Morning all. Think my brake calliper is goosed – pistons will not retract, or be pushed back in (even without any fluid in the system) so am looking to replace it. They are RS785 and for the life of me I can’t find anyone who has them in stock and can deliver for tomorrow (I need it as I am supposed to be leading a ride on Sunday). Does anybody have any idea what else may be compatible? I can find various others, RS405 and RS805, but am not sure if they’ll work. Any thoughts much appreciated!
Or, is there any mileage in taking the thing apart and seeing if the pistons are fouling on something?
Cheers, Ben.

It’s easy to be wise after the event but I always pump the pistons out a bit more, clean around the exposed surface with a cotton bud and lubricate with a drop of shimano fluid before pushing the pistons back to fit new pads (this prevents dirt from being dragged into the seals).
I’ve also made a tool from a small G clamp to push the pistons back squarely.

It’s easy to be wise after the event but I always pump the pistons out a bit more, clean around the exposed surface with a cotton bud and lubricate with a drop of shimano fluid before pushing the pistons back to fit new pads

This is what I thought I’d do as the pistons weren’t retracting fully beforehand. However, they simply don’t want to move at all!

Isn’t the RS785 a rebadged XT785 caliper. It looks the same as my XT brakes and I’m fairly sure when I bought mine the reviews all said it was the same. I’d be surprised if the newer Road calipers weren’t compatible too.

rs405 and rs805 are flat mount. If your frame is compatible then they
should be fine.

rs785 and xt785 are almost identical except the hose enters the
inboard side on the RS785 via a straight connection unlike the
XT which is a banjo on the outside. something to do with heel
clearance I believe.

bike24 seem to have them in stock.

If you’re anywhere near Manchester then I know that bikeshak in Altrincham have a caliper in stock.

Thanks folks, that’s the kind of info I was looking for. The fork is indeed a flat mount, so will have a look at the RS405/805. Had wondered about the XT785, but the different hose entry was bothering me!

Crc have the XT 785 in stock if that’ll work. Easy job to replace, I’ve just done mine this week.

Try these shops as they should have stock –

2 Pedalz in Olney
Biketart in Canterbury
Swinnertons in Stoke On Trent

I have a spare one.
Brand new in box if you need it.
Based in Rugby if that’s any help?
singlespeedtothemax1@hotmail.co.uk
Thanks,
Max
Sorry post mount,just saw flat mount!

Cheers for all the help folks. RS805 on a Saturday delivery from Evans sorted it.
Ta, Ben.

just for info …. flat mount fork can take a post mount caliper – shimano
do a mount adapter for just such an occasion 🙂 (I know – my Mason now
sports one !!)

Got to this late as I had a spare, sorry! I have kit sat around waiting a Mason build. Got to sell the Datum frame first. I had been hoping to score a Definition second hand when someone fancies a move to a Bokeh. I think I’ll be very lucky with that!!