replaced my booster and pedal goes to floor

[kilog55]

ok so i reaplced my booster from a single to a dual diaphragm, my brakes have never really worked that well to begin with soft pedal etc. pedal feel is better but i have to floor the brakes to slow and stay stopped.

now this is on my 79 i modded my booster to work from my 72 on my 79. changed out the rod.

i have a new MC i will try to install if the weather works out i want to do all new lines and adjust the rear pads. etc

am i overlooking something?

[Alvin in AZ]

Only if by "new MC" you meant it!
...and not a "new looking" rebuilt. :/
Do yourself a favor and don't waste your time with a "rebuilt" master cylinder. :)
"New" are available and still no guarantee the first one will be a good one.
...just a better chance of it is all. ;)

BTDT ;)

A friend of mine in the shop told me he used to work at a place that "rebuilt"
fuel pumps. First order of business was when they came in they were tested,
those that tested ok where cleaned and boxed, just like that. :) Cool huh? :)

Another friend from south central Arkansas got a job in an oil bottling plant
in east Texas and was really-upset when he saw his favorite-motor-oil go down
the line and get the same oil from the same hopper as the house brand bottles
(he'd never heard of). So much for brand loyalty, huh? ;) They ain't got any,
why should you? ;)

Alvin in AZ

[kilog55]

well it did make my 72 stop on its nose so i know it works, the on eon the 79 could be the original for all i know. i need to do the hoses and wheel cyl. someday as well day

[fordman]

you have to use the master cylinder that matches your brakes. if you have drum brakes you need the original drum brake master. if you have swapped to discs you need the disc brake master from that year of truck you got the discs from.

[kilog55]

well its a larger res. MC like the ones for disc brakes gotta love cardone for there parts

[fordman]

you problem is unfixable with the wrong master cylinder on it. i'm sorry but it won't ever work right with that wrong master on it. the larger resivor is for larger caliper pistons than the regular drum brake wheel cylinders. you are putting the wrong amoutn of fluid to the front drum brakes. and that will mess up your braking power. proprtioning valves and residue pressure valve are a factor when working with disc vs drums.

[kilog55]

yeah but this is on my 79 i modded my 72 booster to fit

[fordman]

ok i go tconfused about that. i cant picture a 79 booster rod right now what did you have to do to the rod to make it work? maybe you made it too short. i know the 79 brake pedals sit lower to the floor to begin with so maybe it is too short. i'm guessing i haven't seen what you did to it.

[kilog55]

removed the 72 adjustable pedal rod and used my 79 pedal rod from the original booster it angles downwards, wasnt hard to do, i only lost an inch of travel in the pedal or so still have alot of pedal travel though it is alot firmer then before. but i will have to adjust the rear shoes and maybe swap out the MC same part number for my 79 that was on the 72 booster odd i know

[mr_josh]

So wait... do you have 4 wheel disc brakes?

Where did your disc brakes come from? Do you have a stock (not Camper Special) F-250 master cylinder? The reservoir size really has nothing to do with stopping power, the diameter of the master cylinder bore and the length of the master cylinder piston's stroke have everything to do with it. It's still possible that the volume of fluid that's required for your disc brakes is greater than that which is available from your master cylinder.

It's also possible that you've got a bad master cylinder or air in the lines still. The added force from the extra-large booster might be making more evident an internal leak in the master cylinder. You're probably tired of hearing it, but really, it's pretty hard to mix-and-match brake parts and come out with something that works right.