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Resident Wrecker Driver
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I searched and couldn't find an exact location for the "pressure differential valve" or bleeder rod on my 79 bronco. I have no pressure what so ever going to my calipers. I just replaced the calipers and master cylinder.
 

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Pressure what? Bleeder rod? Speakin some kind of foreign tongue to me.


You replaced the calipers and M/C and have no pressure while bleeding the front brakes? Does that sound about right? Let me guess and say you bleed said brakes with the motor off? Start it up, you should get plenty of pressure with some vaccum in the booster.

Did ya bench bleed the M/C?
 

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Discussion Starter #5
the haynes manual said theres some kind of bleeder valve for the front brakes. I bench bled the master and filled it up
 

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I had the same problem recently. A few months ago, my brakes went to crap, and I had a "spongy" pedal to say the very least. I checked the hoses, and they were totally cracked and dry rotted, so I changed all of them. It only took 8 or 10 turns of each bleeder until there was no air left. I figured I'd have to go back and bleed it later, but it never gave me problems.

Fast forward to a week ago...and I had no pedal again. I figured it was just air in the lines that had congregated to the ends after a couple months. When I tried to bleed them, there was no fluid at the front calipers. And, also...on the right rear, I got nothing but pure fluid...the left rear, was nothing but bubbles. I directed my attention to the prop. valve...and I pulled the pin out on the end of it...and that got fluid to the front. Still didn' fix the problem with the air in the rear though. Oddly enough, I'd have a great pedal after bleeding the rear (even with some air still in the lines)...but, after beeding the fronts, I'd have next to no pedal.

When driving, my pedal goes almost all the way down before the brakes even begin to stop...so I'm changing over to an F350 master cylinder, and brake booster...and also changing the rear wheel cylinders to F350 ones. If it still gives me shit, I'm gonna either try to clear out the prop. valve, or just by an adjustable one.
 

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I'm confused, what is being discussed here. Suspect the Haynes was referring to the proportioning valve.
 

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Driving Stuff Henry Built
-90 xlt, 351w, e4od, man 1356, 3.55, sag, warn hubs, 35s. -73, 400, np435, d20j twin, 35s
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the haynes manual said theres some kind of bleeder valve for the front brakes. I bench bled the master and filled it up
Are you asking about the bleeders on the back of each caliper & wheel cylinder? They should be near the top of each. All four corners should be bled after any hydraulic component change. See the 2 man brake bleed below for the how to.

This guy is putting a rubber cap on a bleeder.


2 Man Brake Bleed
1-Usual safety stuff (Block the wheels, trans in correct gear, on safe axle stands if jacked up, etc.). -Broncos are high enough you should be able do do this without jacking it up.
2-Check the level of the brake fluid, add if needed. Recheck periodically & add as needed throughout the bleeding process. Do not allow it to run out. If it runs out, you must start over.
3-Have your helper pump the brake pedal a few times & then hold it down. Do not let the pedal up while the bleeder is open.
4-Open the bleeder valve, observe the fluid flowing from the bleeder. Fluid & air bubbles can spray, it's best to run a clear hose from the bleeder into a container. Some would say wear safety goggles. Keep your mouth closed :toothless.
5-Close the bleeder valve while the pedal is still depressed.
6-Have the helper pump the brake pedal, observe height of pedal.
7-Repeat steps 2-6 until no bubbles are seen in the fluid from the bleeder valve, then move to the next wheel, following this order: RR, LR, RF, LF (On newer trucks with the RABS valve, it's RR, LR, RABS valve, RF, LF. On trucks that are newer still with 4 wheel ABS, I don't know). Be sure that each bleeder is closed before moving on. If the brakes are otherwise in good condition, adjusted, & not leaking, the pedal should be firm when done.
8-Check the level of the brake fluid, add if needed. Recheck again soon to be sure fluid isn't leaking.
 

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the haynes manual said theres some kind of bleeder valve for the front brakes. I bench bled the master and filled it up
On the front of the proportioning valve there's a pin that supposedly needs pulled when bleeding the front brakes. I did know of it and bled my brakes without pulling the pin, had no issues doing so even with the engine off. If you're planning on doing the F350 brake upgrade better check all the steel lines and make sure they're in good condition - when I was doing the hydroboost conversion (another 1-ton brake system) on my Chevy the first time I floored it I blew a front line, so I fixed that and then when I floored it again the rear line popped, so now with my F150 just as a precaution I replaced all brake lines (short of those at the rear axle) prior to the 1-ton brakes install.
 

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Ranger429:
"pressure differential valve" as stated above.

Maybe he's using incorrect terminology................................? :scratchhe

:thumbup
 

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I have never heard of a pressure differential valve, maybe proportioning valve. I think the Haynes manual is reffering to the bleeder screw.

Was the truck running or not when you tried to bleed the system fire? It made a big difference on the amount of pressure at the bleeder screws on the caliper when I did mine and had it off compared to running.
 

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Ranger429:

"pressure differentail switch" is referred to on "How to Fix Stuff", I googled. Maybe on his 90 BKO............? :doh0715:

According to this site and picture the "elec switch" looks like it's located on the passengers side (right) frame rail and is tied in with he brake lines to a "proportioning valve" to send a signal to a sensor/idiot light if there is a leak in the brake system anywhere.

This looks like something that might work in tandum with ABS perhaps, I had an adjustable PV on my 1966 Shelby GT350 years ago but I don't recall seeing anything like this "switch" on my 86...?

Perhaps the more modern vehicles that have ABS have a VALVE tied to the rear diff, somewhere I recall reading or seeing something to that affect, maybe it's just mounted there .....not sure :scratchhe


:thumbup
 
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