proportioning valve or no?
 

I'm doing a front disc conversion on a 56 F-100. I'm using a 1970 Mustang Master Cylinder that is for Front Disc, rear drum set up. I have everything I need except the MC installed. My question is:
"Do I need a "proportioning valve?" I ask this questions, because, the master cylinder is set up for front disc & rear drums already. I'm under the impression that the proportioning valve compensates for front disc to rear drums pressure difference. So,........since the M/C is set up for that type of brake system, do I need the proprtioning valve, or is it built into the M/C?

Thanks
Ricky

While a proportioning valve is not absolutely necesary, after you make a few panic stops on wet pavement you'll see why you need it. It won't keep the rear brakes from locking up, but it will give you a lot more control of when they do.

I agree you would be be happier with a proportioning valve. I know I am.

I'm using a '69 Mustang MC without a proportioning valve. I asked the same question when I purchased the set up from ECI. They suggested trying it without, adding that they felt it probably would not be necessary and if it were, it wouldn't be difficult to add. I've had no problems with rear wheel lockup.

Maybe I can help a bit. First off, lets get the terms correct.

Proprtioning valve (Adjustable): Usually knob or lever type, is used to REDUCE the amount of pressure flow to one part of the brake system. In hot rods, usually in the rear line, so that rear brakes can be 'tuned' down, to match the front brakes ability to stop. The front brakes should lock up just before the rear.

Check valve (residual valve): This is a pressure comensating valve designed to hold a pre-determined amount of pressure in the brake system. These are used to eliminate the 'slack' in the system. Drum brakes have heavy return springs in them, and will continue to push fluid back to the master until the wheel cylinder is fully closed. to overcome this, we use a 10lb check valve, so that once the shoes are no longer touching the drums, they will stay there next to the drum, but not touching, ready for the next stop. Disk brakes have other issues. If the master is frame mounted, gravity will eventually drain the fluid from the caliper back to the master. And/or, the heat differential from the caliper to the master may push excess fluid back. A 2lb valve is used to prevent this. Firewall mounted masters do not have the gravity problem, but may be subject to the heat problem. Although less noticable, a 2lb valve may gain brake perfomance here too.

Metering blocks. This is the factory valve, that is pre-set. They were designed for the specific vehicle considering vehicle wieght, wheelbase, tire size, roll center, center of gravity, suspension style........ With this in mind, it is hard to get one of these to work just right. Oh, you might get one to stop, but not to the best of its ability.

Will it stop without the valves? yes, but NOT to its full potential.
Do the correct valves cost money? Yes, but they save a fender, or more!

Have a great day

My understanding is you want the proportioning valve to control the pressure between front and rear as others have noted. I believe some MCs have it built it.

Personally I would add it when you are doing the brakes. My brake work was not my favorite part of building the truck. I'd rather have it installed than have to cut lines again. You can always open it wide if its not needed.

DROPTOP46 gives a good description of many of the brake components but there is another non-adjustable proportioning valve that serves both the front and the rear systems. Here's a link to an MBM document that may help http://www.piratejack.net/Download-d...tructions.html
These are supplied for Disc-Drum or Disc-Disc configurations.

this is a good read http://www.geocities.com/MotorCity/2...propvalve.html

Thank you, ..that is great info. More to it then you think, eh? (that’s a Canadian word) ;)

(sure hate how the smiles keep changing positions) :-X09

The 2 and 10 pound prevent back flow of fluid back to the master cylinder in systems when the brakes are above the master cylinder (chassis mounted master cylinder) not firewall mounted m/c. I never thought it had anything to do with pressure, just back flow.
The proportioning valve is the two parts combined, thus called the combo valve sometimes. One part senses the difference between the front and back systems and will tell you if there is a difference of a low or loss of fluid in one side or the other( a light is one way to identify the difference). The other part is only in the rear brakes. It allows the front brakes which do the major braking to come on after the rear slightly starts to brake. You need a slight continous drag in the rear brake to keep the vehicle tracking straight forward as the brake pressure is increased. (factory non- adjustable, aftermarket adjustable designed because of various changes made by hot rodders in braking systems and still keep them operating as they should). Both do the braking only the front does the most. As braking is increased the weight of the vehicle dives forward and down which will decrease the downward weight on the rear as it wants to come upward. What works at a slow speed may not work at higher speeds when braking. If you ever have a vehicle switch end on you, you will want a properly adjusted valve. Always wanting to learn more, chuck

Some more info
http://www.classicperform.com/Instructions/PDF/PVK.pdf

http://www.classicperform.com/instructions.htm

Got the all in one from CPP. Need to install, after reading about the metering valve and proportioning valve functions $100 bucks wasnt so much to invest in stopping correctly.

Here's some more information: http://ecihotrodbrakes.com/brake_facts.html

This is how my system looks (no adjustable proportioning valve): http://ecihotrodbrakes.com/images/pic02_brakefacts.gif

I would go with a proportioning valve with that setup. I used the front disc/rear drum setup from a T-bird and also the master cylinder. The valve I used was a Summit adjustable one. After we got the truck on the road and a few adjustments it made a hugh difference. The valve had all the connections for the lines and also a switch for the lights.http://i247.photobucket.com/albums/g...fi/IMG012a.jpg

I put ECI discs on the front. I used a disc/drum master cylinder and booster from a 1973 F150 and no external proportioning valve. I have no rear wheel lock up issues, not even on wet pavement. Just another data point.

I plugged the hole in the top of the valve & ran a "T" off the front lines for the brake light switch & everything works like it should!

Thanks for all your help. Now ...... on to the windshield wipers.....yeah! <!-- / message -->