FD for an old MTB
 

I'm rebuilding my 1993 Trek 950. The front derailleur won't shift to the smallest chain ring as the spring is too weak. So its time to replace it. The cables run along the top tube and I had a few questions about a replacement FD. The tubes are oversized and measure out to 33 mm on my calipers. The chainrings are 46/36/24 and I'm using thumbshifters.

The bike came stock (pics below) by routing the derailleur cable to a stop along the bottom bracket and then back up to the FD. There is a stainless plate attached to the FD which provides both a stop for the cable housing (as the cable snakes down the frame) and the stop for the cable at it comes back up the FD. I could find a bottom pull FD and simply transfer the stainless plate over. I think that's the easiest solution.

(1) Frankly it's a bit of a kludge. I'd like to use a top pull FD but there is no stop on the frame for the cable housing. Does someone make a stop I can use or is there a way to make one?

(2) It might be hard to find a top pull that would work with this right, as I think most of those are MTB FDs and the new ones might not work right with my chainrings (46/36/24)? Or am I wrong about this?

The first pic shows the long run of cable housing from the top tube down to the plate on the FD; the second is a close up of the plate on the FD.

https://cimg4.ibsrv.net/gimg/bikefor...1a73821162.jpg
https://cimg5.ibsrv.net/gimg/bikefor...0f904c6cde.jpg

Looks like it's actually a 92 according to vintage trek. Have you tried unscrewing the inner limit screw to see if that lets it shift to little ring?

If no joy, have you tried disconnecting the cable from the FD to see if it then shifts to little ring?

It looks like an awfully small radius run-around at the bottom. Is it perhaps missing a pulley down there? What exactly is the cable wrapped around at the bottom of the run?

Yeah likely a '92 based on the LX derailleurs; looks like the '93 had an XT RD.

No joy with the FD as it will not shift down even with the cable disconnected.

Yeah there probably was a pulley there at one time but now all I have is the cable wrapped around a screw. I bought the bike around 2 years ago and this is how the bike came to me.

Maybe I need to try to track down a pulley. I guess I'll visit the local hardware store to see if I can find something that will work. Any idea of something that might work?

That will be a non-issue though if I can figure out a way to mount a top pull FD.

You also need to unscrew the inner (low) limit screw. Yours looks like it's screwed almost all the way in. With cable off, you should be able to watch the FD move inward as you unscrew the limit screw. With the chain on big cog in back, and little ring in front, unscrew it until the chain no longer rubs on the inner plate of FD. You may want to go a quarter turn past where it stops rubbing. Then screw the barrel adjuster on the shifter all the way in, then back out about a half turn, then attach cable. Don't pull the cable overly taught if you pull it really taught upon attachment, FD won't shift into small ring. If cable is too loose upon attachment, unscrew the shifter barrel adjuster as needed.

So I think you're right and the lack of a pulley is the source of the problem. The FD doesn't shift down as far as it should with the cable disconnected (I think the spring is weak) but it will shift far enough down to shift to the small chain ring.

The limit screw and cable tension are fine and not the source of the problem.

I'm not sure where to find a pulley though but maybe the local hardware store has something that could work.

https://cimg2.ibsrv.net/gimg/bikefor...75b3c480ee.jpg

Is the bolt right between the chain stays? How much room is in there?

Here are a couple of pulley options:

https://www.jensonusa.com/Problem-So...m-Cable-Pulley

https://www.ebay.com/i/273139871279?...hoCnvgQAvD_BwE

https://cimg4.ibsrv.net/gimg/bikefor...f06def85d5.jpg
So I think you're right and the lack of a pulley is the source of the problem. The FD doesn't shift down as far as it should with the cable disconnected (I think the spring is weak) but it will shift far enough down to shift to the small chain ring.

The limit screw and cable tension are fine and not the source of the problem.

I'm not sure where to find a pulley though but maybe the local hardware store has something that could work.

You might also look at the alignment of your derailer. The picture may be distorted but it looks like the tail of the cage is slightly inboard. This could cause your problem.

Yes, you need that pulley at the bottom. Alternatively, you could add a cable stop on the seat tube using this from Problem Solvers. You’d need a top pull derailer but the routing would be better especially since you seem to be missing the pulley.

