I know this has been covered many times. I have a 41 Mercury coupe, when I got the car it already had a new brake system installed. The PO had used a dual master cylinder conversion from Millworks, new lines, shoes, hoses and wheel cylinders. After 2 years I have finally got the car back together. I started trying to bleed the brakes with no success. I have went through 2 quarts of fluid, and only get mushy peddle, no real pressure buildup. Yesterday I disconnected the rear line from the MS and no fluid came out until I pressed the peddle. All brakes I have done before even with RPVs fluid would drain from MS with the line disconnected and the lines would have a little pressure in them, but this time there is no pressure in the lines. So I'm thinking I may have a bad MS. I'm no brake guru so I'm not sure. Can you guys give your opinion what I need to do to get the brake pressure to build up. There are no leaks that I have found.
Brake bleeding problem.
- Thread starter CallmeBob
- Start date
On many dual res master conventions, you don’t get enough pedal travel ( pushrod travel ) . I would confirm that there is NO slop in the linkage , I mean NO worn pivots, holes , pins , or rods , then make sure you have a min amount of free play between the push rod and master . You need to some , just keep inat min . Then confirm that the brake pedal isn’t hitting anything on its travel , this may require the floor to be removed or at least 2 people, one pushing the pedal and another under the car to makesure no interference when pushing the pedal .
I’ve been in your situation and it required the floor to be removed and many new linkage components before the master would produce its full potential.
Good luck
I’ve been in your situation and it required the floor to be removed and many new linkage components before the master would produce its full potential.
Good luck
hueyhoolihan
Well-known member
i don't know much about bleeding brakes but don't expect liquid to flow uphill. IOW, if the top of the master cylinder's reservoir sits above the open end of the line that's been disconnected fluid will not flow out of it.
and from what i gather, the master cylinder is under the floorboard. and that's pretty low.
coincidentally, as an illustration, just the other day i disconnected a rear brake line from my '41 ford and no fluid came out of the line...until i lowered the line a bit.
and from what i gather, the master cylinder is under the floorboard. and that's pretty low.
coincidentally, as an illustration, just the other day i disconnected a rear brake line from my '41 ford and no fluid came out of the line...until i lowered the line a bit.
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Kurt in NJ
Well-known member
Some new wheel cylinders don’t have the fluid and bleeder holes drilled properly preventing the air from bleeding out.
Have the shoes been adjusted and centered?
The stroke the master cylinder needs may not be what the pedal provides.
Typically these problems go on for 5 pages.
I had a 39 and 46 and solved the re occurring total hydraulic brakes failure problems by trading them in for a 36 with the reliable redundancy of mechanical brakes—
Have the shoes been adjusted and centered?
The stroke the master cylinder needs may not be what the pedal provides.
Typically these problems go on for 5 pages.
I had a 39 and 46 and solved the re occurring total hydraulic brakes failure problems by trading them in for a 36 with the reliable redundancy of mechanical brakes—
Flathead Fever
Well-known member
I was a fleet mechanic for 30-years and have done hundreds maybe even thousands of brake bleeding. Early Fords are a little different being that the master cylinder is located so low on the vehicle. Other vehicles since the master cylinder is way up high on the firewall you can just open a bleeder on a wheel cylinder, and the fluid will come running out. Since you replaced the master cylinder it will need to be bled first. We used to put the master cylinder in a vice and then we had pre-bent brake lines that attached to the two holes and into the reservoir. They sell threaded plastic brake line fittings that have nipples for rubber hoses to stick in the reservoir. We replaced so many master cylinders on a fleet of 400 vehicles that we just bent up some metal brake lines to use to bleed the master cylinders. We'd slowly press the the cylinder in all the way with a large Phillips screwdriver, and the air would come out into the reservoirs until only fluid was coming out, that meant the master cylinder was primed. Depending how fast you are you might lose the prime by the time you get the master cylinder bolted in. You can stick a couple of brass brake plugs in the holes to keep the fluid in there until your ready to hook up the lines and start bleeding.
