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Old 03-25-2012, 04:01 PM   #1
flamedabone
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Default What residual valve for '39 Ford brakes??

My 39, 40 front brakes have big honkin 1 X 1 3/8 bore wheel cyls. Does the big wheel cyl need a 2lb residule valve like for disk, or stick with the regular old 2lb for drums??

Damn near have these all put together...



Thanks, -Abone.
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Last edited by flamedabone; 03-25-2012 at 04:13 PM.
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Old 03-25-2012, 04:05 PM   #2
JeffreyJames
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Default Re: What residual valve for '39 Ford brakes??

I always have gone by 2lb for disk and 10 for drums. That's been listed on ECI's site as well as Wilwood's.
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Old 03-25-2012, 04:06 PM   #3
JeffreyJames
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Default Re: What residual valve for '39 Ford brakes??

AND I'm in the process of putting 10lbs residuals on my '39 Ford brakes with a '68 Mustang Dual Reservoir MC.
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Old 03-25-2012, 04:14 PM   #4
flamedabone
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Default Re: What residual valve for '39 Ford brakes??

So you are using the regular 50/50 style master cyl even with the big ass wheel cyls on the front??

Thanks, -Abone.
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Old 03-25-2012, 04:40 PM   #5
k5hart
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Default Re: What residual valve for '39 Ford brakes??

Alright! Brake question. You know how much I'm loving brakes these days. Does the master cylinder already have a built in residual valve? If not I would say use a 10 lb. like normal. I found this website that has some good info: http://www.hotrodheaven.com/tech/brakes/. There is a lot to read but about 3/4 down the page it has a residual valve section. Might help.

Did I miss anything a lunch yesterday? Had to help someone move again. Oh, by the way, my brake pedal problem is fixed I believe. Need to put it down on the ground and give it a test run. See ya at the drags Saturday.
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Old 03-25-2012, 04:42 PM   #6
JeffreyJames
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Default Re: What residual valve for '39 Ford brakes??

Yes but I wish I could tell you an intelligent reason for doing so other then that's what I researched here on the HAMB. I ordered Wheel cylinders from Dennis Carpenter's or Sactown Vintage Ford (can't remember) and they were 1-3/8" fronts and 1-1/8" rears. I went by CHRIS' recommendations for the MC and also the residuals after also researching on the HAMB.

I looked at Speedway's wheel cylinder's and they're 1-1/4" for the fronts. Wonder why the variance?

Anyways, I hope some other chime in because maybe we're diving into something useful to tell me why I couldn't get a brake pedal prior to me adding these residuals.
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Old 03-25-2012, 04:43 PM   #7
JeffreyJames
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Default Re: What residual valve for '39 Ford brakes??

ALSO I should add that ECI's brass residual valve have a really good reputation around here. If I ever order another set I am going to go that route instead of the Wilwoods.
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Old 03-25-2012, 04:51 PM   #8
Don's Hot Rods
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Default Re: What residual valve for '39 Ford brakes??

You may not even need residual valves. I am running the same setup as you, also on a model a frame, and my car has been setup that way for over 20 years with no residual valves in the system. The only time you really need one is if the MC is lower than the wheel cylinders, and even then they might not be needed. My 23 MC was way lower than the wheel cylinders and I ran none on it either.

I think they just add the potential to one more problem in the system, in fact, we gutted the residual valves on my one Son's T bucket because they were causing issues.

Try it without first to see if you really need them. Nice looking brake setup you have btw, love them Buick drums.


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Old 03-25-2012, 06:53 PM   #9
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Default Re: What residual valve for '39 Ford brakes??

I have '46 brakes with the same wheel cyl. with no residual valve.....my master is under my floor....No issues.......
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Old 03-25-2012, 07:13 PM   #10
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Default Re: What residual valve for '39 Ford brakes??

I read that in 68 govt. passed a law about residual valves. Master cyl. have built in residual in 69??? That's why I went with 69 Mustang for my Drum , Drum brakes on my Comet. You might want check in to it.
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Old 03-25-2012, 09:09 PM   #11
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Default Re: What residual valve for '39 Ford brakes??

can I follow....
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Old 03-26-2012, 09:52 AM   #12
DICK SPADARO
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Default Re: What residual valve for '39 Ford brakes??

