rket56

Installed a duel circuit master cylinder/booster on the firewall of my 56 Olds. This was from a kit I bought several years ago. I have disc on the front and new cylinders/linings/springs on the rear. All new brake lines, connected to a proportioning valve directly under the m/c. Problem: Can't get the air out of the lines. Bled the master cylinder on the car and after several cans of fluid thru the lines, bled it for the 2nd time. Starting with the passenger side rear, my helper pumps the pedal 12 times, presses down, I open the valve, he yells when he hits bottom and I close the valve. I have re-tightened all fittings. I removed the master cylinder and took it apart, checking for blocked port, condition of bore and seals, all looked good. Bled it in the vise, making sure the piston went full travel. Put back in, no change. I can get to a point where I think the air is out, went to the other back wheel, bled it and when I checked the p/s cylinder again, more air. I can hear the wheel cylinders clicking with the pedal strokes, but after bleeding brakes are not engaging. The front discs were engaging but they don't have to move as much as the rears. I did notice that the stroke of the pedal/rod thru the booster is slightly less than the full travel of the master cylinder, but if the bench bled cylinder has no air, would this make a difference? I know it takes a while to get the air out, but at the last try we used over a 1/2 can of fluid with no change. Suggestions/ advise appreciated. Chuck

rket56

Installed a duel circuit master cylinder/booster on the firewall of my 56 Olds. This was from a kit I bought several years ago. I have disc on the front and new cylinders/linings/springs on the rear. All new brake lines, connected to a proportioning valve directly under the m/c. Problem: Can't get the air out of the lines. Bled the master cylinder on the car and after several cans of fluid thru the lines, bled it for the 2nd time. Starting with the passenger side rear, my helper pumps the pedal 12 times, presses down, I open the valve, he yells when he hits bottom and I close the valve. I have re-tightened all fittings. I removed the master cylinder and took it apart, checking for blocked port, condition of bore and seals, all looked good. Bled it in the vise, making sure the piston went full travel. Put back in, no change. I can get to a point where I think the air is out, went to the other back wheel, bled it and when I checked the p/s cylinder again, more air. I can hear the wheel cylinders clicking with the pedal strokes, but after bleeding brakes are not engaging. The front discs were engaging but they don't have to move as much as the rears. I did notice that the stroke of the pedal/rod thru the booster is slightly less than the full travel of the master cylinder, but if the bench bled cylinder has no air, would this make a difference? I know it takes a while to get the air out, but at the last try we used over a 1/2 can of fluid with no change; the master cylinder has not been allowed to run low. Suggestions/ advise appreciated. Chuck

47 Convertible

Didn't see any mention of residual check valves on rear brake line(s). Here is a link to Master Power Brakes troubleshooting page. There are several good suggestions there plus a downloadable check sheet to help you go through things methodically:
http://www.mpbrakes.com/troubleshooting-guide

carjunky

Most prop valves have a pin sticking out at some location that you have to secure in the "down" or "in" position to allow bleeding of all cylinders. Use a "U" shaped piece of metal clamped to the valve to hold it pushed in.

carjunky

Oh yeah, remove it when done.

rket56

Thanks for the input guys. There is no residual valve in this system, apparently someone thought it wasn't needed. I checked the prop valve, it doesn't have a bleed pin. I called Jamco where I bought the master cylinder/booster/ pedal assy and they said no bleeding was necessary on the prop valve. They suggested I clamp off all the hoses and check the pedal travel. With the hoses clamped, the pedal is firm/can't move it. This shows that there is no leakage from the m/c to the clamps. When I removed the rear clamp, the pedal remained firm and when I removed the passenger front at the disc, the pedal went down. This line had not been bled yet so finished that ok. Now can't get the air out of the drivers side front. Will call Jamco again to see what they suggest next. Chuck

rket56

The problem was in the new front disc calipers. All the articles I read mentioned having the bleed valves pointing up while bleeding. Mine had 45 degree fittings, and were pointing down. It was plain to me that turning the fitting was not going to change anything so nothing was done. Finally, I found another article that said to remove the caliper and rotate it so the fitting was facing up......well Duh.........Of course that puts the air pocket under the bleed valve and the air can get out. In my defense, I had just replaced the brake hose on my wife's car and the bleed valve was also down and bled with no problem......because it was designed that way. Add on calipers are a different animal.