I tried to set up the perfect shifter + derailleur. For the last part it is better (for me) to have low-normal version, because reducing gears is essential for me (I bike mostly within city).

So I bought low-normal Shimano derailleur (Shimano-RD M770 SGS XT) and M770 shifter. To my surprise it is asymmetric shifter -- you are able to release gears by 4, and increase by 1 (I tuned M770 already, so I am able to increase gears by 2, just like with XTR).

So with current configuration I can more easily increase gears (by 4) than reduce them -- quite contrary what I wanted.

I can send back derailleur, and order a new one, with top-normal spring, but I would LOVE to improve M770 shifter even further by reversing the direction of cable, i.e. so the thumb level would pull the cable, and index level would release cable.

Such tweaking would result in dream machine (well, part of it).

The question is -- is such modification is possible at all (at home)? I would appreciate firm "no" or "yes" (+how to do it) answers. Thank you very much in advance.

No.

Maybe if you had a machine shop equipped to do precision prototyping work and a few days worth of time to experiment you might make something work, but even then I doubt it. The shifters are disgned to be held in gear with cable tension from the derailleur, and that tension is partially balanced out with a return spring inthe shifter. All mechanisms inside are designed with this in mind and would have to be rebuilt or modified to work backwards.

If I were you I would consider the following solutions (in order of preference):

1. Return derailleur and get high-normal style
2. Replace shifters with continuous-rotation style like bar-ends shifters w/Paul's Thumbies or IRD Thumbshifters
3. Replace shifters with continuous-rotation style like Gripshift

Thank you very much for detailed answer. I will probably simply return derailleur but those shifters you mentioned in (2) look very interested -- I didn't know they even existed, I though that all went with two-level shifters.

You can also hack the 770 shift pod to release two cogs at a time, instead of just one:

https://forums.mtbr.com/drivetrain-sh...tr-549266.html

all single cable mechs have a return spring. cable tension pulls thru ratchet detents ,
open the pawl and the spring pulls back.

The IG hubs with 2 cables are pull/pull and it's fast to shift thru the whole range,
with the 2 cable grip-shifter

All deraileurs have a return spring - some shifters do not (GripShifts and basic friction thumbshifters for example).

To the OP -

Top-mount thumbshifters are, im my opinion, the best thing since sliced bread. Ironically it is a workaround to make a product similar to the old-fashioned shifter style. THe primary advantages are much easier maintenance (as opposed to completely unable to service like rapidfire) and the ability to select 'friction' shifting mode if the indexing is not working properly. And front shifting is friction all the time, which is really a better way to shift.

single cable IG hubs do too , there is a coil spring inside a SA hub that the cable pulls against.

@mechBgon, as I wrote, my M770 is already tweaked, first day I bought this shifter I made a modification :-)

@DCB0, if old Shimano SIS with one lever is top-mount thumbshifter, then I couldn't agree more. Very simply construction, and I could get any gear in no time, not matter if it was up-gear or down. Unfortunately I have to go with mainstream now, since dropping gear is crucial for me, I tried gripshift, but they are bad for my tennis elbow, so now, I ended up with M770, which is not that bad with 4 gears release, however this won't work with reversed spring in derailleur.

Funny thing happened to me yesterday-

I have been racking my brain for the last couple of weeks to decide what type of shifter I need to order to complete a ike I plan to sell. It need Shimano 7 speed shifters. I have a Rapidfire+ (push-trigger) left side shifters with no right shifter, and an old Rapidfire (push-push, not push-trigger) right side shifer, but no matching left shifter. Well I got home from work yesterday and my wife is cleaning out the garage and on top of the pile of bike parts she made was a fully functional set of Shimano 200GS thumbshifters that I had completely forgotten I had!

For your purpose it sounds like returning the low-normal deralleur is the best idea as it shouldn't cosyt you anything to get the bike how you want it. But if you wanted to sink another $150 into the project then either of the thumbshifter options would be great.