Newer ford dual mastercylinder on 40 ford brakes

[sabre62]

I replaced the single master cylinder with a newer 2 chamber type from 79 mustang..can not get any pedal to speak of bled out ok but no full pedal, is this a volume problem ? 1/4 in lines as opposed to 3/16 that the lter mustang used.

[paul2748]

Originally Posted by sabre62

I replaced the single master cylinder with a newer 2 chamber type from 79 mustang..can not get any pedal to speak of bled out ok but no full pedal, is this a volume problem ? 1/4 in lines as opposed to 3/16 that the lter mustang used.

Did you bench bleed the cylinder before installing. Very important with the dual chamber models.

[40cpe]

Richard will probably jump in here on this one, but I think you are on the right track with volume. A small piston master will take a longer stroke to fill the wheel cylinders but require less pedal effort, and vice-versa. I think I got that right. Brake adjustment will also affect stroke.

[41ford1]

I had a similar problem using a 69 Mustang dual circuit M/C on a 40 pickup. I ended up using a dual M/C from a 68- 70 Chev GMC C20. That unit is 1 1/8" cylinder diameter. Currently running it with a speedway disk kit for the front. Works well.

[richard crow]

you have to use a master cyl that has drum brakes front & rear as they have a check valve. i asume your runing orignal drum front & rear on the 40

[Flathead Fever]

Sponsored Links (Register now to hide all advertisements)

Originally Posted by sabre62

I replaced the single master cylinder with a newer 2 chamber type from 79 mustang..can not get any pedal to speak of bled out ok but no full pedal, is this a volume problem ? 1/4 in lines as opposed to 3/16 that the lter mustang used.

Brake tubing size will make no difference. Since the fluid does not compress, what ever amount you pump into one end of the tubing will come out the other side regardless of the size of the tubing. Ford was probably worried about the size of the line restricting the fluid flow so they over engineered it.
　
I dug out my Eis and Bendix Brake catalogs. They list the '40 Ford with 1"X 1 ¼" front wheel cylinders and 1"X1 1/8” rear cylinders. The master cylinder has a 1 1/16" bore.

The 1979 Mustang is equipped with disc brakes. The master cylinder has a 7/8" bore, the rear cylinders are 13/16". The smaller bore in the master cylinder is probably too small to displace enough fluid to expand the larger '40 wheel cylinders. Since it is designed for disk brakes it will not have a residual pressure check valve built into the disc brake half of the cylinder. A slight pressure is required in a drum brake system at all times. This keeps the rubbers cups expanded against the walls of the wheel cylinders so they do not leak. In a disc brake system there are no return springs to pull the pads away from the brake rotor. A residual brake valve would cause a slight pressure causing the disc brakes pads to drag all the time.

You need to find a master cylinder designed for front and rear drum brakes. Most of the Late 60s early 70s Fords had dual reservoirs with an 1-inch bore and 1 1/8” wheel cylinders. Something like this might be a better choice. I’m sure the guys on the HAMB site could recommend something.

There is absolutely nothing wrong with a well maintained single system. Ford used them on heavy duty F600 trucks all the way up into the late 70s. I have to admit it scared me so I always made sure they were in perfect condition. The slightest leak or complaint and it got a new master cylinder and wheel cylinders. Obviously a dual system is safer but it is really rare that you have a catastrophic brake failure on a single system We had a few instances where snow chain cross links broke and sheered off the steel brakes lines but your probably not going to have that problem on your ’40 Ford. In 30 years I only ever saw one brake hose fail and it was because the metal sleeve that crimped the rubber hose on had corroded, it was below the battery box and got acid on it. Most of the time total brake loss is caused by the master cylinder running out of fluid because of a slight leak in the system. Seepage usually takes weeks to empty a master cylinder. If your checking fluid levels you should notice that the master cylinder is low and then find where the fluid is going long before it becomes an emergency situation. You should also flush the fluid out every two years or install silicone fluid. Some people complain that the silicone fluid causes a slightly spongy pedal. I have it in my ‘66 Shelby and it feels the same to me.

A well maintained single system is safe if your inspecting it regularly.

[1oldtimer]

you need to either get a master for 4 wheel drum or use residual valves (also SOME drum masters don't have res valves inside). also you need to get real close to the bore size of the stock master if your using stock wheel cylinders. i made a mount and used a late 60's chrysler master for my '47 ford with lincoln brakes.

http://www.jalopyjournal.com/forum/s...d.php?t=367059

[quickchange34]

The one you should have used is the 67 Mustang master cyl. for drum drum front and rear.

[sabre62]

OK.. Here is what (I know).. I am running the same reservoir on my duece 3/16" lines only difference is 56 ford truck brakes on front mustang 10" on back ..no residual valves no difference works great The 40 brakes are adjusted up rears to back of res (small end) fronts to the large section. The brakes are all new linings turned and so forth. Now the old master was 1" and the new is 7/8 as one of the gentleman pointed out fluid does not compress the only change would be less volume and probably pedal pressure. Have tried two new masters and have no leaks ' I converted because the brakes while having pedal (with the old single cylinder)were not that great anyway. Thinking more truck brakes...

