Hey folks, Just gunna bounce a few off you's to make sure I'm not missing something.

I upgraded my 65 f250 to a power dual master drum/drum from a 72 f250. I had a single pot that had decent brakes , although I had to one pump them to get a great pedal. I put on a new master drum/drum from a 72. I installed the pedal assembly from the 72. All seemed to go well. I did run into some air in the line issues and I still may have some. I used these pedals to 1: get elecrtic brake switch 2: correct rod lenght and pedal leverage.

I used one new line to hook into the rears and blocked the old rear port on distrubution block. rear/front

So as of now, vehicle off, I panic brake and the brakes move about 3" but they are hard. I can pump them and they are about the same. So I most likely have some air in there. I adjusted the drums on all 4 corners till slightly dragging.

Now, the issue: when I start the vehicle I still have about the same pedal (less effort) but my pedal will not return to to the top. My lights stay on. I feel I've hit a wall here. If I turn off the truck they pop up and hit the switch. Fire the itch up and the pedal sucks in about 1/2" . I can easily pull it up but it drops right back with vehicle running?

So do I have more air ?? my old brakes had a spring on the pedal do I still need it? Is the master busted? Booster bad?

I did not have any brakes for a while, then It kinda was popping a little in the pedal then I had brakes this was during several gallons of brake fluid flushing and bleeding.

thanks for any input,

bob

 

I sounds more like you have too much vacum going into the booster, the wrong pedal to master cylinder adjustments, or a weak/broken booster return spring. The booster works off vacum to pull the rod into the master cylinder with a spring to keep it from retracking until you overcome the spring tension with your foot pressing on it lightly. Doesn't the pushrod coming out of the booster have an adjustment screw on it to make slight changes? If so you might have too many threads showing which will cause the brakes to drag. Also check to see if you can adjust the pedal rod going to the booster. Add some length if it's possible. Use a hand held vacum pump with a guage to see if your booster is moving well below what it should. Just a few items to look at before throwing a grenade at it.

 

I don't like to read it when folks start recommending randomly mixing and matching brake system parts. The power disc upgrade had proven to work and be safe at the same time.

Be careful brothers,

John

 

I'm not following you.??

I replaced my single drum/drum manual system with a 72 drum/drum power system master right down to the pedals. I plan to goto discs someday, but It was not an option for me at this time.

thanks,
bob

 

Bob do you know if the brakes were working alright on the donor? Sounds to me like a booster problem. I would put a return spring on the pedal before adjusting the rod length. It should not need it in your situation. Have you driven the truck with the new setup? If so how does it feel. Does it stop better? Does it feel like your pushing the pedal too far before anything is happening? Does it feel solid? Will it lock the wheels up in a panic stop?

 

The donor had working brakes but, I didn't drive it. I can't drive the truck right now I melted the shifter cable. The most I can do is stationary brake testing. I know brake bleed better after a few miles of stop and go. The booster seems to be boosting from my first test drive, but the pedal wasn't returning.

Is there a spring in the booster at all? or does it just hold it back from brake pressure?

bob

 

Yes there are springs in the booster and yes they can fail. Sounds like the spring on the vacuum side of the booster diaphram is weak.

 

HHMMM, I don't remember seeing one in there. maybe it fell down when then the plunger fell out on me.

bob

 

Bob, Did you measure the brake shoe widths on both trucks front and back to see if they were the same?

John

 

John, no.

Still, perhaps I didn't think about it enough. Are you suggesting that the shoe size would cause my static brake issue. Not enough return pressure?? Honestly, after all the articles I've read it seemed a pretty straight forward swap. My thinking was any dual master f250 D/D would be better than the single pot I had. Napa had the same part number for the various years of drum/drum.

In hindsight I sould have just done the dual master manual brakes.

I do have dual piston front and rear drums. The rear is a dana 60

The pedal returns fine when there is no vac on the booster. It had good brakes with the single master on there. My old brake pedal did have a factory return spring. And yess it's lost. The boy was using it now it's gone.

bob

 

Bob,

It sounds like you have the incorrect pushrod length between pedal/lever & booster, Also, without a return spring what would cause the pdeal to return?

The Booster is activated when it gets vacuum from the engine. The diaphram sets up in the ready position. When the vacuum stops, your diaphram is "returning" too far because the push rod is too short, Also because it is too short, switch is not canceling out the lights, thus the lights stay on.

In addition you probably did not install a proportioning valve when you went to a dual chamber, split line, front system. It may not work the way you expect when you try a dynamic application to stop momentum + velocity.

I concur with both Mark & John I offhandedly disagree with mix & match brake system modifications such as yours.

I also catagorically state that adding a power booster to a non power system does not increase braking efficiency, it decreases it, in spite of what the pedal application pressure "feels" like. The problem with drum brakes is they cannot dissapate the heat created by braking, pushing harder by using a booster only exacerbates the problem because the booster is amplifying your personal effort, which = pushing harder against the drums and increasing the heat accumulation rate thereof. I've said this many many times here & elsewhere.

Although change is the only constant, it should be for the better or for improvement, and not just change for changes sake, IMHO.

But what could I possibly know about brakes, or changes. . . . . Huh?

FBp

 

To answer the question of where is the booster spring, it is roughly the same diameter as the booster housing on one side and narrows like a cone to a center cup on the booster diaphram. My thoughts on the booster to master cylinder rod adjustment comes from reading the tech sheet that CPP sent with their master cylinder. It says in a nut shell that if the pushrod is too long it will not allow the master cylinder piston to fully retract which will reduce the volume of fluid being pushed out to fill the wheel cylinders. Being that you took the whole system from the donor the problem most likely lies within the booster. Make sense?

One more thought just occured to me. Is the firewall to brake arm pivot the same distance on the donor compared to your truck? No, that wouldn't be a problem if a few hundred other swaps have already been done without this coming up.