Flamedabone you were not specific as to what you were using for a master cylinder so answering your question is difficult.

If you are using stock Ford wheel cylinders and the original single reservoir master cylinder no residual line valves are necessary.

If you are using a replacement dual reservoir master cylinder you must know if it is a disc /disc application or a drum/disk application as a determining factor since drum units may already have internal residual line valves.

If you are using the disc/disc style application master cylinder in a drum/drum application, residual line valves are needed in both lines front and rear. -10lb on both sides.

If you are using the disc /drum application with drum brake front/ drum rear you are going to need a 10lb valve in the disc side to compensate for the lack of residual valve in the master cylinder disc side port. The drum side should already have a built in residual valve.

Residual line valves are required in disc application master cylinders because they usually do not have have internal valving. When using disc style master cylinders with drum style brakes the increased 10 lb valve is required to prevent the return springs from fully retracting the wheel cylinder pistons and creating a long throw on the pedal as the wheel cylinder refills with fluid.

No retracting springs are used on disc brakes, as the rotor run out is sufficient to move the pads away from the rotor when brake pedal pressure is released. Using a high lbs residual line valve will not allow the brakes pads to retract and produce brake lock problems.
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Old 03-26-2012, 12:01 PM   #13
V8 Bob
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Default Re: What residual valve for '39 Ford brakes??

flamedabone,
All vintage drum brakes need (and had) residual (check) valves, which prevent air from being drawn (partial vacuum) past the wheel cylinder cups during brake release. They were located inside single and dual master cylinders until the mid '70s, when cup expanders, modern designs/materials and standard front disc brakes made drum brake residuals obsolete. (Production U.S. disc brakes never needed or used residuals, as there were no floor-mounted masters with disc brake vehicles. The 2 lb "disc" residual is strictly aftermarket and should only be used with masters located lower than the calipers.

JefferyJames,
Your '68 Mustang master should already have internal residuals, but check to make sure.

Tomkat39,
Not sure what law you refer to, but master cylinders generally already had them internally since the '30s.

Mr. Spadaro,
I say that with all due respect. But there are some corrections I'd like to make.

One, residuals were never required for production disc brakes, but may be needed on custom vehicles with the master located below the floor. (Some '40s-'50s disc designs, like Chrysler's and Kinmont's, used stock floor mounted masters, BUT they operated similar to a clutch with very strong return springs acting on the brake cylinders, and also needed residuals).
Two, residuals do not/cannot prevent the shoe return springs from fully retracting the wheel cylinder pistons. (widely believed, totally wrong)
Three, the caliper piston seal is what does most of the retracting, along with rotor knock back and/or runout.

Last edited by V8 Bob; 03-26-2012 at 03:10 PM. Reason: additional info
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Old 03-26-2012, 12:07 PM   #14
JeffreyJames
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Default Re: What residual valve for '39 Ford brakes??

Quote:
Originally Posted by V8 Bob View Post

JefferyJames,
Your '68 Mustang master should already have internal residuals, but check to make sure.
See that's what I thought so I assembled the entire brake system without external residuals. Bled and bled and bled and just couldn't get a pedal. So as of the past couple months I've taken the entire brake system down to nothing checked everything and I'm not putting it all back together with Wilwood 10lbs residuals because I found that the MC I have didn't have them installed.
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Old 03-26-2012, 01:09 PM   #15
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Default Re: What residual valve for '39 Ford brakes??

Here are the facts....everything previously stated that contradicts below is just not true.

