1939 master cylinder

[rich b]

Originally Posted by Woodie1

I also lengthened the master push rod.

Can you explain that?

Did you adjust the pushrod to provide discernible clearance between the pushrod and master cylinder piston with the pedal at rest pulled back by it's spring?

[Woodie1]

When i move the pedal by hand under the car, I am unable to determine at what point the rod contacts the piston. Either way, I am unable to expel all the air bubbles. I don't see any bubbles after a third bleed at each wheel but when I come around for another try, bubbles show up again. just can't find where they are getting in.

[Kube]

Originally Posted by Woodie1

When i move the pedal by hand under the car, I am unable to determine at what point the rod contacts the piston. Either way, I am unable to expel all the air bubbles. I don't see any bubbles after a third bleed at each wheel but when I come around for another try, bubbles show up again. just can't find where they are getting in.

You shouldn't be having this much trouble. You knew that

How exactly (the process) are you bleeding?

[Woodie1]

The first new mc I put on, I did not bench bleed to start with. Later I did bench bleed it. The new mc I put on last I did not bench bleed. I have a tire tires removed with the car blocked up. I put the wrench on the bleed screw & have my wife pump the brake pedal 3 times slowly & hold down on the 3rd pump. I open the bleeder & keep it open until I don't see bubbles through the hose or into the bottle. Close the bleeder & she will release the pedaal. When the pedal is up, she pumps 3 times slowly again & holds down. I open the screw & watch for bubbles, & then thighten screw when no more bubbles show. We do it one more time. We start with the passenger rear wheel, driver rear wheel, Passenger front & then driver front. After each wheel is bled, I add more fluid to the master. I put the cap back on the master each time but only until it meets the cap seal. I don't tighten it. I am using a bottle with a check valve & a tube submerged in fluid. I have even wrapped the bleeder screws with teflon tape. The screws feel quite loose when they are loosened. I'm open for any ideas. I've read of putting a 1' thick board under the pedal so it can't go to the floor. I haven't tried that yet.

[Kube]

Originally Posted by Woodie1

The first new mc I put on, I did not bench bleed to start with. Later I did bench bleed it. The new mc I put on last I did not bench bleed. I have a tire tires removed with the car blocked up. I put the wrench on the bleed screw & have my wife pump the brake pedal 3 times slowly & hold down on the 3rd pump. I open the bleeder & keep it open until I don't see bubbles through the hose or into the bottle. Close the bleeder & she will release the pedaal. When the pedal is up, she pumps 3 times slowly again & holds down. I open the screw & watch for bubbles, & then thighten screw when no more bubbles show. We do it one more time. We start with the passenger rear wheel, driver rear wheel, Passenger front & then driver front. After each wheel is bled, I add more fluid to the master. I put the cap back on the master each time but only until it meets the cap seal. I don't tighten it. I am using a bottle with a check valve & a tube submerged in fluid. I have even wrapped the bleeder screws with teflon tape. The screws feel quite loose when they are loosened. I'm open for any ideas. I've read of putting a 1' thick board under the pedal so it can't go to the floor. I haven't tried that yet.

Thank you for this detail. I am confident there are others, beside myself, that would really like to help you solve this issue.
It sounds as if you are bleeding the system properly.

I'd asked for the details as I tend to go at things methodically.

Next question of you don't mind...
When you are done bleeding and everything is tightened up, can you pump the brake pedal up until it is firm?
If yes, hold foot pressure on the pedal for perhaps a full minute. The pedal should stay where you started from. Does it?

[Woodie1]

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When we are done bleeding now, the pedal is fairly firm. I can put pressure on the pedal for a minute & it appears to stay . It doesn't go to the floor. I just don't know how long it will act like this.

[Kube]

Originally Posted by Woodie1

When we are done bleeding now, the pedal is fairly firm. I can put pressure on the pedal for a minute & it appears to stay . It doesn't go to the floor. I just don't know how long it will act like this.

If the pedal holds it height for a minute or so and stays firm, there is most likely no bleeding issue.

How far does the pedal go down before braking begins?

[Woodie1]

I would say the pedal goes down a couple inches before braking starts.

[Kube]

Originally Posted by Woodie1

I would say the pedal goes down a couple inches before braking starts.

Two inches isn't terrible. I prefer a bit less than that.
My suggestion? Adjust the rod at the master a little bit at a time. That will bring your pedal travel up.

I'm really starting to think you do not have a bleeding issue.

[1942deluxe]

Mike, if you adjust the master cylinder rod out it should reduce the pedal travel or the opposite? Some of this thread may apply to what I'm finding on my 46 so I'm following.

[rich b]

As far as I know there is only one proper pushrod adjustment; when the pedal is held against the floor by the return spring, there should be 1/16" between the end of the pushrod and the master cylinder piston.

If adjusted more than this there will be wasted motion before the brakes are actuated and if adjusted less than this it could stop the piston from returning fully, possibly to the extent of not releasing the brakes.

Of course you need to be sure the pedal is free and not binding, the return spring is in place, and the master cylinder bore is not corroded hindering the piston from returning fully.

[1942deluxe]

Thanks, Rich. That's helpful.

[Kube]

Originally Posted by 1942deluxe

Mike, if you adjust the master cylinder rod out it should reduce the pedal travel or the opposite? Some of this thread may apply to what I'm finding on my 46 so I'm following.

Making the rod longer reduces pedal travel. In other words, the actual braking begins earlier.
When I restore a car, I like to find the "sweet spot" when adjusting that rod. The sweet spot, as I define it is to obtain the least pedal travel prior to actuating the braking while not restricting the fluid from returning (in)to the master.
It takes me a few attempts but is worth the effort. Well, to me it is...

[Terry,OH]

Ford Spec. for the pedal adjustment is 1/4 to 1/2" free play of the brake pedal. There should be no need add some length to the actuating rod since it has an adjustment on the pedal end, it should be 3.62" long. Also the brake pedal return spring has to be attached to bring the pedal all the way back to its proper resting place, since the free play is measured from pedal rest. Below you can see the adjustment and the fixed length of the operating rod, plus the original 39 brake and clutch pedal return spring.