tbenjaminsen

So, my BMC Speedfox 01 needed some attention.
Over the last few months, the rear brake has become soft/mushy and kinda’ lost its bite. Bike is factory fitted with a mix of Shimano XTR/XT equipment.

Started a normal “quick” bleed, using just the original Shimano funnel at the brake handle end. Loads of trapped air was released almost immediately. Still, the brake felt soft, so I went on to do a full bleed.

After completing the full bleed from the caliper side, I rode the bike for a few days, still feeling a bit unsatisfied with the bleed result.

I’ve now bled the brakes again, bottom to top, left the bleed funnel at the handle, tapping caliper, brake hose and reservoir - the system still releases air, after several days in the work stand 😳

Has anyone else experienced this, and what can be done to amend the situation?

Brake in question is Shimano XT.

Any suggestions welcome!

TIA,

Tom

Narhay

Do you notice any leaks anywhere?

tbenjaminsen

No, from what I can tell, there’s no leaks, at least no brake fluid emerging anywhere during the full bleed process (I even push the fluid back/forth from the bleed point at the caliper).

fietsbob

checked the fittings?

tbenjaminsen

No, haven’t checked the fittings as I wanted to prevent starting from scratch. I’m reluctant to imagine that something suddenly should have happened to them, as they’ve never been disassembled or subject to any damage (that I know of), but that may very well prove to be a naive presumption on my part.

Just adding a little situational update; it seems like things are firming a bit up now. The air bubbles doesn’t appear in the funnel after every caliper/hose/reservoir tapping ritual, and they’re also fewer and smaller when they emerge. Brake handle feels substantially less squishy, so maybe there’s hope 🙄

cpach

Couple tips:
Try orienting the bike hanging vertically (front wheel up)and depressing the lever with a toe strap overnight. This will increase pressure in the system and also allow air to rise naturally.
Try bleeding with the caliper removed from its mount, reorienting it during the bleed.

Depending on the generation of the brake the correct bleed procedure also involves bleeding the caliper. This is done by fitting a hose to the caliper bleed port, then pressurizing the system with the brake lever, then opening up the caliper bleed port slightly, then closing it again before releasing the lever.

tbenjaminsen

Thanks, these are all great suggestions, and also in almost complete alignment with what I’ve been doing for the past couple of days 🙂

I haven’t hung the bike, but it’s been in the work stand at close to 60° angle nose up. I also haven’t had the lever depressed, but used the “rapid lever movement” technique frequently after tapping brake components in the line.

I did a full bleed earlier, including the caliper bleed, but wasn’t satisfied with the result. Maybe I should take a new round at the caliper bleed port.

Thanks!