itsneddy

I just picked up a nearly mint, all original 1990 Trek 720. Everything but the tires was original equipment. I would like to update the drivetrain. It has Suntour shifters a Suntour front and rear derailleurs. The freewheel is 7 speed
Shimano HG 12-28 and I believe the chain is Shimano as well. The shifters are really stiff (even after a cleaning and a significant shot of Tri-Flow)) and the front shifter is friction. The crank is a Sakae 48-38-28. I would like to change it over to SRAM twist grip shifters. Will I need to replace the front and rear derailleurs or will the SRAM shifters have enough pull to operate the existing Suntour derailleurs? If I need to change derailleurs, any recommendations? Any/all help will be much appreciated. Thanks!

hokiefyd 

From what I understand about the indexed Suntour stuff, it's slightly different than the actuation ratio Shimano uses, so index shifters designed for Shimano drivetrains wouldn't work perfectly with Suntour drivetrains. You might get it close, but I don't think it'd be 100%. If you want SRAM Gripshift, you could find some SRT models from back in the day (which came on these bikes starting in the mid-90s or so), or you could look at the MRX Comps available new today. You may be able to find indexed thumb shifters compatible with Suntour if you're open to thumb shifters. Then you wouldn't have to change the derailers.

DorkDisk

If you have the shifters, just try them on. The cable pull ratio on Suntour was the same as Shimano, the variance was in the cog spacing. Since you already have a Shimano freewheel, you may be good to go. I've had similar success with older pre-index Suntour derailleurs, Shimano freewheel, and modern Shimano shifters. I have another bike with a Suntour shifter and the rest Shimano that many people say won't index but it does so YMMV.

t2p

seems odd the bike would have a mix of Suntour and Shimano components

A bike equipped with Suntour shifters and derailleurs would typically have Suntour cogs

DorkDisk

Its quite common but not stock; Suntour freewheels are no more but Shimano ones are.

t2p

Vintage Gripshift shifters are often listed on eBay - including the SRT400, 500, and 600 series 7 speed shifters - and many times they are in great shape and reasonably priced

( note: 600 series and possibly 500 series avail in 7 spd and 8 spd )

The lower Gripshift models use a grub screw to attach/tighten the shifter to the handlebar - would not recommend them especially if you have plans to use a carbon fiber or lightweight high-end / thin-wall alloy handlebar (EA70 for example)

I was not a big fan of Gripshift back in the day - preferred Shimano RF shifters - but recently began to appreciate Gripshift shifters because they are reliable and can be found cheap

The original Gripshift grips can be a bit tough on the hands - but cut ESI grips (Chunky or whatever) or similar can replace the outer grip and will improve comfort significantly
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itsneddy

Here is a pic

hokiefyd 

I'm in the same camp. I've replaced every SRT Gripshift set of shifters that I'd come across on my own bikes with other options...but recently bought a '97 GT Vantara and it has SRT400 Gripshifters and...I've left them on. It has an Acera X 3x7 drivetrain (crankset not recalled) and the thing just shifts perfectly in every reasonable combination. In the middle ring, I can traverse the entire cassette with no cage rub...and then up- or down-shift on the front for the additional range when needed. Small-small will drag a little bit, but I don't use that combo. Large-large is also not optimal...but I don't use that either. Middle-all works great. I have a lot of experience re-cabling bikes and adjusting drivetrains, but I just swapped the handlebar to a wider bar and just carried the original Gripshifters with cables over to the new bar. It just works too well for me to want to mess with it!

t2p

SRT 600 front shifter (and possibly 500 ? - can't recall) offer trim positions - but most times not required

t2p

I don't know if Gripshift shifters will work well with this derailleur (?)

Could need to switch to a Shimano derailleur(s) if issues surface after install of the Gripshift shifters - but the bike looks great and would certainly be worth the added cost and the improvement in shifting should be a plus

I was never a fan of thumb shifters - back in the day they were spec'd on three bikes we had and they were switched out immediately

itsneddy

Thank you. I really hate the Suntour thumb shifters. They're really clunky and not very ergonomic. Any recommendation for a Shimano rear D/R?

DorkDisk

You have Xpress under the bar shifters on that bike. Are those the ones you are talking about? They are not thumb shifters. Thumbshifters are sleek and ergo



over bar thumbs

Suntour and Shimano 7sp shifters and derailleurs used very similar actuation ratios, so it should work, but you might still want to run a Shimano derailleur. Suntour used fixed upper pulleys which require very precise setup whereas Shimano's floating pulley was the secret sauce to their superior indexing system, Suntour used a shifter that overpulled. The reason why Suntour and Shimano is not compatible is the cog spacing. At that time, Suntour was considered to have the superior front shifting.

Any 7,8,9,or 10 sp road derailleur will work, just mind the cage length. However, try to avoid the mid 90s rear derailleurs as they had a light spring to not work as well with non-Shimano shifters.

itsneddy

Thank you all! I think I'm going to go with SRAM MRX shifters and a Shimano Acera or Altus rear D/R. That's a long cage, correct? I had a Univega Rover a while ago (late 80s early 9-0s) that I believe had that set up. Which brings me to the front. If I recall, the MRX front shifter has some trim between shifts. Do you think the MRX would work with the Suntour front D/R?

DorkDisk

Yes