Can I use this brake valve

[Mark B]

I am adding a power booster and new master cylinder to my 4 wheel drum truck. The truck had manual drum brakes and will stay all drums. Can I use the old distribution block (pictured)? My understanding is that since the truck will be still 4 wheel drums, then the old distribution block really does nothing (no proportioning effect), and really only serves to work the brake failure light. I will adding a 10lb residual value downstream on the distribution block on each brake line (one one front line and one on rear line).

thanks very much
Mark

[cdowns]

i believe the distribution block does more than work the brake light// to understand a brake system like this and to entrust your life to it spend the money on a factory sevice manual and save the money you'd of spent needlessly on residual valves

[michael bustamante]

When I added a booster to my 67 I used the original block still and it worked just fine, just make sure the drum brake shoes are properly adjusted and give yourself some stopping distance, remember drum brakes lock up alot easier than disk,

[Mark B]

cdowns, thanks for the reply. I am not taking doing my brake work lightly or without caution. That's why I made the post. I have been doing my research. Residual valves are an important component in a power drum system.

thanks
Mark

[Sinister]

I have 4 wheel power drum brakes and never heard of a residual valve.

[Mark B]

Here is what I read from MP Brakes....

A ten pound residual pressure valve is needed to the drum brake portion of your brakes to maintain a firm pedal. The springs in the drum system will pull the drum brake shoes back in away from the drums. The residual pressure valve maintains a pressure in the system to counteract the spring tension.
This allows instant activation of the drums giving a firmer pedal.

and this from Classic Performance Products....

DRUM / DRUM
A drum / drum master is designed to deliver fluid pressure and volume to the front and the rear of a braking system in equal proportions. Drum brakes will require less fluid and pressure than disc brakes. Typically a drum brake master will be smaller than a disc master and the fluid reservoir chambers will be equal in size. Since drum brakes require the use of residual pressure valves the original drum master cylinders had residual valves built into the outlets. Later model aftermarket units do not have these valves and they must be installed in the lines externally. Failure to incorporate residual valves will cause spongy brakes.

The tech person at the distributor who sold me the booster/mc combo, said I needed these and included two 10lb valves.

So it seams to me you can run without residual valves, with the only effect being a softer peddle. Obvioulsy it works for your setup.


thanks
Mark

[cdowns]

thats all niey nicey// BUt it does not tell you what the components are in the factory distribution block a what purpose they serve does it??? i suggest reading factory service manual for infomation clarification

[storm9c1]

It might be mentioned in the service manual for the different brake systems and if they have different prop valves. But only if you are lucky. I'd have to take a peek in my manuals.

But from experience, I've gone through the same "research" process when I've done drum-to-disc conversions just to be sure. Man, it's much more complicated when you do a disc conversion since you DO need to change the prop valve (some are called combo valves since they often do the prop and resid function together). Finding the right valve for the right car is tricky.

It would also stand to reason that since you are NOT changing the drums, then the existing valve (that you have) would suffice, assuming that you are using a factory or reman power booster and master cyl that was designed to compliment your drums. My logic behind this that you aren't changing much of the actual pressure applied to the drums, you are just changing how much mechanical advantage your foot is given by the power booster. What I don't know is if your existing prop valve or master has a residual valve built in. As I said before, some prop valves do (and some cars even have two discreet valves for each purpose). And as others have said before, sometimes that function is built into the master cyl. If you are unsure, then I'd leave out the resid valve and see how it feels. Too spongy, then that would stand to reason that you need to add it.

Also, you may want to add the resid valve to the front only in some cases. You want those brakes to catch quicker than the rear so that your rear doesn't come around on you on slippery surfaces. Some older Mopars, for example, actually had a secondary valve that DELAYED application of the rear brakes to emulate this same behavior.

It's complicated and it is a good idea to do your homework. But nothing beats testing and common sense once you put it all together and drive it.

