Not enough braking power
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Senior User
Joined: Mar 2002
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From: Phx, AZ
Not enough braking power
i did a search and found nothing like my problem. when i bought my truck the brakes didn't seem to have enough stopping power. the guy i got it from said everything was some what new (2yr old). it just feels like there isn't enough power. the truck was an f250. it now has a dana 60 in front and dana 70 in rear. but it had the f250 booster on it and the guy i got it from said it stopped the same way when it had the dana 44 in front and dana 60 in the rear. this week i went through the whole brake system. i put a new f350 booster and m/c on. new prop valve new calipers and pads new wheel cylinders (right rear was leaking and the front of the m/c was empty) new shoes and all the springs that hold the shoes together. and blead the whole thing. and it's no better than when i got the truck. it feels like i have manual brakes. it stops but i can't get any of the wheels to lock up. i can have both feet on the brake pedal grab the steering wheel and my butt off the seat and it won't stop fast enough. i also adjusted the push rod in the booster to the m/c and the shoes so they just started to touch the drums. everything is new what gives?
Paul
Paul
Last edited by F350SuperCab4x4; Jun 6, 2004 at 01:54 AM.
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From: waco
By any chance do you think you may have a line with some junk in it. Your problem happened to a friend of mine years ago. He ended up finding some junk in one of his rear hardlines. Only thing I can think of is take off the hard lines and blow air through them with an air compressor to make sure that they are clean. Anyone else got any ideas?
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Did you turn the rotors and drums?? With a back brake leaking, odds are the rotors are heavily glazed from being over worked, becouse they were the only brakes being used. What pads did you use??? Organic, semi-metalic, metalic?? Should go to full metalic on older trucks, even more so if you haul with them. Otherwise, check to make sure the power brake booster is not defective.
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From: Phx, AZ
i don't think there is anything in the lines. i had no problem bleeding them.i did cut the drums but not the rotors. i have to get the socket to get the lock nut off the rotor. i have to check to see what the pads and shoes are. i have 50 pounds of vaccum and if i take the vaccum line off of the booster the brake pedal gets even harder to push so it is working. if i put the truck in reverse in the driveway and hit the brakes the truck rolls about 6 to 8 inches before it stops. where it should stop on a dime.
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From: Edgewood, Wa
neverenough sounds like he may of hit it, if you put new pads on glazed rotors, the pads cannot "bite" and will have decreased stopping power.
Also, stay away from "budget" pads, get some nice heavy duty fleet semi- mets, resurface the rotors, and let them seat in... I think you will be alot happier.
Also, stay away from "budget" pads, get some nice heavy duty fleet semi- mets, resurface the rotors, and let them seat in... I think you will be alot happier.
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From: Louisville,Ky.
50" of vacuum? I've never seen an engine have over 20 - 22" of vacuum.
I don't know why it would take that long to stop!! Have you jacked it up and checked each wheel to make sure that all 4 wheels stop rolling when the brake is pushed?
I don't know why it would take that long to stop!! Have you jacked it up and checked each wheel to make sure that all 4 wheels stop rolling when the brake is pushed?
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From: Phx, AZ
at idle i have 40" of vaccum if i touch the gas it goes up to 50". and if i floor it and let off it will go up to 60" for a split sec. the motor only has about 2000 mi on it (400 with RV cam).
when i had the truck on jackstands i put it in 4wd and hit the braes and it stopped on a dime. so i know they work. i know glazed rotors don't help i don't think it's that. i had another 250 4wd supercab 5 yrs ago and i never cut the rotors just put pads on it. and if you lock them up you would go through the windshield and i had a 8ft fisher snow plow on it. but i will cut the rotors when i get the socket to get them off. i read in a thread awhile back something about pushing a reset botton on the prop valve. and i tried to push it but i won't go. so i might TAP it with a hammer and see if that does anything.
and i do appreciate all of you guys imput.
