Help! Need some shifter advice please

[MikeFB]

So, got my fat ebike up and running great. However the previous owner fitted a 7 speed SRAM MRX Comp twist shifter.

On the trails I'm riding I accidently change gear occasionally when riding over bumpy surfaces, so they have to go.

The bike is fitted with hydraulic brakes, so will need something like the Shimano SL-M310 that fits underneath the brake lever. I believe this only comes as an 8 speed shifter though?. However I can replace the 7 speed cassette I have with an 8 speed cassette if needed.

My question is will the SL-M310 be compatible with the Shimano Tourney derailleur I have.

I believe the SRAM shifter has a 2:1 actuation, but I'm confused about what actuation the SL-M310 is as I'm finding conflicting compatibility information on the internet.

Any other suggestions/advice for replacing the twist shifter also welcome.

 

[MontyPAS]

My question is will the SL-M310 be compatible with the Shimano Tourney derailleur I have.

Got Tourney 7 speed shifters on eBay

Shimano SL-TX30 3/7/21 Speed MTB Mountain Bike Thumb Gear Shift Lever Set | eBay

Right shifter is a trigger-type 7speed shifter with one lever for down-shifts and a thumb button for up-shifts. Speed shift indicator. Inner gear cable included. 3x7 Speed Shifter Set（opp bag）.

www.ebay.co.uk

I bought a set of S/H SLX 7 speed on eBay (1990's), they are very slick in use if you can find some.
Ive always mixed and matched Shimano stuff and always seem to work? Thought the actuation ratio was all the same. May be different on the 9/10/11??
I only use 7 & 8!

Edit: just noticed you want underhung shifters, so Tourneys no good?

 

[MikeFB]

Hi, yeah I have those in my spares box, but as you say they don't work with Hydraulic brakes as they can not fit next to them due to the reservoir.

I'm 95% sure that the ones I noted will work, just wanted conformation before I bought the shifter and cassette.

Think I'll just do it anyway, as they're not expensive items.