The Stovebolt Site Forums The Shop Area Driveline Residual valves, proportioning valve etc.

I need some input on brake related stuff on my '53. It's mounted on a '78 Suburban frame with a frame mounted master cylinder. They did not put residual valves in the build. I'm getting ready to add some. I know I need a 2 p.s.i. for the front disc brakes and a 10 p.s.i. for the drums out back. Do I need to install these as close to the master cylinder as possible? They used the stock proportioning valve and it's mounted on a crossmember under the radiator. I have a Willwood adjustable unit I'm replacing it with. Can it go in the same location or should it mount closer the the master also? It needs the adjustable Willwood as the stock unit is preset to the weight of the Suburban which was way heavier in the rear than the bed of my truck. Any input is appreciated!

The stock proportioning valve (technically a combination valve) should be all you need. That's assuming you are using all the parts from the '78 Suburban. I'm using an all Camaro brake system; rear brakes, front brakes, master cylinder and combination valve with master cylinder and booster mounted on the frame under the floor

Not so, the stock valve is preset and non-adjustable. The suburban was much heavier over the rear axle. A lot more sheet metal, glass area and extra seats etc. When you get down hard on the brake pedal the rear end wants to come around because the rear drums are locking up quicker than needed. Can be scary! Thanks for the reply.

Try loading it up with some sacks of concrete or other heavy stuff and see how the brakes work. Maybe another issue...

I mounted my residual valves closer to the brake assemblies. It's meant to keep slight pressure on the drums or calipers.

Yep! Should I remount the proportioning valve closer as well? Thanks for the reply!

Gord&Fran, I might give that a try. I already have the Willwood proportioning valve. Pretty sure it needs it. Just need to know if it needs to mount at a different location from where they mounted it.

Just my 2 cents but I don't think the physical location related to the master cylinder matters, it is really only dealing with pressure and that will be the same regardless of where it is in the system.

Hy 32Fordpuchoptop and guys, the brake valve in the stock Suburban system is a combination valve as Gord and Fran has said. To cure your rear brake lockup you need to install an adjustable proportioning valve in the line to the rear brakes, it will take some testing and adjustments to get the rear brakes dialed in. If the master cylinder is mounted below the level of the calipers or wheel cylinders, residual pressure valve will be required to prevent "drain back", hope that helps.

I'm going in circles, my post stated I have a Wilwood adjustable proportioning valve which I'm going to use to replace the stock Suburban unit. I intend to add residual valves. My question is and has always been, does the new prop valve need to mount closer to the frame mounted master cylinder? It's currently mounted on a crossmember under the radiator support. Thanks for the reply, all the info in your reply is correct. Just doesn't answer my initial question.

Have you been driving the truck? For those of us who don't have residual valves installed, do us a favor and add one set at a time and do some testing for us. Add fronts only and go drive the truck around a day or so before adding the rears. Then when you get some results add the adjustable proportion valve and test it.

I know what my truck did once I added the rear adjustable valve, but I don't have four wheel residuals. If I was a betting man, I would bet you see no difference after adding the four wheel valves. The adjustable will keep the rears from locking up, but your pedal will get harder to push under light stopping since you have to add more pressure to over come the valve. With power brakes you may not notice the added effort, but with manuals you will.


The residual valves on drum systems only keep the wheel cylinder piston pins in contact with the shoes, the shoes will always return to the adjustable stop, they will not fix a poorly adjusted shoe.
I can't see how they do anything to disk caliper, the pads only pull back a few thousands of inch anyway, and 2 psi isn't going to stop or limit that. If you ever tried to push a piston back into a caliper, you know how much effort it takes, 2 psi nothing.

My adjustable valve is under the bed just ahead of the rear axle where I could reach it pretty easy. Since installed 25 years ago, I haven't touched it.

WI Cruiser, thanks for the reply. First one that applies to my question.

To answer you question directly, the adjustable valve just needs to be in the rear line, doesn't matter where. Best place is where you can reach it. You will need to make a lot of hard stops in a clean parking lot. 30 to 40 mph full on panic stops. Add just enough restriction to keep the rears form total lock up.

