Residual pressure valve for rear brakes

[Sedanman]

When I researched the front granada brake swap several years ago, I was told on the Ford six forum all I needed was a disc/drum MC and adjustable prop. valve. Since then I was told that not installing a rear drum residual pressure valve is the reason the rear brakes aren't working (they still look almost new after several k. miles) and my front brakes lock up, even with the prop valved adjusted all the way.

I don't remember the group installing one on Gary's car when we did the brake swap that day - or maybe I just missed it. I just want to clarify that's what I need to do (and anything else) to get my system working the way it's supposed to.

BTW, I'm going to have a leakdown test done on the car at a new shop in Bellevue called Blue Oval Ponycars this week www.blueovalponycars.com - please keep your fingers crossed that my problems are due to just valves, and not rings :)

[MacDee]

Thor,
We did NOT install a proportioning valve on my conversion. After the conversion, I still need to press pretty hard on the brake pedal to stop. I did some "panic stop" testing and found that the rears lock up first, so I know the rears are working. In fact, I'm wondering if I got the wrong MC (non-disc-brake type) and the rears are doing most of the braking. Don't know how I'd check that though....

I got a book on brake systems and it says you only need a residual pressure valve if your MC is LOWER than your rear wheel cylinders. It's to keep the fluid from flowing out of the wheel cylinder back to the MC.

[pbrown]

A car equipped with a disk/drum system needs the following valves:

Metering Valve: This valve is used to control brake timing. It's used to delay the activation of the front disks a few milliseconds until the fluid pressure can move the rear pads to the drum. Most people don't install one of these because they don't know what is does or that it exists. It is most needed when the roads are slippery so that all four wheels engage at the same time.

Proportioning Valve: This valve is used to control brake bias. The weight of the car shifts forward during stopping. This unweights the rear and causes them to lock up first. A proportioning valve reduces the pressure allowed to the rear brakes so that all four wheels have equal braking more or less.

Residual Pressure Valve: A residual pressure valve is a simple spring loaded check valve that is designed to maintain pressure in the lines. It is used one two situations:

One - If the master cylinder is lower than the wheels. This is only the case with low sport cars or hot rods with under floor master cylinders. A two pound valve is used for this in a disk brake system. It would be in line with both the front and rear brakes.

Two - Any car with drum brakes. Drum brakes have springs that retract the shoes from the drum. A ten pound residual valve is used to keep the pads close to the drum. The car would have excessive pedal travel without this valve. This type of valve is typically built into the master cylinder. This is one reason it is important to change the master when changing to or from disk brakes. You would not want a tem pound pressure valve in a disk brake circuit. It would cause excessive pad drag and ware. It would also hurt your times at the drag strip :(.

Gary - A quick check for your MC is this. If the two bowls are different sizes, you have the right one. It is entirely possible that it is hooked up backwards. The larger bowl is closer to the firewall and is used for the front brakes. I see many people assume that the rear port is for the rear brakes. This seems logical but is not the case.

[Sedanman]

Gary - you may or may not have hooked it up wrong - I was told at the time I did this swap that disc brakes take more pedal pressure to stop; It's been 5 years now (!) since I put the granada discs on, so it's hard to compare with the old tiny drums but it does take a fair amount of pressure to stop the car. I've never been able to get my rear brakes to lock up, and in panic situations my front brakes lock up (not good when you have this kind of loose steering!). These front brakes do seem to heat up (and make grinding noises) when I'm doing stop and go driving so I think they are over-working.

I can't remember which way I turned the prop. valve, in or out, but it's all the way one way or the other now. Either way, I tried it both ways and I think I left it at this setting as the front brakes were less touchy.

Patrick - regarding the various valves, it seems to me everyone who's talked about doing the granada swap over the years has said to use the factory combination valve/block, so that says to me that maybe there is not a residual valve in the older master cylinders (?) The guy at Speedway who sold me the valve suggesed I needed both the resid and metering valves when I ordered it and told him what car it was.

Just for clarification, I meant puting the resid valve in the rear brake circuit. So are you suggesting that I should install the metering valve instead? What parts did you use on your conversion? I rarely drive the car in the rain, but when I do it's white knuckle driving compared to my modern car and want it to be as safe as possible :)

I haven't pulled off my rear drums recently (have only driven the car a few hundred miles a year last two years), but after a couple thousand miles of use the rear shoes showed almost no wear. I guess I should go "play" with the prop valve some more before the car goes up on blocks for this and other (front end ) work...

T
PS - I'm using a Fox Mustang MS (an '83, I think) as that's what the store had and it was aluminum which I thought would be good for keeping rust at bay and save some lbs.

[pbrown]

Patrick - regarding the various valves, it seems to me everyone who's talked about doing the granada swap over the years has said to use the factory combination valve/block, so that says to me that maybe there is not a residual valve in the older master cylinders (?) The guy at Speedway who sold me the valve suggesed I needed both the resid and metering valves when I ordered it and told him what car it was.


The combination valve is both a metering and fixed proportioning valve. The residual pressure valve is built into the master. THe old fruit jars had them. You new aluminum master will have one for the rear if it is a disk/drum unit. A disk/disk unit will not andone would need to be added.

I'm using a new cast iron master with a 1" bore and a GM style combination valve.

[Sedanman]

So then theoretically, all I need to add is the metering valve...(?)

I'm wondering if maybe I have bad/clogged rear brake hose to the center section steel lines. I remember having a hell of a time bleeding the rear brakes, and since I'm not getting enough braking power to the back, that's the only thing I can think of as I bought a new one when I did the swap.

[pbrown]

Start with checking the rear lines. Maybe the hard line from the MC to the rear end T is crushed somewhere. Try connectinf a pressure gauge to the end of the flex hose and see how much pressure you get. You can expect in the area of 700-800 PSI. Maybemore if you've been working out ;).