Bicycle Mechanics - What issues with Shimano to Shimano shift component matching?

I want to convert my old Trek friction/downtube shifting to STI shifters while minimizing cost, so ... keeping the 7 speed rear cassette (or upgrading to 8 if necessary). Already have a 7-speed Shimano 105 rear derailleur in possession. My understanding is that 8-speed shifters will work OK with 7 sp. cassette.

Irregardless of what it takes (e.g. cables, braze-ons, etc.) to actually mount the hardware, can I mix-n-match 7 or 8-speed shifter pairs from 105 up to Dura-Ace with that rear derailleur and likewise can I use a 105 or Ultegra or Dura-Ace front derailleur with whatever STI shifters I end up finding?

Thanks!!:D

I upgraded my Trek 1100 to 8-speed 105, definitely a worthwhile upgrade!

Pre 9-speed Dura Ace is an oddball. You can't mix it with anything else from Shimano. Any Shimano derailer meant for indexed shifters will work properly with any Shimano indexed shifters... EXCEPT for pre-9-speed Dura Ace again.

I dunno about 8-speed shifters working with 7-speed cassette. Can anyone confirm this? By the way, Nashbar makes a generic 8-speed Shimano compatible cassette for about $20, and they work very well for me.

Also, you'll probably want a pair of downtube cable stops which fit onto the downtube shifter braze-ons and provide housing stops for the cables. They look very nice, cover up the unsightly downtube braze-ons, and cost about $10.

I dunno about 8-speed shifters working with 7-speed cassette. Can anyone confirm this?


I've used a SRAM 8 speed grip shift to shift a 7 speed Shimano cassette with a Shimano derailler. If you set up the cable tension with the shifter in the middle and the chain on the middle cog so that the spacing error is evenly spread, it will mostly work, but I never found it very satisfactory. The difference in spacing is 0.2mm between 7 and 8 speed (according to Sheldon Brown). I'd say get the right shifter for the purpose.
Also, going from 7 to 8 speed, I believe is where the jump from 126mm spacing to 130mm spacing happens, so the frame may need to be cold set for this.

I've used a SRAM 8 speed grip shift to shift a 7 speed Shimano cassette with a Shimano derailler. If you set up the cable tension with the shifter in the middle and the chain on the middle cog so that the spacing error is evenly spread, it will mostly work, but I never found it very satisfactory. The difference in spacing is 0.2mm between 7 and 8 speed (according to Sheldon Brown). I'd say get the right shifter for the purpose.
Gotcha. I guess it's kind of like using a Shimano 7-speed cassette w/Suntour 7-speed shifters. I'm doing that on my girlfriend's bike and it's very satisfactory (the 0.2 mm difference is only in the upper 3 cogs, weirdly enough).


Also, going from 7 to 8 speed, I believe is where the jump from 126mm spacing to 130mm spacing happens, so the frame may need to be cold set for this.
Yep, to run an 8-speed cassette you need 130 mm spacing supposedly. However, there's a much simpler alternative: just squeeze the dropouts open by 4 mm to get a 130 mm hub into a 126 mm frame. I've done this on both aluminum and steel frames for now 1000+ miles, with no ill effects!

You'll also need a new/wider freehub body if you're going to run an 8-speed cassette. You can get these for $20 from Nashbar sometimes, they're not too expensive wherever you get them. Need a 10mm allen wrench to remove the freehub body from the hub, and that's after you've taken out the axle (same as if you were overhauling and repacking the bearings with new grease).

OK, thanks to all for the additional info. I know I specified 105 and up, but what about the Sora 7 speed brifters? Seems like the most straightforward upgrade. I'm assuming they will work with the 105 7 speed RD. :o

Gotcha. I guess it's kind of like using a Shimano 7-speed cassette w/Suntour 7-speed shifters. I'm doing that on my girlfriend's bike and it's very satisfactory (the 0.2 mm difference is only in the upper 3 cogs, weirdly enough).

Are you using a Suntour derailler? I've tried using an Accushift barcon on an otherwise Shimano system and it doesn't shift right. Do you know if any Suntour derailler has the correct cable pull or only the matching Accushift one? I'd like to use this barcon on some bullhorns if I could get it to index properly.

OK, thanks to all for the additional info. I know I specified 105 and up, but what about the Sora 7 speed brifters? Seems like the most straightforward upgrade. I'm assuming they will work with the 105 7 speed RD. :o

Any Shimano compatible 7 speed shifter (except old Dura Ace) should work fine.

Sora 7-speed brifters are your best option, or you can track down old 7-speed RSX brifters that have the normal STI lever-configuration.
All Shimano rear deraillers designed for indexed shifting have the same cable-pull ratio (excluding pre-9-speed dura-ace). So you could use a current Ultegra derailler designed officially for 10-speed systems, with 6-speed indexed 105 shifters and freewheel from 1987. Or vice versa. So your rear derailler that came with 7-speed will work fine for 8-speed.

Also, an 8-speed freehub body is the same width as a 9- speed freehub body. In face, 8/9/10 speed cassettes are all the same width and fit on the same width of freehub bodies. 7-speed freehub bodies and cassettes are slightly narrower.

Are you using a Suntour derailler? I've tried using an Accushift barcon on an otherwise Shimano system and it doesn't shift right. Do you know if any Suntour derailler has the correct cable pull or only the matching Accushift one? I'd like to use this barcon on some bullhorns if I could get it to index properly.
Yes, the combination I'm talking about is Suntour derailler + Suntour Accushift shifter + Shimano freewheel (consult Sheldon Brown's page to see that the Shimano freewheel spacing is very close to Suntour).

I've tried combining Suntour Accushift shifters with several different Suntour derailers, and they all seem to work fine! I have a small hoard of spare Suntour stuff myself: 2 pairs of Accushift 7 bar-end shifters, 1 of downtube shifters, 1 long cage RD, 1 short cage RD, various FDs.

I'm SURE there's a way to combine Shimano derailer + Suntour shifter, with a little ingenuity, as in Sheldon Brown's trick for combining old DuraAce with standard Shimano derailer: http://sheldonbrown.com/dura-ace.html#indexing. If my supply of Suntour RDs ever runs out, I'll probably try to cook up such a trick.