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Shimano 6 speed XT thumbie indexing

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Shimano 6 speed XT thumbie indexing

Old 10-03-12, 05:20 PM
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Niloc
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Shimano 6 speed XT thumbie indexing

Hello all, I've searched the forums and the interwebs for answers to my questions and have not come up with much, so here goes:

I have an old mid-80s Cyclopro mountain bike. It's a nice double-butted steel frame made by Kuwahara, the same folks that made Nishiki. Anyways it's currently the host bike for my Xtracycle, but for a number of reasons I'll be swapping it out and turning it back to a mountain / get-around-the-neighborhood bike.

The bike has mostly Diacompe and Suntour components, and the original rear wheel which I'll be putting back on has a 5 speed Suntour "Perfect" freewheel. I'm not real familiar with freewheels, but what I'm hoping to do is put a Suntour Ultra 6 speed freewheel on it and use an old Shimano 6 speed SiS XT thumbie (the classic M-730 series) I have laying around to index shift it. The bike came with a non-original XT deraileur of the same era so I'm good there.

My question is, will this work? I realize I can put it in friction mode to shift if need be, but I really want the indexing and I don't want to chase down the freewheel if it's not going to work, I'll stick with the 5 speed or maybe consider going for a 7 speed upgrade.

Here's my thinking about why it should work: The XT thumbie has a "phantom" seventh click that apparently lets you use it with the 7 speed cassettes that came along later - I guess Shimano was anticipating? Similarly the 7 speed XT thumbies have a phantom eighth click. Well my understanding is that the cog spacing on for Suntour Ultra 6 speed (not "regular" 6) is the same as the 7 speed that came along later, being slightly tighter than the earlier 5 and regular 6 speeds. That's why an Ultra 6 will replace a 5 speed freewheel without having to respace and redish the wheel and bend the frame; things I'm hoping to avoid. So the 6 speed thumbie should index Suntour Ultra 6 fine. It was originally mated to an early Shimano 6 speed Uniglide freehub, but I don't know what the spacing on those is.

Can anybody shed some light on this bit of bicycle drivetrain arcana?

I guess I could get a new 7 speed freewheel, but then I'll have to respace, redish, spread the frame (or maybe just squeeze it in). And if my thumbie won't work with the Ultra 6 freewheel, then why should I expect it to work with a 7 speed? 7 speed would be hyperglide which would be a plus I guess.

Thanks - Colin
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Old 10-03-12, 09:42 PM
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Probably not. SunTour "Ultra" cog spacing is closer to the Shimano 7-speed cog spacing, but the Suntour spacing isn't equal across all of the cogs. Also, IME, the SunTour freewheel shifting is far inferior to the Shimano twist-tooth shifting.

I would take another look and see if a 6-speed freewheel will fit there. If the rear wheel is 126mm or 130mm OLD, it might fit without any modifications. Harris sells a couple 6-speed Hyperglide freewheels: http://sheldonbrown.com/harris/freewheels.html , as does IRD: http://www.interlocracing.com/freewheels_steel.html

Reference: http://sheldonbrown.com/cribsheet-spacing.html
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Old 10-03-12, 10:53 PM
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Hey Jeff, thanks for the information. I'm guessing the frame is 120mm OLD since it had a 5-speed freewheel as original equipment. I can't measure it right now since it's hooked up to the xtracycle free radical. A 126mm hub might squeeze in there or the frame could be tweaked a little, but if I'm going to go to 126mm, and I have to re-space and re-dish I might as well get a 7-speed hyperglide freewheel at that point. Do you think I'm right in thinking that the 6-speed SiS XT thumbie I have would index that with the "phantom" click?

Thanks for the link to the IRD site, those look like nice units with hyperglide style ramps. A little spendy but if it's my only outlay to do this upgrade not too bad. Hey look what they say about stack height - 5-spd: 29.2mm, 6-spd: 31.5mm, 7-spd: 34.1mm

That 6-spd is pretty close to the 5-spd, so I'm guessing it's using the tighter 7-spd cog spacing? If that 2mm is the only additional width, I'm sure that would squeeze into my drop-outs and no worries about re-dishing. And it would probably work with my 6-speed XT thumbie?

Guess there's only one way to find out.

BTW I have the old wheel from the bike the XT thumbies came off, so I thought about using it, but the cogs are pretty worn and finding 6-speed Uniglide cassettes seems difficult these days. Also the hub bearings sound and feel horrible so I'm afraid the races may be shot. And I kinda want to keep the original rear wheel from the bike going as it matches the front and is in good condition. (even though it would have a non-original rear deraileur and thumb shifter).
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Old 10-04-12, 01:23 AM
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http://sheldonbrown.com/cribsheet-spacing.html

If you scroll down the page to cassette/freewheel spacing, You'll see this:

"Regular" 5-speed 5.3 mm
"Regular" 6-speed 5.3 mm
Sun Tour "Ultra" Freewheel 6-speed 5.0 mm
Sun Tour Accushift XCD-6 6-speed 5.5 mm
Shimano HG 7-speed 5.0 mm

I haven't come across a Shimano 6spd cassette in a while, but I guess it'd be the 5.3mm spacing. You might be able to get your XT shifter/RD to shift a 5mm spacing by clamping the cable a little further from the parallelogram pivot (the one on the arm with the pinch bolt nearest the barrel adjuster). There may be a tabbed washer under the pinch bolt; try messing with it so you can wrap the cable around it so it pivots further from the pinch bolt.

