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Master cylinder issue...

1971Chevelle

1971Chevelle

Veteran Member
Senior Member
My pedal was going to the floor, so I had to pump it a few times to stop. I exchanged the master cylinder under warranty today. I bench bled it, but I am not getting any pressure to the rear. If I disconnect the rear line at the master cylinder and push the pedal, fluid squirts out. Could it still be faulty, or is there another problem I need to look for? I could feel it moving the shoes in the drum while someone was pumping, so the lack of rear pressure out of the bleeder is baffling. It seemed to come out good the first couple of times, but now it just dribbles.
 
Only 2 things I can think of, 1 being the distribution block (unlikely), or check the rear wheel cylinder. I just had issues with the Starfire and all the wheel cylinders looked great EXCEPT when I pulled the rubber cap and saw it was leaking.

I think it's possible the master is bad out of the box (although it's never happened to me), but it has happened to Jon and Von.
 
1971Chevelle said:
My pedal was going to the floor, so I had to pump it a few times to stop. I exchanged the master cylinder under warranty today. I bench bled it, but I am not getting any pressure to the rear. If I disconnect the rear line at the master cylinder and push the pedal, fluid squirts out. Could it still be faulty, or is there another problem I need to look for? I could feel it moving the shoes in the drum while someone was pumping, so the lack of rear pressure out of the bleeder is baffling. It seemed to come out good the first couple of times, but now it just dribbles.
Click to expand...
There is too much air in the lines. Use a brake bleeding vacuum tool and someone in the car to pump the brakes. Eventually fluid will make it to the back.
 
Sorry. I made the assumption the lines were bled. All lines need to be bled completely. I usually start at the farthest point and work my way back.

I like using the hand pump vacuum bleeder myself, but someone pushing on the pedal will work.
 
kmakar said:
Sorry. I made the assumption the lines were bled. All lines need to be bled completely. I usually start at the farthest point and work my way back.

I like using the hand pump vacuum bleeder myself, but someone pushing on the pedal will work.
Click to expand...
Mine gave such a fit I had someone pushing and I was using a suction bleeder.
 
I was bleeding the brakes, starting at the right rear. Occasionally it will give a good squirt, but after that it will just dribble out. I ended up replacing both wheel cylinders,
as I discovered that one of them had a leak. My neighbor was helping me with the bleeding, and now my starter won't engage. I think he may have hit some wiring under
the dash with his foot (yes, it's a mess - it needs a new harness, but it is not something that I will attempt to do by myself). So, now I get to track down whatever is perventing
the start from engaging (it could actually be the switch on top of the column). Oh, and the brake light is on. I just can't win with this car.
 
Okay, we can work through each issue. Brake light. Check the switch over the pedal and make sure no wiring is interfering with the brake bar and the swtich. If there is nothing interfering, next look at the adjustment of the switch. easy way to tell if it's on (by yourself) use a mirror leaned against the back of a chair so you can see it from up front.

Next, I don't know how bad it is under your dash, but if pumping the brake pedal messed with some wiring, look there first to see if you see anything loose. Pictures might help us to help you.
 
Did you notice the rear drum backing plates looking wet from fluid? you said you replaced the wheel cylinders but I'd still check the new ones, Harbor Fright brake/vac pumps come in handy, I think my Mighty Vac came from there
 
kmakar said:
Okay, we can work through each issue. Brake light. Check the switch over the pedal and make sure no wiring is interfering with the brake bar and the swtich. If there is nothing interfering, next look at the adjustment of the switch. easy way to tell if it's on (by yourself) use a mirror leaned against the back of a chair so you can see it from up front.

Next, I don't know how bad it is under your dash, but if pumping the brake pedal messed with some wiring, look there first to see if you see anything loose. Pictures might help us to help you.
Click to expand...

From what I understand, the brake light has nothing to do with the switch on the brake pedal. It only comes on when triggered by the combination switch. I am going to drop the column in the morning and see if adjusting the ignition switch makes a difference.
 
Ok, you tripped the combination valve. There is a metal button on the end where you can push it back in, hard to do but you can.

When bleeding you need one of these:

1672370781836.png

It will prevent the combination valve from moving.

I have heard slamming on the pedal will also reset it, I had no luck with that.

Brakes Dragging

My Gold 72's front calipers (front disc rear drum factory set up) seem to be dragging more than normal, left side more than right. I have taken the caliper off, cleaned the pads, and lubed the pins. No dice. Brake hoses are new. I replaced the left front caliper and master cylinder. Checked the...
oldchevelles.com oldchevelles.com
 
Chevelle_Nut said:
Ok, you tripped the combination valve. There is a metal button on the end where you can push it back in, hard to do but you can.

When bleeding you need one of these:

View attachment 10029

It will prevent the combination valve from moving.

I have heard slamming on the pedal will also reset it, I had no luck with that.

Brakes Dragging

My Gold 72's front calipers (front disc rear drum factory set up) seem to be dragging more than normal, left side more than right. I have taken the caliper off, cleaned the pads, and lubed the pins. No dice. Brake hoses are new. I replaced the left front caliper and master cylinder. Checked the...
oldchevelles.com oldchevelles.com
Click to expand...

Mine moves fairly easily. I pushed it more than once, but the light is still on.
 
I hate to say it but you may need to take the valve out and look in it and make sure the rod is centered through the warning light sensor hole.
 
1971Chevelle said:
From what I understand, the brake light has nothing to do with the switch on the brake pedal. It only comes on when triggered by the combination switch. I am going to drop the column in the morning and see if adjusting the ignition switch makes a difference.
Click to expand...

I misunderstood. I thought you meant tail lights.
 
On fresh systems, dry lines and dry cylinders and calipers, I've spent over a half hour pumping to bring the fluid to all 4. I typically use the speed bleeders after bench bleeding the master. Did have an autozone master for the jeep that wouldn't pump the rear on the bench. Took it all apart and noticed nothing wrong, then re bench bleed....still nothing. Exchanged it, and everything's fine.
That's not your problem. I did purchase one of those pin locks for the prop valve, but have done dozens of systems not using one.
 
I got the brake light to shut off by pushing the brake pedal 3 times very hard. Here are some pictures of the installed brakes and wheel cylinders. There is some residual fluid on the driver side wheel cylinder pin that I didn't clean off (because I was tired of turning wrenches).

DSC03855.jpeg

DSC03856.jpeg

DSC03857.jpeg

DSC03858.jpeg
 
My brakes are hard, so they still need to be fully bled. I ordered a bleeder that works off of a compressor, so hopefully it will do the trick.
 
Chevelle_Nut said:
I tried one of those too, sort of works. The little hand pumps seem to do the best IMO
Click to expand...

The one I ordered gets good reviews. I just need to set the pressure lower on the compressor, start the bleeder to build vacuum, then open the bleeder valve. If I do that, it should pull it through fine.
 
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