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Discussion Starter · #1 ·
I have a 1953 chevy truck that has a gm chevy front end approx 1979 and an s10 rear axle with shoes. After bench bleeding the master and bleeding all wheels several times the brakes still wont work. One shoe on the back slightly moves when pushing the brake pedal, nothing else does. ???
 

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Sounds like the M/C needs more bench bleeding. Sometimes it seems to take forever to get all the air out when bench bleeding. Brake lines usually have "humps" in them that require fast (and often) pumping of the pedal to move the air out. Make sure you start with the right rear, get a good solid stream then move to the next further from the M/C.
 

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I have never bench blead.

Install the system dry.
Open up the furthest corner.
Grab a soda bottle, fill it 1/3 the way up with fluid. Stick a clear hose with 1/8id inside the bottle so it hits the bottom, stick the other end on the cracked open bleeder.

Fill up your master.
Pump it once slowly, check it again topping it off.
Repete until you have fluid coming out the line.

Now go around doing the other corners.

Then go around a full second time bleeding until all the bubles are out of the lines then pump a few more times before closing off the bleeders..
If the soda bottle gets full pour the excess bacm into the master just make sure the line is always submerged.
 

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Discussion Starter · #5 ·
Make sure the MC piston is retracting fully.
If the piston wasn’t fully retracting would I still be getting a solid stream at each wheel? I am getting a good solid stream but the pads and shoes don’t move. I have bled the system more times than you can imagine at different times and after each time I drove it. I bleed with a clear tube and bottle method. I see absolutely no bubbles in the tube when I’m done. Thanks for your help!
 

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Could just be your design.
For example.
what master cylinder?
where is it located? On the firewall or under the floor?
what combination valve and where is it located?
 

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It sounds like a mismatch or air in the master.

Did you research master bore/stroke versus the components at each corner? They have to match. If you use a small master and a large wheel cylinder/caliper, they won't move enough. You'll have a soft pedal and little engagement/long travel. Other way around and you'll have grabby brakes and not enough leverage so you'll have a hard pedal.
 

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Most likely. It's just a common thing to have happen.
When the piston retracts far enough to uncover the port the fluid should then lower in the resovior as the lines are refilled with fluid that was pushed out with the bleeder open.

Answer the other MC bore and caliper bores and specs. Also, the pedal ration would be good and we can figure it out.
 

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Discussion Starter · #10 ·
It sounds like a mismatch or air in the master.

Did you research master bore/stroke versus the components at each corner? They have to match. If you use a small master and a large wheel cylinder/caliper, they won't move enough. You'll have a soft pedal and little engagement/long travel. Other way around and you'll have grabby brakes and not enough leverage so you'll have a hard pedal.
All I know is it’s all GM and it was already installed when I got it. I think the front end is out of a 70s Camero and the rear end is out of an s10 not sure of the year. I took the front calipers off and it takes hard fast pumping to move the pistons. On the back I took one side completely apart and noticed the pistons won’t move with the shoes on but will move when the shoes are off. Wrong or bad master not putting out enough pressure?
 

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Discussion Starter · #11 ·
All I know is it’s all GM and it was already installed when I got it. I think the front end is out of a 70s Camero and the rear end is out of an s10 not sure of the year. I took the front calipers off and it takes hard fast pumping to move the pistons. On the back I took one side completely apart and noticed the pistons won’t move with the shoes on but will move when the shoes are off. Wrong or bad master not putting out enough pressure?
I know I have a solid stream of brake fluid to each wheel.
 

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Something to try. Remove the lines from the master cylinder and apply air pressure to them.
50-75lbs is enough. Are the calipers clamped right now? If Yes, you have a MC problem. If niot, you have a line or combination valve or caliper problem.
To further diagnose, verify pressure at various points in the system working from the bleeder to the Master Cylinder with a cheap air gauge and a brass fitting from the local hardware store. Attach the guage to the bleeder screws and hit the brakes. Medium brake pedal pressure should net you around 100 pounds of pressure. Try the same thing on the lines at the caliper and Master Cylinder ports.
One of those points will give you a clue and start looking there.
I suspect from over here, the Master Cylinder isn’t moving enough fluid or not building pressure as if fluid is bypassing the piston seal under pressure.
 