Since you have two separate systems you can leave the plug in the front master cylinder port and start bleeding the rear. Open the bleeder furthest from the master cylinder which is the right rear. Have somebody "slowly" push down on the pedal until it bottoms out and shut the bleeder. Then let the pedal back up and open the bleeder and have them push down again. Repeat this, it will spit air until there is a nice steady flow of fluid coming out. Close the bleeder before letting off of the pedal. Recheck the master cylinders fluid level, if you run out in the middle of bleeding the brakes you get to start all over again because you have trapped air in the master cylinder. Do the same thing with the front wheel cylinders, first the passenger side and then the driver's side.
Do not gorilla tighten the wheel cylinder bleeders. You want them tight, but you don't want to break them off
You should have a good pedal, if not than you need to adjust the brakes up, so they are adjusted "evenly". With no pedal pressure they should just barely rub while spinning the wheels on all four-wheels
Make sure your lines are hooked up correctly to the master cylinder You have the fronts and the rears hooked to their correct fittings It makes a difference.
Check the clearance of the master cylinder rod. The piston inside of the master cylinder needs to come all the way back to the snap ring. Then there should just be a little play between the rod and the piston, just enough that it's not pushing the piston in. If there is no play the fluid will not return the master cylinder reservoir, and your brakes will lock up and stay locked up until you loosen a line and let some fluid out.
Make sure your rubber brake hoses have some slack too them when turned all the way right and left and there not rubbing on anything.
Since you have two separate systems you can leave the plug in the front master cylinder port and start bleeding the rear. Open the bleeder furthest from the master cylinder which is the right rear. Have somebody "slowly" push down on the pedal until it bottoms out and shut the bleeder. Then let the pedal back up and open the bleeder and have them push down again. Repeat this, it will spit air until there is a nice steady flow of fluid coming out. Close the bleeder before letting off of the pedal. Recheck the master cylinders fluid level, if you run out in the middle of bleeding the brakes you get to start all over again because you have trapped air in the master cylinder. Do the same thing with the front wheel cylinders, first the passenger side and then the driver's side.
Do not gorilla tighten the wheel cylinder bleeders. You want them tight, but you don't want to break them off
You should have a good pedal, if not than you need to adjust the brakes up, so they are adjusted "evenly". With no pedal pressure they should just barely rub while spinning the wheels on all four-wheels
Make sure your lines are hooked up correctly to the master cylinder You have the fronts and the rears hooked to their correct fittings It makes a difference.
Check the clearance of the master cylinder rod. The piston inside of the master cylinder needs to come all the way back to the snap ring. Then there should just be a little play between the rod and the piston, just enough that it's not pushing the piston in. If there is no play the fluid will not return the master cylinder reservoir, and your brakes will lock up and stay locked up until you loosen a line and let some fluid out.
Make sure your rubber brake hoses have some slack too them when turned all the way right and left and there not rubbing on anything.
TerryOH
Well-known member
On the Ford master cylinder there is a residual valve that keeps a small amount of pressure in the lines. Disconnecting the rear brake lines should result in a small amount of fluid to leak out. Contact Millworks and inquire. It may be good to adj brake shoes up tight and after bleeding readjust to the proper clearance.
Drbrown
Well-known member
For what its worth: (1) I installed "Speed Bleeders" on my '47 wheel cyclinders which saves effort in the procedure an d allows one person to do the job. (2) I have an 1980's GM car with dual master cylinder. One cylinder chamber works the RR and LF brakes and the other the LR and RF brakes. Its mounted mid-height on fire wall. I had to get use to the car's braking system since it has vacuum assit and I do not get the pedal height or need to apply the usual pedal force as with a standard system.
I bled the master cylinder again with the same results. My neighbor who is a metal fabricator made a push rod [ the screw part that connects to the pedal ] to take out some of the play in the original, still did not work. Then I replaced the master cylinder and now I have brakes. So it must have been a bad master cylinder.