I placed a power brake umit on my '55 F350 and the pedal still goes to the floor board. I filled the master cylnder and bled the lines until they squirted. The vacuum line runs from the intake manifold to the booster under the floor (in the original location). I need it to stop. I was thinking maybe it is not creating enough vacuum. Any ideas? Help!

Mike

 

What vacumm are you useing off the intake manifold???
Mike K
Bay City MI

 

What's the master cylinder originally made for? You can't mix disc/drum drum/drum master cylinders. Plus you need to bleed the brakes more than just "squirted". You need to bleed till you get a smooth steady stream. Put a small hose on the bleeder and run it into a jar if you don't want to waste all that fluid. Also, you need to bench bleed the master cylinder before installing it.

 

I did bench bleed it before I mounted it. Had to because its location makes it hard to fill up. I used the word "squirt" as slang. Yes it did spray a steady stream from each cylinder. The master cyllinder is from an early model mustang so it is drum and drum. As for the vacuum, it is coming straight from the connection I placed on the front, passenger side of the intake. Any ideas?

 

The vavumm should be coming from the base of the carb or the back of th manifold just below the carb. It should be a 3/8 I.D hose and the fitting should be at least 3/8 just below the carb or at the bottom fitting on the carb.
Mike K
Bay City MI

 

Can you pump them up or does it always go to the floor? If you can pump them up, the first thing I would do is go and adjust all the shoes so they are as close to the drums as possible. Jack up each wheel and adjust the shoes out till the wheel won't turn and then back the adjusters off till you can turn the wheel with a little bit of rubbing still on the drum.

 

The manifold connection I hooked to was from a boss at the front of the manifold on the passenger side. There is no access from the carb area. Does this mean I have to find a spacer plate for the carb?

The brakes do not pump up.

 

The more I think about it I do not believe it is vacumm! If you cannot pump them up it is in the master or wheel cylinders or an adjustment in the shoes. The vacumm only makes the brakes work better. You must not have it bleed well enough. I have bleed many brake systems and some come up right away and some can take as much as an hour.Try bleeding them till you go through a whole bottle of fluid. Make sure you are using DOT 3 fluid and that all the shoes are adjusted as close as you can! Make sure all you're connections are tight and sealing. You could have a leak and be sucking in air every time you bleed them. Contrary to how they tell you to bleed them go to the one furthest from the wheel cylinder.then to the closest then to the farthest again. Have someone pump the pedal 5 times then hold the pedal till it goes to the floor, then release the bleeder then tighten again, then release the pedal and stert over . Do this about 5 times per wheel and keep going around the vehichle until you start getting a good pedal. I have found that bleeding the brakes while the vehichle is running is best. The vacumm assist seems to help.
Try this and if it does'nt help let us know. We will keep working on this till we get it fixed!!!!!!
Mike K
Bay City MI

 

I always bleed the brakes with the engine running to get the vacuum boost. But... I will try again. I know that persistence pays off.


Mike

 

You could just have a bad master cylinder. It could be leaking the pressure backwards when you push the brake and all the lines are closed. It would still squirt if it wasn't a real bad leak but leak once under full pressure. It's hard to tell if it's not a remote resevior. You can sometimes see the bubbles. Other times it just kinda goes back and forth inside the cylinder itself. It's supposed to work like a oneway valve inside the master. Sometimes it can go both ways if it's messed up inside. I went through two supposedly brand new master cylinders from a local parts place before getting one that worked.
Hope this helps a little. Don't get discouraged even though it really bites.

 

The same thing happens to a clutch master cylinder sometimes.

 

You need to make sure your master cylinder is for a power brake unit. The booster output rod has to be compatible with the master cylinder. It sounds like you may have a gap which will prevent the booster from moving the master cylinder piston.

The brake pedal is usually different too for a power brake vehicle, but it would still produce at least some output.

 

You may have this problem caused by the swap of the master cylinder. The early Mustang cyl is mounted above the wheel cylinders and does not use any type of check valve to maintain residual pressure to the wheel cylinders. If this is then mounted below the floor in your truck the brake fluid will return to the master cylinder when the brakes are not applied thus leaving the wheel cylinders without enough fluid in them to operate properly. If you can get the brakes to operate by pumping them several times this is probably your problem. You can correct it by installing residual check valves in the lines leading to the front and rear brakes.Use either 2lb. or 10lb. check valves depending on wheter or not you are useing drum or disc brakes. You might also want to reconsider using a single resevior Mustang master cylinder and use a double resevior master cylinder for safety sake. Hope this may help you.

 

>You could just have a bad master cylinder. It could be
>leaking the pressure backwards when you push the brake and
>all the lines are closed. It would still squirt if it
>wasn't a real bad leak but leak once under full pressure.
>It's hard to tell if it's not a remote resevior. You can
>sometimes see the bubbles. Other times it just kinda goes
>back and forth inside the cylinder itself. It's supposed to
>work like a oneway valve inside the master. Sometimes it
>can go both ways if it's messed up inside. I went through
>two supposedly brand new master cylinders from a local parts
>place before getting one that worked.
>Hope this helps a little. Don't get discouraged even though
>it really bites.

okay i'm going through hell trying to get my brakes blead.

no matter what i do i can't seem to get any reasonable pedal. i have gone back around an made sure all fittings are tight.

when i started to bleed one of the wheels i had mistakingly left the cover off the master cylinder and as my wife pushed on the pedal the master cylinder acted like a fountain. not air bubbles but a stream of fluid shot all over the car. it seems to me if the master cylinder is pushing fluid back into reservior, then i might have a defective master cylinder. is this a correct assumption? this would be the second one, the first wouldn't even bench bleed. both were remanufactored units which i've read warning about using. any thoughts oh wonderful gurus?

btw i'm using a 70 dual disc/drums mastang master cylinder with a mid 80 mustang booster. booster rod is adjusted correctly for the master cylinder.

thanks,
rick