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Discussion Starter · #13 ·
Something to try. Remove the lines from the master cylinder and apply air pressure to them.
50-75lbs is enough. Are the calipers clamped right now? If Yes, you have a MC problem. If niot, you have a line or combination valve or caliper problem.
To further diagnose, verify pressure at various points in the system working from the bleeder to the Master Cylinder with a cheap air gauge and a brass fitting from the local hardware store. Attach the guage to the bleeder screws and hit the brakes. Medium brake pedal pressure should net you around 100 pounds of pressure. Try the same thing on the lines at the caliper and Master Cylinder ports.
One of those points will give you a clue and start looking there.
I suspect from over here, the Master Cylinder isn’t moving enough fluid or not building pressure as if fluid is bypassing the piston seal under pressure.
I’m also thinking the mc is the problem because the front and the back both are not working properly and it seems like a pressure problem. I’ll give this a try. Thanks!
 

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I’m also thinking the mc is the problem because the front and the back both are not working properly and it seems like a pressure problem. I’ll give this a try. Thanks!
Definitely sounds to me like you’re not getting full travel of the piston in the master cylinder. The actuator rod has to be just touching the bottom of the socket in the back end of the M/C piston when the pedal is all the way up, and the linkage needs to have enough travel to bottom the piston in the M/C bore when the pedal is on the floor. This can be easily overlooked in a new setup. You can use a ruler and a welding rod to check for proper engagement depth. Take into account the shoulder on the mounting tab of the M/C when measuring the depth. And the ruler and a friend to check the stroke. Put the M/C in a vise and use a screwdriver as a pushrod to measure the stroke of the piston in the M/C. I’ve been down this road before. When I installed the vacuum brake booster on my T-bucket with the brake M/C under the floor, I found that the booster didn’t come with an actuator rod.
 

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Discussion Starter · #15 ·
Definitely sounds to me like you’re not getting full travel of the piston in the master cylinder. The actuator rod has to be just touching the bottom of the socket in the back end of the M/C piston when the pedal is all the way up, and the linkage needs to have enough travel to bottom the piston in the M/C bore when the pedal is on the floor. This can be easily overlooked in a new setup. You can use a ruler and a welding rod to check for proper engagement depth. Take into account the shoulder on the mounting tab of the M/C when measuring the depth. And the ruler and a friend to check the stroke. Put the M/C in a vise and use a screwdriver as a pushrod to measure the stroke of the piston in the M/C. I’ve been down this road before. When I installed the vacuum brake booster on my T-bucket with the brake M/C under the floor, I found that the booster didn’t come with an actuator rod.
Thanks for the info! I tried putting a spacer between the mc and the mounting bracket and that made it worse. I had no brakes at all! I’ll see if I can take some measurements otherwise I may have to take it all apart and start over. I didn’t do the initial installation so I don’t know if it was all calculated or not. Thanks!
 

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Thanks for the info! I tried putting a spacer between the mc and the mounting bracket and that made it worse. I had no brakes at all! I’ll see if I can take some measurements otherwise I may have to take it all apart and start over. I didn’t do the initial installation so I don’t know if it was all calculated or not. Thanks!
Definitely sounds like you need to pull the MC and take measurements. Imperative that that is as I described before bothering to check anything else.
 

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Discussion Starter · #17 ·
Definitely sounds like you need to pull the MC and take measurements. Imperative that that is as I described before bothering to check anything else.
Also I’m thinking getting a mc that matches up to the front sub frame might help too. The one that’s on there is a universal and I’m wondering if it’s putting out enough pressure
 

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Also I’m thinking getting a mc that matches up to the front sub frame might help too. The one that’s on there is a universal and I’m wondering if it’s putting out enough pressure
P
Also I’m thinking getting a mc that matches up to the front sub frame might help too. The one that’s on there is a universal and I’m wondering if it’s putting out enough pressure
N
Also I’m thinking getting a mc that matches up to the front sub frame might help too. The one that’s on there is a universal and I’m wondering if it’s putting out enough pressure
[/QUOTE). No matter what master cylinder you choose it still needs to be set up as I outlined to get pressure. A adjustable proportioning valve can get the pressure that you need to each end of the vehicle. As long as you have a master cylinder that is set up for front disc rear drum, you shouldn’t have any problems. I’ve rebuilt many master cylinders. Interesting thing is that the piston is NOT one piece. The pressure applied to the rear section of the piston drives the front section.
 

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I can’t stress it enough. Even if you were to install a $1,000 master cylinder, you won’t get pressure unless the relationship between the brake linkage and the master cylinder is correct. Get that done before you even consider anything else. Come back after you have done that. You are overthinking right now. Time to get back to basics and go from there.
 

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Please read my posts again. Get the relationship between the master cylinder correct before even thinking about anything else. It is basic and essential for your brake system to function properly. Get back to us after you have done that and again bled the brakes.
 
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