A quick search didn't yield the answer. I realize it varies somewhat but what do you guys with power boost brakes feel is a reasonable pedal travel before you begin to feel pressure? The unit is a CPP unit installed on the frame. I've centered the shoes and adjusted them. Now ready to bleed the brakes and would like some kind of standard to shoot for. I assume the travel can be adjusted somewhat by the adjustment length of the push rod. Forgot to add that it's a rear drum/front disc system Thanks Bill

 

Normally I get brake application at about 1/4 travel. The pedal should be hard and the brakes locked at or just below 1/2 way. Normally.
The adjusting rod for the booster should only adjust the pedal up to the toeboard. The perfomance of the system can depend on a few different things.
CPP's proportioning valve that is under the master cylinder does not have check valves in it. You need to be sure to install a 2lb in the front (for discs) and a 10lb in the rear (for drums) This will keep that amount of pressure in the lines to keep the pads and shoes up against the rotor/drum. This is important for pedal travel. If you don't use them it will take more pedal travel to apply the brakes. This is especially true when the master is mounted down on the frame and the wheels are higher than the master cyl.
You said you have already, but the rear shoes also need to be adjusted up properly.
ALWAYS bench bleed the master cylinder before starting. It's messy and a pain to reinstall with fluid in it but if you don't bleed it first by itself, you'll never build pressure in the system.
All lines should be 3/16". (-3 for stainless)
I ALWAYS use a pressure bleeder when bleeding a new system. I can do it myself and it is alot quicker and more effiecient.
Hope that helps!!

 

Hey Bill,
Thanks for posting this question about brake pedal travel.
I've got that issue in my truck currently - It stops & the brakes work but I'm not comfortable with how much the pedal has to go down to get the brakes working. I'd like the pedal to engage the brakes quicker.

Proportioning valves sounds like the solution. The other issue I found in
getting "the brake feel" right in these old trucks is the actual brake pedal. I've got the little round brake pedal - I think changing to a more horizontal rectangular pedal is more like a modern set up & will improve "the feel" of your system as well. I live in fear of missing that little round pedal when I really need braking. I wasn't sure which pedal you were using in your set up.

I love your truck.

Ben in Austin

 

If you want to keep the "stock" look of the round pedal, the F4 and larger trucks have larger round pedals for clutch and brake. I know this because mine came with a set of each, one installed and one in a parts box. I saw new larger ones online in one of the catalogs (don't remember which right now).

Just a thought...

EDIT: It was on Dennis Carpenter...
http://www.parts123.com/parts123/yb....Z5Z5Z50000024C

 

Thanks guys this is all great info! You don't feel quite so alone out in the garage with the FTE bunch standing by. BBKtech, I might be back at you with a few more questions in a few days. Bill

 

Would 2 check valves be required for the front? I'm not familiar with CPP's prop valve. Just wondering if the lines come out of the valve for each front wheel?

 

One line for both front disks comes out of the prop. valve

 

Good to know, Thanks

 

Just to be clear, the 2 lb front and 10 lb rear valves discussed here are called residual pressure valves. A proportioning valve is an entirely different item. As mentioned, residual pressure valves keep a tiny bit of pressure in the lines for better brake actuation. They are a must for under-floor master cylinders to keep the fluid from running back out of the brake wheel cylinders to the master cylinder due to gravity.

 

If the system doesn't leak, cant it not find its way back down?
(like a straw with your thumb over it)

And aren't the wheel-cylinders still lower than the MC?
As they are wheel mounted.

 

The piston seals in drum brake wheel cylinders are cup-shaped. Hydraulic pressure applied to the back of the cup forces the lip around the outside of the cup into firm contact with the cylinder creating a tight, efficient seal. If you didn't maintain that pressure when the brakes were not applied, air would easily pull into the system past the cups. That's the purpose of a residual pressure valve. It keeps a small amount of pressure on the wheel cylinders at all times. It's not enough to cause drag or apply the brakes, but it's enought to maintain a seal on the wheel cylinder cups. Even later model cars with firewall-mounted master cylinders need residual pressure valves when used with drum brakes. The valves in those applications are normally integral to the master cylinder so you never really notice them.

With disc brakes, it's more of a matter of keeping the pistons and therefore the pads in close proximity to the rotor to keep pedal travel to a minimum. Gravity acting on the fluid performs that function when the master cylinder is firewall-mounted, but when it's mounted low on the frame, the fluid can easily siphon back to the master cylinder and pull the caliper pistons back with it. Then you get excessive pedal travel as the master cylinder has to move a larger volume of fluid to push the pistons and pads back into contact with the rotors when you step on the brakes. A 2 lb. residual pressure valve prevents this.

 

Since I started the thread I guess I can ask a slightly off thread question. After using the brakes to hold the truck while I run through the gears on the auto trans,I shut it off and there are no leaks. Then after several days there is a thimble of fluid on the floor under the master cylinder . Can't seem to find the source. As I said earlier it's fitted with a combo proprtioning valve for disk/drums. Could it be associated with the residual valve? Any thoughts?

 

My drum/disc brakes work fine, but I have prolly, no joke, 6" of pedal travel b4 braking begins. I have Volare clip with Chrysler MC/booster with a 77 Ford P/U hanging pedals. I have no residual valves that I am aware of. Do they simply screw into the proportionong valve, followed by the brake lines?

 

The aftermarket RPV's are designed to be mounted in-line and have a port on either end for a common 3/16" brake line. If you're running a firewall-mounted setup and you're using a master cylinder that was originally in a disc/drum setup, there should be a residual valve already built into the master cylinder in the port for the rear brakes and one shouldn't be necessary for the discs. I'd go through your system and check the shoe adjustment in the rear and free travel in the pedal. It sounds like something else isn't quite right.