[Richard (EV8G)]

Originally Posted by sabre62

I replaced the single master cylinder with a newer 2 chamber type from 79 mustang..can not get any pedal to speak of bled out ok but no full pedal, is this a volume problem ? 1/4 in lines as opposed to 3/16 that the lter mustang used.

In addition to everything posted by others, it is helpful to understand how the so-called "dual" MC's work. Because the two systems are not totally independent, but are co-dependent on pressure in each other, bleeding them using the typical "pump and hold" method will not purge all of the air out, with resulting low or no pedal, and/or very spongy pedal, due to air in the system. IF the MC you have is in fact a 7/8", it will not move enough fluid in the pedal travel/piston stroke available. Should replace with a 1", as the original MC for the brakes you have was 1-1/16" - I do not think a "dual" with 1-1/16" is available??? Also, it was mentioned that the front forward piston diameter on a 40 was 1-1/4" - Ford increased that to 1-3/8" in 1942 (in an attempt to increase front braking and reduce pedal effort...) and all new front WC's are the larger size. With a 7/8" MC, that makes the problem worse...

The method to bleed these dual MC's is to bench-bleed them so both chambers are filled with fluid and no air is present, then plug off the outlets and install on the vehicle. Connect ONE END of the system, probably the front, but leave the other plugged so it will stay full of fluid and provide a "wall" so the rear piston cannot move when the pedal is pumped, and therefore all fluid will be directed to the front brakes only. Then bleed the front brakes, checking and adding fluid as necessary so it does not run dry and you have to start over. When the fronts have been bled and the pedal is rock-hard, connect the rears and bleed them. The front system will have pressure, so fluid will now be directed to the rear brakes, allowing the air to be purged. When the pedal is again rock-hard, redo the fronts and then the rears to be sure that ALL air has been removed.

The dual MC design requires pressure in both ends in order to function under normal conditions. If a failure in either end occurs, the "back-pressure" is lost and the inner workings of the MC must resort to mechanical operation between the front-rear in order to recover any braking in the surviving end. This unfortunately takes ALOT of pedal travel, which is largely not available on the old Fords (look at pedal stem length - available travel is measurement from
bottom of pedal to top of floor/carpeting/mat etc.) If there is not enough, a dual MC may not be able to recover ANY braking... this does not mean that dual MC's are a bad thing, but when retrofit to an old Ford, one should be aware of the limitations... Most people do not understand how the duals work, so cannot visualize what is going on or what to expect in case of a failure - they are not all that they are "cracked up" (what does that mean???) to be...

I run singles on my own cars... but this is one of those on-going controversial subjects... (DOT 3 vs. DOT 5, mechanical vs. hydraulic, etc.) I can furnish my 1932 and 33-34 conversions with either type, but 35-36's and 37-38's are limited by space constraints... which is also an issue when a 39-later is converted to a
dual MC.

[sabre62]

All the info is well taken,I am mixing apples and oranges... I will investigate an alternate master cylinder . As usual this forum provides a wealth of knowledge learned the hard way and is most appreciated. G Man aka Gordon

[345 DeSoto]

RICHARD (EV8G) - Of all the discussions, arguments, and BS I've seen written over the years on dual master cylinder conversions, this is probably the most informative I've read. NOW I know what the theory is, behind the practical. I've come across an NOS '67 Corvette, 1" bore, manual disc/disc master cylinder (free). I will be using it to replace the what-the -hell-EVER-it-is dual master I now have on the 32 in my Avatar. Your Post has helped me immensely with what to do, as far as bleeding the Master and installing it on the system. I've included a representative picture of the MC. BTW, what is the procedure to bleed a MC which has bleeder screws on it?...

[Richard (EV8G)]

Glad to be of help... The bleeders on the MC can be opened to bench bleed both ends, maybe instead of the usual procedure of running lines from the ports back into the reservoirs, which can be messy. After installation and during the bleeding operation, open them again just to be sure that no air is trapped.

BTW, the operation of dual/tandem mc's is explained in Motor's and other shop manuals. The basic design was created in response to the Fed's National Highway Safety Act, or whatever it was actually called, of around 1966? which mandated two separate braking systems and a warning light. The people who wrote the bill probably had a truly independent setup in mind, but this is what the people in charge of enforcing the new law apparently signed off on... They are not what people think they are... and not much has changed...

[V8 Bob]

" Most people do not understand how the duals work, so cannot visualize what is going on or what to expect in case of a failure - they are not all that they are "cracked up" (what does that mean???) to be..."

I find it hard to believe so many "car" people still do not understand hydraulic brake operation , especially the safety advantages of the dual system found on all US cars/light trucks since 1966.

"I run singles on my own cars... but this is one of those on-going controversial subjects... (DOT 3 vs. DOT 5, mechanical vs. hydraulic, etc.) "

There should be NO controversy. Hydraulic brakes ARE safer than mechanical, and dual systems, when set up properly, ARE safer than single, period! These are facts, not opinions.

