OFF OFFF Off topic; making a 79 F350 stop. Brake Booster???

[FinalImpact]

OK - so I've got this 79 F350 I've had sense 97. Its never stopped worth a damn no matter what I've done to it. From the day I bought until now it has NEVER locked up the wheels except on the snow and ice and maybe a few times in the rain. You just can't push the pedal hard enough.

It's a 460 V8 (7.8liter) 4X4, long bed crew cab. Its got huge brakes on it. I've replaced every piece of hardware except the damn steel lines going along the frames structure to the rubber lines at the wheel. No help.
Big discs up front with dual piston calipers and 12" X 3" drums out back.

So - I have this to ask:
When I bought it, it came with a brake booster of 11.5" in diameter and is a single diaphragm unit.

The master cylinder is 1.0625" bore. Its the only one listed for most all of the trucks. So I could drop the bore size to increase the PSI at the lines from another model and do an experiment. Option 1. (Oh - never replaced the proportioning valve either)

OR (option 2) - I could try a dual diaphragm booster. Again, not listed for this combo but they are out there. A 9-1/4" dual diaphragm unit.

Doing the math: Single vs dual brake booster it seems as though you end up with more surface area which could result in more vacuum assist and less pedal effort to make it stop. That is our goal here.

Anyone have any experience with this kinda swap?

I don't have any technical info on the boosters. GM tends to run dual dia boosters on many vehicles and the two diaphragms are different in size. I can't say anything about the Ford units other than they don't appear to have a step down leading me to believe the two dia's are different in size.

If this is true the dual unit could be as much as 134 in square vs the single dia unit having roughly 101 in square and significantly reduce pedal effort and make the 2 ton beast stop! I'm at wits end. . .

Replaced:
MASTER CYLINDER X 3!!!! EDIT caz red_rock_beetle pointed out the obvious!
Calipers
pads
hoses
drums
wheel cylinders
brake hardware blah blah blah

Rotors are true
Drums are true
lines are not crushed
no leaks
booster holds vacuum
Bearing have no free play
Shoes pads are dry - again, no leaks
Shoes are properly adjusted
There are no vacuum leaks and the engine runs great from idle to WOT.

OK - let me know you're thoughts -

 

[ChevyFazer]

Easy solution....




Sell it and buy a chevy!!!


Sorry I'm useless for brakes

 

[red_rock_beetle]

that's a dilly of a pickle

in the Audi world , it is common to swap master cylinders on the A6 to that of a RS6 for a smaller bore and better braking, so this is a possibility. but i don't see that you have replaced the master cylinder is the pedal hard or spongy?

 

[FinalImpact]

that's a dilly of a pickle

in the Audi world , it is common to swap master cylinders on the A6 to that of a RS6 for a smaller bore and better braking, so this is a possibility. but i don't see that you have replaced the master cylinder is the pedal hard or spongy?

ya - I'z forgot that on the master list. . . smaller bore is tempting me tho!

Also didn't list the Booster! Been there, done that!

 

[champion221elite]

Any chance you could add a Hydroboost? My 2004 Tahoe came with a Hydroboost which mounts on your firewall. The master cylinder then mounts on the front face of the Hydroboost. A pressure and return line are connected to the power steering pump which provides substantially increased brake pressure over a typical vacuum assist.

Typical vacuum assist brakes operate between 1000 to 1600 psi. A Hydroboost system operates at 2400 to 3000 psi.

Here's some info that might be helpful to you.

powerbrakes hydroboosts vacuum boosters everything for your extreme braking needs

 

[red_rock_beetle]

in '87 chevy had a hydroboost system on their 1 tons, it was a great setup

 

[FinalImpact]

Any chance you could add a Hydroboost? My 2004 Tahoe came with a Hydroboost which mounts on your firewall. The master cylinder then mounts on the front face of the Hydroboost. A pressure and return line are connected to the power steering pump which provides substantially increased brake pressure over a typical vacuum assist.

Typical vacuum assist brakes operate between 1000 to 1600 psi. A Hydroboost system operates at 2400 to 3000 psi.

Here's some info that might be helpful to you.

powerbrakes hydroboosts vacuum boosters everything for your extreme braking needs

I've seen those on Cadies and things where they alter the firing pattern to conserve fuel. Never thought about doing a heavy mod, as I had a 77 F250 that stopped with camper and a 30ft boat so I know they can but this thing is going to kill me and someone else.

EDIT: What I didn't say was that diesels and anything as big as or bigger than 1 ton is not out of the norm to see this. . . OK - the gears are turning. . .

So that that is an option!!!

Thanks!

 

[red_rock_beetle]

the reason diesels use them a lot is because they don't produce a vacuum at the manifold like a gasoline engine, so its either a hydro-boost setup or external vacuum pump

 

[FinalImpact]

the reason diesels use them a lot is because they don't produce a vacuum at the manifold like a gasoline engine, so its either a hydro-boost setup or external vacuum pump

check - I know. This is an RV cam and vacuum is good. Actually I had it in the 77 F250 and kept it swapping the 400c.i. for my fresh 460c.i. from the 77.

I'm looking for advice on the master cylinder or the vacuum booster. Specifically anyone knowing something about FORD vacuum boosters. :thumbup:

 

[FinalImpact]

Easy solution....

Sell it and buy a :ban: chevy!!! :ban:


Sorry I'm useless for brakes

Thanks (-) MINUS TEN!
Where is that Button? haha!