Rear brake problems

[SimpleT]

I am finally finishing my 1927 T. Evrything works great except the rear brakes. I have a dual master cylinder mounted below the floor - disc brakes on the front ad S-10 drum brakes on the rear. I have new cylinders, drums and shoes on the rear. I have the 10psi valve on the rear and just after it I have the propotioning valve. Right now the proportioning valve is opened up all the way (counter clockwise). I have bleed the brakes numerous times - but when I bpress on the pedal the rear tires still turn. I am stumped.

 

[ellis8500]

Check to be sure that you do not have the residual valve in backwards. If you can, make a tube that will bypass the valves to see if it's a master cylinder problem. Did you adjust your drum brake shoes after you installed them?

 

[SimpleT]

Check to be sure that you do not have the residual valve in backwards. If you can, make a tube that will bypass the valves to see if it's a master cylinder problem. Did you adjust your drum brake shoes after you installed them?

I will verify that the valves have the arrows going the correct way. I know I could bleed the brakes at the wheels. Also, the first time I adjusted the brakes - I went too tight. I backed them off - probably too much.

 

[putz]

When adjusting the brakes have them off the ground and adjust them till they are just dragging.Then test them with it jacked up just spinning by hand. One more thing you might think the rears are not working due to the small front tires grabbing so quick better brakes on front with smaller tires can screw up your thinking sometimes.JMO

 

[Chief-T]

I am finally finishing my 1927 T. Evrything works great except the rear brakes. I have a dual master cylinder mounted below the floor - disc brakes on the front ad S-10 drum brakes on the rear. I have new cylinders, drums and shoes on the rear. I have the 10psi valve on the rear and just after it I have the propotioning valve. Right now the proportioning valve is opened up all the way (counter clockwise). I have bleed the brakes numerous times - but when I bpress on the pedal the rear tires still turn. I am stumped.

I have the same components as you only plumbed different. My proportioning valve is between the MC and the residual valves. Brakes work great.

 

[oino]

I have the 10psi valve on the rear and just after it I have the propotioning valve.

Doesn't the propotioning valve need to be on the front brake side of the master cylinder to reduce fluid to the front so more goes to the rear?

At lease thats how I have mine. :hooray:

 

[Hotrod46]

Right now the proportioning valve is opened up all the way (counter clockwise).

If your prop valve works like mine, then turning it counter clockwise LOWERS the line pressure. Try turning it clockwise and see it that helps.

Also, the S10 rears have very small wheel cylinder bores (3/4"). Depending on the bore size of your master, you may not be getting a lot of mechanical advantage. The Astro van from the mid 90's have 7/8" bore wheel cylinders and should bolt right on.

Some S10's also have semi-metallic brake shoes and will require a lot of pressure and heat to develope good friction. As I understand it, GM was having problems with the rear brakes locking up and went to the hard material to help eliminate that. Swapping to organic linings will help and be cheaper too.

Mike

 

[SimpleT]

My master cylinder is the dual feed master cylinder from Speedway (p/n 910-31420). I do not know the bore size. I did verify last night that my res valvaes are at least installed in the correct direction. Thanks for all of the great ideas. They all make sence. I will start from adjusting my proportioning valve the other direction - then place the proportioning valve in front of the rear resid valve - etc

Thanks again

Tom

 

[oino]

Something like this

(image from Spirits Instruction Manual, edited by me)

[attachment=4075ropotioning valve.jpg]

 

[Hotrod46]

The Astro van from the mid 90's have 7/8" bore wheel cylinders and should bolt right on.

This is not completely correct. The van cylinders will only work on the later model S10 rears. The older brakes used a cylinder that was made completely different and unusual. Not sure what the year models for each type were.

I looked up the MC that you are using. It has a 1" bore according to Speedway. If you have 3/4" bore wheel cylinders, then you're going to have a hard time getting the rear brakes to hold. Depending on what discs you're using, you will probably find that the front brakes will lock up long before the rears even start to do anything. I'm guessing that's why Spirit puts the prop valve on the front.

Mike

 

[Ted Brown]

I would find a way to use larger wheel cyls, even if you have to change bolt patterns... or go to a smaller master, plus I would take the pro, valve out all together till you get things ironed out with the rear brakes.. Just me here...