Exploded Diagram of ST-M900 RH Shifter?

[Tallpaul]

Anyone?

 

[bduc61]

you are daring :shock:

to me it surely looks like a "devil in the box " issue

if you open it, it may spring all over the place

or you opened it already and want to put it back

 

[Tallpaul]

or you opened it already and want to put it back

It's open, I think the problem is the position of a return spring on a pawl. But they're may be something else broken too, but I have not point of reference for what a working one looks like!

I found this, but it lack the necessary detail.

 

[Xesh]

......I found this, but it lack the necessary detail.

You won't find anything from Shimano that's more detailed because Shimano never meant the gear levers to be serviceable. It was intended that the entire unit would be replaced in the event it went wrong.

I've had a go at servicing one of these myself (not an M900 one though) and found that most parts inside were riveted and not meant to come apart. Also there seemed to be about 30-40 parts that I could see. Needless to say I failed to repair it and just sourced another unit instead.

The most common problem with these is the ratchet mechanism getting stuck. Usually this is because of dirt or grease that's solidified over time. They can generally be freed up by removing the outer casing and spraying the ratchet with GT85 and then moving it back and forth with a small screwdriver until it moves freely.

 

[SF Klein]

This has a bit more detail but I think it's from an ST-M900. They might be close enough for the particular piece you're looking at though.

 

[Tallpaul]

I was bored last night and had another go at this.

I stripped it right down to it's individual components. It's a sandwich of parts, but essentially consists of one central ratchet and two return springs (one for the up shifter, one for the down. The up shifter has a single pawl which engages the outer teeth of the central ratchet. The down shifter actuates two separate pawls that engage teeth inside the ratchet. The whole sandwich mounts on a splined shaft which dictates their orientation.

It's actually pretty easy to strip down and put back together.

When I got mine apart I found three separate issues.

- One of the internal pawls had snapped.
- A brass washer was chewed up.
- The plastic carrier which the cable sits in was split.

So, the common issue of 'a sticky shifter' could just be muck in the ratchet mechanism or a broken or failing part. I'd like to get these working, so am looking for another shifter to take parts from. If I can revive it I'll photograph each component as a guide for others.