Mine will just leave black marks, but not total lock up. The more restriction you add, the less braking you have. You just have keep adjusting till you are comfortable will how it stops. Mine is on the edge, I can go full on stop and make the rears slide, but I prefer it this way so I can modulate the pedal for the shortest stop possible. As you know, the shortest possible stopping distance is right before total lock up, I am my own Antilock Brake System.

All of my vehicles have ABS brakes too, Joe H.

That's Anticipatory Braking System

Funny Otto! Thanks what I'm hoping to eliminate.

Joe H. Finally a good usable answer. I sometimes wonder if people actually read posts completely before posting an answer.

Hy again 32Fordpuchoptop, the valve in the original Suburban system is much more than a mere proportioning valve and it be a mistake to replace it with your Wilwood valve. Mount your Wilwood valve somewhere accessible in the line to the rear brakes so that you can adjust and test until you get it where you like it. As far as location other than accessibility any where in the system if fine, once the system is bled the pressures in the system are the same everywhere in the system, except after valves, hope that helps.

IF you replace parts with parts for brakes you need to confirm the system is complete.
IF you change parts think drum to disc then you need to update parts.
If you modernize systems then terminology changes

You have now in modern drum/disc systems with a engine bay mounted dual reservoir brake master a combination of things

Metering Valve: Holds off pressure to the front disc brakes, allowing the rear drum brakes to engage first for smoother, balanced braking. (NOT TO BE CONFUSED WITH RESIDUAL )
Proportioning Valve: Controls hydraulic pressure to the rear brakes during heavy braking to prevent rear wheel lock-up.
Optional Pressure Differential Switch: Detects a loss of pressure in either the front or rear brake lines and triggers the brake warning light on the dashboard.

(hence the combination valve in a 1978 suburban that looks like this).
A combination valve is a critical, multi-purpose brass component in vehicle braking systems—typically front disc/rear drum setups—that houses three distinct functions in one unit: a metering valve, a pressure differential switch, and a proportioning valve. It balances brake pressure, prevents rear wheel lock-up during hard braking, and activates a warning light if a system leak is detected.

Now lets talk Residual Valves. (Typically NOT found in combo valves) Because the master is above calipers and drain back will not occur in most modern vehicles.

By adding 2lb (disc side) and 10lb d(rum side) Residual valves to his system. He can go to a frame mounted master.

Now to add more fun. Some dual masters had Residuals built into the master. You could see them in the ports.
So if you go by that theory, it would be master - residual - proportion - brakes order. But you will find this all over the place looking online.


This is why what word you use matters and in the automotive industry there is a lot of "overlap" of terms on some items. Brake combo valves being one for sure.

The mechanic masters can update as necessary.

Thanks for info. I do have a frame mounted master, that's why I need residual valves. The prop valve is mounted higher the master. The truck has stock disc brake front, drum rear. The prop valve is the stock unit and not adjustable. It doesn't work correctly because the truck is much lighter over the rear axle by having just the weight of a bed, instead of all the extra weight of the Suburban body, glass area and seating etc. A lot heavier in factory form. The new prop valve is a Wilwood adjustable type. It should solve the problem of the rear end wanting to come around in a hard stop situation. If any of this doesn't make sense please let me know. Thanks again.

Totally makes sense The prop being higher is ok. Put it where you can reach it without having to get down up and under.
But your totally correct on why the donor combo does not work well. it is sized for that suburban and not the light rear end of a unloaded pickup.
The adjustable one should solve rear end lockups as long as you adjust it correctly. Follow the steps Joe H gave you above.

hcb3200- - - - -That's an excellent synopsis of what's needed to do a proper brake conversion to a more modern system. Over the past 20-something years here at Stovebolt, I've attempted several similar conversations. Here's a little commentary that's appropriate to these situations. Kris Kristofferson says it much more eloquently than I could ever do!

www.youtube.com/watch?v=faF0wOsVucw

Jerry

Thanks hcb3200, seemed like i was heading down the right path. Maybe I wasn't using the proper amount of words to clarify what I was trying to make happen. It would be much easier to mount the new prop valve on the crossmember where the current one is. Will be better for fine tuning the valve.

