replacing piston seals on a shimano BR RS505 road bike caliper

Hi Folks. Has anyone done the above? I’ve got a set of calipers and there seems to be some contamination on the back of my pads and i’m fairly sure its a seal issue as there prone to this and have been sitting idle for a few months. Availability of replacement calipers is bad so if i can fix them i will.

thanks

I’m a bit pushed for time, but briefly. I’d reserve opinion until you get the caliper apart & the seals out. In all of the Shimano calipers I’ve revived the seals have been ok. The issue was the alloy corroding & the corrosion getting into the bottom of the seal groove & creating a leak path. I clean this out with a dremel, put some corrosion inhibitor in there & the leaks stop.

Might be worth a look.

If you do a search there has been some success by splitting the caliper into its two halves and replacing a small O ring seal between them.

This may not be the case if you have identified that it is from the pistons….

I think this is the one that failed on my road bike. I can’t remember 100% as mine has post mount front and flat mount rear.

Having read lots of threads it sounded not worth trying to revive it – I replaced it with a Hope RX4 caliper specifically designed to replace Shimano road bike calipers.

So far so good – I wouldn’t say it’s any more or less powerful than the Shimano one but hopefully it’ll be reliable. Came with several sets of brake pads. I’d say it took a few commutes to properly bed them in and get to full power despite me doing the usual 10 runs up to full speed and then bang both brakes on as hard as you can.

After striping it down its definitely the piston seal (bike was sitting for a while unused). I can see replacement seals for the BR805 caliper but not the 505, does anyone know if the seal is the same?

Check the piston size. Doesnt matter what the model is, they’re all square section seals, only the piston size needs to be correct.

I’d clean the pistons first, I didn’t think you could buy replacements

Any sign of corrosion in there?

Is the Shimano fluid DOT4 (corrosive), or something else?

Last time I had a caliper apart (Promax), the fluid had caused corrosion. Polished it all out, replaced O rings, and then used hydraulic oil, SAE 5, without any further problems whatsoever.

Just a thought.

Is the Shimano fluid DOT4 (corrosive), or something else?

Shimano use mineral oil.