One mistake often made is not picking a dual master with the proper bore size, as has been stated. Too small a bore can lead to inadequate fluid volumn and excessive pedal travel.
The biggest issue with any master cylinder is making sure the master cylinder piston(s) can be bottomed out BEFORE the pedal hits the floor. A single piston master will not have its full displacement potential, and a dual will loose most/all its safety advantage, along with never attaining a full bleed.
When working with brakes and unsure about something, consult with someone who does know...or grab a book, shop manual, etc, and take the time to try and learn. Hydraulic brakes have been around for over 70 years, and dual systems for over 45. Its not rocket science...
Some masters have bleeders located above the ports because the port passages, through design, orientation, etc, can have air pockets that normal bleeding will not dislodge. Bleed these first before any others.

[FRANK PKNY]

I can tell you from expierence that a single master cylinder set up should never be used. I lost my brakes years ago in a dump truck and went straight through a intersection off the road and into a building. Luck had me and I survived and no one got hurt. Ever since then I have always converted my brakes to a dual system. Better to be on the safe side. Frankpkny

[Richard (EV8G)]

[QUOTE=V8 Bob;103056]"

"There should be NO controversy. Hydraulic brakes ARE safer than mechanical, and dual systems, when set up properly, ARE safer than single, period! These are facts, not opinions."

There are still differing "opinions" on what is "fact" ... You may be hearing from the "properly set up and adjusted mechanicals are just as good as hydraulics" group?

[37fatfender]

" ARE safer than single".......... I don't know why? From my first hand expeience, I don't believe it. I lost all my brake fluid in the rear resivor due to a small gradual leak in a street rod that I had owned. I always ASSUMED that if you lost fluid in one you would have brakes to back you up. NOT in my experience. I was traveling from Kalamzaoo, Mi to north of Chicago on interstate 294 at 70 mph and nearly killed my self and almost totaled my car. If I lost the rear fluld I should have front brakes....right NOT so. I darted around cars like a bumble bee in slowing traffic.....using only the emergency brake.......virtually no use for stopping at any substantial speed. I got the car to the next exit called the wrecker. I did not know why any of this happened at the time. Upon tear down when I got home the leak at a residual valve fitting was discovered. I fixed the leak and decided a new master cylinder was in order also. Thinking ahead of my self I decided that I would install the new master, bleed the system and then recreate the problem and open the rear bleeder......guess what NO brakes........pedal to the floor. I have never gotten any satisfactory explanation as to why. I do know that my master cylinder and brake lines are checked VERY regularly.

[V8 Bob]

Originally Posted by 37fatfender

" ARE safer than single".......... I don't know why? From my first hand expeience, I don't believe it. I lost all my brake fluid in the rear resivor due to a small gradual leak in a street rod that I had owned. I always ASSUMED that if you lost fluid in one you would have brakes to back you up. NOT in my experience. I was traveling from Kalamzaoo, Mi to north of Chicago on interstate 294 at 70 mph and nearly killed my self and almost totaled my car. If I lost the rear fluld I should have front brakes....right NOT so. I darted around cars like a bumble bee in slowing traffic.....using only the emergency brake.......virtually no use for stopping at any substantial speed. I got the car to the next exit called the wrecker. I did not know why any of this happened at the time. Upon tear down when I got home the leak at a residual valve fitting was discovered. I fixed the leak and decided a new master cylinder was in order also. Thinking ahead of my self I decided that I would install the new master, bleed the system and then recreate the problem and open the rear bleeder......guess what NO brakes........pedal to the floor. I have never gotten any satisfactory explanation as to why. I do know that my master cylinder and brake lines are checked VERY regularly.

IF the master can be FULL stroked BEFORE the pedal bottoms out, and IF the bore size is adequate for the calipers (system), you will have FULL FRONT BRAKING from the master in the event of a rear failure, and FULL rear braking in the event of a front failure, PERIOD, on a typical front/rear system. You WILL have increased pedal travel, BUT FULL FRONT or REAR BRAKING.

Sorry you don't believe dual systems are safer, but its something you are doing/did wrong that caused your brake failure. Do you know DOT brake testing requires the primary AND secondary systems to stop vehicles from 60 MPH and/or 100 KPH in a certain measured distance, loaded and empty? Do you really think DOT has mandated the dual system since 1967 because it sounds like a good idea?

The dual systems work, and work damm well, but you have to use some logic, common sense, and knowledge to put together a custom brake system that performs like it should, not just "throwing" a dual master on a vehicle and expecting it to work correctly.

Not saying that's what you did, but you have to find out what you are or are not doing, and correct the problem, not give up on the dual master.

[Pat B]

I use a Monte Carlo / Chevelle master cylinder with 40 brakes on the roadster.....Works great!

Pat

[345 DeSoto]

I have seen, on at least 2 vehicles (plus my own) that "stopped great" either the front only, or the back only brakes were working...giving the appearence of "great brakes". However, they wouldn't lock up all four brakes, but would stop the car fine. Unless all four brakes can be locked up, something's not right...including mine...which is why I'm replacing the MC...