proportioning valve on a 77 F250

michaelbrainard · Post by **michaelbrainard** » Thu Sep 28, 2006 7:55 pm

Hey all.

1977 F250 ext cab camper special - dual piston front disk brakes, and originally 2.5" rear drum.

The brakes are new all around, even the master cylinder, pistons and calipers are new.

It takes a leg like a gorilla to get the brakes to work well. I really can't get the brakes to lock, even on a gravel road. This is typical at idle or with the rpms up ( I was considering low vac, but I don't think that is the case...) Action is smooth and they don't pull one way or the other. No fluid leakage to be found....

I found what I THINK is the proportioning valve this evening while changing the oil. It was mounted somewhat inside the drivers side frame channel under the cab. There appears to be somewhat of a "knob" on it...is this an adjustment? What does it do?

fordman · Post by **fordman** » Thu Sep 28, 2006 8:41 pm

what is the condition of the power booster? is it definetly good? did it work previouly?

rboeding · Post by **rboeding** » Thu Sep 28, 2006 9:49 pm

That knob is there to pull when you bleed the brakes. I am not sure what it does.

Post by **FORDification** » Thu Sep 28, 2006 9:54 pm

The factory proportioning valve is non-adjustable, but many folks add an adjustable version, which allows them to tweak the front-to-rear bias to suit their needs. That's what it sounds like your truck has. Do a quick Google search for "adjustable proportioning valve" and see what turns up...does it look like the ones in the pictures shown?

michaelbrainard · Post by **michaelbrainard** » Fri Sep 29, 2006 7:34 am

rboeding wrote:That knob is there to pull when you bleed the brakes. I am not sure what it does.

Well, this I have never done.......

michaelbrainard · Post by **michaelbrainard** » Fri Sep 29, 2006 7:35 am

fordman wrote:what is the condition of the power booster? is it definetly good? did it work previouly?

This is how it has worked since I purhcased the truck a couple years ago. I really have no way of knowing if it is working or not. How does one check?

jor · Post by **jor** » Fri Sep 29, 2006 9:16 am

Michael, do you have a dedicated vacuum source for your brake booster? If you don't that may be your problem. I tried putting a "T" in my system once with a poor outcome. The intake manifold was the source and I Teed it to the booster and to the PCV valve. With this setup, my brakes performed just as you describe. Back to a dedicated source and back to good brakes.

BTW, I have the stock proportioning valve on my 67 along with the after market one you mentioned. The adjusting knob is frozen on it and I have never used it. Wish we had the photo posting feature back and I'd show you a photo.
jor

fordman · Post by **fordman** » Fri Sep 29, 2006 9:58 am

i'm not real sure how to test the bosster for a vacuum. i think you need a gauge of some sort. but the best way to know is if you hear a hissing type of sound when you push on the brakes with the engine running.

michaelbrainard · Post by **michaelbrainard** » Fri Sep 29, 2006 10:47 am

jor wrote:Michael, do you have a dedicated vacuum source for your brake booster?

That is very interesting because NO i do NOT have a dedicated source for vac...it too is "t-ed" along with another vac line at the intake manifold.

If I remove the PCV valve ( if that is what is connect here....I don't remember off hand) from this vac point, where should I connect it?

Wait......the above may not be the case...it is the case on my 69...I'll check at lunch time..

fordman · Post by **fordman** » Fri Sep 29, 2006 11:35 am

your pvc goes directly to the carb base plate and the bosster goes to the intake.

michaelbrainard · Post by **michaelbrainard** » Fri Sep 29, 2006 12:59 pm

The connection on the intake is shared with the booster and two other vac lines...didn't have time to track them down to see what goes where.

flyboy2610 · Post by **flyboy2610** » Fri Sep 29, 2006 10:13 pm

michaelbrainard wrote:The connection on the intake is shared with the booster and two other vac lines...didn't have time to track them down to see what goes where.

I'm betting that's your problem.

rboeding · Post by **rboeding** » Sat Sep 30, 2006 9:11 pm

michaelbrainard wrote:
rboeding wrote:That knob is there to pull when you bleed the brakes. I am not sure what it does.
Well, this I have never done.......

Me neither but somewhere else I was told to do this and my brakes work great. I just replaced everthing but the valve and I couldn't be more pleased with the brakes. Before, I needed Arnold to stop the truck.

fordman · Post by **fordman** » Sat Sep 30, 2006 11:00 pm

yea one large booster line and two other smaller lines are on all fe's that was original from the factory. all of them i have seen have been hooked up like that. so you may have problems else where is the brake system.

Tim P. · Post by **Tim P.** » Mon Oct 02, 2006 8:49 pm

Im betting the booster has issues or a misadjusted pushrod between the m/c and booster.