1983 F350 break question

TDJD · Dec 17, 2020

I have a 1983 F350 cab and chassis with duels, and the 6.9 IDI. I
bought the truck for hauling tractors, hay and other things around the
farm. The truck weighs 6,000 lbs, and it’s rated for 10,000 GVW.
Back a few months ago I got a load of gravel, (about 4,000 lbs, within
the GVW limit) I was driving home and noticed that when I pushed on
the brake pedal, it wouldn’t stop good. Also the brake pedal is
somewhat hard to push, I know it isn’t supposed to be as easy to
push as my grandfather’s new Silverado, but it seems it should push
easier than that. I have changed the front brake pads to heavy duty
pads and change the springs in the rear brakes. For reference, my
grandfather's Silverado 1500 will stop a 14,000 lbs trailer without
trailer brakes better than my f350 with 4,000 lbs on the bed. The truck
stops pretty good empty, but not good with a load. Does anybody
know if some thing I can do to the brakes to get it to stop better?
Thanks

grizz02 · Dec 17, 2020

sounds like the power booster is bad , does it run or idle rough ? it runs off of engine vacuum if it ruptures it will have a vacuum leak

4520BW · Dec 17, 2020

My 86 f350 did the same and it was the booster.

DRussell · Dec 17, 2020

Check the vacuum pump on the front of the engine. The diesels have a separate pump to create vacuum for the brakes and for the vent doors under the dash. Maybe the belt to the vacuum pump is loose or bad and needs replaced.

rustred · Dec 17, 2020

yes , should be vacuum assist. just sitting in the truck with engine running will feel and hear it work.

TDJD · Dec 17, 2020

It runs and idles smooth, but this is the diesel engine so it has a separate vacuum pump. So I think that wouldn’t affect the way that runs.

TDJD · Dec 17, 2020

I know the pump is working somewhat, because the pedal pushes easier when the truck is running, than when it’s off.

TDJD · Dec 17, 2020

Where did you get your new booster from?

4520BW · Dec 17, 2020

I believe oreilys . it was simple to change.

TDJD · Dec 17, 2020

Ok, thanks.

Mike M · Dec 17, 2020

I have a 1981 F350 with a dump bed and put a 460 gas engine in it. I have been over GVW many times but drive careful on the back roads and so far it has held together ! Now on the brake issue if you ever figure it out let me know as I have tried about everything and still am not satisfied with the brakes on this truck. The truck we had before was a 1965 Ford 1 ton dump and it had drum brakes all around. That old truck would darn near throw you thru the windshield if you hit the brakes real hard even with a load on it.

4520BW · Dec 17, 2020

I think I bought the booster with master cylinder combo.

DRussell · Dec 17, 2020

I used to have a 1991 with a 7.3. It never had great brakes. The brake light would flicker at times at an idle then go out when you revved the engine.

However, everything is relative. I also used to have a 1971 F350 that had a decent brake on one front wheel on the third pump of the pedal. You had to plan ahead when that truck got driven.

My 2000 F550 with a 7.3 about puts you through the windshield if you get into the brake pedal too much.

mjsnodgrass · Dec 17, 2020

i've been waiting a week for my rebuilt booster. they make one for trucks over 8600, and one for trucks under 8600. for some reason the one i need are hard to find. i'll order one from rock auto if mine doesn't show up in the next couple of days.

TDJD · Dec 17, 2020

The masters cylinder was put on just before I bought it, so I probably only need the booster.

wore out · Dec 17, 2020

(quoted from post at 11:51:56 12/17/20) The masters cylinder was put on just before I bought it, so I probably only need the booster.

BEFORE throwing $$$$ check the actual vacuum. Have to look up the "spec.", I would GUESS 15", give or take.

This will show that the vacuum pump is working, reservoir is intact, the lines aren't leaking, and that the booster hasn't failed in a way that it's leaking and vacuum can't be built up.

Some years back a customer with a "tonner" had poor brakes and the light lit on the dash, turned out to be that the vacuum reservoir (a Ford "tomato juice can" special) had a pinhole rusted in it.

I don't know if yours is set up that way/what reservoir is used, but in any case I would start with a vacuum gauge.

Also, is the brake/low vacuum light in the dash working?

JK-NY · Dec 17, 2020

Are your rear brakes properly adjusted? And are they working properly and in decent shape ( good amount of lining, drums not worn beyond spec?)

acresgreen · Dec 17, 2020

One other thing to check, My '88 f450 has a proportioning valve on the rear axle to apply more stopping power to the rear the heavier the load. There is an arm that connects the valve to to the frame [ more weight more fluid flow] Mine was out of adjustment. just saying....

504 · Dec 17, 2020

Check the diameter of the rear drums.If they are worn out you only use a small part of the shoe,I fought one of the local schools over the problem with their E350 bus. That thing would not stop for anything till I put new drums on it, it stopped, and then I sent them the bill(before they said it was too much money) To check a booster,shut the motor off pump the brake pedal 3 or 4 times,hold the pedal down and start the truck. If the pedal goes down, the booster is working. This is the book way to test a vacuum booster. Make sure the wheel cylinders are not frozen from rust,if the parking brake is hanging up in the drum you will never be able to adjust the brakes correctly either. With the drum off you will see a steel bar running between the shoes below the wheel cyl and above the axle. That is the mechanical bar that makes the parking brake work,it has a spring on one end. That bar has to be able to move back and forth when you try to move it,if it doesn't you will never get the brakes to work right.

4play · Dec 18, 2020

Check vacuum pressure, check in a couple different places and with/without lines connected (booster, HVAC etc). I'm not sure if there is an actual spec or not, I remember seeing 24-26 in.Hg. I would probably consider anything under 20 in.Hg to be low. If you have low readings, check directly at the pump, and see if increased RPM changes it. Increased RPM should not be needed to get a better vacuum pressure reading, but it might indicate a vacuum leak or weak pump.

1983 F350 break question

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