TDHudson

My wife and I ride a Trek T900 tandem -- got it around 2011 and have over 6000 miles on it, mostly trouble free.

Two weeks ago we had a problem where we were riding along and the chain jammed -- turned out the chain ring bolts on the stoker crank had come loose over time -- a couple were totally gone and the others were loose, causing the chain rings to move around and the chain to jam. I took the two larger rings off and we rode home on the small ring. Took it to the local bike shop for repair.

They replaced the two larger chain rings, and I asked that they also adjust the shifters since I hadn't done it in a while. Turned out the chain was also stretched (not a big surprise) so they replaced both. We got back on the bike yesterday and what a mess...

First, I hadn't noticed that they had set up the bike so that the cranks were out of phase. We want them in the same position for easier starting.... that was easy enough to fix.

The worst part was that as we rode, we immediately had awful chain slippage in every gear except the lowest. I thought it was the rear derailleur being out of adjustment, so we went home and I readjusted it so it was super smooth. I thought we were done.

This morning we took it out and immediately had chain slippage again. Something is VERY WRONG with the bike. It has NEVER had chain slippage, ever.

So many things were done to it that I wonder what could be wrong. I tried to attach some photos of the rear derailleur but since I'm new, I can't -- The rear derailleur is a Shimano Deore, the original equipment -- but the jockey/idler assembly looks like it's from another set -- "MEGA 9"? This is an 8-speed setup -- isn't that from a different derailleur? I'm trying to figure out when this was done -- I didn't do it. I wouldn't think that would cause slippage though.

I have read that the chain for this bike might be different (narrower) than others.... Was the wrong chain used? Could rear chain length be a factor? How many links should there be? I can't find any specs for this bike.

I'd say that maybe the rear sprockets are worn and causing slippage, but before this "repair" it never slipped. Ever. I have to think that some other part of the work that was done is causing this.

Please let me know what you think. I'm now kind of gun-shy about taking this bike back to that shop.

mibike

The first thing I would look at is the cassette. As the chain wares it will ware the cassette. If you let it go too far the cassette will be too worn to work with a new chain and the chain will slip.

ClydeClydeson

Replacing a badly worn chain without replacing the cassette on which it wore out will always cause the skipping under load as you described. A new cassette will make it right. Your shop should have known this and could have warned you. If it had been me fixing the bike I would have recommended replacing both because this was so likely to happen.

Alcanbrad

I completely agree with the above responses, however, do you know where the chain is slipping? If you have been riding on worn (stretched) chains, the cogs on the chainrings, cassette, and timing rings would all wear. If you can't determine what is slipping, I would replace ALL the old gearing (cassette, small chain ring, and timing rings. (As for the timing rings, if the phase of the cranks does not change after slippage, it's not your chain TIMING rings).

In my personal experience over more years than I would want to admit, chain slippage was always tracked down to the smallest chainring, so minimally, I would change the cassette and small ring, and see if the timing rings need to be changed next.

(Small correction)

TDHudson

Thanks for all the input -- this makes total sense, especially in light of the fact that the gear that isn't slipping is the lowest gear, which we almost never use -- so it wouldn't be worn enough to slip. In fact, I was wondering this when I was looking over the bike this morning. I'm checking with the shop now to see if they can deal with this relatively quickly -- over two weeks without our bike sucks.

jethro00

We currently ride a T900 every day while I complete my odyssey of repairing our daVinci Grand Junction, which odyssey began when we rode it with stretched chains. A lesson I learned is to buy a chain checking tool (inexpensive) and check for chain stretch on a regular basis. Also, learn how to oil your chains and to tighten your timing chain (rotate the eccentric). Once you get the hang of loosening the Allen screw and rotating the eccentric to tighten the timing chain, it's no big deal. One other suggestion, get a pin spanner to rotate the eccentric. They're really cheap (maybe $12) and make it a lot easier. Also, if you reply to each post just saying "got it" or "thanks," you'll have enough posts to attach pics shortly

TDHudson

Great advice -- thanks! I tend to be a do-it-yourselfer in most things so having the tools makes a lot of sense.

I have to admit, I've never ridden a bike as much as I've ridden this tandem with my wife -- so I've never actually worn out a chain or cassette before. Lessons learned.

TDHudson

The new cassette totally fixed the problem. We took it out for a ride this morning and it was rock solid.

THANKS again for the help!

Philly Tandem

Usually it's the cassette, as you found out. But a worn chain can also wear the chainrings enough that they will slip under load (climbing, etc.). So be sure to also test each of the front rings with the new chain under load, too, before you head out on a long ride.

LV2TNDM

This is 100% correct.
The shop not only "should have known," but is derelict in their repair duty! Every time a chain is replaced, a test ride must be performed to confirm the new chain meshes with the old cassette.* When it doesn't, you get the classic skip. And even before replacing the chain, a good mechanic will measure the chain to assess how much "stretch" the old chain has. This will tell them right away if other components will need replacing. Over 1/16" stretch, and the cassette's usually worn. More than 1/8" then you should suspect rings are also worn. And given the bike's age, the mechanic should have assumed the new chain would skip. Then they didn't test ride to confirm after service. This is VERY SHODDY work and they should be embarrassed! This is beyond sloppy. Talk to the owner and let 'em know they have a liability time bomb ready to explode. If you two had crashed as a result, they'd have TWO injured parties to deal with!

The owner should throw in follow up service and parts for free to make amends. If not, then please post the name of the shop so others can avoid them like the plague. I'd also suggest posting on Google or Yelp to let others know what level of "service" they provide. Inexcusable.

And you don't need to buy a "chain checker!" Jesus, people! Spend your money on NECESSARY bike tools, not that. All you need is a good RULER! Measure a 12" span of chain EXACTLY. (Old folks, put on those glasses!) Measure to pin center or edge, whatever is easiest. Measuring from 1" to 13" is oftentimes best so you can compare how the lines line up and are not dealing with the edge. If the chain has "stretched" 1/16" or more in this distance, it's time to replace. If it's well beyond that, then other components will need replacing as well. Cassette for sure, chain rings maybe. Probably the middle since it's ridden the vast majority of the time and has fewer teeth than the large.

*Actually, EVERY repair requires a test ride. Any shop not test riding their work is asking for trouble.