boomhauer

I've been maintaining my hydraulic brake bike by flipping it upside down to service the drive train, change a tire, etc...
When I do this my hydraulic brake brake acts as though there is an air pocket. I have to pump it to make it work.
This only lasts a day and then it disappears. Everything is back to normal.

Question...
Should I not continue to service my bike it the upside down position?
Am I slowly draining fluid somehow? I don't see any. How does the air get in there? Has it always been in there?

I purchased these Shimano Saint Hydro brakes on the internet. They came pre assembled and bled and have performed flawlessly for 18 months.

xenologer

air bubble in the reservoir
that migrates into the piston when brakes are squeezed while upside down
Then floats back out after a few pumps rightside up

So,
bleed the brakes so there's no big bubble in the reservoir
and/or
just don't touch the brakes at all when the bike is upside down

bogydave

I have the same on a mt bike.
New bike , First time I
Fixed a flat , took off no front brake .
“PANICK” time!!
Few pumps
& it worked, whew !

Now I pump it after upside down.
Fixable , yes
but haven’t taken the time to yet.
4 years now.

cpach

Hydraulic brakes are not closed systems because one of their features is that the pistons automatically advance with pad wear, which ends up storing more fluid in the caliper in the space that the pistons previously occupied. In the lever, there's a reservoir of fluid and air. When you depress the lever, the master cylinder moves past the inlet from the reservoir and temporarily closes the system, but when you release the lever fluid and air can move between the master cylinder and the reservoir. When the bike is inverted, air can move from the reservoir into the rest of the braking system. As air is compressible, this means the brakes don't really work. Thankfully, gravity moves the air to the top of the system, so with a few lever pulls things are typically well again.

This behavior will be drastically lessoned if you bleed your brakes. While Shimano brakes truly require bleeding less frequently than many, they still formally recommend annual bleeds. At 18 months, you should probably bleed your brakes, or at least top bleed them.

Flipping your bike for brief work should be OK for your brakes, although I personally hate working on flipped bikes. Its really rough on the grips and saddle and is an awkward way to work. For flat changes, I remove the wheel upright and lay the bike gently on the non drive side if I don't have a stand. All drivetrain work is easier with the bike upright, even without a stand. Also get a stand if you do much work on your bike (if you can).

Canker

It isn't a problem. With a mtn bike it is actually GOOD to turn the bike upside down every now and again to get oil on the foam rings/seals in the fork.

trailangel

When will ya'lll learn.......Rule 49:
Velominati ? The Rules

fietsbob

disc brake Master cylinder/lever expansion tanks have a gasket in them.. they should allow you to do that.

skimaxpower

For real.
Won't somebody please think of the children?