Drivetrain Overhaul

Yesterday's chainsuck problems weren't just a result of some rain-induced slop, but rather the result of lots of mileage on the same chain, cassette, and chainrings. I had bought enough replacement parts prior to TransRockies to replace the entire drivetrain two or three times over, but chose not to to fix what wasn't broken last August so I let the parts hibernate... until now.

I had never replaced chainrings before but after one look at my bike maintenance book and the Shimano XTR instructions, I decided that it was definitely something I could handle. And I was right; the external bottom bracket makes removing the XTR crankset a piece of cake and taking the rings off was as simple as turning a 4mm hex wrench.

But before I could get started on that, I had to wash the bike. Fortunately, the rain let up long enough for me to wash the bike from tip to tail without soaking myself too badly.

Once the bike was clean, it was time to bring it back into the garage, fire up the shop lamps, and remove the crankset. I got a good deal on the XTR M960 crankset last year when I was building up the Moots and then, later in the summer, stocked up on Blackspire replacement rings. The Shimano replacement rings are super expensive compared to these Made in Canada third-party rings, so I thought I'd give them a try. I'd love to say I'm going to upgrade to the new titanium-tipped XTR M970 crankset, but at $550 for the crankset, I think I'll pass until the price comes down.

Nevertheless, removing the crankset simply requires a 5mm allen wrench to loosen the screws on the left-side crankarm, then a couple of twists of the plastic wheel-like tool that loosens the cap. The left crank comes off easily then it's just a matter of knocking the spindle back through the bottom bracket to remove the drive-side.

Conventional wisdom states that when the teeth on the chainrings start to resemble cresting waves that it's time to replace them. I took one look at those rings and knew the surf was up and my Moots was headed for a close-out. I carrefully mounted the crankarm in my workbench vise and backed all of the bolts out, briefly doused them in some citrus degreaser and gave the crankarms a thorough wiping. I also cleaned out some muddy residue from inside the bottom bracket and around the bearing caps. A little teflon grease, lined up the chainrings so the words all match, and had everything back together and mounted before long.

With the chainrings replaced and the cranks back on the bike, it was time to tackle the cassette. The previous cassette was a mid-grade SRAM cassette that bit into the aluminum spindle on the Chris King hub and proved to be a bit of a nightmare to get off. I had to pry each individual cog off one by one. I was replacing it with the uber Sram 990 one-piece cassette, but couldn't get it one due to the gouging from the older cogs. It went halfway on then required some force. And force was applied.

And this is where things got interesting...

I had the cassette fully on, but it didn't look like it was fully on. So I continued to carefully apply force. Too much force. I eventually, accidentally, dented the outer lip of the hub where the cassette's locking cap screws into place. So I gave my buddy Eric a call and he recommended taking it to his fave bike guy Zeb at Fluid Ride. Zeb just opened a new shop in Issaquah and was at the shop. Eric gave him a call (thanks man!) to let him know I was coming and as soon as I arrived, Zeb took the wheel to the bench and gave me the verdict: the cassette was fully on, but I dented the threads. No worries though because he was able to quickly undo my damage and had the cassette on and tight. He also elaborated a bit on why the gouging happened originally and gave me peace of mind that so long as I stuck with the one-piece SRAM 990 cassettes (or something similar) that I shouldn't need to replace the hub's freewheel spindle.

Zeb was all set to send me on my way free of charge, but since I was going to be putting a new chain on and wasn't sure if I had unopened 971 or 991 chains at home, I decided to buy a SRAM 991 chain from him. Turned out I actually had three unopened SRAM 991 chains in my parts box, but I don't care -- I'll use them eventually and the guy quickly helped me out in a pinch.

So, back home, I remounted the wheel, installed the chain (may have to remove a link, it was hard to tell) and got it all spruced up. It runs flawlessly and I couldn't be happier.

Well, I would be happier if SRAM either made their cassette bodies in different colors or at least offered an all-silver version. That red really clashes with my mango-colored CK hubs. Well, that and if I could finally eliminate the brake rub on my front wheel...


Eric Floyd said...

glad it worked out for you...


Brandon said...


ZEB is Da'man and I am glad he was there to help you out!! I have started riding a bit but I am still sore and under thumb Dr.s orders NOT to MTB. Regardless I have gotten about 6 MTB rides in in the past few weeks!!