I have 84 f150 just put new wheel cylinders and a proportioning valve on it have firm brake when truck is off spongey while running brakes seem like they are working properly I was wondering if i still have air somewhere in the system or what my problem was. Master cylinder and booster is only couple months old also.

 

Did you try bleeding them again to see? I'd bleed all 4 corners again just to make sure there was no air left in them.

 

thanks im going try to bleeding them again tomorrow and see what happens

 

It's not a proportioning valve. It's a brake pressure differential valve. They don't often go bad on these trucks. Typically, when people think they're going bad, they're usually just doing their job.

When air gets into the brake lines, usually due to a leak of some sort, the brake pressure differential valve has a plunger in the body of the valve that slides back and forth. This plunger will block off the hole for the line that is getting air pumped into it by sliding when hydraulic force (when you step on the brakes) is applied. This jumpers the contacts in the BPDV that triggers the brake light on your dash. When all of this happens, it warns you there is an issue, you'll feel it when you go to slow down and definitely know something is wrong with the brakes, and you're supposed to have enough braking power left to limp home or limp to a parts store.

I know you've replaced the wheel cylinders already, but just as a general guide...

Typical things to check are to make sure there are first no leaks from the wheel cylinders at the rear drums. This is usually a typical problem for vehicles that have sat for a long time and then braking force is suddenly applied. Check all of your brake lines, make sure all of your connections are tight, and make sure the master cylinder is full on fluid. You'll also want to check the pistons in the front brake calipers as well.

Once this is done, bleed the lines starting with right rear, left rear, right front, and finally left front.

After the lines are bled and your problem isn't fixed, it's time to check the master cylinder.

Undo the two bolts holding the master cylinder to the brake booster. Carefully slide it off, and look at the back of the master cylinder. There's a snap ring that holds in a metal plunger where the rod from the brake booster goes. Behind the snap ring is also a seal, and when the seals get old or have to put up with old brake fluid for a long time, this can cause brake fluid to leak out of the M/C, letting air into the M/C and brake fluid into the brake booster. This will impair your braking ability, and you'll either have to take apart the M/C or replace the M/C entirely and then re-bleed the lines.

Once that's done, you'll also want to replace the brake booster. Chances are, the booster is full of brake fluid and the booster is probably leaking or not too far off. And, every time you step on the brake pedal, you're sucking brake fluid into the motor, you don't have full braking force, and you're also putting more air into the brake lines and more brake fluid into the brake booster.

Always replace the booster and M/C in pairs.

Welcome to FTE, and if there are any more questions, feel free to ask. We have a lot of knowledgeable members here at FTE.

 

Thanks i had to replace the valve because it was stuck closed from the truck sitting and i took it apart and cleaned a pile of dirt out of it put it back together and it was leaking then.

 

adjust your rear brakes manually

 

We think alike . That Was my call also . People do not understand the importance of brake adjustment on peddle feel . I drove a 73 Beetle for 15 years , I could always tell when the brakes needed adjusting .

 

jwc back in my past life i worked on a farm. i took care of a number of vehicles and equipment. these old fords just made up half the fleet of vehicles besides tractors lol. there isnt much i don know about this generation and the next. but yea good hunch.
once upon a time the beetle was listed in guiness as the number 1 vehicle driven on the e brake

 

I also worked on a farm back in the 80's .Learned a little about a lot , LOL . We had old eguipment . Fords , GMC , Deutz , Oliver ,Moline , ect . Amazing though how much I remember , And have forgot . Now I work with scanners and the internet . Fuel injecton is the norm. I only see a couple of carbs a year ( besides at home ) . But , Drum brakes have not changed that much .

 

I have a 85 F-350 6.9 IDI dually with this same problem(s)....I am also working on checking out Items listed above to find the problems

 

The brakes on these trucks have a self-adjuster in them. To "automatically" adjust the brakes (after it has been sitting a while or if they've been stuck, etc.), put it in reverse and get up to about 10 miles an hour and slam on brakes. It'll force the ratchet on the self-adjuster to turn and tighten up your rear brakes.

The other way is to jack up one tire, use a flat headed screw driver or a brake "adjusting tool", and spin the wheel while tightening up your adjuster until it just begins to catch and drag. Do this for both tires.

If the automatic adjusters in your drums are working, they should adjust as you drive.

If this doesn't work, and you've checked both the front calipers and put in the new wheel cylinders, it's a safe bet that it's your master cylinder.

