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 -
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 -
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