I’ve stripped and rebuilt a few of the Shimano 2 piece calipers without replacing any parts. All of the calipers that I’ve had apart have had corrosion issues in the sealing ring groove allowing fluid to seep out. Once properly cleaned and reassembled they’ve held pressure and didn’t leak. For how long???
There are plenty vids on youtube showing how to strip the calipers. Where it get awkward is getting the pistons out. I used compressed air with the caliper halves wrapped in a rag. Once out the seals are exposed and can be removed. All of the seals I looked at were like new. The O ring between the halves also in good condition. Once the seals are out it was obvious that there was dirt and corrosion in the ring groove. I polished this out using some metal polish and a synthetic brush on a Dremmel. The pistons got a quick clean up with some 1200 wet and dry and soapy water.
Reassembling I put a wee bit corrosion inhibitor in the ring groove & used an anaerobic sealer between the caliper halves. Pistons and seals given a light coating of silicon.
The alloy Shimano have used doesn’t seem very resistant to corrosion and the calipers aren’t anodised. The other thing that became obvious was how much the caliper flexes when under pressure. The two halves visibly distort & this makes the bores go out of line with each other. There were witness marks in the caliper bores where I assume the pistons had been binding.
As pointed out you can get a new caliper for 22 Euro. I don’t think I would bother refurbishing any more of these. It’s simply not worth the effort.
