MTB derailleur with downtube shifters?

[bychosis]

I've got an old steel roadie (mid 70s) with downtube shifters and currently a Suntour rear mech. I have fitted a modern wheelset with room for 8-9spd and running a 7spd (12-26?)cassette(with a spacer behind it). Currently the old derailleur will not reach far enough in so i am stuck with 6 gears (12-23) on a 7spd cassette. I like the look of the old derailleur and have kept it for aesthetics for now. The lowest gear is a little high for climbing some of the local hills which is fine for shorter rides, but in contemplating Loop the Lake next year would appreciate some lower gearing for a much longer than usual ride (ie at my limits).

I have at my disposal a couple of MTB derailleurs, one SRAM (low end) and one Shimano XT. Does anyone know if either of these would work better than the other? I am aware of the different pull ratio between SRAM and Shimano. The bike is old and for commuting and I like to reuse parts for it rather than shell out where possible.

[high_tea]

I use a Suntour barcon with a Shimano XT rear derailleur. No probs at all, uses most of the cable travel. Easy to adjust too (not bothering has worked great so far ). I've also had good results with the same barcon + Sora, so I doubt the low-end-ness of your SRAM would be a problem. It's just the pull ratio issue, about which I have no clue. How low-end is the SRAM? I gather the real low-end (7-speed?) ones have the same pull ratio as Shimano.

[bychosis]

Not sure about the SRAM, maybe X5 from a few years ago. Gonna have to rummage through the parts bin.

[drubie]

Not sure about the SRAM, maybe X5 from a few years ago. Gonna have to rummage through the parts bin.

You have to be careful with SRAM as a lot of the rear derailleurs run a 1:1 pull ratio so they might not work well with down tube shifters. Use the shimano one. Or perhaps see if you can back out the limit screws on the existing sun tour job, it should work a 7 speed cassette no worries unless it is from the early 1970s

[Wal42]

I was using Suntour Edge (non-indexed) shifters & an Edge RD, was running with a 7 speed shim cassette, worked perfectly, I'm now running shimano 7700 D/T indexed shifters, with Shimano 7700 RD & 9 speed , getting all 9 gears, the 7700 brifters are the expensive bit, you can pick up new 7700 D/T shifters for under $80, get a full setup (9 speed) for around $250.

You just need to fit a later model RD (you could probably tune a 7700 or similar vintage RD to run 7, 8 or 9 speed), with friction shifting Suntour D/T levers.

[bychosis]

Thanks for the replies. I just about took the limit screws out to get it to reach the 7th gear, no luck. I did date the derailleur a while ago hwile trying to date the bike as early 70s (73 I think) I have kept it on due to the looks, and would probably just switch the derailleur short term if required. Shimano it is (later).

[Baalzamon]

I used Shimano 9 Dura Ace bar ends with can be used by downtube shifter. And I had a Shimano SLX M662 Shadow 9sp Rear Mech which was working beautiful with friction shifting