8 speed cassette fitting issues and options

[ishaw]

First time in a while I've stumbled upon a compatibility issue with retro bits, but here I am.

I'm trying to make a bike complete so I can sell it whole, fully working and ready to ride.

The other night I spent degreasing and fettling cup and come bearings which went well. Today I set aside some time to build the bike.

However, I can't get an 8sp cassette on the freehub. It's a Shimano fh-rm40 which research suggests came in 7sp or 8sp. I'm guessing I have the 7sp (see pics) as I can't get the last cog on the spline.

So, what are my options as the intended gearing is 8sp.

Is it possible to simply switch out the 7sp freehub for an 8sp? If so, what Shimano ones are compatible? I'm sure I must have some Shimano hubs kicking about I can pillage from. Do I need longer axle or worse like a reddish? I'm hoping to avoid anything too time consuming as I need to clear a lot of stuff fast due to renovations and less space afterwards.

Assume it's an Allen key through the hub to remove? Been a while since I've played with anything that wasn't hope or just pulls apart.

Rather annoying as I had the hub spinning perfectly after the service.

Any help gratefully received

 

[Twozaskars]

First time in a while I've stumbled upon a compatibility issue with retro bits, but here I am.

I'm trying to make a bike complete so I can sell it whole, fully working and ready to ride.

The other night I spent degreasing and fettling cup and come bearings which went well. Today I set aside some time to build the bike.

However, I can't get an 8sp cassette on the freehub. It's a Shimano fh-rm40 which research suggests came in 7sp or 8sp. I'm guessing I have the 7sp (see pics) as I can't get the last cog on the spline.

So, what are my options as the intended gearing is 8sp.

Is it possible to simply switch out the 7sp freehub for an 8sp? If so, what Shimano ones are compatible? I'm sure I must have some Shimano hubs kicking about I can pillage from. Do I need longer axle or worse like a reddish? I'm hoping to avoid anything too time consuming as I need to clear a lot of stuff fast due to renovations and less space afterwards.

Assume it's an Allen key through the hub to remove? Been a while since I've played with anything that wasn't hope or just pulls apart.

Rather annoying as I had the hub spinning perfectly after the service.

Any help gratefully received

How long are the splines as per red arrows?

 

[2manyoranges]

First time in a while I've stumbled upon a compatibility issue with retro bits, but here I am.

I'm trying to make a bike complete so I can sell it whole, fully working and ready to ride.

The other night I spent degreasing and fettling cup and come bearings which went well. Today I set aside some time to build the bike.

However, I can't get an 8sp cassette on the freehub. It's a Shimano fh-rm40 which research suggests came in 7sp or 8sp. I'm guessing I have the 7sp (see pics) as I can't get the last cog on the spline.

So, what are my options as the intended gearing is 8sp.

Is it possible to simply switch out the 7sp freehub for an 8sp? If so, what Shimano ones are compatible? I'm sure I must have some Shimano hubs kicking about I can pillage from. Do I need longer axle or worse like a reddish? I'm hoping to avoid anything too time consuming as I need to clear a lot of stuff fast due to renovations and less space afterwards.

Assume it's an Allen key through the hub to remove? Been a while since I've played with anything that wasn't hope or just pulls apart.

Rather annoying as I had the hub spinning perfectly after the service.

Any help gratefully received

Yep it’s a strip down.

BUT first, grab an 8spd HG freehub body (can be on wheel) and indeed measure up in the manner 2Zs suggests.

Then….

Strip down. Axle and bearings out.
Then 10mm allen key to undo hollow bolt inside freehub.
May need a big extension bar on the allen key - do it by whatever cobbled system you can rig.
I use 10mm socket onto allen key with long breakers’ bar
Then on with 8spd freehub HG body.
Reverse assembly.

Final thought - I don’t think that the 8spd body is longer than the 7speed. It’s just more recessed at the spoke end.
BUT I seem to remember Sheldon Brown mentioning that wheel dish can be an issue with early 7speed. Is your dropout spacing 130 or 135? It’s the case that 8-10 is entirely cross compatible. Seven is not.

 

[FluffyChicken]

Once upon a time you would use a screw in cog to make it 8speed (did this in the turn of the 90s)
iirc a UG 13T cog or similar (they may have done other sizes)
You would need to alter your axle and re-dish as you would a freehub change* (the better option now.)

Honestly with the availability, just get an 8speed hub and rebuild the wheel.
or a whole 8 speed wheel.

*You can look here for the spacers and where they would go, between the 7 and 8 speed

si.shimano.com

si.shimano.com

 

[ishaw]

Preference is to sort existing wheel, it matching the front after all. I could throw odd wheels at it, but that's too easy.

I'm not with hub at the moment but will measure the splines.

Rear spacing is 135mm, so no issues there at least.

I have an lx hub I can take bits off. Will the freehub be compatible? It's a black Parallax hub, 560 series I think?

 

[2manyoranges]

Preference is to sort existing wheel, it matching the front after all. I could throw odd wheels at it, but that's too easy.

I'm not with hub at the moment but will measure the splines.

Rear spacing is 135mm, so no issues there at least.

I have an lx hub I can take bits off. Will the freehub be compatible? It's a black Parallax hub, 560 series I think?

Good that it’s 135 - more space to fettle with.
The only compatibility that rules things out completely is the dish on the static bearing cups in the hub. And the non drive side static cup should be standard across the hubs and the drive side is determined by the freehub. So all good.

The wheel MAY not sit absolutely in the centre of the frame - hence the need for re-dishing. But when I have fiddled with this kind of thing in the past it’s only been a question of a couple of mm and without the need for scalpel like handling by using the bike on the ragged edge or racing, it‘s just not a big issue.

 

[2manyoranges]

Nice vid with high production values and good measurements.

I am not sure about the axle length issue. I think this might be a mix of wheels one from 130 spacing and one with 135 spacing.
If both 135 then axle should be right length but you may need different size spacers on the non-drive side to push the wheel over to rider's left a tad.

 

[Tootyred]

Spindle should be right length if the wheels already 135mm it should be a 146mm spindle. Nearly all 8 speed freehubs from shimano will fit, the only issue is you may need a spacer washer behind it.....especially if swapping from big to small freehub indents (the lugs). SjSc sell these......else the cassette will bind on the hub.

As suggested above, you will need to chuck a spindle washer across fronm non drive to drive to balance it out.

Once the new freehub is on, pop the cassette on and put it in the frame. Your aim is to get it as close to the frame, without the chain hitting...Then tighten the whole thing up. A pile of old spindle spacers really helps for this type of messing about!

Then its just a minor redish as said above.

 

[FluffyChicken]

To above,
I posted the documents above, it's easy to read the size spacers, and hence total space, you need from that as it tells you. No guessing needed.