It's also said that as the rubber lines going to the wheels age they'll get spongy and flex under hydraulic pressure. I don't doubt this, but since 1983, my rubber lines have been just fine.

I adjusted my rear drums before finding out it was the master cylinder that was causing my own issues. While it did minimally help the pedal feel, the best thing to help pedal feel is no leaks. You can also be confident that your rear drums are grabbing like they're supposed too.

Hope you guys find out the issues soon. It can be a frightening experience to pull out on asphalt and need to throw on brakes and not have anything!

 

I have the exact same experience at the OP. I had a master cylinder done front left brake caliper done + new rotors and pads. Got a universal proportioning valve put it in place of the one it used to have. Feels firmish but weak, when I slam on the brakes I can get a 4 wheel skid going. If I'm resting my foot on the brake the truck moves forward, I have to put pressure on it to make it stay stopped. The master cylinder level has been within about 1mm for at least two months so no leaks. I'm going to try the adjustment thing

Ps. Truck is for sale. 3 grand

 

Reviving old thread, if possible. I am having similar issues and am running out of ideas. Truck is an '85 F150, 2 wheel drive with the 300 I6 and 4 spd trans. A couple weeks ago, the brakes started to get soft - actually, they would engage as normal, then suddenly give way and the pedal would travel another several inches before grabbing again. I noticed the front reservoir for the rear brakes was empty, so I topped it off and checked every corner, every fitting, everything for leaks and the only one I found was out of the back of the master cylinder dripping down the brake booster.

So, yesterday I finally replaced the master cylinder and bled all four corners with a hand pump until clean fluid was coming out. This resulted in a slightly soft pedal and a new hissing sound when depressing the brake pedal inside the cab. I figured that was the brake booster (which I should have just replaced anyway) so I just put a new one one today and re-bled the system the old fashioned way with a helper in the cab. The brakes are still super spongey and the hissing sound is still present.

What am I missing here? I tried the auto-adjusting trick for the rear brakes, and it didn't change anything. I don't think I have a new leak anywhere that I can find, but it's pretty hard to tell since there is brake fluid everywhere from the initial master cylinder leak and bleeding all four corners again today. I realize the brakes are a pretty simple system, so I'm thinking it has to be air or a leak somewhere, but I just can't seem to figure it out.

Any ideas? Thanks for all the help you guys offer...it is much appreciated and you probably don't hear that enough.

 

This sounds like the place to look for the help and advice I need. Mine is a 90 F350, XLT Lariet, Dually with anti lock rears. Needed to redo the brakes. Felt it needed to be a complete job partially because of age and the bad ware it had. I have replaced almost everything. Power Booster, MC, Calipers, Disks, pads, front brake lines, drums, shoes, wheel cylinders, all springs and hardware, everything that is inside he brake drum that can be replaced. Bench bled the MC, plugged the holes and mounted it on the PB with the rod readjusted to the length the book had. Hooked up the lines and a Motive Brake Power Bleeder set @ 15 psi. Bled the MC by loosening the lines until the air stopped, bled the the anitlock valve on the frame under the drivers seat, RR, LR, RF, and LF. Let the RR run about a quart out all together. No more air coming out. All new clean fluid. Took the bleeder off and the MC cap on. Pushed the pedal down 3 times and she was hard as a rock at about 1/3 travel. Started the truck and pushed down on the pedal 6 times. It went to the floor every time. Hooked up the bleeder again and bled the RR again. Got a lot of air after a about 60 seconds. Bled it until no more air for 2 min. Did the LR the same. As well as the front. No air in the front. Took off the power bleeder and locked it back up. Pedal was rock hard after 2 pumps. Started the engine and pedal went to the floor. Same as before. Gone thru this process 5 times. Even rereplaced the MC. Everything is very clean. There are no leaks but I keep getting air in the system when I start the truck. Sounds funny but it seems like something is putting air in the system when I start the truck. This is the work I did when I was in the Marines. Hyd. and air over Hyd. braking systems. "School trained" in NC too. Been doing brakes for 39 years and never seen anything like this. Wife had an Aerostar and a 98 Expedition with full anti locks, and she was bad on brakes, never had a problem getting them to work properly when I was done. Now I feel stupid. Any help/ideas would be greatly appreciated.

 

Block off the mc port to the rear. See how it feels. Then post back.