[Mark B]

Thank Tom for the well thought out reply. Good idea - maybe my existing original prop valve has a residual valve built in. I'll look into that. Any idea how to tell? Are there new prop valves available for all drum setups that have the residual?

The residual valves that I have are for 3/16 inch brake lines, and the truck is all plumbed 1/4" front and back. I searched suppliers for 1/4" line residual valves, but none of the supplier even mentions line size, so I am assuming they are all 3/16. Does anyone know for sure?

And if residual valves are all 3/16", how do they get fitted into 1/4" lines?

You guys with no residual valves - is your brake peddle soft? Do you think this is all a waste of time? Logic suggests that if the peddle was OK before a booster was added, it should be OK after the power booster is added.

I am taking my daughter to her wedding in this truck, so I have to get it right!

thanks
Mark

[Sinister]

Originally Posted by Mark B

Here is what I read from MP Brakes....

DRUM / DRUM
...Since drum brakes require the use of residual pressure valves the original drum master cylinders had residual valves built into the outlets....

If your using a drum/drum master cylinder I think you'll be alright. I would be more concerned with getting the pushrod length right going to the booster. Also I believe there are two different ways the brake pedal can be hooked up to the push rod depending on whether it's power brakes or manual.

[Hottrucks]

all of this is correct...and you will see when you mount the booster brackets..alittle common sence and it will all fall into place....yu dont even need to crack the brake lines..loosen all the line brackets gentaly pull it out then install the booster and bracket then mount the master to it...done...it should take you about an hour plus tool clean up

[Mark B]

Hottrucks... I am not using the original MC. A new drum/drum MC came with the new booster. The old original MC was decrepid, and buying them as a set ensures that they are set up correctly to work together.

It just occured to me that the residual valves could be installed upstream of the distribution block using 3/16" line to the MC. Everything south of the MC could remain 1/4" line. Anyone see any problems with this?

Mark

[Hottrucks]

thats what mine is....just be sure to bench bleed the MC...then a piece of hose on the RR and RF bleeders to a jar and open them up and just let it gravity for a couple hours to avoid popping the vavle to one side...

[Sinister]

I'd bet the new drum/drum master cylinder has the residual valves built in. I've never heard of having to add them in.

[Mark B]

It has taken me a while to learn all this, so maybe it can help someone else who wants to do the same thing - add power boost to their 4 wheel drum set up by using a new MC and booster.

Many of you have added a booster and used your old MC. I am not using the old MC and have a new booster with MC.

The new MC is intended only for 4 wheel drums. A 4 wheel drum MC has the same size reservoirs for front and back brake circuits. The reservoir cover will be same front to back.

The original MC had built in residual valves. The new one does not. You need to install external residual valves when using a new MC.

Residual valves come with fittings for 3/16" inch lines. The fittings can be changed to accomodate 1/4" lines. My truck has already 1/4 lines, so changing the fittings on the residual valve allows the lines to stay all 1/4".

The old distribution block can be re-used as long as the brake failure warning switch is working. The original distribution block does not have a proportioning valve built in to it because 4 wheel drums set up don't need proportioning like front disc/rear drum setups.

The residual valves should be installed between the MC and distribution block. One in each line. The arrow on the valve should point to the brake side (or distribution block in this case).

Having figured all this out, I will now do the plumbing, paint the new MC and booster, bench bleed, and reinstall everything, bleed the system, and hopefuly be good to go (or should I say stop). Oh, and hook up vacuum.

Mark

[RichardJ]

It looks like you have worked through most of the chaff.

If your new MC does not have the residual valves, then you are going to a lot of expense and trouble for something that should be there as part of the original MC.
It can be hard to tell if they are there or not. In the picture below the valves are the two rubber pieces and springs that fit behind the brass "tube seats". The valve end is a narrow rubber blade with a tiny slit through the blade end.

