ratio range comparable to a 20 speed.

 

[Jim 5]

Thanks for the pictures! I have to say that until now I'd never laid eyes on a shaft drive bicycle (but then I'm not really up on my mountain bikes any more). I have a boring old Gary Fisher that was pretty good (I think) when I bought it about a decade ago. It's actually pretty light. I also prefer the BMX style pedals. Never really got over the BMX bikes of my youth. And as always, nice photography mori!

 

[moribundman]

No problem! Shaft drive bikes are still rarer than hen's teeth in the US. In Asia they are quite common and their popularity is increasing in Europe. For serious mountain biking I can't recommend the bike or the drive. For some mild offroad riding and small drops it's fine. Let's be honest, my wild riding days are over and that bike suits me just fine. I like flat pedals. These are Diamondback BigFoot magnesium pedals with removable traction studs and serviceable sealed bearings. I was never a fan of toe clips. In the '90s I had a Fisher Mt Tam, but it was stolen out of my garage a few years back. Back in the stone age I had BMX bikes (Haro and Kuwahara).