Manipulating a 7-speed freewheel
 

Asking to see if this is a possible solution.

I'm building up an old (1988) Miyata 312, and I'll be using a set of wheels that has a Shimano 7-speed freewheel (126mm spacing). I'll also be using an 8-speed Tiagra brifter on the bike. I understand the problems with the difference in spacing between the shifter and freewheel. That combination seems to work well for some and just so-so for others. I'm wondering if it would be possible to replace the spacers between the freewheel cogs with ones that would allow the 8-speed to smoothly match up? I know I'll have to set the limit screws to block the one extra click on the Tiagra. But can I improve shifting by swapping in different spacers?

Thanks for any advice!

My guess is that you'll quickly find the pyramid shape of the freewheel bodies to be frustrating to work with, but it might work.

There are, of course, 8 speed freewheels, but that might require changing the dishing, or going to an off-center rim. Or, perhaps using an 8 speed freewheel as a donor.

Any chance of using a 7-speed freehub, and building a cassette, 7 of 8 (for 8-speed) or 8 of 9 (for using 9-speed parts)?

Clifford, thanks for the input and other possibilities. Anything is possible at this point. The actual measurement between the drpouts is 128mm, so I could easily squeeze in a 130mm hub with an 8-speed cassette. There are a couple pretty solid deals on the local craigslist for wheels that would work, so that might be an easier way to go. But I can pretty much try anything that isn't too expensive.

Is your frame steel? If yes, you could respace the dropouts to 135mm. Not that hard to do. Just need some ingenuity to execute the surgery. There are some videos on youtube showing this with some homemade tools.

I did this before on an Omitaya Sogno 111. 130mm 6 speed to 135mm 8 speed.

I have contemplated trying this with a freewheel since I have done this with a cassette.

With a cassette, I just sand the plastic spacers down, or use 8 speed cassette spacers. The same can probably be done with a freewheel, but as already noted above, you have to work off of the freewheel body shoulder that separates the lowest (larger) cogs from the middle and highest (smallest) cogs. I think there are 3 cogs and I believe 3 spacers that need to go from 3.15mm to 3.00mm (the rest of the spacers also have to go to 3.00mm). Even if you use donor spacers, you will need to place a .5mm spacer behind the last cog so you can keep everything tight. Finding that spacer will be the hard part. Depending on being able to get the lock ring tight, you may also need a spacer between the lock ring and the 1st cog. It may be more work than it is worth.

Sachs Aris makes an 8 speed freewheel that can be converted to 7 speed by removing the first cog, but I don't know what cog spacing is used. I have one and haven't got around to measuring it, but I'd be surprised if it wasn't a 7 speed freewheel body with the cogs spaced at 7 speeds.

John

One thing that may be doable is to leave the last 3 cogs as they are and only reduce the spacing on the first 4 cogs. You will be a little off on the lowest cog, but the rest will probably be fine.

However, breaking open a current freewheel to remove cogs may not be that easy. Older freewheels just required unscrewing the small cog. The new ones have lock rings. I once made a tool to work with the Sunrace lock ring, but the new ones are on too tight. I haven't tried to remove a current Shimano lock ring.

I still run freewheels on a couple of bikes and as much as I'd love to try it, it is even too much time and effort for me. So I run down tube shifters and 7 speed triggers and call it a day.

I will one day re-space a Dura Ace 7700 cassette hub to fit my 126mm Cannondale dropouts. I already have the wheels waiting for me to get around to it.

John

my advice is to give up on modifying the freewheel, and go find a cassette hub/wheel that will accept an 8 speed cassette.

i'd search the local community bike shop, or Craigslist, for a decent used 8 speed wheel and cassette.... and then recenter the hub /wheel to 130mm O.L.D. (Outside Locknut Dimension), or even the 128mm your frame has... and even an aluminum frame can be reset a couple of millimeters...... steel frame ? no problem resetting it to 135mm.


freewheels have specific sprocket thread diameters that are not the same as a cassette, btw... so the spacer rings from a cassette will not fit.

used cassette wheels are about 25 bucks and up, depending on quality...

Connecting an 8 speed shifter to a 7 cog freewheel will be a problem. RD shifters have to match RD cogs. I would just punt and go find a cheap 7 speed brifter. Microshift has them for around $45 - $50. But, it takes a long long time for them to arrive (from China).

The 126mm rear dropout spacing and 130mm rear dropout spacing have nothing to with it.

Cog spacing between 7 and 8 speed Shimano freewheels/cassettes are identical. You can freely use 8sp shifters with 7 speed cassettes/freewheels.

By the book there is a variance of 4.8mm c-c on 8sp cogs vs 5.0mm c-c on 7sp cogs but effectively that 0.2mm is within the range of the floating top pulley. Treat them as completely interchangeable.

Your Omitaya must be a mountain bike. On road bikes such as the OP's, 6-speed is 126mm and 8-speed is 130mm.

