Help: Rebuilding a Mountain Bike

My mountain bike (2007 Cannondale Rush 4) suffered a season ending injury today, three minutes into my ride. I was going uphill, over a fairly good size branch that snapped and went through the rear spokes. It took out my rear derailluer and broke the (thankfully replaceable) rear hanger.

Honestly, I had been a little disappointed with the way it had been shifting lately and was contemplating replacing the Shimano shifters and rear derailleur with Sram stuff. Now it seems as if I've been given the opportunity to do so. I also need to replace the rear cassette since it has a tooth missing and figure out why my rear brake disc has been dragging.

So, my questions:

I've never replaced a cassette before. What special tools do I need?

I think the front chainrings are good, but since I'm replacing the cassette should I replace the chain, too?

I suspect that the rear disc is slightly bent (it has been rubbing all season). Any tricks to replacing it or do they just bolt on?

Can I salvage my existing shifter cables or do they need to be replaced when I change the shifters?

You'll need a chain-whip to hold the cassette in place, and the correct (Shimano) lock-ring tool to get it off. A bike shop ought to do that for you for not-very-much-money if you didn't want to buy the tools. Or I suppose you could pretty easily rig up a chain-whip tool yourself, this being GRM and all

You should definitely replace the chain, too, as the chain and cassette wear together as one unit. Old chain on new cassette will most likely result in skipped shifts.

Your disc should just bolt on, (6 bolts) Unless it's the center-lock type, (Shimano).And it would be prudent to replace your cables (outer and inner) at the same time, since they're quite cheap.

Thanks. The original cassette is the only non-Shimano part on there. It's a Sram. Is there a different tool for that?

Park FR-5.

IIRC Shimano and Sram should be the same.

This tool, a vise, and a chain whip makes removal of the cassette super easy.

Previous posters are correct on how to remove the cassette and that Shimano and SRAM will be exactly the same. You can buy the splined lockring remover and chain whip (or make your chain whip fairly easily) at any local bike shop.

Front chainrings do last longer than a chain and cassette under most riding conditions. Inspect them, if they look like shark teeth then they need to be replaced.

The rear disc will mount to the hub one of two ways. If it's a Shimano disc, it may have a splined lockring, same as the one for the cassette. Some Shimano and any other manufacturers will use a 6 bolt pattern. This is more prevalent, and the bolts are T25. If the rotor is really bent, pull it, wrap it a paper tower, lay it on a perfectly flat surface, and whack it all over with a non-metal hammer. Disclaimer: Be careful here, you can do more damage than good.

Safer (and preferential if it's only a little bent) is to simply bend it straight while on the bike. There is a nifty tool for this, it's sort of a two pronged fork, and the cutout fits the rotor perfectly. Use the caliper as a reference, and straighten accordingly. You can make your own tool with a small, cleaned adjustable blade wrench.

If you replace the shifters, the cables themselves will likely come with shifters. If your housing is in good shape you can probably reuse it, just lube it prior to inserting the cables. Tri-flow, or any other teflon base chain lube will work. Just dribble a few drops in the housing prior to inserting the cable.

FWIW, I prefer Shimano shifters and deraillers to SRAM stuff. They just seem to shift a little quicker and smoother. If your chain and cassette are pretty worn, you're going to see vast improvements in shifting by just replacing those, so that should fix that issue. Also, even if you don't replace shifters or cables, still lube the cable/housing periodically.

SRAM is good stuff, I just think the Shimano stuff generally works a little better. I myself run a SRAM cassette and Shimano shifters/derailleurs on all my bikes.

Feel free to ask more questions.

BTW, I'm employed as mechanic/tech (whatever we are called these days) at a bike shop, been doing it for 10+ years now.

Oh, I run SRAM chains instead of Shimano chains too. The Powerlink works very well, and you don't have to carry around those blasted Shimano Hyperglide pins and chain tool.

Park makes a little wrench that is for straightening brake discs. Annoying trial-and-error process, but it can be done. Otherwise, spring for a new one.

As others have said--replacing a cassette is up there w/ the simplest tasks in bike repair. The tools are worth owning (chain whip and cassette tool) and you probably already have a big crescent wrench. 5 minute job.

the park tool to straigthen the brake disc can be done on the super cheap with a worm gear adjustable wrench (a large one)... it's a lot of trial and error... flip the bike and spin... look between the pads and the rotor and watch for where it rubs... trial and error...

Wow, great tips from everyone. Thanks.

Next questions:

How tightly should I torque down the new cassette?

Should I use Loctite on the mounting bolts for the derailleur and disc?

Chains: I've heard that Sram chains are easier to fix and replace, but Shimanos are quieter. I'm probably leaning toward the Sram.

I wasn't in love with the Shimano shifters when everything was working properly, so that's why I was going to swap them for Srams.

The lock-ring should have a torque rating specified on it somewhere, (usually 40 Nm.)

Like The_Pirate said, Sram chains have the nifty 'powerlink', so you don't have to use a chain-tool to install them. But you can also buy the Powerlink separately, and use it on your Shimano chain. I'm not sure Sram acknowledges this compatibility, but plenty of people do it.

Switching to Sram will also give you the option of running grip-shift shifters (starting with the X7 groupset, I think.)

