[Oilyrascal]

Lets just say that a guy needed more fluid volume to his rear drum brakes or maybe all of the drum brakes on all 4 wheels but there was no larger bore master cylinder avail than the one he had now, what could he do?

Ok heres the deal, I have 4 rear wheel cylinders on my rear axle, I have installed the largest diam bore master cylinder I could find that will fit on my power brake booster ( 1 1/4 inch ) still cannot get a brake pedal. There is a possibility that my master just cannot push enough fluid to fill all 6 wheel cylinders.

What can I do to increase the volume/pressure?

I have been looking at different ideas and believe there is a solution but what might that be?

I understand there is products such as hydroassist ect but these rely on the engine to be running ect, I need to figure out first how to get a pedal whilst the truck is just sitting in a no run situation

[scholman]

Oilyrascal,

I am guessing that you have bled the air out of the lines. But on rear brake cylinders some times you need to raise the back of the car WAY up and use a power bleeder. Once all of the air is out make sure the brake shoes are adjusted properly. Adding a larger diameter master cylinder is not going to help your problem. I am figuring there is air in the lines. Otherwise you would have pedal.

Did you by chance bleed the front brakes? They could be causing the problem.

Scholman

[Oilyrascal]

Originally Posted by scholman

Oilyrascal,

I am guessing that you have bled the air out of the lines. But on rear brake cylinders some times you need to raise the back of the car WAY up and use a power bleeder. Once all of the air is out make sure the brake shoes are adjusted properly. Adding a larger diameter master cylinder is not going to help your problem. I am figuring there is air in the lines. Otherwise you would have pedal.

Did you by chance bleed the front brakes? They could be causing the problem.

Scholman

It would be a task to raise the rear up waay up on this truck but I could lower the front down to the ground, I think I have heard of this and may just give it a try, thanks

[1971BB427]

Make sure there's no air in the system, but also make sure you've got proper shoe adjustment too. If the shoes aren't adjusted up properly, then no amount of fluid will be enough to make them contact the drum. They need to be close enough to barely drag, and then when you hit the pedal they wont travel far to full contact.

[Oilyrascal]

Thanks, yes I have all this covered, I assumed there was a way to increase my fluid volume, something I could add too my system, maybe I was wrong

[MARTINSR]

What bore master went with the four wheel cylinders originally? What did these wheel cylinders come out of, I assume you didn't make up this system creating the four wheel cylinders where there once was two, what did it come from?

A smaller cyl is needed to provide more fluid pressure, maybe you have went to big? The thing is once the system is full of fluid, hardly any needs to actually "move". So I don't see how adding another wheel cylinder would change anything anyway.

Brian

[Oilyrascal]

Originally Posted by MARTINSR

What bore master went with the four wheel cylinders originally? What did these wheel cylinders come out of, I assume you didn't make up this system creating the four wheel cylinders where there once was two, what did it come from?

A smaller cyl is needed to provide more fluid pressure, maybe you have went to big? The thing is once the system is full of fluid, hardly any needs to actually "move". So I don't see how adding another wheel cylinder would change anything anyway.

Brian

Its 6 wheel cylinders total, 4 in the rear two in the front, 1.5 original bore with some sort of hydrovac booster mounted under the cab. 1952 F-7 Ford truck

This is something that is definitely part of the equation .....maybe you have went to big?

[MARTINSR]

That is what I am asking, what was the bore of the original master? When the truck sold they did stop right?


Brian

[Oilyrascal]

Originally Posted by MARTINSR

That is what I am asking, what was the bore of the original master? When the truck sold they did stop right?


Brian

1.5 original bore with some sort of hydrovac booster mounted under the cab

[MARTINSR]

Well if it originally had a 1.5 and it stopped you don't need a bigger one, there is some other problem like it isn't bled properly or shoes aren't adjusted properly or something. You aren't running a power brake booster at all now? If that is the case you may need to change your leverage on the brake pedal. I know that on sixties cars that I have worked on switching them from power to manual requires moving the rod that pushes the piston in the master cylinder nearer the pivot point on the brake pedal so you have more leverage. Maybe this is the problem? It makes a BIG difference on the amount of leverage you have.

Brian

[scholman]

Oilyrascal,

I have worked on this type truck and they can be a pain in the neck.
You have air in the system. Use a pressure tank at the master cylinder and start bleeding the system from the right rear then the left rear then the front right and lastly the front left.
Your hydrovac could be letting air into the system too. check the bleed valve on it also.

[cobalt327]

You can have a slight drag and still not be fully adjusted. I take the brake shoes out until they're tight in the drum then back them off to a ever-so-light drag.

[Oilyrascal]

Originally Posted by MARTINSR

Well if it originally had a 1.5 and it stopped you don't need a bigger one, there is some other problem like it isn't bled properly or shoes aren't adjusted properly or something. You aren't running a power brake booster at all now? If that is the case you may need to change your leverage on the brake pedal. I know that on sixties cars that I have worked on switching them from power to manual requires moving the rod that pushes the piston in the master cylinder nearer the pivot point on the brake pedal so you have more leverage. Maybe this is the problem? It makes a BIG difference on the amount of leverage you have.

Brian

I am sorry, maybe my math is not so good or how I typed my letters, original it had a 1 1/2 bore, the biggest master I have been able to find thus far that woul dmount onto my power brake booster is 1 1/4 inch, a difference of 1/4 inch.

I hope this is clearer

Moving the pivot point closer, that is something I will have to remember and look into further so I am clearer on what you mean. Thanks

[Oilyrascal]

Originally Posted by scholman

Oilyrascal,

I have worked on this type truck and they can be a pain in the neck.
You have air in the system. Use a pressure tank at the master cylinder and start bleeding the system from the right rear then the left rear then the front right and lastly the front left.
Your hydrovac could be letting air into the system too. check the bleed valve on it also.

I have no hydrovac, that is what was original for the truck, I have mounted a late model master and power brake booster onto the firewall, also put pedals up under the dash to move all of this.

So you have bled them? What do you mean by use a pressure tank at the master, can you show me what you mean with a picture, explain to me better the procedure?

[Oilyrascal]

Originally Posted by cobalt327

You can have a slight drag and still not be fully adjusted. I take the brake shoes out until they're tight in the drum then back them off to a ever-so-light drag.

Thats pretty much where they are at now, I mounted a new master today, I went thru 2 of the Napa Cordone masters, I did not like how they bench bled. I now have one I got at autozone, I did like how it benchbled.

I need to get some more info maybe on best way to bleed them, I have been told to raise the rear end, I like this idea, makes sense, also pressurize the master, I like this also, will wait to hear more on how to do this. Thanks again