Technical Weird Brake Problem - Can anyone recommend a good dual drum/drum master cylinder?

The master cylinder on my 41 pickup will not release all of the pressure when the pedal is lifted. After an hour of driving, all four brakes are dragging badly. I've adjusted the pedal play out to the limit, still does it. I have the same master cylinder on my roadster and it is starting to exhibit the same problem.

Both vehicles have the same setup 67 mustang mc, two 10 lb residual valves, 40 ford brakes.

At this point, I have tried everything and just want to go with a different master cylinder.

What do you guys like to use?

Thanks,
Rich

 

Does it have free play between the pushrod, and the piston? You didn't really say...

 

I have had a late 60’s Mustang master on my sedan with early Ford brakes, for 15 years. Never had that problem. Maybe you need a different brand of rebuilt master?

 

I had that master on my t bucket and it worked great with residual pressure valves after I established the right pushrod length. Another master you could look into is from a 1967 Chevy C-10 1/2ton truck.

 

Back to what squirrel point's out, one of our group had the same issue when we arrived at our hotel at a car show last year. The brakes were dragging very hard. When we asked if he worked on the brakes recently, he told us he replaced the master cylinder a week ago. Someone asked about the pushrod play and he said he it was tight. He loosened the pushrod and the problem went away.

 

you might want to check if the MC has internal residual pressure valves if you have externals installed. I have the same setup on my 40 sedan without any external valves and it works fine.

 

The master probably has residual valves too, but iirc they are only about 2psi. I would take out the external valves.

 

Yes, and each time that I adjust it for more freeplay, It just takes up the slack when I drive it.

 

Might see if the master cylinder piston is hanging up and not returning fully, due to corrosion or something.

How old is it?

 

That's what I'm thinking, just wanted a recommendation of a proven part..

Her is what I currently have.

https://www.oreillyauto.com/detail/...car-1969-ford-mustang?q=master+cylinder&pos=2

 

That really sounds like the problem, it's only 4 years old, stored in the dry.

 

I think so, or new, got a part number?

 

I have had good luck using a Ford F-100 MC, from the last year that manual brakes were offered - I think it was 1977.

[EDIT: My bad. I just noticed from the thread title you are needing a drum/drum setup. The '77 F-100 was a disc / drum deal.]

 

Production residual valves, whether internal in master cylinders or external, were/are for drum brakes, and varied in pressure usually around 10-15 psi. The "2" psi residual is strictly aftermarket, and for modern disc calipers positioned higher than the master cylinder. No need to remove the master cylinder residuals for drum brakes.

 

If you have actual freeplay in the push rod, meaning you can get under the car and pull down on the pedal arm and actually watch the pushrod move before you feel it start pushing on the piston I'd be inclined to agree with Squirrel in that you may have a problem with the piston sticking in the bore. The hardest thing on brake hydraulic systems is sitting for long lengths of time. You seldom have trouble with one you drive all the time but let it sit for more than a few months and things go down hill in a hurry.
The residual valves should just maintain a slight fluid pressure against the cups in the wheel cylnders to keep the cups sealed against the bores so air doesn't get in. With no residual valves you often have mushy brakes after the vehicle sits for a couple of weeks without being driven. That was my experience with my 48. The brakes worked good as long as I was driving it on a regular basis but let it sit for three weeks while I was driving my work truck and I'd have to bleed the brakes. Then I was good until I let it sit again. That was with a 68 Chevy C10 manual brake master cylinder.

 

Sorry no part number. I replaced mine last year because the first one was leaking a bit. Who'da thought a 14 year old master would leak. I just got the house brand rebuild from our local parts place. But, I'd think RockAuto would have a nice Raybestos or Wagner for you. Just search for a drum/drum '69 Mustang with manual brakes.

 

ECI once told me that I did not need to remove any internal residual valves when I installed an inline valve as well. And, ECI sells GOOD brass residual valves, not cheap aluminum ones.

And, some great advice I read on the HAMB years ago was to hop in your car at least once a month and press the brakes, whether you drive it anywhere or not. Keeps the master and wheel cylinders moist and helps prevent corrosion and sticking.

 

At O'Reillys;
Cardone Brake Master Cylinder - #10-1485 Looks like it comes with the pushrod, too.

 

Don't use the provided snap-in push rods. A royal pain in the ass if you ever need to remove it.

 

Your comment on ECI and the quality BRASS residuals is right on the money. That is all we sold at the rod shop, had a whole drawer of pretty anodized JUNK Wilwood and Speedway ones that we took off customer cars.

 

Just thought I'd throw this out there for future reference, for those who use the mustang master cylinders on early Fords... There is an AMC master cylinder that is essentially the same unit except the ports are on the other side, so you don't have to wrap the lines around the X member, on a 35-40 for example.

https://www.amclives.com/products/1...master-cylinder-new-lifetime-limited-warranty

 

You might think about the MC and lines being too close to an exhaust pipe.....that will heat up the brake system, expanding the fluid and dragging/locking the brakes. I put a heat shield adjacent to the MC on my '40 Ford and that issue went away.

 

If that is what they said, they are wrong. You cannot use tandem RPV's as funny things can happen

 

https://www.ecihotrodbrakes.com/brake-facts

Read towards the bottom of that page. You are saying they don’t know what they are talking about?

 

Maybe point out exactly what you are referring to and we can discuss it.

 

Second and third to last sentences in the "10 PSI Valves" section.

 

I'm using a Mustang style fruit jar MC and a Speedway bracket in my new '29 roadster with Wilson Welding brakes. Brand new parts. I had, after about 500 miles, the pedal seize up on the pivot shaft. Same thing you've got happening. I had neglected to grease the shaft when I put the chassis together last fall. I have a return spring on the pedal but it wouldn't pull it back far enough to keep the brakes from dragging, finally wouldn't come back AT ALL unless I pulled the pedal up. A bit of grease fixed it, I'm going to put a Zerk on the pedal.

 

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.
From the ECI page

 

Yes, the 10 pounds (or 20 if you also have a 10 pounder in the master already) from the inline valve is only to keep a little pressure on the cups. It won't even begin to move the shoes.

I'm all ears as to what funny stuff happens when there are two valves installed. Let us know Mr. Kult.

 

I doubt if it is the M/C

Those symptoms you describe sound like the brakes are not fully returning BUT the M/C is fully returning.
Then the M/C proceeds to fill itself up. [taking up the slack]

A faulty proportioning valve OR too high pressure residual valves could be holding the brakes on.
Your symptoms are similar to what "flap" inside brake hoses will do [but this only affects individual corners]
Because it affects all 4 corners I would be looking at the "check valve" [in the base of the M/C or in the main line somewhere]

Is your M/C under floor? [below the wheel cylinder level?]
Use a tandem M/C of the same bore ,BUT convert it to a remote reservoir mounted higher up on the firewall to prevent siphoning back.
Then use lower pressure residual valves in each circuit to just hold enough on the cups.
Also check all the wheel cylinders AND return springs , they could not be returning. A recent adjustment could've moved the cups further back [and they now stick]

Here's a Wilwood remote reservoir M/C [example]