This is worth a shot, cause a 7spd HG freewheel would be a worthy upgrade.
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Old 10-04-12, 10:52 AM
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Originally Posted by Niloc View Post
Hello all, I've searched the forums and the interwebs for answers to my questions and have not come up with much, so here goes:

Thanks - Colin
Sorry Colin: mating some 6-speed SIS thumbshifters with a Shimano rear derailleur and 5.0mm cassette spacing will not work. No matter how you futz around with the cable clamping. The travel of the derailleur will be too much to align with the cog spacing.

And in case anyone is wondering, a Suntour Accushift indexing rear derailleur will travel even further, compounding the problem.

Some 7-speed XT or DX thumbshifters are what you need. Or a 6-speed Shimano freewheel. I would go all-out with the latter solution. The current generation of Shimano Hyperglide freewheels, when combined with a current HG or IG chain shift very very well. Far better than the old Suntour freewheels ever did.
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Old 10-04-12, 11:53 AM
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Thanks Kimmo and Dave. I was hoping that maybe Shimano's 6-spd cassettes were 5.0mm because they were anticipating going to 7-spd and that's why the thumbie also has an extra 7th click. If not I guess the shifter won't work with an Ultra 6-spd or a 7-spd HG freewheel. I don't have a caliper to measure the spacing on the old 6-spd Uniglide cassette, but maybe I'll take it down to the LBS and see if they can tell me.

Judging by the stack height, I'm wondering if the 6-spd IRD freewheels that Jeff linked to above are on 5.0mm "utlra" spacing. Dave, what do you think, are those IRD 6-spd freewheels likely "standard" spacing? Would those likely work with my XT SiS 6-spd shifters? I'm guessing that's why IRD made them. I don't know if stack height is the whole story, but if it only adds ~2mm to my OLD I'm sure that would work with my frame with a minimum of fuss. Harris cyclery has a couple of 6-spd Shimano freewheels, but they smallest cog is 14t and I'd like to get a little lower.

As far as adjusting the pinch bolt on the RD to tweak the shifting, good idea, but that looks like a no-go. The pinch bolt has a slotted (like an oval) shaft to fit snugly in its slotted hole and can't be rotated. There's a machined groove to place the cable in. I suppose if one could grind off part of the slotted portion of the bolt shaft, then the bolt could be placed *slightly* further away from the barrel adjuster on the parallelogram arm. However the cable tension would want to pull the bolt back towards the barrel adjuster end.

Hmm, I've discovered an interesting feature about the XT shifter: there's a means of adjusting the positioning of the shifter unit on the mount that clamps to the handlebar. It can be mounted in one of three positions, as indicated by a little arrow pointing down at three machined dots on the handlebar clamp. You can see these in the attached photo. Do you suppose this feature provides a means of adjusting the amount of cable pulled and therefore what cog spacing it will index with? I can't figure how it would do that but then I'm not as clever as Shimano. Perhaps it just provides a way to tweak the position of the shifter lever on the handlebar for user preference / ergonomics. The left hand shifter for the FD, which is friction only, also has this feature.

Thanks for your input - Colin

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Old 10-04-12, 08:45 PM
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Originally Posted by Niloc View Post

Hmm, I've discovered an interesting feature about the XT shifter: there's a means of adjusting the positioning of the shifter unit on the mount that clamps to the handlebar. It can be mounted in one of three positions, as indicated by a little arrow pointing down at three machined dots on the handlebar clamp. You can see these in the attached photo. Do you suppose this feature provides a means of adjusting the amount of cable pulled and therefore what cog spacing it will index with? I can't figure how it would do that but then I'm not as clever as Shimano. Perhaps it just provides a way to tweak the position of the shifter lever on the handlebar for user preference / ergonomics. The left hand shifter for the FD, which is friction only, also has this feature.

Thanks for your input - Colin

As you surmised, it was a way to adjust the position of the lever relative to the handlebar. 6-speed shifters worked with 6-cog cassettes or freewheels, 7-speed shift levers worked with 7-cog cassettes or freewheels. Shimano did all sorts of things in that era, but you had to match the shift lever with the number of cogs.

(FWIW: I worked in the industry back when those were new. All your questions were asked back then, and the answers have not changed. Mostly.)

I'm pretty sure the IRD freewheels are built to match the "standard" (aka not-Ultra) spacing, which is to say they would work with your 6-speed XT shifters.
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Old 10-04-12, 11:45 PM
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Thanks Jeff and everybody who replied. OK yep I get it and the mechanic at my LBS concurs about the indexing. I could use my XT thumbie with the 5-spd Suntour freewheel currently on the rear wheel since it has the same spacing as 6-spd. Obviously there's one click I wouldn't use. Seems like a big improvement in shifting could be made if I went to a HG freewheel, Shimano and IRD make 6-spd HG freewheels if I want to use the XT thumbie I have with this rear wheel. Or try to eBay a NOS Shimano unit from the 80s. It would be tempting at that point to get a 7-spd freewheel, but then I'd need a new thumbie as well.

Now I do have some questions about stack height and frame spacing.
According the IRD website here's how their freewheels stack up:
stack height - 5-spd: 29.2mm, 6-spd: 31.5mm, 7-spd: 34.1mm
I don't quite understand these numbers, based on multiplying the number of cogs by the cog spacing, i.e. shouldn't 6-spd be the 5-spd number + 5.3mm (the width of another cog)? Does it just have less room on either end of the cogset?

In any case it only adds 2.3mm more than the 5-spd so I'm guessing I wouldn't have to stretch the frame OLD the full 6mm from 120 to 126mm to make it fit, like I would if I went to 7-spd, and I might be able to get away without re-dishing (and weakening) the wheel.

OK that's all for now - Colin
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