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Front Derailleur for 1984 Stumpjumper Sport - 68* Seat Angle

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Front Derailleur for 1984 Stumpjumper Sport - 68* Seat Angle

Old 07-27-15, 09:20 AM
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Front Derailleur for 1984 Stumpjumper Sport - 68* Seat Angle

I'm having difficulty shifting down to the smallest chainring on a triple and I think it's because the shape of the cage of the Deore XT triple I have currently isn't the right shape. Would a contemporary Deore work or need I seek out a vintage appropriate front derailleur with the right shape to the cage? If the latter is the case what should I be looking for?
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Old 07-27-15, 09:37 AM
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You do not say how you reached the above conclusion, and the fact that you include the seat tube angle (which is irrelevant) leads me to believe you are guessing as to the cause. First make sure you have completely followed the correct procedure for both positioning and adjusting the front derailleur (parktool.com/blog or sheldonbrown.com are good sources). Once you've done that we need a better description of what "difficulty" means, as well as when the problem started and if anything significant occurred (accident, part replacement, maintenance procedure) just prior to the problem arising.
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Old 07-27-15, 09:37 AM
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go down range I expect XT is for a more NORBA competition MTB frame geometry like a 73 seat post angle.

I've been using a Deore I got 17 years ago on my old stumpie . (48,36,24t chain ring set)

another approach involves adapter bands to braze on FD
(which mtb builders dont use and so road triple FD will be all you find in braze on style)

but the interface is useful to the adapter band to rotate the FD relative to the adapter and seat tube
with wedges you make and place between those 2 parts.

Actually the FD cages use the Plane described by the disc that is the chain ring as much as the size(diameter)

will it down shift with the cable un hooked?
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Old 07-27-15, 10:47 AM
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Originally Posted by cny-bikeman View Post
You do not say how you reached the above conclusion, and the fact that you include the seat tube angle (which is irrelevant) leads me to believe you are guessing as to the cause. First make sure you have completely followed the correct procedure for both positioning and adjusting the front derailleur (parktool.com/blog or sheldonbrown.com are good sources). Once you've done that we need a better description of what "difficulty" means, as well as when the problem started and if anything significant occurred (accident, part replacement, maintenance procedure) just prior to the problem arising.
ST angle is relevant.

FD is proper.

Cable tension is plenty slack in lowest position.

The "difficulty" is that it won't shift to the smallest ring without first shifting into the larger chainring. 48-36-24 combo.
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Old 07-27-15, 11:41 AM
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I always found the granny shifting on the old bikes to be crap. Won't shift under any load, always takes planning. On my 86 Cannondale I took the large ring off so I could lower the derailleur as far as possible. That helped a lot. Is your derailleur height set correctly?
Make sure the chain is sized properly. Make sure you are shifting when the chain is on the larger rear cogs. You could try a middle chainring with ramps and cut teeth - although I would expect that to help more with upshifting. Make sure your limit is set as far in as possible without falling off to the inside.
Make sure you shift with authority since I assume it is friction.
I wouldn't expect the derailleur itself to make much difference on the downshift since the more or less flat side of the derailleur is doing the work.
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Old 07-27-15, 11:44 AM
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Originally Posted by Slash5 View Post
I always found the granny shifting on the old bikes to be crap. Won't shift under any load, always takes planning. On my 86 Cannondale I took the large ring off so I could lower the derailleur as far as possible. That helped a lot. Is your derailleur height set correctly?
Make sure the chain is sized properly. Make sure you are shifting when the chain is on the larger rear cogs. You could try a middle chainring with ramps and cut teeth - although I would expect that to help more with upshifting. Make sure your limit is set as far in as possible without falling off to the inside.
Make sure you shift with authority since I assume it is friction.
I wouldn't expect the derailleur itself to make much difference on the downshift since the more or less flat side of the derailleur is doing the work.
Yes, I've done all of the above except a middle chainring with ramps and pins.
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Old 07-27-15, 12:41 PM
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Since the FD mounts to the seat tube, it's going to "rotate" with it if you slacken or steepen the angle. I don't think STA is contributing much, if at all, to this issue.

Isn't Deore XT what came on this bike, anyway? What generation is your FD?

Which cog are you in when trying to shift down to the granny? If you're in one of the smaller ones, the chain angle will make it reluctant to shift down from the middle ring, and I can see how you'd need the "running start" of shifting from the big ring.
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Old 07-27-15, 01:00 PM
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I think that bike was equipped with Suntour Mountec.
Specialized Specs

What's the model# of the Shimano FDER you are trying to use?
Size of your rings?

Shimano sell FDER's for STA's of 63-66 & 66-69, so apparently THEY think it matters.
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Old 08-02-15, 11:59 PM
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Me seem to remember the original ft. der. on Stumpies was a SunTour "Mountech". Maybe search Ebay for one of those ? They usually go for cheap.
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Old 10-28-15, 07:25 PM
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Originally Posted by ThermionicScott View Post
Since the FD mounts to the seat tube, it's going to "rotate" with it if you slacken or steepen the angle. I don't think STA is contributing much, if at all, to this issue.

Isn't Deore XT what came on this bike, anyway? What generation is your FD?

