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Suntour Mountech FD Won't Shift to Smallest Chainring

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Suntour Mountech FD Won't Shift to Smallest Chainring

Old 04-12-21, 07:43 PM
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Rooney 
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Suntour Mountech FD Won't Shift to Smallest Chainring

I've had this Suntour Mountech front derailleur (bought NOS) on my bike since the beginning of the year and I've been wrestling with it most of that time. I'm running a 46-36-26 triple. The shifts between the 46 and 36 are fine, but whenever I try to go down into the 26, it never wants to shift. The cage is parallel to the rings and set as close to the 46T chainring as possible. When I have the bike in the stand, it shifts from 36 to 26 without hesitation but won't while I'm out riding. Any ideas? I feel like the low limit screw is set properly because it works in the stand. Should I ride around and let it out little by little until I get the shift to happen? Thanks!
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Old 04-12-21, 08:09 PM
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I would.
I often find I have to adjust a click or 2 on the barrel adjuster from stand to road.
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Old 04-12-21, 08:22 PM
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I have a Mountech shifting a 22-34-45 (slightly wider gaps than yours) on my oddball Cimarron and it works acceptably. You can see I had to get the cage really close to the largest ring. It's been a while since I had to mess with it but I might have had to tweak the inner and outer plates of the cage.
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Old 04-12-21, 08:30 PM
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thumpism — I can't get mine mounted quite as low as yours due to the RD cable being routed along the top of the chainstay. I have the FD as low as it can go while clearing the shifter cable. It's reassuring to know the jumps shouldn't be a problem. It's too late to tinker today, but I'll get to it tomorrow or Wednesday.

I'm realizing I failed to mention it's friction shifting using Suntour Barcons.
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Old 04-12-21, 08:41 PM
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That pesky cable routing would do it.
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Old 04-13-21, 05:02 AM
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Is the 36t ring worn at all?
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Old 04-13-21, 09:06 AM
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I always set the low limit screw as the first step and leave it alone. I have never had to readjust it to be able to make a shift.
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Old 04-13-21, 09:49 AM
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Does it shift from the 36t when you are in the lowest cog?

Can the cage be adjusted any closer to the seat post?

Also, exactly parallel to the chainring sounds good on paper, but in reality it might not be the best for every situation.

John
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Old 04-13-21, 10:58 AM
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And the not mentioned pedal pressures affecting the tension on the chain's upper run being the biggie issue for so many riders. Chain side to side flex (not really a measurable aspect) and chain ring tooth profiles (wear and symmetrical vs ramps and pins) are also factors.

Ft ders have improved WRT the cage plate surface contours, inner/outer plate curvatures and heights and overall cage/body stiffness. The Mountech is a rather "basic" design regarding the above aspects. I have test fitted a few ders on the same bike many times to find the best one for that bike's set up. Unfortunately ft shifting is far less black and white then the rear end is. The bottom line is to experiment with all the aspects that you can and try other ders if still not happy.

BTW one can reroute the cable to a below the BB shell/stay path is really wanted. An under BB cable guide is easy to install and chainstay clamp on casing stops are around for the looking. I won't say that the small amount of lowering the der will make a big difference though and that sometimes the up shift can become problematic with the cage too close to the large ring teeth tops. Andy
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Old 04-13-21, 07:23 PM
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The cage won’t shift regardless of which cog the chain is on while riding. It’s an old Sugino AT crankset and rings (on an 85 Schwinn Voyageur SP, so all older parts), so there could be wear. I’m not near the bike until tomorrow afternoon, but wear could certainly be a factor.

It’s seeming like I should start with letting out the low limit screw. There’s still room so I’ll start there and report back tomorrow.
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Old 04-14-21, 04:38 PM
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I had a chance to mess with the derailleur today:

The low limit screw was, in fact, maxed out. I tried re-aligning the cage next and realized the outer plate angles in from back to front. Next, I set the inner cage plate parallel to the chainrings, and shifting between the middle and low rings improved, but shifting to the big ring suffered. I played with the angle some more and got pedal strike at the outside rear corner of the cage, then did some more adjusting, and it sort of shifts between all three. I'm a bit tired today, so I called it quits before messing anything up too bad. I'll play with it some more tomorrow.
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Old 04-14-21, 07:27 PM
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Just on passing, what chain are you using?

Not that it is a problem, but if you are running a narrower chain, it might be just enough that the wider derailleur cage can’t quite move it enough, especially since it is now happening on both ends of the shifting.

John
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Old 04-15-21, 02:50 PM
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It’s a 5/6 speed chain. After posting last night I watched a couple videos and one said to set the outside plate parallel to the chain rings vs. the inside as I did. I tried it before going to bed but it was too dark out while riding to see if there was any improvement. Today, I took it around the block and am happy to say I now have access to all 15 gears. It seems it was a combination of lowering the derailleur as much as I could, then rotating the cage slightly.
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Old 04-16-21, 01:09 AM
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If more travel to the inside is essential it might be possible to grind the body of the front derailleur where the inner limit screw strikes so that there is less metal and the screw can be backed out even further, allowing the cage to move just a little further before hitting a stop. Might be worth a try. I have not looked at my Mountech to see if this is possible but I have done it on a different derailleur.

'Net photo.

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Old 04-16-21, 02:34 AM
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been a while since they made that thing, spring tension could be weak,

i remember having to ease off pedal pressure when shifting the 84 stumpjumper into low, so you kind of have to plan ahead and get into gear before the grade gets too steep.

make sure all the bushings are clean , work the derailleur with your hand and see if it feels like tight bushings

most of the time those things work great, got one on the road bike, you shift the lever an ka-chunk, your in gear with no need to trim cage for rubbing,

kind of a long shot but it happened to me, down tube came loose in bottom bracket lug, so when i sat on the bike, cable tension increased, good thing on the routing, that cable kept the frame together til i got home.

IIRC there was a derailleur way back when that had two cables, so one cable was for getting into the big ring, and the other forced you into the small ring, this was to solve the exact issue you are having, it was a flop that only lasted a few months, forget the name of the thing,

Last edited by cjenrick; 04-16-21 at 02:45 AM.
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