The Stovebolt Site Forums The Shop Area The HiPo Shop power brake and dual master cylinder plumbing

I'm preparing to install a firewall mounted pedal assembly with a power booster and dual master cylinder in my 52. I got the booster and master cylinder out of a 99-02 Chevy Silverado (base model truck) and bought the pedal assembly (pirate jacks) from Carolina Classic Trucks.

Anyways I read on their website that when running drum brakes (all around) you need a 10lb residual pressure valve on the line going to the front and going to the back. I also read that its best to put them as close as possible to the master cylinder. I'm planning to follow Cletis's tech-tip about installing a dual master cylinder as far as line sizes, But because I'm mounting the m/c on the firewall and can't leave well enough alone, im going to flip the line to the rear from the passenger side of the frame, to the drivers. All else will be about the same.

My question in all of this is about the residual valves. The residual valves have a 1/8" inlet and outlet, so I imagine I just use a reducer fitting to go from 1/4" down to 1/8"? So the line coming out of the m/c will be 1/4", which then goes to a reducer fitting that goes from 1/4" to 1/8" into the residual valve, then out to another reducer fitting that brings the line from 1/8" back to 1/4" which then goes a tee that splits the line down to 2 3/16" lines to the rear or front drums.

Correct?

this is the tech-tip
http://www.stovebolt.com/techtips/master_cylinder/index.html

My experience with Power brakes, firewall mounted is that you do not need residual valves since the master cylinder is much higher than the wheel cylinders/ calipers. You only need residuals when your master cylinder is the same level or lower than the wheel cylinders/calipers. The brake fluid has a tendency to run backward into the mastercylinder when it is lower, Never happens when the cylinder is mounted higher.. Good luck.

I'll second that,
Grigg

What type of brakes did the new truck have? and what type does your old one have? If they are both drum/drum should be fine, could even use the proportioning valve from the new truck. But if the new one had disc, and you have all drums, then some more investigation may be necessary. I'm not sure if that MC will work or not, but worth checking into. You for sure need a proportioning valve from a vehicle with similar brake system.

Grigg

the silverado was a base model truck, it had a v6 engine and the brakes were disc in front and drums in the back, it also had no ABS.

My truck will have all drums, for now.

OK, well the general consensus I've been getting is to do away with the residual pressure valves so thats what im going to do. I am going to plumb in a adjustable porportioning valve for the rear. Where would the best place to mount this be? Is it possible or safe to mount it in the cab (say under the dash or on the floor by the drivers seat)? Or is it best to just keep it out of the cab on the firewall or frame?

So nothing goes on the line to the front? Just a 1/4" line coming out of the master cylinder, which will go to a Tee mounted close by the driver front wheel. Coming out of the Tee will be two 1/4" lines, one looping around to the driver front wheel, and the other running along the front crossmember to the passenger front wheel.

The rear will have a 1/4" line coming out of the m/c which will go into a adjustable porportioning valve mounted somewhere via a reducer (1/4" down to 1/8"). Out of the apv the line will jump back up to 1/4 via another reducer (1/8" up to 1/4") and from there back to a Tee mounted on the rear axle. Out of the tee will be 2 3/16" lines going to the wheel cylinders. Correct?

If you mount porportioning valve in the cab you can dial all your braking into the fronts and do smokey burn-out donuts just like Jimmie Johnson (or your fav-0-rite NASCAR jockey).

If you watch closely in cockpit shots, you can see them twisting away at the knob after they take the checkered...

So the answer is, you can mount in the cab if you want, and racers do, but if you are only using to adjust once and then forget it, I wouldn't necessarily bother. I'd think a frame mount with access door in the cab floor would be almost the best of both worlds.

I never thought of that! That would be a plus.

I more thought of mounting it in the cab so it would be easier to fine tune it, rather than making a stop, getting out, turning the dial a little bit, getting back in, making another stop, getting out, etc. In the cab, hit the brakes, turn dial, hit the brakes, turn the dial.....

I may just put it in the cab, mounted on the under side of the dash. The rear line would come off the M/C, make a 90 degree turn, through the firewall to the apv and then from there back towards and through the firewall, then down towards the frame.