Just now saw your reply Joe H. Yes, this truck is my daily driver. I've been having to do a lot of anticipated braking. A couple of times I've had to do a O.M.G. stop. The rear wants to come around pretty easy. That's why I'm doing these changes. Thanks for your reply!

Could you get the stock proportioning valve for a 1978 Chevy pickup of the same tonnage as your Suburban frame? That would most likely be the correct solution and it might even be a direct bolt in fit with no tubing changes.

Good thought, I didn't think of that! Too bad I've already bought the Wilwood unit.

The problem I have with residual valves is the part where the fluid drains back. Just how does it drain back? Is it pulling the disk caliper piston back into the housing? is it pulling the wheel cylinder pistons back? It can't be pulling air into the system, and fluid can't simply return leaving a vacuum in the line.

My is frame mounted, I have never had it overflow or had to pump the pedal.

Just how low of frame do you have if the master is lower than the center of the wheels, because all brake cylinders are above the center of the wheels. These trucks all had frame mounted master cylinders with out residual valves when new, so do most of the old cars, how did they work for all these years?

The old gm masters had internal Residual valves built in. Most Masters that have a drum configuration have them in. Here are the imagesI have seen in the past on 50s manuals. In theory you should not have air in system via drain back. Think finger on straw. But My guess was engineers wanted to eliminate it from happening. If something started leaking downstream and the larger springs on drum brakes pushed back.

The way my master is mounted it's lower than the proportioning valve, which I believe is the problem. I do have to pump my brake pedal most of the time, but not always. I never know for sure whether it will be required at any given time. As a result I've had a couple of bad reaction stops. It's about to change.

the valve can be above the master. But if you bought a new master it may not have residuals built in. so the drum springs are pushing fluid back easily. you can tell if the shoes have a gap after sitting between drum and shoe. if they are tight and you are pumping look for some air in that system.

The master was on the truck when I bought it. Dual reservoir 7" power booster unit. Probably doesn't have built in residual valves. Thanks for the reply.

Sounds like you still have some air in the lines to the front brakes. I found that bleeding the brakes was a PITA with the frame mounted master. They seemed fine but then the rears would be doing all the work. I tried bleeding with the rear wheels jacked up - seemed OK - but it wasn't. Finally figured out that I needed to turn the steering hard over so the flex hose on the wheel that I was bleeding was stretched out. Found some more air. Now it's all good.

May be worth trying before making more modifications, thanks! Just wanting to get good solid and reliable pedal. I'd like to modify the actual pedal, take a couple of inches out and change the angle of the pad. Very awkward as is.

So it is interesting that the proportioning valve ratio has not been mentioned. I believe there are a variety of ratios available . Another interesting design feature Chrysler used on their minivans was an adjustable proportioning valve that was linked to to the rear suspension. I found it worked flawlessly with no difference in braking between a light load and a full van.

I used the word adjustable in my post and that is not correct. I should have said that the proportioning valve was activated by a link to the suspension in the rear.

The first generation Dodge Dakota used a similar device involving a spring. The spring would change the tension based on the height of the rear end. Heavy load in bed made the suspension sit lower and allowed the spring to relax and compress.

On a side note about bleeding brakes, I recently finished a total brake job on a being-restored '79 trans Am. They used a rear disk brake set-up that was marginal from the get go along with the normal front disk brakes. I tried for three cans of fluid to get the air out of the rear system, had up in the air, a special hold-off plug to keep the safety valve centered, nothing seemed to work. I made up a 1/4" clear plastic master cylinder cover with two threaded holes for brass fittings. My plan was to attach a vacuum hose to the fittings and pull a vacuum in the master cylinder. Using my Toyota as a vacuum source with a long hose, I proceeded to apply vacuum to the cap, as soon as I got it close, I could see the fluid foam up and a couple big bubbles pop up. I didn't even need to plug the hose on, just got it close. The pedal was perfect after that. I have no idea where the air was trapped, but repeated bleeding didn't move it, it took a vacuum to pull it out. I had the master cylinder off twice for bleeding before I tried the vacuum.

Joe