Ok have a brake question for yall.
 

1970 GMC. half ton. Drum brakes
I have replaced the master cylinder and all 4 wheel cylinders and the front brake shoes. The back ones look good. My pedal is still spongy I have bleed the hell out of the lines. Heres the odd thing though if I set the parking brake and step on the brake pedal, the pedal is stiff like its suppose to be.
Any ideas what might be wrong?????? Im going to pull the back wheels off and make sure the back drums are adjusted and tight like they are suppose to be. What else can I do? This just became my daily driver so I need to get fixed tonight.

Re: Ok have a brake question for yall.
 

Did you bench bleed the mastercylinder? If not you need to. Also you should also make sure that the brake shoes all touch the drums when the brakes are not applied. If you bleed them again, start with the brake farthest from the master cylinder and work your way to the closest. WES

Re: Ok have a brake question for yall.
 

Yeah I bench bled the master and I did bleed them the way you suggested. Gonna make sure the brakes are touching like you said, I have a feeling the back ones are not adjusted properly.

Re: Ok have a brake question for yall.
 

Spongy means air in the system. If you mean that the pedal travels too much before the brakes actually engage, then that's usually a different cause. Also, make sure you have the proper drum/drum master cylinder that has the built in residual valves in the front and back ports. If you have a disc/drum master, that could cause your problem because one port will not have the required residual valve and could allow the shoes controlled by it to retract too far after you disengage the brakes. Also, I would try leaning/tilting the front of the master cylinder down a little bit so that the front is lower than the back of it (without breaking loose the hard lines) and tap it lightly with a hammer to see if any trapped air bubbles come out. Might be easier if you back into your driveway, assuming the driveway is on an incline or lift the rear of the truck.

Re: Ok have a brake question for yall.
 

What you said about the E-brake, makes me think that the cross bar is installed wrong. Did you make sure the spring is on there, and that it is on correctly? Check to see if the bar is contacting the backing plate bolts to the axle tube, if they are then the bar is on wrong and could be binding.

Re: Ok have a brake question for yall.
 

Hey guys thanks for the fast replies. The first one hit it on the head. The adjuster stars had frozen up on the back. I took them apart and cleaned them up and adjusted the back brakes and the pedal feels great now. Thanks for all your help. I think Ill go ahead and replace the shoes this weekend too, they looked worse than they did this summer when I checked them.

Re: Ok have a brake question for yall.
 

Just my two cents. I did the same thing you did and replaced everything cyl/flex lines/ mast cyl and got the same outcome. My suggestion is to replace the adjusters next time you change out the shoes. A complete spring/adjuster kit from Autozone/Advanced/etc costs about 14.95 per wheel and is well worth changing out. Do it right and you won't have to touch it again. My adjusters were shot and needed to be changed out. Made the adjustments and found that the pedal was only traveling b/c the shoes weren't in contact with the drums. There should be very little drag on the wheels when adjusting them to proper specs. Recommend adding on self adjuster arms/spring if you have the time/$$$. Not terribly expensive either. Just looking out for you in the longrun. Nobody likes tearing apart drum brakes!!!

Re: Ok have a brake question for yall.
 

I think I will do that when I have the extra cash. Between the heat of the summer and all the rain we have had in the fall its been hard to work on my truck. No garage or carport. Just the gravel I park on.