Is a proportioning valve needed???

I'm setting up the brakes in my Dad's '41 Plymouth. It has a '79 Nova 10 bolt rear axle(drums), stock '41 Plymouth drums up front and a master cylinder/power booster(disc/drum) from a '79 Ford Fairmont wagon.

So do I need a proportioning valve or can I just run a tee for the front and back?

 

I would use one. HRP

 

Why are you using a disc master on your drums? I am not sure if that's going to work well, might be way to much master for the drums.

 

Do yourself a favor and get a Drum/Drum master

 

Assuming your front wheel cylinders are in good condition, no leaks, I don't think the pressure will be too great on your front drum wheel cylinders. It takes the same line pressure to stop with or without power brakes....but with power brakes the PEDAL pressure required is reduced.

However, your use of a disc/drum master cylinder suggests you do not have the proper residual valve in the front circuit, IIRC, disc M/C do not use a residual valve. You can add an inline 10# residual pressure valve and solve that problem. They are available from many sources, but I get mine from Speedway.

You original question was about a proportioning valve. It seems many people immediately say "YES..you need a proportioning valve".....I think the correct answer is "it depends". What it depends on is, whether or not you have a significant mismatch of brake components and/or weight differences front to rear brought on by other mods to the vehicle or a particular combination of parts.

Given that you are using stock front brakes and a Nova rear end with stock drums, I would speculate that the Nova brakes are about the equal of the original Plymouth rear brakes. Since the car weight isn't changing much...I doubt you will have any problem.

One way to determine that is to get the car on a dry surface and make several stops with increasing brake pressure up to and including a "panic" stop. What you are looking for is rear brake lockup PRIOR to front brake lockup. Rear brakes locking before the fronts cause directional instability...i.e.. the rear end skids and wants to 'swing out' and subsequently changes your direction of travel. No lockup, no problem, and no proportioning valve needed.



Ray

 

Where should I put the inline valve at? I think I might try it without a proportioning valve and if it needs it I can always go back and put it in.

I'm using the disc/drum because it's what I had. And we are planning on installing disc brakes up front in the near future.

 

The Residual Pressure Valve (RPV) needs to go somewhere between the outlet port of the master cylinder and the "tee" fitting where the brake line splits to go to each front wheel.

Ray

 

So I put it after the tee going up to the master cylinder??? I swear sometimes I think somebody needs to draw me a picture.

 

You only need a residual pressure valve if your MC is mounted lower than your caliper/wheel cyl's.

They act as a check valve to prevent fluid from gravity draining back into your MC.

This applies to disc brakes.

Drum brakes need a 10 lb RPV.

 

My MC is on the firewall.

 

http://www.piratejack.net/index.php?option=com_content&view=article&id=11:typical-brake-system-configurations&catid=12:tech-support&Itemid=18 Brake set ups Bill aka Tnomoldw

 

Go to Bill's link above ^^^^^^^^^. It explains everything.

 

The diagram in the link in post #11 shows two RPV's on the from brake system.......no harm in that.....but in my experience one was all that was needed. 10#'s pressure is 10#'s pressure, whether provided by one valve or two. It also indicates you 'need' a metering valve......I disagree with that. Cars and trucks were built for many, many years without 'metering valves' . The diagram is from a vendor who sells parts. Again, you could put one in, no harm done, but in my opinion, unnecessary. Your call.

Ray

 

No, that's not the purpose of a RPV.
Usually you use a 2# RPV for discs, and a 10# for drums.
And you need them no matter where the MC is mounted (due to the real reason for using RPVs)

 

Yeah you're right just looked into it. It's been a while since I messed with designing a brake system. Did it way back in college for my senior design formula car. I remember using 2# RPV's for the system specifically because we had the MC mounted down low by the driver's feet, with a mechanical bias bar to take care of the front/rear brake bias. I also remember as part of my research that it does prevent fluid drain back in the situation that the MC is lower than your calipers. That was a fun project!

 

I used a dodge datona on the 52 mounted in the stock location. I also used a 10 Lb residuel valve on the rear and as I had disks a 2 lb on the front.it stopped better then my driver did. theres shots in my album of the system.

 

Go get A street rodder magazine. Next find ECI brakes for hot rods etc in the advertiser directory [last few pages in the magazine.]l They will hook you up ,with exactly what you need. There is another company now that does this install in their parts book also. Believe me man. you can get brakes on old kars screwed up quick .and have no idea why this problem is happening ,but everything is new!!!!!!.I have been there and done that, its not A pretty sight , bob s

ps yes ! they have every combination ofwheel cylinder sizes, and how to match chevy up, with ford.,and plymouth etc. Whatever anyone one is trying!......... to make there kar stop good. HTH

 

Are those '41 brakes single servo?
No way I'd run single servo on the front and duo servo on the rear. YMMV

 

What is single servo????

 

Non servo has a fixed anchor between the shoes at the bottom of the backing plate.