The main difference between a Power MC and a Manual MC is the hole in the back of the primary piston that the rod fits into. The Manual MC has a deep hole so that the brake rod will not drop(fall) out when you take your foot off the brake pedal. The brake rod is attached only to the brake pedal and not the MC. The brake rod or "push rod" slides half way inside the manual MC piston.
The pedal brake rod on a Power Booster is part of the booster.
The rod on the front of the booster fits into a very shallow hole on the Power MC piston. Even though the MC and Booster are both new, you need to check the length of the booster rod to make sure it doesn't hold the MC piston even slightly depressed.

Factory disc brake systems use Combination Valves. There is no hidden meaning there. It is a device with three or more valves combined into one. In some applications a residual valve may also be included in a combo valve for the rear brakes. Most new style wheel cylinders have cup expanders which negate the need for the residual pressure valve. It is nothing more than a spring with an alminum cup on both ends that holds the lip of the rubber cups out against the cylinder bore.

[storm9c1]

Originally Posted by Mark B

It has taken me a while to learn all this, so maybe it can help someone else who wants to do the same thing - add power boost to their 4 wheel drum set up by using a new MC and booster.

...and I give you props for the proper research. I've done several drum-to-disc conversions over the years, and I've learned that research is one of the most critical steps since brakes are important! Not only are various makes and models different, but aftermarket parts are also different yet. Mixing universal parts with factory parts make bad brake systems.

Sometimes it's hard to actually find explicit details on particular models as well, even with FSMs.

The original MC had built in residual valves. The new one does not. You need to install external residual valves when using a new MC.

Now I find this interesting. In my experience, reman MCs usually are improved versions of what was stock. Who (or what) indicated that your new MC certainly does not contain the resid valves? That seems like a regression to me.

Residual valves come with fittings for 3/16" inch lines. The fittings can be changed to accomodate 1/4" lines. My truck has already 1/4 lines, so changing the fittings on the residual valve allows the lines to stay all 1/4".

Correct. I've also learned that an incremental up/down line size doesn't matter as much as what fittings you can actually use without adapters.

The old distribution block can be re-used as long as the brake failure warning switch is working. The original distribution block does not have a proportioning valve built in to it because 4 wheel drums set up don't need proportioning like front disc/rear drum setups.

+1

Having figured all this out, I will now do the plumbing, paint the new MC and booster, bench bleed, and reinstall everything, bleed the system, and hopefuly be good to go (or should I say stop). Oh, and hook up vacuum.

Good job!

A tip for bench bleeding...if you don't already know this... Some new/reman MCs come with instructions to keep the plastic plugs in place and pump the MC (in a vise) filled with fluid. This is supposed to be the "new" way to do bench bleeding and eliminate air bubbles. I do not like this "new" approach. I have found that this procedure is not as thorough as an old fashioned method that I've been using for years. I have done the new procedure, followed by the old fashioned method, and found air bubbles!

The old fashioned method consists of mounting the MC in a vise, and using two tubes (with the threaded flare fittings attached to the MC) looped back into the MC reservoir. Yes you will need to waste a short section of brake line with flared ends (cheap from the local auto parts store). But it makes for a nice bench jig. It's reusable. And will certainly get all of the air bubbles out, and you can actually visually verify the fluid movement as you pump. Be sure that the looped ends are submerged in fluid. I use a short piece of clear PVC tubing attached to the metal tube so I can see even closer that I got the bubbles out. I hope I described this well enough.

[Mark B]

You guys are all great to help me. Thanks for the information.

Storm9c1: The MC supplier said the new MC has no residual valves built in. This was from the technical guy at a company that specializes in custom brakes and brake installations. The MC is new, not rebuilt. And I will take your advice on bleeding.

Richardj: Thanks for the better explanation of the differences in MC for 4 wheel drums.

One other thing, the new MC has ports on both sides. I assume I just plug the ones on the side I am not using?

Mark

[Mark B]

Thought someone might appreciate pics of the MC plumbing. I still have to connect vacuum source to the booster.

Mark