Hello gents.

I have a 72 F250 with power assist brakes. Disc front and drum rear. The Master cylinder went bad. I replaced the master ( I didn't bench bleed the master as I didn't have a vise big enough to secure it ) The truck also has a trailer brake system and this has a line running from the resevoir for the rear brakes ( brass fitting w/ 2 outlets ) to the switch box in the cab.

I bolted the master on and hooked up all the lines and proceeded to bleed all four wheels hence, bleeding the master in the process. Or so I think? The only line I didn't bleed is the trailer brake line as I couldn't find anywhere to bleed it ( no bleeder screw? ).

The brakes work but the pedal does not come back all the way and when applied the pedal is almost to the floor.

One thing I noted when doing the bleeding was the rear resevoir would actually " geyser " fluid up when the brake was pumped. The front resevoir did not do this.

I went through bleeding all four wheels 3 times in this sequence: Right rear, left rear, right front, left front.

So my questions are ,

Should I disconnect the lines and try to bleed just the master and then go through all the lines again?

Should I just disconnect the trailer brake line and plug the port?

Should I try bleeding the trailer brake line by unscrewing the end that goes into the switch box? ( messy ).

I'm thinking the trailer line is the culprit but since I didn't bench bleed the master and it is doing that geyser thing maybe that is the problem.

Considering the pedal is so lame I'm wondering if that 3 foot line from the rear resevoir to the trailer brake box is really an issue? I know it really should be bled, it's just odd how there isn't a bleeder screw.

FWIW, The trailer brake switch box has a **** on it that moves left to right when the brake pedal is depressed and it does do it now.


Thanks for any insight, Todd.

 

Was hoping for more responses. I really need to get these brakes working since the brakes on my daily driver just crapped the bed a few days ago!

One ( actually two things ) I didn't mention in my description is that I took out all the bleeder valves and cleaned them and also pulled the lines that go into the master and snaked those out.

Any help guys would be great. Thanks again, Todd.

 

You have an unusual trailer brake system. Most are electric, or have their on master cylinder.

First time I recall reading operating trailer brakes from a pickup. Those lines will have to be bled too.

Are you using them or were they from a prev. owner?



John

 

Hey John. Thank you for responding. It was from a previous owner. The weird thing ( at least to me ) is it appears the line running from the rear brake resevoir to the trailer brake switch box ( in cab ) only acts as an impetus for a signal to the box. The box has wires coming out of it into the harness and at the back of the truck there is only an electrical harness for what seems to be an elctrical brake system hook up.

Is it odd that I have fluid geysering up in the rear brake resevoir when I pump the brakes? Bashby here said both should geyser and a guy at the parts store said neither should?

I have bled a few systems in the past but, never had to do it 3 times and still end up with a lame pedal.

 

Can you eliminate it?

Maybe describe how the rest of the trucks system are connected to the MC.




John

 

Good morning John. I only have access at work

Brakes: There are three lines connected to the MC.

There is a splitter block attached to the the rear brake resevoir that the rear brake line and the trailer brake line attach to.

The third line is the line attached to the front brake resevoir.

The trailer brake line runs to the switch box in the cab

The lines for the front and rear brakes run down to a splitter box? Proportion valve? which has electrical wires running from it.

From there the front brake line runs to another splitter box for lines running to each disc brake caliper.

The rear brake runs to a splitter mounted on the axle housing ( center of meatball and sperates to the two rear drum brake pistons.

Today I am going to get a brass plug bolt and disconnect the trailer brake and bleed the whole system again.

Unless you have another clue or idea if that doesn't work I'm going to disconnect or loosen both MC connections ( front, rear ) and try bleeding the master itself and then do all the wheels again. What do you think?

Also, what about the geysering issue?

 

is the new master cylinder the right one? and is everything hooked up to the power assist? i have the same type of trailer brake has the line from master cyl through firewall to a electronic box same deal wires in harness only thing was my trailer brakes were hooked up to the front reservior for the front brakes went from master to a T fitting going in the cab and front brakes block. i just unhooked the whole system and plugged the T port mine was 4 wheel drum

 

1969/72 F250 2WD's with optional front discs use a specific master cylinder.

It's not the same as 1968 F250's with discs, not the same as 1968/72 F250 2WD's with manual or power drum brakes

1968/72 F250 2WD's with discs use a specific disc brake proportioning valve and a metering valve.

 

Good morning guys. Well I disconnected the trailer brake line and connected the front brake line and rear brake line and re bled the system 3 times again. Virtually no differnce in the brake pedal. Still stays about 1.5 inches down from where it should be and when depressed it moves about 4 inches.

I'm having a hard time accepting there is still air in the lines. On the 3rd time bleeding there was no air bubbles from any of the lines.

The only things I can think of is, the Master is bad, or it is the wrong one?

 

i would do research on the master cylinder if everything worked until that went out and all you did was replace it i'm kind of leaning towards you having the wrong one for your setup hey NumberDummy what are the differences in these master cyl's is it the bore size in them different?

 

DOAZ2140C (replaced C9TZ2140F) .. Master Cylinder / Bore diameter 1 1/4" / Use with Power Disc Brakes / Obsolete

Fits: 1969/72 F250 2WD & F350 / Despite this master cylinder having a Passenger Car part number prefix, it was not used on a Passenger Car.
-----------------------------------------------------------------------------------------------------------------------------------------
C9TZ2140C .. Master Cylinder / Bore diameter 1" / Use with Manual Drum Brakes / Obsolete

Fits: 1969/72 F250 2WD.
------------------------
C9TZ2140H .. Master Cylinder / Bore diameter 1" / Use with Power Drum Brakes / Obsolete

Fits: 1969/72 F100/250 2WD.

 

I had an Issue with the rod between the master cylinder and the power booster on an f350 with disk. On mine the front brakes wouldn't release because this rod wasn't adjusted properly. This was a rebuilt master/booster combo that came bolted together. The little rod pulled out of the booster on mine and had to be adjusted in. I'd think along with everyone else that your master is the variable and be sure its correct. If you've turned in your core ND's info would be a good place to start.

 

I have a 72 F100 Highboy 4x4. i need to replace a wheel stud and i am having trouble removing the front drum brakes. My question is does the drum seperate from the hub or is it all one piece. Thanks guys... Fallon Highboy

 

It sounds as though you may still have some air in the master. Get 2 short pieces of brake line with fittings that will screw into your master cylinder. Cut these to about 1" in length and get some fuel line (preferably clear) that fit firmly on the 1" long brake lines. Make these about 10" long. Screw the fittings into the master and put the other ends into their respective reservoirs, making sure that the ends remain completely submerged in the brake fluid in the full reservoirs. Now have a helper SLOWLY push the brake pedal down and release while you watch the clear tubes and reservoir for any signs of tiny air bubbles. Repeat the pedal down/up until no bubbles are seen and, one at a time, remove the fittings and reconnect your brake lines to the master. Then bleed fittings at the master. 1 or 2 air bubbles trapped in the master can cause the symptoms you describe.
HTH
Gene

 

The Master cylinder they gave me was the wrong one. I had NAPA order another one using the number ND gave me and VIOLA'. problem solved. I figured after bleeding the brakes six times with no psitive result it had to be the master was bad or it was the wrong one.

The real pisser is I painted the first one before I put it on so they probably won't take it back