Rear Brake Drum Problem. Cant Stop

[sedav1]

Trying to get the truck on the road but I just can't lock up the rear wheels.

I bought a TBP Power Brake Kit with Front Disks and replaced the rear 10" Drums with some from Tom's as well.

The front disks lock up just fine but the rear drums are killing me.

I am running 17" wheels & 35" tires.

I adjusted the drums so that there is resistance when turning the wheels and I have bled the brakes multiple times, multiple ways so I don't think there is air in the line. When running in gear at idle (900 RPM) I can't stop the rear wheels at all.

I pulled one of the wheels today and I had my little helper pump the brakes and I noticed that the piston was pressing out the forward pad only. The rear pad was not being moved one bit. There are brand new brake cylinders on both sides. I haven't pulled the other wheel yet but I can't stop that wheel either so I am assuming the same.

What could it be. The cylinders, lack of hydraulic pressure, e-brake cable tension, something stuck that is not allowing the rear pad to function correctly, wrong springs? I am trying to work thru the options so let me know your thoughts.

Thanks in advance,

Steve

 

[broncodriver99]

When you say lock up do you mean while driving or while on jack stands?

 

[sedav1]

Jack stands. The car is up on stands right now.

 

[Rustytruck]

Make sure the rod between the booster and master cylinder isnt adjusted too long or too short.

 

[DirtDonk]

Hey Steve. Sorry to hear you're having trouble. These things are often quite hard to figure out even with such a simple system.
But yes, I'd say you're having a hydraulic pressure issue to the rear system.
Do you have a proportioning valve installed?

I adjusted the drums so that there is resistance when turning the wheels and I have bled the brakes multiple times, multiple ways so I don't think there is air in the line....

Probably correct. But how firm is the pedal? Should be pretty firm or something isn't adjusted correctly yet.
Does it start engaging pretty quickly, or travel quite a bit? Once it does, is it firm or mushy?

I pulled one of the wheels today and I had my little helper pump the brakes and I noticed that the piston was pressing out the forward pad only. The rear pad was not being moved one bit.

Gotta love having the little helpers around. And they love it too. Just be careful or you won't own your Bronco anymore once they get to High School!
The moving of one shoe only might seem wrong, but because the drum is off, there really is no resistance to speak of. So if one side has springs that are under less tension than the other, that side will get all the motion.
You need to restrain the one side that's moving somehow to see if the other side will then start moving. If not, then you have something amiss in the cylinder.
But I don't think that's what is causing the trouble. Sounds more like you don't have any pressure to the rear system.

What could it be. The cylinders, lack of hydraulic pressure, e-brake cable tension, something stuck that is not allowing the rear pad to function correctly, wrong springs? I am trying to work thru the options so let me know your thoughts.

Same as you. Still some more detective work ahead to narrow it down.
Starting with shoe arrangement, is the shorter shoe on the forward side of the brake or the rear? Should be to the front. That's the "primary" shoe.
As for adjustment, it sounds like you have it correct, but you can check by applying the parking brake to see if the pedal gets any firmer. If so, then there is some more adjustment left in there. Maybe getting false signals from shoes that are not fitting properly into the drums. Very common these days I'm thinking.
Speaking of the parking brakes... Can you lock up the brakes with just the parking brake?

Good luck. Keep plugging away.

Paul

 

[smokinjoe]

Do you have a proportioning valve installed?

^^^^ This! That's the first thing that went through my mind Paul.

 

[sedav1]

The P-valve was already installed.

So I think I got it. It just took a bit of adjustment and going thru the system. I pulled the Master Cylinder and adjusted the rod a little bit. I then bench bled the MC to make sure there was no air there. That helped some but didn't get it stopped all the way.

I tried locking the brakes up with the e-brake and it turned out that that wasn't adjusted so I tightened that down so that it locks up the wheels when engaged.

I re-bled the brakes again and it seems to work now.

Thanks for the help. I am sure it will need some fine tuning but it is raining here so I will have to wait for another day to road test.