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Jul 21st, 2025 | | | | Joined: Aug 2007 Posts: 116 Shop Shark | | Shop Shark Joined: Aug 2007 Posts: 116 | I have a 4 wheel disc set up in my 39 chevy.... Dual master cylinder is mounted below the floor... I bled the brakes and thought I did a good job... but now the pedal feels mushy and im not getting any air spurts when i bleed them...
Do I have to have the caliper below the master to bleed?
thanks
matt
http://www.flickr.com/photos/50657267@N08/sets/
1939 1/2 ton Resto-mod
1937 1 1/2 ton Is in the driveway
| | | | | Joined: Jan 2010 Posts: 4,263 Shop Shark | | Shop Shark Joined: Jan 2010 Posts: 4,263 | Matt
Was it a new master cylinder?
Was all the air removed from the master cylinder when it was bench bleed?
Something to look at.
You should be able to successfully bleed the calipers as installed.
| | | | | Joined: Aug 2007 Posts: 116 Shop Shark | | Shop Shark Joined: Aug 2007 Posts: 116 | Yes I bled it first.... All new lines and calipers
Matt
http://www.flickr.com/photos/50657267@N08/sets/
1939 1/2 ton Resto-mod
1937 1 1/2 ton Is in the driveway
| | | | | Joined: Jul 2010 Posts: 4 New Guy | | New Guy Joined: Jul 2010 Posts: 4 | Something else to check is that none of the rubber hoses are failing and bulging when the pedel is pressed.
However, it is most likely there is still some air in the system closer to the master cylinder end... keep on bleeding and don't ever let the resivoir get down so low that it sucks air or you will have to start all over again.
72 Suburban K20 350/T350/HO52
| | | | | Joined: Jul 2010 Posts: 89 Wrench Fetcher | | Wrench Fetcher Joined: Jul 2010 Posts: 89 | if you continue to have problems try reverse bleeding.
it's almost a nessesitey on my motorcycle.
it ain't YOURS 'till it ain't stock!
1951 chevy 3100
| | | | | Joined: Nov 2005 Posts: 6,061 'Bolter | | 'Bolter Joined: Nov 2005 Posts: 6,061 | Hy fatboy0169, when master cylinders are mounted below the level of the calipers, they should have a 2 p.s.i. residual pressure valve installed in the line, this keeps the fluid from draining back toward the master cylinder, which creates a negative pressure inside the caliper, which may cause air to be drawn into the caliper past the piston seal, hope that helps. | | | | | Joined: Feb 2000 Posts: 4,886 'Bolter | | 'Bolter Joined: Feb 2000 Posts: 4,886 | You can also try real fast short pumps of the pedal. Keep the bleeders shut and just give real quick short pumps, this helps bleed the master and pull air out of the lines.
If you are worried about the height difference, jack up the body and let the axle you are working on hang lower then the master, reverse the jack stands to bleed the other axle. I have even parked on a steep hill so the fluid would tend to run to the lowest point.
Joe | | | | | Joined: Feb 2006 Posts: 150 Shop Shark | | Shop Shark Joined: Feb 2006 Posts: 150 | 3B is right on target.
Just to share a couple of ideas I recently read is tapping on the caliper while bleeding helps move trapped bubbles out. Another point I came across is when the caliper bleed valve is lower than the M/C you may UNBOLT the caliper from mounting and lower it a far the the flex hose will allow....ensuring the bleed valve is "clocked" at highest point of the caliper.
Not to stir a swarm, I also read that DOT 5 is sensitive to pressure bleeding..... for what it's worth.
Good luck | | |
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