SethAZ 

Ok, it looks as if I've killed the BR-RS805 front brake caliper on my bike. It's leaking mineral oil around one of the pistons.

Background: I was swapping my handlebar to one with internal routing. Had to disconnect brake line from brifter on bike, cut end with olive off, route it through handlebar, fit new insert and olive, then reinstall into brifter and then refill/bleed with new mineral oil. I'd removed the wheel, removed the brake pads. The brake kit I'd bought didn't have the right size wedge to fit between the pistons (one that came in the kit was a little too thick) so I'd carved the block down a bit and then pushed it in between the pistons to hold them in place. After I removed the block I saw the pistons were canted a bit (my carved block was apparently still too thick and had only gone partway in between the pistons, and pushed them into a bit of an angle). <--- this is almost certainly the point where the caliper was dead but I didn't realize it yet.

When all was in place again I attached the bleeder cup to the brifter, attached the syringe with fluid to the input port, turned the input port 1/4 turn or so, then pumped fluid in until it rose up maybe an inch into the bleeder cup. First I was kind of shocked at the fluid being a fairly dark gray, so there was some wear matter in there or something. The bike has just under 3000 miles on it and the brakes hadn't yet been serviced. I wouldn't have thought 3000 miles would require it. Apparently I'll have to check this more often.

Anyhow, with the plastic block still wedged in between the pistons I pumped the brifter handle to try to clear any air bubbles, and it didn't have much resistance. It was then I noticed mineral oil dripping to the floor from the caliper, and upon closer examination it seems to be leaking around the edges of the piston.

I whipped out a simple block design and 3D printed it for a block that wouldn't be too thick to sit in between the calipers, pushed it in between them and straightened them out. Pumped in more mineral oil, squeezed the brifter lever, it's still leaking oil around that piston with little resistance felt in the lever.

I think the act of me wedging that too-thick plastic block in between the pistons to the point where they turned at a bit of an angle damaged the piston seal. With no functional front brake, the bike is deadlined. I'm really bummed because I really don't want to be off the bike for days to fix this, but it looks like that's where I am.

Am I correct that there's nothing for it but to replace the whole caliper?

The caliper that's on there now is a Shimano BR-RS805, which is from the Ultegra 6800 generation. I've found that online and could order it as a straight up 1:1 replacement.

I could also upgrade to the Ultegra BR-R8070 front caliper. It's a generation newer, so it would ensure parts easy availability further into the future. Not sure if that's really a concern, since it seems parts don't really come into play here if I'm having to replace the whole caliper. The BR-RS805 and BR-R8070 seem to weigh about the same, within a gram or so. I would hope that the BR-R8070 would be a new and improved design, but I have no idea what its advantages would be. Any opinions?

So, the questions are:

1) Is this definitely a case where the caliper must be replaced? I believe it is, but I'm new to hydraulic brake servicing, so perhaps there's some way to fix this situation that I'm just not aware of.

2) Is there any reason I should prefer either a direct BR-RS805 caliper replacement or replace it with the Ultegra R8000-generation BR-R8070? The difference in cost is around $30, which I'm willing to pay if the newer design has some actual advantages.

3) Are the flat mount adaptors all common? Ie: is there there anything I need to know about the flat mount adaptor that's on there now in order to ensure I get the right thing? I'm assuming that with the BR-RS805 as a replacement, if it comes with an incompatible adaptor I could just unmount my current caliper and reuse its adaptor with the new caliper. Is this correct, or am I missing something? I'm unfamiliar with mounting requirements. My current caliper says for 160 on it, but I've seen photos online of these calipers with both for 140 and 160, and I'm not sure what the difference is. I'd have assumed that they'd be the same, only mounted 10mm further up the fork for use with 160mm rotors. Is that the case?

4) The pads I've currently got appear to have plenty of life left (around 1.5mm, Shimano manual says replace when down to .5mm), and are L02A Resin pads. I see on Shimano's site that these pads are compatible with both BR-8070 and also the BR-RS805 calipers, so in theory I could use re-use my existing pads on either model. Is there any reason I'm not aware of why I shouldn't just reuse the existing pads? They've never gotten any mineral oil or anything on them, nor is there any obvious damage.

I also see that there is the L04C metal pad as an option, and that it's specced for both caliper models. Would metal pads be better than resin pads? My braking until now seems to have been just fine with the resin pads, so I'm not sure what sort of advantage the metal pads would have. If I can just re-use my current resin pads and the potential advantages of metal pads aren't great, I'd be saving around $30 to just reuse the pads I've got.

cpach

Metal pads wear longer, and have a stronger initial bite, work better in the wet, but modulate worse. If you like your current braking resin is fine, and is probably what I'd prefer on a road bike.

Shimano mineral fluid turns gray in the master cylinder because the seals absorb the dye, and this isn't necessarily a sign of serious contamination. When it's seriously contaminated it turns closer to dark purple/black.

