How to fix Shimano STIs (DA 7900, Ultegra 6800)

Hi all

This year I came across various brifters that quit working. Given that those parts are fairly expensive, i would like to know if there‘s any common problem (broken spring?) which you could easily fix yourself instead of buying and collecting further STIs?

I once disassembled a 7700 STI but in the end it was impossible to rebuild it and it ended in the bin

Also thankful for good tutorials/videos

Cheers

I think Howard Zinn's art of road bike maintenance has exploded views of these brifters. Lemme check

Would also be interested in the exploded versions

Took apart 7400 and put it back together couple of times. Not easy but duable. Will find the manual and video how to and post here
https://imgur.com/a/4IT1J

Same priciple But look out for small parts on later edition of DA shifters like a tiny ball bearing and other bits.

https://www.youtube.com/watch?v=xkGNN_2CfCY

I've had a few pairs of 7900 apart, the most common issue with them was the ratchet skipping/not engaging because it was either flared out of position or the 'teeth' on the ratchet had worn down (or both!)

I found bending the ratchet so it 'meshes' more closely solves the issue but only temporarily.

I've never taken photos but I have a bag of old 7900 STIs, mainly for spares for the set on my road bike. But if I'm ever in the bag having a fiddle I'll take some pics of the offending area. I'd say I've repaired or attempted to repair this issue on about 4 sets of 7900 alone.

https://youtu.be/wJj6dASBMN0

Here's where I've had the most trouble. The red arrow points to the steel carrier for one part of the ratchet, the part that moves up and down when skipping to the next 'tooth'. That carrier (I think over time with normal use) deviates from it's position and pulls one half of the ratchet away from the other.

The green arrow points to the part of the ratchet (what I'm calling teeth) that I find worn down if it sometimes doesn't engage.
I've never attempted to have that out or replace it so not sure if it's possible (but I doubt it) I mean, it obviously comes out, but I haven't seen that part of the ratchet available separately.
There are however more expensive options like this https://www.ebay.co.uk/itm/Shimano-lever-mount-for-ST-7900-right/313167224036?hash=item48ea389ce4:g:b2YAAOSw-L5fI9OP

But then that's replacing most of the shifter

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https://forum.cyclinguk.org/viewtopic.php?f=5&t=136787

@psg1ben @Foreigner65
Very helpful, thanks so much!

My exploded view was a not hugely detailed version of a 9 spd DA. Best of luck