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7 speed Dura-Ace with 8 speed wheel?(4 posts)

7 speed Dura-Ace with 8 speed wheel?coolie
Jul 11, 2001 2:08 AM
Been having drivetrain problems with building up an older frame. It currently has a Dura-Ace SL-7402 7 speed SIS downtube shifters and a D/A RD-7400 rear derailleur. The dropout spacing on the frame is designed for 7 speed but I picked up a newer 105 8 speed wheel with 8 sp. cogset. The frame only needs to be spread 1 mm every time I put on the rear wheel, so it isn't a big deal. Shifting only works cleanly in friction mode, which also isn't a big deal to me.

The problem is that I can't get on the largest cog. Also, the derailleur cage rubs the largest cog when the chain's on the second largest cog. I played with the B-tension, but it's not enough to fix it.

Is the 8 speed rear wheel incompatible with my shifter/derailleur combo? Is it possible to get an 8 speed downtube shifter that will work in indexed mode with the old RD-7400 (so maybe indexing is a big deal...)?
re: 7 speed Dura-Ace with 8 speed wheel?Rusty Coggs
Jul 11, 2001 7:10 AM
You need DA 8 speed downtube shifters to work with the DA rear derailer. The 9 speed DA barends or any shimano 9 speed STi will also work with the 7400 rear derailer to shift a shimano 8 speed cogset. Did you reset the low limit screw to permit shifting to the 8th cog. Are you adjusting the 'b' tension correctly. The DA RD is speced for 26 teeth max rear cog but will probably handle a few more.
re: 7 speed Dura-Ace with 8 speed wheel?coolie
Jul 11, 2001 12:09 PM
Woops, looks like I hadn't played with the low limit screw to its fullest extent. It now shifts on to the biggest cog, but it's not at all clean. The top jockey wheel is way too close to the cog (26T biggest) despite the B-tension being cranked all the way (for sure this time).

I've read that the DA shifters and derailleur use less cable pull than other systems. Won't that bugger up the shifting because of the non-DA cogset, which I assume would have wider spacing than DA stuff? Also, if I were to somehow find 8 speed DA DT shifters, would it index properly?

re: 7 speed Dura-Ace with 8 speed wheel?Rusty Coggs
Jul 11, 2001 12:42 PM
Non DA cogset has nothing to do with it,8 speed DA cog spacing is the sme as the other 8 speed. its the combination cable pull/dererailer throw that is unique.8 speed DA downtubes will work fine. My old DA shifts to an 8 speed 26 cog just fine.9 speed barends will work just fine, and will mount on your brazrons.. you will have an extra click which would correspond to the non-existant 9th cog.I often see suitable shifters in the classifieds here.