Which cog are you in when trying to shift down to the granny? If you're in one of the smaller ones, the chain angle will make it reluctant to shift down from the middle ring, and I can see how you'd need the "running start" of shifting from the big ring.
Front derailleurs tried:

Shimano FD-M730
Shimano FD-CX70

It won't shift down to the inner ring in any cog, even without tension on the front derailleur. 14-32 5-speed Shimano freewheel.
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Old 10-28-15, 07:44 PM
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Originally Posted by Wheels Of Steel View Post
Front derailleurs tried:

Shimano FD-M730
Shimano FD-CX70

It won't shift down to the inner ring in any cog, even without tension on the front derailleur. 14-32 5-speed Shimano freewheel.
Hmm, that's confounding. I'm not suspecting a too-short BB, as I would expect the granny to grind on the chainstay before it would be out of reach of the FD, especially on an MTB. And I assume you tried letting out the low limit screw until it no longer made a difference... perhaps someone else has an idea?
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Last edited by ThermionicScott; 10-28-15 at 07:50 PM. Reason: too slow on the draw!
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Old 10-28-15, 08:02 PM
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Originally Posted by ThermionicScott View Post
Hmm, that's confounding. I'm not suspecting a too-short BB, as I would expect the granny to grind on the chainstay before it would be out of reach of the FD, especially on an MTB. And I assume you tried letting out the low limit screw until it no longer made a difference... perhaps someone else has an idea?
Yes. Plenty of chainring clearance at the chainstay. Stock BB was 68x135. Replaced with 68x127.5, which improved chainline.
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Old 10-28-15, 08:44 PM
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Can we assume that the chain is new, too? Worn ones are more flexible laterally, so may hang on to the gear they're on rather than shifting.

(Sorry if that sounds condescending, grasping at straws now. Wish I could see and put my hands on it in person. )
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Old 10-28-15, 09:13 PM
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Originally Posted by Bill Kapaun View Post
I think that bike was equipped with Suntour Mountec.
Specialized Specs

What's the model# of the Shimano FDER you are trying to use?
Size of your rings?

Shimano sell FDER's for STA's of 63-66 & 66-69, so apparently THEY think it matters.
I was about to say Suntour Mountech fd, and you beat me to it.
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Old 10-28-15, 10:03 PM
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Does the front derailleur guide the chain onto the granny ring when there's no cable attached?
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Old 10-28-15, 10:20 PM
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How about a photo from above of the FD cage and chain when the FD is trying but failing to shift to the granny.
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Old 10-29-15, 08:04 AM
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The limit screw is not preventing full movement?
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Old 10-29-15, 10:43 AM
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Originally Posted by ThermionicScott View Post
Can we assume that the chain is new, too? Worn ones are more flexible laterally, so may hang on to the gear they're on rather than shifting.

(Sorry if that sounds condescending, grasping at straws now. Wish I could see and put my hands on it in person. )
Yes, new chain. SRAM PC-951. I'd like to avoid picking up another derailleur as I've already tried two tried and true FDs. Again, with no tension on the front derailleur the chain will not shift to the smaller chainring in any gear in back. FD outer cage plate is parallel with outer chainring. 2 mm of clearance or so above outer chainring. Still at a loss.
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Old 11-04-15, 07:49 PM
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The only solution I can come up with to marginally improve the shifting in the front is to replace the middle chainring with one that has ramps and pins. This is a class B solution in my opinion. Other thoughts?
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Old 11-04-15, 08:00 PM
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Originally Posted by Wheels Of Steel View Post
Front derailleurs tried:

Shimano FD-M730
Shimano FD-CX70

It won't shift down to the inner ring in any cog, even without tension on the front derailleur. 14-32 5-speed Shimano freewheel.
I can nearly guarantee you that the issue is your use of a 9 speed chain with a 7/8 speed front derailleur (the FD-M730). The FD-CX70 is a double FD so it is not surprising that it won't derail a chain from the middle ring either.

I once tried setting up a vintage Cannondale road bike with a new Shimamo compact crank which needed a 9 speed chain. For the life of me I couldn't get the thing to consistenly down shift. Swapped the FD for a 9 speed version and problem instantly solved.

In your case, the cheapest fix is an 8 speed chain unless your crankset needs a 9 speed chain.
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Old 11-04-15, 08:58 PM
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Originally Posted by joejack951 View Post
I can nearly guarantee you that the issue is your use of a 9 speed chain with a 7/8 speed front derailleur (the FD-M730). The FD-CX70 is a double FD so it is not surprising that it won't derail a chain from the middle ring either.

I once tried setting up a vintage Cannondale road bike with a new Shimamo compact crank which needed a 9 speed chain. For the life of me I couldn't get the thing to consistenly down shift. Swapped the FD for a 9 speed version and problem instantly solved.

In your case, the cheapest fix is an 8 speed chain unless your crankset needs a 9 speed chain.
I like your thinking. Interesting because I'm using the FD-CX70 FD on another bike with the same chainring configuration and similar Q factor cranks and it works better than a 9-speed Deore XT FD. The tail of the CX70 is much closer to the chainrings than the tail on the M730.

Back to it...
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Old 11-05-15, 11:22 PM
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9-speed chain replaced with 8-speed chain. No improvement. Again I find myself at a loss.
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Old 11-09-15, 11:42 AM
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bump
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Old 11-09-15, 11:47 AM
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What shifters again? (maybe I missed this earlier)

Have you tried a new middle ring/crankset? A heavily worn middle ring could want to hang onto the chain enough so that it won't easily derail down to the granny. Clear, close-up pics of the area could help this diagnosis.
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Old 11-09-15, 11:51 AM
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I think the Mountech was reversed .. High Normal from the return spring, cable pulls it into Low .

They were from that same Mid 80's era..
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