Screw on freewheel swap

gregmcc

Hi Everybody,

I have decided to upgrade parts of my (very) old mountain bike, and need some help please.

It has an old Shimano 6 speed screw on freewheel block on the back and want to put on a 7 speed job. Can I just do a straight swap or would I need to change the whole setup?

Hope you can help

Thanks

gclark8

You will need to widen the hub and increase the rear drop-out spacing.

Shifters, may need to be upgraded to 7 speed.

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Cheers,
George.

gregmcc

Thanks George,

Will a 7 speed shifter work with a 6 speed block, I mean could you select the first 6 gears and not select he 7th. excuse the possibly stupid question, but I really dont have any idea.
Cheers
Greg

gclark8

Some will, though 7 speed is cheap, 7/8 are compatible, I use a 8 speed cassete on a 7 speed bike some times.

I do a lot of old 10 speed (2x5) conversions, 7x3 and single speed, so I am adjusting the drop out to suit new hubs on most old steel frames.

__________________
Cheers,
George.

dabac

Probably not that well. According to This site the sprocket spacing differs with 0.5 mm between 5/6 and 7 speeds. That's probably too much for good performance.



You can do that, there's no problem with leaving a position or two empty simply use the range limitation screws on the RD to block out any unwanted movement.
But I can't see the point of it for you, as the indexing in the shifters won't match the spacing in the cassette if you're mixing 6 and 7-speed components.
The only time I can think of when it's useful to block out positions is when youre using stuff with the same spacing but different speeds, as when you're running 8 of 9 sprockets from a Shimano 9 spd cassette on a Shimano 7spd body. Or maybe a Campa 8 shifter + RD on a Shimano 7 spd hub.

I prefer to keep the highest gears and leave the lowest empty in such a set-up. It feels like there's less risk to accidentally shift into the spokes that way.

garage sale GT

You could always spread the frame apart a bit and slap in a modern cassette wheel, though you will have to buy a cassette and a new shifter.

I personally don't think it's certain that you would need to widen the frame to go with the seven speed fw. There seems to be a lot of clearance between the smallest sprocket and the frame on many bikes.

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alfeng

This is actually a straight swap ... the hardest part will be removing the old freewheel.

A SunRace 7-speed FREEWHEEL will fit a frame with 126mm spacing & is RAMPED & has the same cog spacing as a 7-speed Shimano CASSETTE -- a pleasant surprise on all counts since I bought mine sight-unseen in the pre-eBay days through a line-of-text mail-order listing which had no other information. I reckon your frame has either 130mm, or possibly even 135mm spacing, so fitting it really shouldn't be an issue ...

If your frame does have 130mm rear spacing (not uncommon on many of the earliest MTBs ... presuming it wasn't bought from a Wally World equivalent), then you could even buy an 8-speed SunRace freewheel ...

Either freewheel should be in the £10 + shipping price range ... slightly more if you find one at an LBS, of course.

I believe that most of the other freewheels (e.g., Shimano, SunTour, etc.) that you will find in a bike shop will be old inventory from the 80s, and the teeth will not be ramped & the spacing will be traditional (i.e., wider -- nothing wrong with that OTHER THAN the fit issues you're concerned with).

You CAN just set your derailleur to shift across only six of the gears OR if you have thumb shifters, you can probably "toggle" to FRICTION MODE and use all seven gears after you adjust the derailleurs stops ...

FYI. The 7-speed Shimano cassette has essentially the same spacing as a 8-speed cassette, so if you ever want to buy new shifters, you'll be good to go if you opt for (or, can only find OR get a great deal on) a set of 8-speed shifters. Of course, the 8-speed SunRace freewheel has the same spacing as 8-speed cassettes (in case you ever get a new rear wheel OR relace your current rim on a new, Shimano freehub).

BTW. The SunRace "corporation" is the resurrected SunTour (if that means anything to you). Consequently, the ONLY (?) thing that was disappointing about the SunRace freewheel was that it uses a new freewheel "removal" tool that is splined rather than the old SunTour freewheel removal tool. I do not know if the internals (i.e., pawl mechanism, freewheel body, whatever) are SunTour's, or different.