What is J-kit wrt Shimano brakes?

Regarding Shimano brakes, what does J-kit mean and is it something I should actively look for or actively avoid? How does it impact compatibility of calipers? When on-line shopping, it seems some versions are J-kit compatible and I’ve no idea whether it makes any difference…

And on a related subject, the brakes I’m looking at changing are BL-M4100 levers and/or BR-MT410 calipers and/or SM-RT26 rotors. The rotors are resin-only but the Shimano website seems to imply the calipers are also resin-only. Am I reading this correctly or can I just swap the rotors if I want to switch to metallic/sintered pads?

I believe it means theirs a plastic stopper on the levers and hose end with caliper so you can fit them through the frame and then fit back togeather without the need to rebleed

and yes caliper will come fitted with resin only pads, I think they’ll be the standard smaller Shimano pad that come in many materials, so switch them

ps seen quite a few Shimano lever / caliper deals on CRC , when I fitted my old drop gravel bike with post mount brakes I used the lower level Shimano caliper and hose and just took of the levers, note their are two standard sizes of end olive/barbs so double check that

iirc j-kit is just a plugged master cylinder with olive in place behind nut and a pre bled caliper/hose with a membrane over the end.
you can essentially just pop the rubber boot onto the hose and push the end into the master cylinder and tighten the nut.

non j-kit sets are just pre assembled systems

non j kit calipers would be empty calipers with no hose I guess.

Ok thanks

Anyone care to comment about whether some calipers can only be used with resin pads?

i thought the resin pads was just a rotor thing (like you did).

As others have already said J-Kit is a pre bled calliper and Lever. The lever is plugged as in the picture below, the hose is connect at the calliper and plugged with a membrane at the lever end. You remove the yellow plug and insert the hose into the lever. The membrane in the hose gets pierced and you tighten up the flare nut. If you need to trim the hose you will need to insert a barb into hose. Cut the old one out or get a new one. MT410 callipers use the BH59 hose which uses the gold coloured barb. It’s a slightly different size to the silver barb used in the BH90 hose.

As to why you can’t use metal pads with the callipers, possibly due heat affecting the pistons. The lower spec Shimano pistons are resin and the higher spec are ceramic. The MT410 uses the wide Shimano pads and Shimano do not make any wide metal pads or list any metal pad compatible discs for the MT410 callipers. Also the Shimano metal pad compatible discs require the narrower Shimano pads. If you were to use a metal pad compatible disc with the wider resin pads, part of the pads will wear at a different rate as the pads are not fully on braking surface. I am actually using narrower type discs with wide resin pads because I didn’t know there were narrow and wide discs. I’ve left them on at the moment but will swap them out.

Thanks ctr! Sounds as though it may be worth replacing those calipers anyway…