bmanpgh

I'm just learning a lot of this stuff and I seem to have backed myself into a bit of a corner.

I have a 1995 Trek 720 (Bikepedia page). The problem is, until today, I thought I had a 1997 Trek 720 (Bikepedia page).

The 1995 has a 24/32/38 crankset that I needed to replace but I thought I had a 1997 and, instead of counting the teeth, I ordered a 24/34/42 crankset (yeah, dumb move).

The rest of the drive chain:

• Grip Shift MRX-100
• 7-speed, 11 - 28 teeth
• Shimano Altus C90, bottom-pull (it was bracket mount but bikepedia says clamp-on 28.6 mm)
• Shimano AceraX 7-speed (not sure that matters, but adding it in case)

What I have now is a Shimano Tourney TY501 6/7/8-Speed 170mm 24/34/42t.
Since the derailleur was bracket mount, it does not have the clearance to go with this crankset.
I can't seem to find a 38/32/24t crankset and the old one is not useable.
I do not want to get into buying new shifters and upgrading the entire drivetrain

So I'm wondering if any of the following options are feasible:

• Buy a clamp-on bottom-pull like the SHIMANO FD-M310 Aultus Front Derailleur (28.6-34.9-mm 3x7/8 Speed Low-Clamp.
• Buy a 1x crankset and ditch the front shifter. I don't really use anything but the middle chainring anyway

Or any other ideas. Thanks in advance for the help!

brokewheelspoke

Big fan of tossing out those triples and front derailleurs and replacing with 1x. But you'll usually need to replace the bottom bracket with a shorter spindle to get the chainline right.

bmanpgh

Thanks - I didn't even think of that! That's the trouble I'm finding with this stuff -- change one thing and you have to change another, which makes you change something else, and so-on and so-on.

maddog34

the "bracket derailleur" (e-type mount? a plate behind the bottom bracket?) should have adjustment range to handle a 42 big chainring since that is what most of them are used with. there is very little difference in overall diameter.

that rear Cassette won't have enough range to make you happy ..

the only real issue should be that the chain will possibly be a couple links too short to use a big/big combo when you install the 24-34-42 crankset, but will work in all the other gear combos.

bmanpgh

I did a search and I think I see what you mean but this is not that. This attaches to the bike between the bottom bracket shell and the crank. It looks like this:



I have a new chain that has some extra length so I think that will be OK.

I eventually might want to upgrade the rear but certainly didn't want to get too into things now.

maddog34

that's the bracket-behind-the-BB type.. there should be slots in the derailler that allow height adjustments... you want @ 2mm between the top of the sprocket teeth and the der. Cage AS IT PASSES OVER the big chainring...

Russ Roth

If its the factory crankset check the back to see if its a CT90, should be. If so, walk into the lbs with this page https://bike.shimano.com/en-US/infor...12-cranks.html and collect your new crank, BB, front der and chain. Arrival time may take 1-3 weeks depending on the shop. Note in the site, shimano pays the install. Though I usually just bring in the cranks and get my box o parts.


Original e-type, doesn't have that option.

maddog34

[QUOTE=Russ Roth;23016961]If its the factory crankset check the back to see if its a CT90, should be. If so, walk into the lbs with this page https://bike.shimano.com/en-US/infor...12-cranks.html and collect your new crank, BB, front der and chain. Arrival time may take 1-3 weeks depending on the shop. Note in the site, shimano pays the install. Though I usually just bring in the cranks and get my box o parts.

Thank you for the Recall info.. i run across quite a few of these cranksets.

i believe someone here posted about an MC12 just recently!
i've written those part codes on the whiteboard for reference.. thanks again!
now i need to go dig thru my "salvaged cranks" binS..... sigh.

Russ Roth

Did dozens of these back in the day, eventually had to put a tag on the bench as they got scarcer but I still find them to turn in from time to time. Amazing how many shops now have no clue but there's still a ton of these cranks running around.

maddog34

Kind of like the "Close TOO Far" Quick releases... i'm still finding those buggers...

bmanpgh

Damn, I just bought all of those things. I checked and it is a CT90. I banged up the cranks pretty bad getting them off -- I wonder if that will make a difference.

What front derailleur do they replace it with at this point?

Russ Roth

Shouldn't make a difference being banged up, my last set was an altus crank and front der. The front I got had band shims to fit different diameters, top and bottom pull and top swing.