Quote:

Residual Pressure Valves are used in a both front and rear brake system as follows:
    • 2 PSI Valves - These valves are used in a disc brake system only and are required when the master cylinder is at, or below, the height of the calipers. It's purpose is to act as an anti-siphon valve preventing the brake fluid from siphoning back into the master cylinder when the brake pedal is released. Even if the master cylinder is even or slightly above the calipers, put one in anyway. If you don't and you park on a hill, fluid will siphon! These valves are cheap insurance - put them in!
      • NOTE: You will know if you need one of these valves if you had to pump the pedal twice to get a good pedal. See illustration for more.
    • 10 PSI Valves - These valves are used in a drum brake system to prevent air from being ingested into the hydraulic system when you release the brake pedal. Typical wheel cylinder seals only seal when there is pressure behind them. Rapid release of the brake pedal creates a vacuum in the system which causes the seals to relax and air is ingested into the wheel cylinders. Maintaining 10 PSI in the system at all times prevents this. Some disc/drum master cylinders have 10 PSI residual pressure valves installed internally, some don't. If you're not sure, call us and we can tell you how to check. Also, some new style wheel cylinders have cup expanders which negate the need for the residual pressure valve. Either way, if you are not sure whether you have one or not, put one in. They are not cumulative and it won't hurt anything if you have two. Don't worry about brake drag, it takes roughly 75 PSI to overcome the return springs.



In summary, drum brakes NEED residual valves. Whether they are in your master cylinder or added externally they need to be there.

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Old 03-26-2012, 01:22 PM   #16
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Default Re: What residual valve for '39 Ford brakes??

drums all around my T roadster, 10# RPVs and zero problems. Matter of fact,it stops like it hit a wall o' jello!
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Old 03-26-2012, 01:35 PM   #17
Don's Hot Rods
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Default Re: What residual valve for '39 Ford brakes??

I'm using 40 Ford front brakes, 68 Mercury rear brakes, and a dual master cylinder as used on the 60-66 Chevy pickps (one half for brakes, the other half for my hydraulic clutch. ) There has never been an external residual valve in the system since I put it together 23 years ago, and the brakes stop as well as my newer daily driver.

What I interpreted the OP's original question to be was, does his car need an add on residual valve. In that instance, if he is using a MC that has them incorporated, then he does not need them. If the MC has them internally, that will be all you need.

My 23 had the same system, basically, except the MC was a 68 Mustang drum/drum unit. Again, no external RV and that MC was below the level of the wheel cylinders, and it never needed one.

I can only go by what I know has worked for me for years.

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Old 03-26-2012, 04:31 PM   #18
DICK SPADARO
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Default Re: What residual valve for '39 Ford brakes??

Mr. Spadaro,
I say that with all due respect. But there are some corrections I'd like to make. No problem Never worried about having things corrected, try not to post incorrectly

One, residuals were never required for production disc brakes, but may be needed on custom vehicles with the master located below the floor.

Did not think I said that, though I said using original style Ford drum brakes with non valved disc master cylinder did require external valve. Just assumed that this was in a low mount application. Don't recall anything about being required for production brakes.


Two, residuals do not/cannot prevent the shoe return springs from fully retracting. (widely believed, totally wrong)

In early Ford application upper adjustment cam controls return stop of the brake shoe but the residual line valve maintains pressure in the system for more positive pedal, once the shoe seats on the upper adjustment cam. But if the application does not have a return stop once the return spring pressure lowers to 10 lbs the valve prevents any further contraction.

Three, the caliper piston seal is what does most of the retracting, along with rotor knock back and/or runout.

Well technically you are correct that the seal elasticity is the return spring on a disc puck, try to explain that easily, in this case rotor run out is more prominent and the easiest to explain.
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Old 03-26-2012, 07:08 PM   #19
flamedabone
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Default Re: What residual valve for '39 Ford brakes??

Thanks, guys. Lots of info there, but pretty much exactly what I was looking for. Looks like I will be running a 10lb valve in the front with my big ass wheel cyls and my disk/drum 76 Pontiac master cyl and none in the rear as the master most likely has them.

That said, I had '40 brakes on my daily driver for years with no residual valves at all, and still don't run them now that I have disk and the car stops great. Add to that, my 40 brakes stopped just as well as the disks I have now, just less pain in the ass with the disk. Next year, I'm putting 40 brakes back on her.

Thanks, guys. -Abone.

PS. Dick, I always appricate your giant vault of old Ford knowledge.
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