84 f250 brake conundrum
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Junior Member
Joined: Apr 2018
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84 f250 brake conundrum
I have an issue. actually, its a problem.
truck was brought to me to repair the brakes. whole system was marginal at best. rear brakes not functional, fronts were grinding, pedal spongy. we replaced the front pads, rotors, and calipers. we replaced the axle seals (rear), rear shoes, hardware, wheel cylinders, and adjuster assemblies. replaced master cylinder with a new one, not reman.
after completion, road-test was unsatisfactory--front brakes locked up on the icy road, and the drivetrain kept pushing the vehicle forward, even though i was practically standing on the pedal. the rear brakes were still nonfunctional, or just barely activating. i could not get the rears to lockup, even on the ice. once on asphalt, i could get a little brake action from the rears, but nowhere near where they should be. i rechecked the rears, found that i had a defective wheel cylinder at the right rear, and replaced it. still not sufficient braking. checked fluid pressure at the splitter for the rear lines--had approx. 380 psi brake fluid pressure, and the same at the right rear bleeder port. this should be plenty to activate the rear brakes. when i run the truck in the air with the tires off the deck, it still does not lock them up, even at full brake application. there is no binding problem at the rear brakes, and the cylinders extend fully with the drums off. everything mechanically and hydraulically appears to be working smoothly, yet i have little braking at the rear.
now, i know brakes, and its not rocket science, but this is kicking my butt, and its ticking me off!! does anyone out there have a similar experience and maybe a fix?
truck was brought to me to repair the brakes. whole system was marginal at best. rear brakes not functional, fronts were grinding, pedal spongy. we replaced the front pads, rotors, and calipers. we replaced the axle seals (rear), rear shoes, hardware, wheel cylinders, and adjuster assemblies. replaced master cylinder with a new one, not reman.
after completion, road-test was unsatisfactory--front brakes locked up on the icy road, and the drivetrain kept pushing the vehicle forward, even though i was practically standing on the pedal. the rear brakes were still nonfunctional, or just barely activating. i could not get the rears to lockup, even on the ice. once on asphalt, i could get a little brake action from the rears, but nowhere near where they should be. i rechecked the rears, found that i had a defective wheel cylinder at the right rear, and replaced it. still not sufficient braking. checked fluid pressure at the splitter for the rear lines--had approx. 380 psi brake fluid pressure, and the same at the right rear bleeder port. this should be plenty to activate the rear brakes. when i run the truck in the air with the tires off the deck, it still does not lock them up, even at full brake application. there is no binding problem at the rear brakes, and the cylinders extend fully with the drums off. everything mechanically and hydraulically appears to be working smoothly, yet i have little braking at the rear.
now, i know brakes, and its not rocket science, but this is kicking my butt, and its ticking me off!! does anyone out there have a similar experience and maybe a fix?
Senior Member
Joined: Jun 2010
Posts: 16,557
There should be a combination metering/proportioning valve on your vehicle.Usually located down from the master cyl near the chassis. It's job is to hold off hyd pressure to the calipers until the rear cyl overcome return spring pressure.
Once that is done, the proportioning section regulates how much hyd pressure goes to the calipers up front and how much goes to the wheel cyls in the rear. The object is to limit hyd pressure to the rear when stopping to prevent wheel lock-up as weight is transferred to the front brakes. The percentages were something like 80% to front brakes , 20% to the rears. If you suspect the combo valve is not functioning correctly , just replace it.
Once that is done, the proportioning section regulates how much hyd pressure goes to the calipers up front and how much goes to the wheel cyls in the rear. The object is to limit hyd pressure to the rear when stopping to prevent wheel lock-up as weight is transferred to the front brakes. The percentages were something like 80% to front brakes , 20% to the rears. If you suspect the combo valve is not functioning correctly , just replace it.
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