Go Back  Bike Forums > Bike Forums > Bicycle Mechanics
Reload this Page >

New Shimano Hydraulic brake lever wont suck in oil during lever bleeding

Notices
Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

New Shimano Hydraulic brake lever wont suck in oil during lever bleeding

Old 09-01-22, 04:22 PM
  #1  
karldub
Newbie
Thread Starter
 
Join Date: Nov 2020
Posts: 67
Mentioned: 4 Post(s)
Tagged: 0 Thread(s)
Quoted: 42 Post(s)
Liked 5 Times in 4 Posts
New Shimano Hydraulic brake lever wont suck in oil during lever bleeding

Hi,

I Installed a new front hydraulic brake lever and did an easy ”lever bleed” (maybe called gravity bleed - not an expert here) where mineral oil is simply ”sucked in”/transfered through the funnel connected to the lever while pushing the lever a few times. Brake caliper oil valve is closed during such a bleed. Worked perfectly and lever is very responsive.

On the rear brake, Ive had a bunch of problems and tried different solutions. The bleeding process itselt however worked fine for the first times and lever were responsive (but had other issues to solve).

Now when I try to again ”bleed”/refill the rear system the same way, it doesnt take in any oil, although it’s obviously lacking (leaked) oil. The funnel just stays full, although the lever is dead and the system lacks oil. Brake caliper oil valve still closed.

Is the lever broken and it what way would that be? It doesnt show any visual signs of breakage.
karldub is offline  
Old 09-01-22, 04:33 PM
  #2  
Polaris OBark
ignominious poltroon
 
Polaris OBark's Avatar
 
Join Date: Jan 2022
Posts: 1,991
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 1129 Post(s)
Liked 1,655 Times in 918 Posts
Open the bleed port on the caliper and push mineral oil through it using a syringe and tubing, keeping the funnel in place to catch the excess. Make sure there are no local minima in the brakeline where air can get trapped, and make sure the levers are well above the caliper height when you are working on it. Squeezing the lever can dislodge air bubbles, but I think Shimano actually recommends doing this, as it can suck air in as well.

If the rear brake leaked, air had to get in to displace the volume of mineral oil that leaked out. It is trapped in there, somewhere.

I presume also you have fixed the source of the leak? If not, you can't pressurize the system, since it needs to be closed.
Polaris OBark is offline  
Old 09-01-22, 11:05 PM
  #3  
icemilkcoffee 
Senior Member
 
icemilkcoffee's Avatar
 
Join Date: Aug 2009
Posts: 1,547
Mentioned: 8 Post(s)
Tagged: 0 Thread(s)
Quoted: 896 Post(s)
Liked 798 Times in 481 Posts
I've never actually worked on hydraulic brakes on a bike, but in a car, you sometimes have to do 'bench bleeding'. Take the brake hose off of the brake lever. pull the brake lever all the way in and hold it there. Now cover the hole on the lever body where the brake hose attaches with your finger. Let the brake lever out. It should have sucked mineral oil into the master cylinder. Now you can re-install the brake hose and proceed with pumping and bleeding.
icemilkcoffee is offline  
Likes For icemilkcoffee:
Old 09-04-22, 10:24 PM
  #4  
oldbobcat
Senior Member
 
oldbobcat's Avatar
 
Join Date: Jul 2005
Location: Boulder County, CO
Posts: 3,806

Bikes: '79 Gios, '80 Masi, '06 Felt, early '60s Frejus

Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 306 Post(s)
Liked 246 Times in 187 Posts
Before you bleed, bounce the bike vertically on the rear wheel a few times to float bubbles up toward the lever. Then restart your top bleed. If that doesn't work, you likely have air stuck in the caliper and you'll need to do a full bleed.
oldbobcat is offline  
Old 09-05-22, 12:31 AM
  #5  
masonv45
Junior Member
 
Join Date: Nov 2014
Location: Arlington, TN
Posts: 129

Bikes: 2005 Giant OCRc2, 2016 GT Aggressor Expert

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 41 Post(s)
Liked 54 Times in 29 Posts
Originally Posted by icemilkcoffee View Post
I've never actually worked on hydraulic brakes on a bike, but in a car, you sometimes have to do 'bench bleeding'. Take the brake hose off of the brake lever. pull the brake lever all the way in and hold it there. Now cover the hole on the lever body where the brake hose attaches with your finger. Let the brake lever out. It should have sucked mineral oil into the master cylinder. Now you can re-install the brake hose and proceed with pumping and bleeding.
In the motorcycle world - that's called priming the master cylinder. Usually performed on a completely "dry" hydraulic system.
masonv45 is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2022 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.