Bench bled master cylinder and all 4 wheels, spongy brakes

Just put on a new master cylinder cause the old one leaked out the back where it meets the brake booster. I bench bled it per instructions and then installed it on the power booster. Then I bled the front brakes at the calipers and the rears at the back of the drums. The brakes are spongy and the brake lights stay on. What have I missed or could I be doing wrong?

DDDVVV,

Did you bleed all locations until you purged air? That usually takes about a pint or more of fluid.

Did you have an ABS unit? A few GMs as early as 1983 had Teves and Bosch systems.

Then I bled the front brakes at the calipers and the rears at the back of the drums. The brakes are spongy and the brake lights stay on. What have I missed or could I be doing wrong?

The correct procedure for bleeding is to start at the wheel farthest from the master cylinder and work towards it.
ie: right rear
left rear
right front
left front

Just do not let the M/C run out of fluid in the process.

Give it another try and see what happens :grinyes:

Just put on a new master cylinder cause the old one leaked out the back where it meets the brake booster. I bench bled it per instructions and then installed it on the power booster. Then I bled the front brakes at the calipers and the rears at the back of the drums. The brakes are spongy and the brake lights stay on. What have I missed or could I be doing wrong?

spongy brakes mean your have air traped in the system.
when bleeding open the bleed fittings slowly.this will reduce air bubbles being created.the person pumping the brake pedal should not do any fast pumping slowly push down and repeat until the pedal is high and firm then bleed .

bleed the furthest first, closest last..

Just put on a new master cylinder cause the old one leaked out the back where it meets the brake booster. I bench bled it per instructions and then installed it on the power booster. Then I bled the front brakes at the calipers and the rears at the back of the drums. The brakes are spongy and the brake lights stay on. What have I missed or could I be doing wrong?


make sure there are no leaks..even with air in the system the pedal should not slowly drop.if it does then you have a leak..

Re bench bled the master cylinder and will bleed all four corners in sequence bit2lst described tonight.

I rebled and still the brake light stays on and the pedal is mushy. Could it be anything to do with that junction that bolts
to the frame below the brake booster? The only new thing is the master cylinder. When I restored the engine compartment originally I had removed the junction thing and the master cylinder and booster and when I put it back together I only bled the front brakes and it was fine. Now I repainted my frame down there so I disconnected all lines at the junction and electrical connector and hooked it all back
up nice and tight, bench bled mc and installed then bled all four brakes in correct sequence. Still mushy I don't get it?
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Could something be wrong with my new master cylinder?

I rebled and still the brake light stays on and the pedal is mushy. Could it be anything to do with that junction that bolts
to the frame below the brake booster? The only new thing is the master cylinder. When I restored the engine compartment originally I had removed the junction thing and the master cylinder and booster and when I put it back together I only bled the front brakes and it was fine. Now I repainted my frame down there so I disconnected all lines at the junction and electrical connector and hooked it all back
up nice and tight, bench bled mc and installed then bled all four brakes in correct sequence. Still mushy I don't get it?
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the removal of the junction block may be the area of , why the brake light is on..this block I believe has a metal stub that must be pushed in , like a reset button..since you disturbed a lot of fittings recheck all for leak especially at this area as this would cause this .

if the master cylinder is bad it would be pedal to floor like you ran out of fluid...booster bad hard pedal, very weak braking..

next would be removal of the drums check for leak...if the brake light continues to stay on...when the front/ rear brake pressure is different this light will come on...

the removal of the junction block may be the area of , why the brake light is on..this block I believe has a metal stub that must be pushed in , like a reset button..since you disturbed a lot of fittings recheck all for leak especially at this area as this would cause this .

if the master cylinder is bad it would be pedal to floor like you ran out of fluid...booster bad hard pedal, very weak braking..

next would be removal of the drums check for leak...if the brake light continues to stay on...when the front/ rear brake pressure is different this light will come on...

I checked all fittings and they're all tight. Checked drums and calipers and there's no leaks. Tried pushing in the tab on the front of the junction (the one with the rubber seal around it) and couldn't push it in. Service manual says you have to apply some brake pressure, tried that and still couldn't push it in.

In the service manual the only thing I can find out that pin is in the "pressure bleeding" section:

http://i121.photobucket.com/albums/o219/ernestmayhand/Caprice%20resto/a39386e9.jpg

Not sure about all this.

The button on the prop valve pulls out, for bleed ing the rear.

The button on the prop valve pulls out, for bleed ing the rear.

Okay well it is out, is there something I need to do to push it in or does it just take some muscle?