Will enough air in the hydraulic brake lines prevent the pistons from returning?
07-09-20, 11:14 AM
#1
Old Dog, New Tricks
Thread Starter
Will enough air in the hydraulic brake lines prevent the pistons from returning?
I cleaned the front pistons on my TRP hylex brakes. Now there is air in the system and the pistons won't return to the recessed/open position when brake lever is released. Is this because of the air in the system?
Will a system bleed get the pistons to return to open position?
I got bike brand new (Co-Op ADV 3.2 road/gravel/touring) 13 months ago, and the TRP Hylex brakes came with it. Since then I've put nearly 4,000 miles on the bike, Had three full tune ups, two sets of pads (front and back), two system bleeds (front and back) and one new set of rotors (F&B).
Will a system bleed get the pistons to return to open position?
I got bike brand new (Co-Op ADV 3.2 road/gravel/touring) 13 months ago, and the TRP Hylex brakes came with it. Since then I've put nearly 4,000 miles on the bike, Had three full tune ups, two sets of pads (front and back), two system bleeds (front and back) and one new set of rotors (F&B).
07-09-20, 11:53 AM
#2
Banned
IDK, did you touch the lever with no wheel disc in the caliper?
the system's auto pad wear compensation kicked in, as if the pad was very worn, then it wont return..
Put a "keeper" in when removing the wheel..
Or, ?
Did you bleed out the air bubbles and did that fix the issue?
then its possible that was the problem..
...
the system's auto pad wear compensation kicked in, as if the pad was very worn, then it wont return..
Put a "keeper" in when removing the wheel..
Or, ?
Did you bleed out the air bubbles and did that fix the issue?
then its possible that was the problem..
...
Last edited by fietsbob; 07-09-20 at 11:59 AM. Reason: added to post
07-09-20, 11:57 AM
#3
Old Dog, New Tricks
Thread Starter
07-09-20, 02:00 PM
#4
Senior Member
Join Date: Sep 2010
Location: Roswell, GA
Posts: 8,319
Bikes: '93 Trek 750, '92 Schwinn Crisscross, '93 Mongoose Alta
Mentioned: 30 Post(s)
Tagged: 0 Thread(s)
Quoted: 1438 Post(s)
Liked 1,092 Times
in
723 Posts
On most hydraulic brakes, the force to return the pistons is provided by flexure of the square-section O-rings which also provide the piston seal. If there is any slight pressure in the system, as might be caused by an air bubble, this could cause the pistons to not retract. And they will only retract a small amount, so if you pulled the lever with the wheel out they may not retract enough and will need to be pushed back manually.
07-09-20, 02:15 PM
#5
Old Dog, New Tricks
Thread Starter
On most hydraulic brakes, the force to return the pistons is provided by flexure of the square-section O-rings which also provide the piston seal. If there is any slight pressure in the system, as might be caused by an air bubble, this could cause the pistons to not retract. And they will only retract a small amount, so if you pulled the lever with the wheel out they may not retract enough and will need to be pushed back manually.
I did the manual reset of the pistons with the bleed block. After removing the bleed block, the pistons rose back out of the cylinders without any actuation of the brake lever.
The bleed kit I ordered just arrived in the mail.
Update pending.
07-09-20, 05:21 PM
#6
Old Dog, New Tricks
Thread Starter
Bleeding worked. The Pistons now return to recessed position when brake lever is released.
Last edited by AllWeatherJeff; 07-10-20 at 12:23 PM.