Your problem doesn't seem normal to me. The most common cause of caliper failure on Shimano brakes is cracking the ceramic brake piston, which can be caused by forcing the caliper in at an angle or simply overaggressive tool use on the pistons. If you have time on your hand, you could try removing the caliper, disassembling it, and pushing out the pistons and inspecting them closely and reinstalling them. Otherwise, yeah, new caliper.

SethAZ 

Yeah, if I'm going to have to replace the caliper anyway, there's no good reason not to pull it apart and have a look.

SethAZ 

Welp. Took apart the caliper but couldn't get the pistons out. I've read the only reliable ways to do it would be compressed air or perhaps pumping mineral oil back into the caliper. After making sure the pistons were at least nice and straight, I put it back together and pumped the mineral oil back in and sure enough it just leaked out around the piston again. The ceramic piston wasn't obviously damaged, but the seal apparently is.

Oh well. I've ordered the Ultegra R8070 front caliper, but I'm going to call around some bike shops near me and if anyone has one or the BR805 on hand that I can pick up tomorrow. If nobody does then it looks like I'm just going to have to wait this out. I've really started hitting my stride as far as weekly mileage, so this is a bummer.

SethAZ 

I took the caliper apart, but couldn't get the pistons out. They aren't obviously damaged, but the seal or something inside is, and when I reassembled it and tested it again with more mineral oil it just leaked out around the piston as before. When I pushed the over-thick spacer in beween the calipers and canted them, I'm guessing maybe I pinched a seal or something. I don't know.

I've ordered the BR8070 front caliper, but it's looking like it'll take till the end of the week to arrive. I'll call around in the morning and see if anyone has one or the BR805 on hand that I can pick up tomorrow, but if not it looks like I'm off the road this next week. I'd started hitting my stride lately getting my weekly mileage back up, so that's a bummer.

I'm chalking this one up as a learning experience. When I get the replacement caliper I'll just reuse the pads I already have. They've still got 1mm worth of life in them according to Shimano, and they're so easy to swap out there's no reason not to use them up.

Elvo

Yup and next time use a stack of credit cards if you don't have the right spacer

SethAZ 

The dumb thing is that later in the day when I was trying to get the pistons back to facing straight again (instead of that little tilt) I was able to 3D print a perfectly fine spacer in under an hour from opening the CAD program to removing the finished spacer from the print bed. I was in too much of a hurry to get past that point earlier in the day, now I get to spend a week off the bike waiting for a new part. But yeah, even a stack of old credit cards would have been better than just carving some plastic off a too-thick plastic spacer, but then pushing it in while it was still a little too thick. Stupid me.

Cyclist0108

I did this years ago. Briefly, I put it all back together and pretended it didn't happen. It is still fine.

Less briefly, if you over-extend the pistons, they will leak. Assuming they are clean, push them back in all the way, re-bleed the brakes, and you should be fine. If it still leaks, it will be very obvious very quickly.

schulz46

WOW, you do 3D printing. Do you do it at work or do you have your own 3D printer... impressed.

SethAZ 

Yeah, it was obvious very quickly. With the pistons pushed back in and nice and even and all I refilled with fluid, attempted to bleed, and with any pressure on the lever the fluid just pumped out around the piston and onto a towel on the garage floor. If I can figure out a way to get the pistons out I'd be very interested in seeing exactly what the deal is (ie: pinched seal), but it wasn't obvious to me last night how I'd get them out. I've read of ways using compressed air that aren't practical for me.
This is a hobbyist-grade 3D printer printing with plastic filaments, not an industrial 3D printer capable of printing with metal or anything like that. My 3D printer is one I built myself from plans that are out there on the internet. A good fraction of the time I've spent designing things it was designing parts to improve the printer, and tinkering with it. It occasionally comes in handy for other purposes. Most of the things I've ever printed that weren't upgrade parts for the printer itself were things like figurines or other decorative knicknacks. It's not something that's paid for itself, put it that way, but that pretty much is the definition of a hobby.

One might be tempted to say if I just had a pro work on my bike I'd avoid expenses like replacing this caliper. Thing is, I like tinkering with and maintaining my own bikes, and the money I've saved over the years figuring it out and doing it myself has far more than paid for the occasional mistake like this one. And I won't make this mistake again. What I'm learning right now as I become better aquainted with hydraulic disk brakes is going to come in handy when I overhaul my MTB.

Cyclist0108

Sometimes the pistons crack. This happened on my rear one soon after I got it. I had it warranty-replaced at a bike shop. They put an XT caliper on (the 2-piston kind). Those were interchangeable. Now that Ultegra went to flat-mount, the choices are a bit more limited.

Edit: Here is the 805 for $50. I would just get that and forget about upgrading. I doubt the newer ones are that much different/better.
https://www.universalcycles.com/shop...s.php?id=81313