Not sure on the Loctite....suppose it wouldn't hurt, though. Especially on the disc bolts.

Off topic(ish): how do you like that Lefty on your Cannondale? I've always wanted to try one.

I'll be throwing a bike build thread up very shortly (road bike, though).

I can say that a SRAM 9sp cassette and SRAM PC58 (I think it's a PC58) chain work together beautifully and VERY quietly (alarmingly quiet).

I've never bothered doing a torque wrench on a cassette. You'll know when it's tight enough. Doesn't really matter because your pedaling will make it as tight as it needs to be.

I'd suggest staying away from Grip Shift - very hard to brake and downshift/upshift at the same time.

My 2 cents. 25 year bike shop owner.

Pedaling does not tighten cassettes, that applies to freewheels.

Make sure you cut the chain to the same number of links (not the stretched length) as the original chain. I like the slip on connectors but Shimano pin types work fine when correctly installed.

Use blue locktite on the disc bolts if you remove them. New disks usually come with bolts with locktite on them.

Sharp bend in disc from whacking a rock or something use the tool to straighten. If it's just not quite tru stick a big screwdriver though and bend accordingly.

As stated previously 40Nm typical for lockring. You can use the quick release skewer (loosely) to keep the tool from slipping out of the lockring when loosening the ring with a large adjustable wrench otherwise you'll wish you had another hand.

Since you need a derailleur and cassette, replace the front rings you use regularly. If you don't, you may get chain suck right away ruining a new chain. Also worn front rings wear the chain quicker which also wears out the cassette quicker (but does not affect derailleur).

Shifters are the least likely thing that causes poor shifting. The wear on the derailleur pivot points and/or cable drag is usually what reduces shifting performance over time. Derailleur wear is most likely. This is due to side to side play. Adjusting the cable on a worn derailleur can usually get good upshifting or downshifting but not both. If the cables are shot then only upshifting is hard to get adjusted (unless you have reversed shifting XTR etc. in which case downshifts would be hard to adjust). As mentioned Shimano shifters work very well, if you do switch, make sure the Srams you choose are compatable with the shifter cable pull required for the derailleur you use.

A derailleur hanger alignment tool should be used on the new hanger after it's installed before the derailleur is attached to be sure the hanger is in vertical and horizontal alignment with the wheel. This is a common reason people working at home can't make the shifting as nice as a bike shop can.

Thanks!

A friend gave me a set of new take-off Sram X7 thumb shifters with cables (from a similarly equipped Cannondale) that I have already fallen in love with, even though they're still in the box.

I'll put a dial indicator on the rim, then the disc and see if I can try to save it.

I had never heard of a derailleur hanger alignment tool, so that was another great tip. Is that a Cannondale specific tool? How is it used?

I run Sram stuff exclusively (chains, derailleurs, shifters, cassettes) and love it. one thing though, you will need to pick up a Sram rear dee to use with that X7, due to the differences in cable pull. I'd try to find a year or two old X9, and go with the shortest cage you can run (general rule of thumb for me is long cage for 3x9, mid cage or long cage for 2x9, cage length doesn't matter for 1x9 but short cage works best), along with the shortest chain you can run, there should be a good chain length how-to in the box the chain comes in if you get a Sram chain. the shorter you can get your dee cage and chain, the better your shifting will be, but run it too short and bad things will happen. I don't remember what, but it seems to me it was something along the lines of snapping the chain or the dee cage.

like brakes and clutches, chains, cassettes, and chainrings wear into each other, so they need to be replaced in sets. for a 2x9 or 3x9 setup, you'll want to get a ramped and pinned chainring at least on the middle ring if not both or all 3. if you have a bunch of climbing in your area, it might be worth getting an 11-34t cassette. as far as places to buy, try and support your LBS, but if you need to buy online, I'd recommend Chain Reaction Cycles, I've had good experience with them. also, if you need to get a new wheel and want to get a custom wheel built, they are my go-to shop, I've had them build a pair of wheelsets for me and they have worked out very well for me so far

Woody wrote: Thanks! A friend gave me a set of new take-off Sram X7 thumb shifters with cables (from a similarly equipped Cannondale) that I have already fallen in love with, even though they're still in the box. I'll put a dial indicator on the rim, then the disc and see if I can try to save it. I had never heard of a derailleur hanger alignment tool, so that was another great tip. Is that a Cannondale specific tool? How is it used?

As mentioned, you'll need a SRAM rear derailleur to work with the SRAM shifters. Amount of cable pull is different between SRAM and Shimano.

This is a derailleur hanger alignment gage. Not Cannondale specific, it's used for all bicycles with a derailleur. It's $50 to $60 new, not sure how much you want to spend. It threads into the hanger, and aligns it by rotating around and bending the hanger back to straight using the guide.

If you took the bike to your local shop they'd probably align it for minimal money. If you're installing a new hanger you may or may not need to do this.

Slyp-Dawg is spot on with cage length/drivetrain configuration.

I'm planning on a Sram derailleur and chain, and I need to replace the breakaway hanger. My wheels are good so I'll reuse those.

I love to climb big hills and I have a 3x9 setup with an 11-34 cassette now, so I'll stick with that.

This is the first time I've really turned wrenches on a bike and I'm pretty excited about it.