Good call on the cable stop, thank you. Yeah I agree that a top pull FD is likely to work better but I'm not sure if the MTB FDs which I think are dual pull will work with 46/36/24 rings. I don't believe--and I could be wrong--that the road type triple FDs are top or dual pull.

The clamp diameter should be stamped on the inside of the clamp.

https://www.ebay.com/itm/1-set-Foldi...edirect=mobile

The problem solvers pulley is 27 mm wide which is far too wide for this bike as the space between the chain stays is 20 mm. The ones that @curbtender linked to on eBay look good but they are too wide as well at 23.3 mm (assuming the info on ebay is right). @LesterOfPuppets was right on the money on this.

https://problemsolversbike.com/produ...pulley_-_24765

Solution 1 is to take it down to the bike shop to see if they have a pulley that works.

Solution 2 would be to get a problem solvers clamp with a pulley like this

https://www.modernbike.com/problem-s...ley-31.8-black

Solution 3 would be to follow @cycocommute's suggestion and get a seat tube cable stop. I like this this one because I think it will end up being less of a kludge but I'm not confident that a modern MTB FD with dual pull with handle my chainrings.

It really shouldn’t be an issue. You are really only asking the derailer to move the chain on a slightly larger chainring. There are lots of comfort bikes out there using MTB derailers on 48 tooth chainrings.

Trek may have fitted a pulley on a bracket to get it above the stays, or possibly on a spacer to get it back far enough to fit.

This guy has been selling these for years if you are looking for a stop...
https://sfbay.craigslist.org/sby/bop...994558854.html

Misc Bolts and Small Parts - $1 (san jose north)

can you just run that FD as a bottom pull by rerouting the cable ? the top pull does not look like a smooth shifting set up.

Mark Petry
Bainbridge Island, WA USA

It was set up as a bottom pull but I'm missing the pulley. The aftermarket pulleys I've seen are too large to fit within the chain stays. So the simplest choices are (1) a 31.8 cross clamp with a pulley (this way I stay with a bottom pull FD) or (2) go with a top pull FD and buy a clamp with a stop for the cable housing to fit on the seat tube.

I reckon this will work a bit better with a top pull FD as the cable run will be cleaner but either option should work.

Not sure on sizes, but maybe you could use a sewing bobbin.

I am shifting a 42/32/22 crankset with an Alivio FD-M410, and it worked fine when had I put on a 46 tooth chainring; I removed it only because I preferred the lower gearing.

First make sure the existing derailleur is not binding due to corrosion, dirt, etc. -- it's rare for modern FD springs to weaken.

There's a fourth & simpler solution for this setup:
Run housing directly to the anchor on the FD (with some slack from the stop on the top tube -- probably enough slack as-is) and let the inner cable slide past the anchor bolt while the housing ferrule presses on the top of the anchor. Don't tighten the anchor bolt. Then anchor the inner with the lower bolt.

You mean run the FD as a top pull? It's not designed to be a top pull but I like the idea. It's cheap!

I hear you guys and I think that's the solution I'm going with (top pull FD and a cable stop for the frame). This will make for a cleaner cable run and that should help the FD.

But a lot of the MTB FDs are rated to 40 teeth, right? This shimano alivio is rated to just 40 teeth:

https://www.amazon.com/Shimano-9-Spe.../dp/B00OZPPC72

I'm not saying it won't work with a 46 tooth chainring; I'm just saying I'd rather not be the guinea pig on this one.

Here we go

https://www.bikeforums.net/bicycle-m...o-fd-m591.html

Post 11 talks about how modern MTB FDs are made for 12 tooth jumps and may not work right with a triple with 10 tooth jumps. Some of the reviews of the Deore FD on Amazon make the same point.

So this may be a different reason to stick with a bottom pull road type FD on this set up as I'm running 46/36/26 rings.

No. The housing pushes so it's a "top push" which is the same as bottom pull, only with a cleaner cable run in this case.

One more option for your pulley if you go that way.

https://www.ebay.com/itm/Sturmey-arc...kAAOSwhL9c6z5c

Perhaps but go looking for older front derailers. There are a ton of them around on Fleabay. Go with the ones further down the line (lower than XT) because those are far easier to set up and far more forgiving.