Here is another question, when you switch to powered brakes with a dual master cylinder, do you increase the line size. I was looking at the stock plumbing today and the driver side front wheel cylinder has a 3/16" line coming right from the m/c. The other wheel cylinders have a line coming off the m/c, I think 1/4", which goes to a Tee on the passenger side frame, where it splits and a 3/16" line goes to the passenger side front wheel cylinder and another 3/16" line goes to the rear. On the rear axle it splits and looks like the lines to the rear wheel cylinders are slightly bigger than 1/8". Is this correct?

I would mount the porportioning valve either beside the MC, or in a convienent spot on the frame. You will probably set it once and forget about it.
I used one on the last truck I put together, it was under the cab outside the frame, I may have gotten out and adjusted it 2 or 3 times when I first got the truck on the road, then never touched it again.
I can't think of a good reason to mount it in the dash, as close as I would get to in the cab is have the lines outside and just the stem and knob poke through the floor board. But then you may want to consider the cab moving on the mounts and flexing the line, overtime could cause a crack. now you have another reason to leave it outside the cab on the frame..

For your truck I would suggest 1/4" line back to the rear axle, then 3/16" to each wheel.
Front probably 1/4 to the T, then 3/16 from there, or could do it all with 1/4 if you like.
Really should be fine with what the factory setup was, as you still have original brakes right?

Either power or manual brakes, same line size.

Grigg

well it sort of has the stock brake setup, the front I know is stock, but the rear axle was switched out by the previous owner so there is no torque tube anymore. Im not sure what the axle was out of (was told a nova, but not sure). Anyways its got drum brakes on all 4 corners.

When I did the brakes on my 39, i pulled all the brake stuff off the same donor vehicle with the brake setup I was looking for.. ie.. disk front/drum rear, no power brakes... It works very well.

Here's another thought/question (I know Im full of them). Would you be able to use a combination valve (porportioning valve/metering valve/differential pressure switch) with a drum brake system. It seems logical that I could, seeing that the porportioning valve would regulate the rear pressure, the metering valve would hold off the fronts until the rear starts braking (I know this is only for vehicles with front disc's) and the pressure switch would just be an extra as I could mount a warning light in the cab.

Im planning on putting disc brakes on the front so this will have to be plumbed in eventually. And it will only be in this configuration driving around my yard as it will have front disc's by time it hits the road.

What do you think?

Now there's some info that would have helped earlier..
In that case I would recommend 3/16" lines to the front.
Also go ahead and complete the system in preparation for the disc swap, use the proper lines and valve for that setup.
Then assuming you really won't be driving any more than in the yard you should be fine, you may not even want to hook up the front drum brakes and don't put any fluid in that part of the MC, then carefully drive around the yard as needed, and plan on that front disc conversion before the truck is on the road.

Grigg

So from the combination valve I would have two 3/16" lines coming out and going to the front brakes. Now currently my truck has a 3/16" line coming out of the stock m/c to the rear axle (after splitting and going to the passenger front). At the rear axle it splits into two lines that look slightly bigger than 1/8". Is it fine to keep that size to the rear. So just have a 3/16" line come out of the combination valve, run down along the driver side frame and split on the rear axle, using the +/- 1/8" lines going to the rear wheel cylinders?

You should be fine with 3/16" for everything from front to rear, all of them.
I doubt the rear axle lines are 1/8", probably 3/16", but I don't usually play with small trucks.. so you're probably right.

If I were to deviate any from all 3/16" lines it would be 1/4" line from MC to proportioning valve and from valve to the T at the rear axle where it splits to 3/16. But if you have a relatively small axle with the appropriate brakes the 3/16 should be fine for that.

In my case I have relatively large disc brakes front and rear, and the factory setup was 1/4" feeding the rear brakes where it split to 3/16" on the axle.

Some folks will say disc brake systems use 3/16" for everything, (I believed that at one time) and some systems do, but not all. The disc I have from the P30 chassis uses the 1/4" rear line, and the last project truck I had used 1/4" for every bit of the brake lines, and it had disc front and rear.

In the end you are trying to duplicate a factory system, not redesign one. So what ever size line the wheel cylinder and calipers had originally, then that's what you want to use again.

Grigg

OK I don't know how but I was measuring wrong. All the lines currently on the truck in stock form are 1/4", except the lines on the rear axle. They are 3/16". So should I stick with 1/4" lines for everything, and 3/16" for the lines on the rear axle? Im waiting for my pedal assembly to be delivered so Im looking at ordering all the supplies that I need now, so that I have them for the weekend when I go to install it. Im going to plumb in the combination valve so that its there when I switch the front drums out for disc brakes.