Disc Brake conversion - can’t get pedal pressure

[65_Satellite]

I read through some of the other forums and didn’t see anything that helped. I recently converted my 65 Satellite to manual front discs. I used the Right Stuff Detailing disc brake kit which came with the 15/16 master cylinder, adjustable pushrod, adjustable proportioning valve, spindles, rotors, calipers and hoses. I also purchased from Inline Tube the complete hardline brake lines from front to back. I then bought the complete rear drum rebuild kit from Doctor Diff with new wheel cylinders. So I ultimately have an entirely brand new brake system in the car. I do want to note that I re-used the brake pedal pushrod from my single reservoir master cylinder as that has the bump in it that activates the brake light switch under the dash. The adjustable pushrod was not the same design and would not come close to the brake light switch to activate it. My issue is I’ve bench bled the master, and installed it and bleed the brakes all the way around going from right rear to left rear to right front to left front. After an hour or so, there appears to be no more air bubbles but the pedal is very spongy and goes right to the floor. If I have someone pressing the pedal, I can see the rear drums activating as they should and if it spin the drums and have someone hit the brakes, it stops them. The front discs are really tight fit and it’s hard to move the rotor but I can (with a lot of drag) and if you hit the pedal it stops them from moving. So they seem to be operating but the pedal is so soft and travels all the way to floor. What am I missing here? What can I do to get more pressure and prevent the pedal from going to floor?

 

[Beekeeper]

Did you install a residual valve in the master rear brake port or in the line?
You gotta have this valve to hold residual pressure in the rear wheel cylinders
The springs on the rear shoes will retract them too far from the drums and will cause them to travel too far before contacting the drums. This will cause the problem you are having. Also are these power brakes?

 

[65_Satellite]

Did you install a residual valve in the master rear brake port or in the line?
You gotta have this valve to hold residual pressure in the rear wheel cylinders
The springs on the rear shoes will retract them too far from the drums and will cause them to travel too far before contacting the drums. This will cause the problem you are having. Also are these power brakes?

These are manual disc/drum. I don’t know what a residual valve is. Are you referring to the proportioning valve?

 

[hunt2elk]

Did you install a residual valve in the master rear brake port or in the line?
You gotta have this valve to hold residual pressure in the rear wheel cylinders
The springs on the rear shoes will retract them too far from the drums and will cause them to travel too far before contacting the drums. This will cause the problem you are having. Also are these power brakes?

From what I have learned, all the newer rear wheel cylinders do not need a residual valve in the master cylinder. None of the aluminum masters that Dr Diff sells have the valve. The cast iron versions that I don't believe he sells anymore did come with the valve installed in the rear line port.
To me it sounds like there is still air in the system, or a bad master cylinder.

 

[65_Satellite]

From what I have learned, all the newer rear wheel cylinders do not need a residual valve in the master cylinder. None of the aluminum masters that Dr Diff sells have the valve. The cast iron versions that I don't believe he sells anymore did come with the valve installed in the rear line port.
To me it sounds like there is still air in the system, or a bad master cylinder.

This is the second master cylinder. The first one had an issue with the threads in the front port and it kept leaking. They sent me a replacement one that I just installed.

 

[hunt2elk]

These are manual disc/drum. I don’t know what a residual valve is. Are you referring to the proportioning valve?

No. The valve is inside the master cylinder port where your line screws in. Looks like a little orfice. If your master is full of fluid, remove the line going to the rear of the car. If no fluid leaks out, it has the valve. Like I stated earlier though, you don't need the valve with new wheel cylinders.

 

[Beekeeper]

I’m aware of the newer wheel cylinders having residual valves but I didn’t see any mention of the OP installing new ones.

 

[khryslerkid]

Have to ask...are the bleeders at the top on the front calipers?

Rear shoes adjusted properly, barely dragging to take any play/travel out?

What brake fluid are you using?

 

[hunt2elk]

I’m aware of the newer wheel cylinders having residual valves but I didn’t see any mention of the OP installing new ones.

"I then bought the complete rear drum rebuild kit from Doctor Diff with new wheel cylinders"
Actually too bad he didn't get everything from Cass instead of 3 different places.

 

[hunt2elk]

Have to ask...are the bleeders at the top on the front calipers?

Rear shoes adjusted properly, barely dragging to take any play/travel out?

What brake fluid are you using?

Good ideas as well. Rear shoes not adjusted properly will act just like the op is experiencing.

 

[cbcborm]

my problem was basic the same but
the bleeders were at bottom. air couldn't scape, they need to be at the top on the front calipers.
I switch calipers position and case solved.

 

[Beekeeper]

"I then bought the complete rear drum rebuild kit from Doctor Diff with new wheel cylinders"
Actually too bad he didn't get everything from Cass instead of 3 different places.

so much for my reading skills

 

[65_Satellite]

I’m aware of the newer wheel cylinders having residual valves but I didn’t see any mention of the OP installing new ones.

Yes I mentioned that I bought the complete rear drum rebuild kit including the wheel cylinders from doctor diff

 

[65_Satellite]

Have to ask...are the bleeders at the top on the front calipers?

Rear shoes adjusted properly, barely dragging to take any play/travel out?

What brake fluid are you using?

Yes bleeders at the top, rears adjusted with slight drag and using DOT3

 

[khryslerkid]

What master cylinder did you get?

 

[65_Satellite]

"I then bought the complete rear drum rebuild kit from Doctor Diff with new wheel cylinders"
Actually too bad he didn't get everything from Cass instead of 3 different places.

I had the front disc kit and I did call Cass about the all the lines but the shipping was so costly it wasn’t in the budget.

 

[hunt2elk]

How much time did you spend bench bleeding the master? Sometimes it takes quite a bit to get all the air out of them.

 

[65_Satellite]

What master cylinder did you get?

It was part of the kit I bought. It’s a cast iron 15/16 bore

 

[65_Satellite]

How much time did you spend bench bleeding the master? Sometimes it takes quite a bit to get all the air out of them.

Maybe about 5 minutes or so. A lot of air bubbles at first and then all fluid. The first master I did in a vice. This is the second one (replacement) and I mounted it to the car and then bled it using the pedal and then attached the lines and bled the system

 

[hunt2elk]

I had the front disc kit and I did call Cass about the all the lines but the shipping was so costly it wasn’t in the budget.

I shouldn't have said that. Just that he is so good about dealing with problems and taking care of you if there is an issue with something he sells. He doesn't stock lines and some other stuff, but has them shipped from The Right Stuff or Inline Tube. So that is why his shipping is higher on some things.