Overhaul Suntour XC Pro Rear Hub

7-speed Cassette Body

I've managed to pick up a variety of Suntour cassette hubs and cassettes over the past year.  Anything Suntour from Japan is at least 20 years old at this point (though all these parts were brand new), but the products that Suntour was making at the end of their road were among the best available at the time.  The XC Pro hubs used cartridge bearings and had a feature called GreaseGuard, that allowed you to inject grease into two ports that directed the grease into the inside of the cartridge bearings, flushing out any contaminants.  The concept, created by Charlie Cunningham and licensed to Suntour by WTB, was pure genius, though some of the advertising makes highly suspect claims (do headsets really blow out grease when the altitude changes, and would this even matter?  I think not).  The best thing about these hubs, made by Sanshin, was that the cartridge bearings are a standard size that is very inexpensive to purchase and easy to replace.  The bearings are also well-supported, strengthening the standard diameter axles.

The big downside of the Suntour hubs is that they used their own spline arrangement for the cassette versions, which is not interchangeable with anything else on the market.  Suntour was always known for making outstanding freewheels, so their cassettes were among the best of the best at the time and they used their PowerFlo tooth profile, which improved shifting.  Many people didn't like the locking design, which used a threaded sixth or seventh cog, requiring two chainwhips to remove.  If you find one of these that hasn't been serviced in many years, you may have a bear of a time getting it off, though a well-maintained one will present no problems.  There were also a few different variations of the cassettes and bodies that could make it difficult to find matching replacements and many of the 7-speed versions that you find today were designed for Suntour's MicroDrive system, which used smaller chainrings (for the time) and only offered an 11-24 seven-speed cassette.  Finally, almost all the 8-speed cassettes you can still find are 11-28 MD, though that happens to be a size that works very well for my commute with its steep climbs and I settled on 28 as the bottom cog on my mountain bikes decades ago.

Here are some useful body dimensions I found online:

Suntour Cassette spline lengths

6 speed = 23.7mm
7 speed = 26.1mm
8 speed = 30.8mm

Microdrive

7 speed MD = 20.7mm
8 speed MD = 25.4mm

 I was cleaning up the drivetrain on a commuter bike, a mid-range Bianmchi from 1984, on which I had laced an XC Pro hub into the rear wheel.  I was using a 7-speed version of the hub with an 8-speed cassette that had the threading for the last cog removed and the O.L.D. reduced to 126mm to fit the frame spacing.  I noticed a bit of roughness in the cassette body and decided to take the time to dismantle it to see if there was any dirt inside.  I looked online for any instructions on how to overhaul the hub and couldn't find much, so I decided to post some tips for anyone else who is still riding these hubs.  Most forum posts seemed to be authored by those with little direct experience (no surprise there) and consisted primarily of warnings against dismantling the cassette body, which actually proved to be quite easy.

The cassette body is held tightly to the hub shell by a threaded sleeve that is tightened with a right-hand thread, accessed from the non-drive side of the hub with a 10mm hex key.  The IceToolz tool for removing Shimano cassette bodies worked quite well for me.

Disassembly

1. Remove the left side locknut, washers and cone.
2. Slide the axle out,. taking care to catch the nine 1/4" balls that support the right side of the axle.  (This is another weakness of the design, in that there is no cartridge bearing on the right side of the rear hub.  However, the placement of the bearing makes the assembly quite strong, like Shimano's designs.) Carefully pry the steel labyrinth seal from the cassette body, if it's a non-MicroDrive 7-spd hub, working evenly around.
3. The cup for the outer bearing doubles as the locknut for the cassette body.  You could use a punch to loosen this, but I found that the old Shimano cassette lockring tool I have worked fine.  I held it tight against the hub with a long 5/16" bolt and nut, and loosened the reverse-thread locking race with a wrench on the Shimano tool.  Only loosen the locknut; do not remove it at this point.
4. Remove the sleeve that holds the body to the hub by inserting a 10mm hex key into the left side of the hub.  This one is right-hand thread.
5. Once you have the body off, put a clean cloth in a shallow box or tray and complete the disassembly of the body, taking care not to mix the 1/8" balls from one side with those of the other, if you plan on re-using them.  I found that there was no dirt inside mine.  The body could probably have used another shim, but it wasn't binding and the bearings were in great shape, so I just cleaned and reassembled it.

Reassembly

1. Place some tacky grease (white lith works well) in the inner bearing race and arrange the balls.  Alternatively, you could simply install the inner body into the outer body and then insert the balls with the two parts just far enough apart to provide clearance.
2. With the shims in place, insert the remaining 1/8" balls into the outer race.  If you are going to use grease for these balls, drip some oil onto the pawls, first.  If you like grease on the pawls (I don't), make sure it is very light stuff.
3. Drip some 30-weight oil into the body to lube the outer bearings and pawls.
4. Install the reverse-threaded locking race, but don't try to cinch it down yet.
5. Reinstall the cassette body to the hub shell.
6. Cinch down the cassette body locking race.
7. Tap the labyrinth seal back in, using a light hammer and flat plate.
8. Reinstall the axle.  Adjust using standard QR axle techniques. Read Sheldon's article at http://sheldonbrown.com/cone-adjustment.html if you don't have any idea what I'm talking about.

That's all there is to it.  The entire process shouldn't take more than a half hour the first time you do it.  There are two tiny holes on each side of the cassette body that I believe are the path that grease is supposed to take, using the GreaseGuard system.  It looks like the grease pressure is supposed to move grease through the cassette body to the outer bearing and then out.  If you submerge your hubs completely in water, then this is probably a good feature, but that's a lot of grease to have inside the cassette body and I've had troubles in the past with greased pawls, so I prefer to only inject grease into the left side cartridge bearing, which is more exposed, and leave the drive side lubed in a more traditional manner.  Of course, you will need to disassemble the hub to service a non-GreaseGuard version.

www.retrobike.co.uk

The MicroDrive hubs had the smallest cog threaded onto the next cog, which then threaded onto the body.  The outer seal for this hub is a custom rubber piece that will probably dry out someday, rendering the hub useless.  The seal does not work as well as the labyrinth seal of the standard bodies, making GreaseGuard a more useful version on these hubs, but you need to use MD if you want an 11t cog for some reason.

More classic Suntour fun at The Bicycle Info Project and MOMBAT