Paul
when i had the truck on jackstands i put it in 4wd and hit the braes and it stopped on a dime. so i know they work. i know glazed rotors don't help i don't think it's that. i had another 250 4wd supercab 5 yrs ago and i never cut the rotors just put pads on it. and if you lock them up you would go through the windshield and i had a 8ft fisher snow plow on it. but i will cut the rotors when i get the socket to get them off. i read in a thread awhile back something about pushing a reset botton on the prop valve. and i tried to push it but i won't go. so i might TAP it with a hammer and see if that does anything.
and i do appreciate all of you guys imput.
Paul
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From: Edgewood, Wa
Originally Posted by F350SuperCab4x4
i read in a thread awhile back something about pushing a reset botton on the prop valve. and i tried to push it but i won't go. so i might TAP it with a hammer and see if that does anything.
and i do appreciate all of you guys imput.
Paul
and i do appreciate all of you guys imput.
Paul
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From: Phx, AZ
i know it's been awhile since i wrote last. but been working alot. i just got the rotors cut and put back on today. and no change. as far as the 50" of vac. i was reading the wrong side of the gage. it was 25" of vac. i checked the front rubber hose's when i had a friend step on the brake pedal. and they didn't swell up. i also checked the rear one. i even took the truck to a brake shop and they just scratched their heads and said, i don't know. and i also pulled the button on the prop valve, NOTHING.
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From: Hartland, MI
What size tires do you have? I had a buddy with 38.5 inch tires and his truck wouldnt stop good either, but it was simply because the large tires put too much leverage on the brakes. He only had a 1/2 Ton truck though.
Zac
Zac
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From: Spokane WA
Originally Posted by F350SuperCab4x4
at idle i have 40" of vaccum if i touch the gas it goes up to 50". and if i floor it and let off it will go up to 60" for a split sec. the motor only has about 2000 mi on it (400 with RV cam).
sounds like you have a V-1710 allison under the hood
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From: Spokane WA
Originally Posted by F350SuperCab4x4
and i also pulled the button on the prop valve, NOTHING.
new pads, lines, master, booster ( I know the booster was bad but it wasn't the cause of this problem) etc., but no decent brakes.
we plumbed around the prop valve (lines are really cheap), re-bled the system and tried it in the driveway at slow speeds and at about 30mph, the truck would almost put you through the windshield, it would stop so hard.
$120 later and a new prop valve solved the proplem.
Last edited by oldhalftons; Jul 31, 2004 at 11:27 AM.
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From: Long Island USA
I had a situation in exact reverse. I had TOO much brake - a light touch would take me off the seat into the steering wheel if I wasn't wearing the lap belt (hate just lap belts).
Anyway, I got it working OK after a few years by getting a different master cylinder. Turned out there were two or more sizes and I got the wrong one for my system.
See, it's hydraulics - if the master cylinder is too big a diameter, it will push too MUCH fluid and not have enough power (leverage). With a smaller diameter master cylinder, the actual line pressure increases, but so does pedal travel. Like gearing or leverage, see?
Do you have very little pedal travel before they start to do anything?
If so, is it possible that going to a smaller diameter master cylinder will get you more power ?
Oh, and just for the heck of it, pull that one-way valve out of the power booster and see if it really gets vacuum there...
I could be barking up the wrong tree however...
Anyway, I got it working OK after a few years by getting a different master cylinder. Turned out there were two or more sizes and I got the wrong one for my system.
See, it's hydraulics - if the master cylinder is too big a diameter, it will push too MUCH fluid and not have enough power (leverage). With a smaller diameter master cylinder, the actual line pressure increases, but so does pedal travel. Like gearing or leverage, see?
Do you have very little pedal travel before they start to do anything?
If so, is it possible that going to a smaller diameter master cylinder will get you more power ?
Oh, and just for the heck of it, pull that one-way valve out of the power booster and see if it really gets vacuum there...
I could be barking up the wrong tree however...