Truck Brakes/No petal

Anonymous-0 · Mar 23, 2009

Truck: Later 70's F600 Ford grain truck Problem: Had to replace one brake line. Truck brakes were bled. All six wheels were bleed. No petal. Replaced master cylinder as it leaked a littl bit. Brakes were power bleed at a reliable dealer who has a power bleeder. Problem: Push on the petal, petal fall to the floor. Where do we go from here? I don't know dealer said in over 20+ years never seen one like it. No external leaks. Brakes worked good last fall when truck was put away. It is a tandem axle truck. Thanks in advance. J.

bison · Mar 23, 2009

I would suspect that new master cylinder aint any good, might have a bad cup in it from the get go.or it is installed backwards.
i had a new master for a wheel loader i have, and that one acted the opposite of your problem, it would keep the brakes ON after release of the pedal

rrlund · Mar 23, 2009

I know this isn't it J,but it reminds me of something on Car Talk on the radio. A guy took the disc brake calipers off of his Jeep. Took them in the house and rebuilt them himself and put them back on. Bled the air out and no brakes. Finally threw in the towel and took it to the dealer,they put it up on the hoist,bled it over and over,couldn't get it. Finally an old mechanic walked under it and said right away "I see your problem". He had both of them off at the same time and put them back on the wrong sides. Had the bleeder at the bottom instead of the top. Since the air raises to the top,they couldn't get it bled out. Switched them,fixed it. Like I said,not your answer,but probably something simple. Good story anyway.

the tractor vet · Mar 23, 2009

Well first off start with adjusting ALL the brakes up correctly , Then go back and do a brake bleed . Juice brakes are a pain and it seems like the new mechanic's have a problem working on them. And also as the oold trucks get old i have been deeing a bunch of problems with the hoses as they seem to be coming apart inside of the hose and this will drive ya nuts . Now also the rweplacement boosters and some master cyl. are not good out of the box as here last year i got a call from one of my old customers to help him with his brakes on a I H loadstar and we went thru three hydro vac.'s before we got a good one . And were having the same problem as i had adjusted all the brakes up and afet a lot of thinking it came down to the hoses and i pulled all of them off and replaces all the hoses . Then took the old hoses and cut them in half and out of the five hoses on the truck three were coming apart inside . My feeling on brakes for anything over a one ton should be AIR.

El Toro · Mar 23, 2009

I would agree with bison on the new master cylinder being defective. Did they bleed the air from the bleeder ball before connecting the hose to the master cylinder? Hal

Anonymous-0 · Mar 23, 2009

I had a light go on when I read Tractor Vet's post with the word "hydrovac." Bleeding a system with a hydrovac takes a different procedure than bleeding the brakes on your passenger car.

First impulse is to blame the new master cylinder. Was the master cylinder bench-bled before it was installed? Lots to consider, but since there's no electronics involved, it should be relatively simple to diagnose if you take it one step at a time.

Drill · Mar 23, 2009

Those old Fords had a vacuum booster under the cab, drivers side, it had to be bled separately.

Paul in MN · Mar 23, 2009

I suspect a young mechanic who has little or no experience with the hydrovac. Did he find the bleeder on the front of the hydrovac?? Do the wheels of that truck have both a LOWER and UPPER hydraulic cylinder. Is somebody finding a lower cylinder bleeder and NOT finding the upper cylinder bleeder. Even a power bleeder hooked to the lower one will not do the job. The hydrovac unit is often a real bi_ch to bleed. Sometimes we work on it one day and let it rest overnight and have at it again the next day...but I don't have a power bleeder. It seems that the air bubbles will come together with the rest time. Did you bench bleed the new master before installing? If so you saw it work and it is OK.

Good luck!

Paul in MN

37 chief · Mar 23, 2009

My chevy 6400 series truck had tha same problem. I would power bleed the system and have good brakes for one day, maybe two, then it would just get no peddle again, I replaced all wheel cylinders, had the master cylinder sleeved. same problem. Now here is what my problem was. The hydrovac unit was leaking internally, sucking brake fluid into the motor through the vac line. I could never figure why my master cylinder kept going down, and could see no leaks.To check this remove the vacuum fitting at the hydrovac and see if it is wet inside. There should be no wetness. My rebuilt hydrovac unit cost 160.00, Let us know what you found. stan

Tramway Guy · Mar 23, 2009

Hydrovac.....or vacuum booster as it is also called.
Bleeding the booster unit

Allan in NE · Mar 24, 2009

Bleed the Hydro-Vac!

If your mechanic doesn't know where it's located, find another mechanic. :>)

Allan

cj in wisconsin · Mar 24, 2009

Allen's right, bleed the booster, on the old Fords its under the drivers seat floorboard.

Truck Brakes/No petal

Anonymous-0

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bison

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rrlund

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the tractor vet

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El Toro

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Anonymous-0

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Drill

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Paul in MN

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37 chief

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Tramway Guy

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Allan in NE

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cj in wisconsin

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