Last week I switched around some seats on two unis and some days later I noticed there was no pressure on the brake cable anymore. First I thought it would be easy to fix by pulling the metal wire in it as I do on the brakes of my normal bike, but then I noticed it was a hydraulic brake, which doesn’t have a wire inside.
I took it to the bike store and they asked if I had seen it leak. I hadn’t so they made the conclusion that somehow air had come in and has to be let out. I asked them if I could do this myself, but they claimed I needed special tools and only they could do it. Also they said it would take them 30-45 minutes to fix.
Is it really so complicated to let the air out or are they just saying it to earn something on me? They say I’d pay the hourly wage, so 27 eur if it takes 30 mins. If it happens again, I’d rather be able to fix it myself.
You need to buy a bleed kit for your brake. Search for “bleed shimano brakes” (or whatever brand). You can do it yourself, but in my experience it helps to be 2 people to do the job.
Agreed. It’s not that complex, but it can get messy quickly! Add a big syringe (no needle required) to the bleeding kit you buy - a few cents at any pharmacy.
Actualy bleeding of Shimano brakes is pretty easy. You need the Shimano bleeding kit and the Shimano oil for brakes. As Shimano is using oil and not DOT4/5 all parts can be cleaned easily if you drop some oil. Make sure to remove pads before bleeding.
Some brakes really don’t like being upside down, if I remember correctly Shimano is one of them. Just putting the unicycle back the correct way around, and pulling the lever a lot can sometimes help. If the lever stays soft, definetely bleed the brake.
I recommend not buying the cheapest bleed kit you can find. You don’t need shop grade equipment either, but the super cheap stuff tends to suck. Put some cardboard anwhere the fluid could drip, and as others said, remove the brake pads. Use brake clean to get rid of any residue from spilled fluid.
Shimano is fine with beeing upside down. Old Magura disks definatly had this issue. No idea about new ones. I also had older Hopes which were sensitive on position. For the kit I agree to Finnspin, get an original (for the maker you have) bleeding kit. They are not expensive and fit well. Especially on the brake lever every maker uses different screws.
It is not a Shimano on my Nimbus 29" from 2015. Don’t remember what brand brake it is. It is at the LBS now and hopefully will soon be fixed. And yes I had the uni upside down when screwing the seat back on (basically screwed the uni onto the seat). Next time I will take the seat out of the frame first, but I was lazy.
Having your uni upside down for a few minutes shouldn’t cause any problems regardless of brand (it’s extended periods of storage that some don’t like). But if there was air trapped somewhere in the lines/pistons it could have been dislodged by having it upside down shortly. I’ve had plenty of trouble with brake sets that were supposedly pre-bled and ready to go.
It’s fairly easy to do, but like they said you need the tools. The first time it’s a hassle, but once you figure out what you are doing it’s a piece of cake. Youtube will be your friend 
You’re probably right. As this is just the first time in the 4 years I’ve been riding it happened, I won’t spend money on the tools, but if it will happen more often I will and I saw on youtube there are quite some vidz about it.