68 4 wheel drum issues
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Registered User
Joined: Mar 2012
Posts: 129
From: Olympia, Wa
68 4 wheel drum issues
I’m having an issue with the brakes for my 68 442. I can’t seem to get a firm pedal and all the air out of the system. This is a frame off restoration, 4 wheel drum car, everything is new (new brake lines, hoses, wheel cylinders, shoes, hardware and master cylinder).
First thing, I bench bleed the master cylinder, I did noticed that the rear port (rear line) doesn’t seem like I can remove 100% of the bubbles (I’m using the clear vinyl tubes routed back into the master cylinder reservoir), I can see very fine air bubbles in the tube. Front port looks great. After I vacuum bleed the system, using a liberal amount of fluid until I see no more air bubbles, I have spongy pedal (even after pumping the brakes) Go back and vacuum bleed and I find more air. So I try the old proven method of having the wife in the car, push in the pedal while I open and close the bleed screw. After going thru 20oz of fluid for the right rear, I’m unable to remove all the air, I’ll get like 4 pumps without air then back to fine air bubbles and then it will clear and then back to air. So I have to assume at this point, somehow I’m sucking air into the system. I have look at the entire system and don’t see any leaks or weeping from anywhere on the system. My first assumption was a bad master cylinder, the problem with that, this is my 2nd master cylinder with the same results. At this point, I have no idea how to trouble shoot this? Is it possible for a master cylinder or wheel cylinder to allow air into the system without leaking fluid?
First thing, I bench bleed the master cylinder, I did noticed that the rear port (rear line) doesn’t seem like I can remove 100% of the bubbles (I’m using the clear vinyl tubes routed back into the master cylinder reservoir), I can see very fine air bubbles in the tube. Front port looks great. After I vacuum bleed the system, using a liberal amount of fluid until I see no more air bubbles, I have spongy pedal (even after pumping the brakes) Go back and vacuum bleed and I find more air. So I try the old proven method of having the wife in the car, push in the pedal while I open and close the bleed screw. After going thru 20oz of fluid for the right rear, I’m unable to remove all the air, I’ll get like 4 pumps without air then back to fine air bubbles and then it will clear and then back to air. So I have to assume at this point, somehow I’m sucking air into the system. I have look at the entire system and don’t see any leaks or weeping from anywhere on the system. My first assumption was a bad master cylinder, the problem with that, this is my 2nd master cylinder with the same results. At this point, I have no idea how to trouble shoot this? Is it possible for a master cylinder or wheel cylinder to allow air into the system without leaking fluid?
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Joined: Oct 2009
Posts: 42,475
From: Poteau, Ok
How I bleed the brakes with the use of a warm bodied helper after adjusting all four brake shoes for light contact against the drums.
1 Have the helper pump the brakes until the pedal is firm and hold light steady pressure.
2 I open the bleeder at the RR wheel cylinder which in turn the helper pushes the brake pedal gently to the floor and holds it there.
3 Close the bleeder.
4 Repeat until there is no noticeable bubbles and getting a steady stream of fluid from the bleeder.
5 Periodically check fluid level to ensure the bowls don't empty.
6 Perform the same exercise on the remaining wheels.
Note, the helper needs to hold the pedal to the floor until the bleeder is closed, letting it come back up with the bleeder open allows air back into the system.
1 Have the helper pump the brakes until the pedal is firm and hold light steady pressure.
2 I open the bleeder at the RR wheel cylinder which in turn the helper pushes the brake pedal gently to the floor and holds it there.
3 Close the bleeder.
4 Repeat until there is no noticeable bubbles and getting a steady stream of fluid from the bleeder.
5 Periodically check fluid level to ensure the bowls don't empty.
6 Perform the same exercise on the remaining wheels.
Note, the helper needs to hold the pedal to the floor until the bleeder is closed, letting it come back up with the bleeder open allows air back into the system.
Thread Starter
Registered User
Joined: Mar 2012
Posts: 129
From: Olympia, Wa
How I bleed the brakes with the use of a warm bodied helper after adjusting all four brake shoes for light contact against the drums.
1 Have the helper pump the brakes until the pedal is firm and hold light steady pressure.
2 I open the bleeder at the RR wheel cylinder which in turn the helper pushes the brake pedal gently to the floor and holds it there.
3 Close the bleeder.
4 Repeat until there is no noticeable bubbles and getting a steady stream of fluid from the bleeder.
5 Periodically check fluid level to ensure the bowls don't empty.
6 Perform the same exercise on the remaining wheels.
Note, the helper needs to hold the pedal to the floor until the bleeder is closed, letting it come back up with the bleeder open allows air back into the system.
1 Have the helper pump the brakes until the pedal is firm and hold light steady pressure.
2 I open the bleeder at the RR wheel cylinder which in turn the helper pushes the brake pedal gently to the floor and holds it there.
3 Close the bleeder.
4 Repeat until there is no noticeable bubbles and getting a steady stream of fluid from the bleeder.
5 Periodically check fluid level to ensure the bowls don't empty.
6 Perform the same exercise on the remaining wheels.
Note, the helper needs to hold the pedal to the floor until the bleeder is closed, letting it come back up with the bleeder open allows air back into the system.
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