Wow: so much fussing and expensive complicated solutions for a non-existent problem. The difference between Shimano 7 and 8-speed cog spacing is 0.2mm, well within tolerances for indexed shifting.

Try it; set up the derailleur in the middle of the 7 cogs on your new wheel. That way, the cumulative error on the ends of the freewheel is less than 1mm.

I once had to customize the spacing on a Suntour Winner Pro 7-speed freewheel to enable a crazy kludge involving Campagnolo shifters and Simplex derailleurs. Possible with custom spacers, but difficult to pull off. Especially with the latest generation of freewheels with hard to remove lockrings.

Dave Mayer sez:
This is my first choice, since it costs nothing and has worked (with reportedly varying degrees of success) for others. Beyond that, it looks like I have quite a few options.

Thanks for all the input - I appreciate it!

7 and 8 spd spacing are close enough that your 8spd shifter might work as is.

if not, rather than mess with spacers,
you might try fudging the cable clamp on the derailer to very slightly alter the cable pull ratio
ie. clamping the cable slightly inboard/outboard of the groove to make the derailer swing less/more per indexing detent.

ummm_______ .2 mm difference PER GEAR equals.... 1.2mm total misalignment on a 7 sp. cluster, guys... think about that for a moment, ok?

still think that 8 speed shifter will work for a 7 speed cluster?

overshift city... i can see the bent/chewed spokes now..... better install the dork guard.

This is definitely one of my main concerns, but from what I understand, zeroing in on the middle cog of the 7-speed should allow for a total of .6mm of difference on the two cogs at the extremities. I don't know if the whole mechanism has enough latitude to compensate. That's what I'll try first. Plus, I understand that there will be an extra "click" on the shifter - I'll position that extra one one outboard side of the freewheel, away from the spokes. I'm assuming that proper adjustment of the derailleur travel will also keep the chain on the freewheel.

Additionally (and correct me if I'm wrong here), the original freewheel on this frame was a 6-speed and the 7-speed freewheel has been installed. That's the max that a 126mm hub can take from what I understand. Going to an 8-speed hub would push things into the 130mm spacing. As I mentioned earlier, the actual dropout spacing measures 128mm, so if I had to go to a new set of wheels with an 8-speed cassette, I should be able to squeeze it in without doing a cold set.

Mostly, I'm doing all this to learn a bit more about this stuff as well as to make the shifting as smooth as possible. I already have done this to another old bike, but I used the basic Shimano Tourney 7-speed shifters (which are OK, but not as nice as the 8-speed shifters).

Again, thanks for the responses.

If I understand this correctly it is a modification of the alternate cable routing that is needed to run pre-9speed Dura Ace shifters with a non-dura Ace rear derailleur. The alternate routing moves the derailleur more than the normal cable routing. I am running a 910 XTR rear deraileur with Dura Ace levers and it works great with the alternate.

The same principle can be applied to a 8 or 9 speed shifter to a 7 or 8 speed cassette. I have always wanted to test it out, but It would require less cable pull than the alternate cable routing. My gut thinks that drilling a hold through the drailleur attach bolt and run the cable through it like a vintage brake attach might be close, but I haven't actually tried it.

John

If you think 0.2mm per shift less will cause overshifts into the spokes, perhaps you should think about it for another moment, ok? :lol:

you should think about not laughing.
the op has already considered a solution to the extra shift position... you did not. I guess you are the one that needs to think.

and i still advise the OP get an 8 speed rear wheel, as i did above.

the hassle involved with misaligning a chain with almost every shift is immense, and will compound itself via wear and false shifting caused by bumps in the road/trail.

laugh at yourself, scott.

Lighten up, Francis. The "extra shift" problem is solved by setting the RD limits properly, it's barely worth mentioning among people who know what they're doing. Furthermore, people have successfully used 8-speed shifters to index a 7-speed cassette. As posted above, the accumulated error need only be 0.6mm at each end.

Less than a month ago I set up XT 8-speed shifters with a 7-speed hub and 7-speed cassette. Worked perfectly. Didn't even touch the barrel adjuster.

I think too many people post to Internet forums who don't actually work on bikes, with advice on how to work on bikes! Take out your Vernier calipers and set them at 0.20mm, it's an absurdly small variance. Then using that same Vernier caliper measure the float range of a floating top pulley. Enough said. When you're wiggle is on the magnitude of 2.00mm plus you don't fret 0.20mm

My 2 mountain bikes are setup with 7 speeds spaced as 8 with 8 speed shifters. Been running this setup and it works perfectly. The derailleur does not shift into the spokes. Setup is easy, setup in first and rear limit screw is properly set so it stops at 7.

I have not tried 8 speed shifters with 7 speed spacing. Can't imagine I'd be happy with the poor indexing. I'll tweak 1/4 turn on barrel adjuster to dial in shifting so hard to accept built in inaccuracy. Maybe others can accept less than ideal.

John