Need brake help again...

[Matrix37495]

I've always had soft brakes, and kinda just lived with it. Now i'm looking at getting a camping trailer, so i want my brakes to be the best possible.

I have replaced the master cylinder, vacuum booster (twice), both front rubber hoses, the left front caliper, and sanded the pads. I have good instant vacuum. None of it has made a difference. Pressing the pedal as hard as i can brings the truck to a fairly slow, gentle stop. I bled the brakes well, and bench bled the master before installing. What is left short of hydroboost that i can do? I need my truck to be able to stop 16k plus the truck (Double NH3 wagons weight 15500...)

 

[sassyrel]

BOTH sides of the rotors ok??? i had half of the back side of my rotors rusted gone!!!,they always felt a bit odd,,and when i had the front apart for new ball joints,,is when i seen it.. and have been mechanic for over 40 years, and never seen that before!! check out al your hardware,,and check for adjustment being right. almost sounds like you still have a bad brake booster..some things can tax a persons patience....

 

[Matrix37495]

I know CarDone makes low quality stuff, but two bad boosters in a row? The thing is, the pedal isn't hard like theres no assist....What are the places air could get trapped? Thats what it feels like, but i wasnt getting any more air when i was bleeding them, and with all the driving i would have thought any air would work itself out.

My rotors are in good shape, both sides. The only part of the system i havent looked at is the rear brakes. I was told they were new across the axle when i bought it.

 

[franklin2]

Driving it will migrate the air around, but usually and hopefully out near the bleeders, it almost never migrates it's way back to the master cylinder reservoir. So if you haven't bled them for awhile, I would try that again.

The only other situation i have run into that gave me spongy brakes, was people turning the rear drums too much. Some shops do not follow the rules, and if you want the drums turned, they turn them. When they get too thin, they flex when the shoes make contact, giving you a spongy pedal and they also do not dissapate heat very well, and that it what stops the truck, turning motion into heat. When the brakes can't take any more heat, the truck will not stop no matter how hard you push the pedal.

 

[Matrix37495]

Sounds fair.... Looks like its back under the truck...

 

['94IDITurbo7.3]

i wish you good luck with your brakes.

If you ever figure out why you have a soft pedal please share.

 

[riotwarrior]

We just did this a few days ago...people need to learn to use the Search Function!

Ok..for starters...check MC bore size, 1 1/8" should be the minimum hopefully you have the min at least.

Now as I said before in a previous thread, there are/is issues and I cannot recall where I read this at what forum what thread, that the MC is too small and cannot in some instances move enough fluid to actuate the brakes. The solution was to use a larger bore MC and it cured the problem, moving enough fluid to displace the shoes and pads and have reserve to complete the braking procedure with pressure.

Not recalling where I read this is the bane of my thread brake knowledge....I don't like forgetting and it's happening more...CRAFT...mom would say...cant remember a ******* thing..

Anyway, try to determine the bore size..

also clicky here
http://www.fullsizebronco.com/forum/showthread.php?t=140620 this looks like a useful tool

and here too

http://www.oilburners.net/forums/showthread.php?t=52552

 

[icanfixall]

Usually we forget the rear self adjusters because they are supposed to work.. Well they don't work. Check your brake peddle when it stops the truck. If its half way to the floor that means the rears are way out of adjustment. To test this apply the parking brake about 1/4 to 1/2. Now slowly drive the truck and try the brakes again. Does the brake peddle now stop the truck better and not slowly sink to the floor... This is proven to work every time. Whats happening is your front brakes are doing all the stopping. Then as you sit at a stop with pressure on the brake peddle your forcing fluid into the rear cylinders trying to expand them. But you feel the peddle sinking and the rig finally rolls forwards. Bottom line is the rears will not self adjust properly so we manually adjust them. Or install the hydroboost with the 1 5/16 master cylinder.. That large mc can supply enough brake fluid to fill the rear out of adjustment cylinders....

 

[Matrix37495]

Gary, i dont have a parking brake right now...

roit, can that be determined by measuring the outside, or do i need to pull the master off (lines still attached)? I ask because if the out side is x that could mean its a 1.125" bore but if the outside is y it could be smaller....make sense?

 

[icanfixall]

Nealy every master cylinder I have seen has the bore diameter cast into the side of it. About not having a parking brake... Does your peddle stop the truck when its applyed and half way or more to the floor. Does it slowly sink once your fully stopped...

 

[Matrix37495]

I looked at both sides and the bottom... theres something on the bottom but i cant read it, nothing on the sides.


Went out an put a new main cable on my parking brake, pushed the pedal and the other cables are stuck....

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The pedal is more than halfway when i'm stopping. If i hold it with as much force as i can it doesn't sink.

 

[Matrix37495]

Used my camera as a mirror and found two castings. One says BENDIX, the other on the drivers side of the underside of the reservoir says 0120. That help any?

 

[riotwarrior]

Used my camera as a mirror and found two castings. One says BENDIX, the other on the drivers side of the underside of the reservoir says 0120. That help any?

Usually the size is on the opposite side of the brake tubing and cast right in...look at these pics for some reference, the first with two MC's one is stock for the Bronco, then the other is the one of a 90 hydro boost setup, the second pic is a 03 SD 350 diesel hydro MC

 

[Diesel_brad]

I agree with gary. Check your rear brakes and adjustment

 

[DeepRoots]

making sure the adjusters actually move is an important thing on older trucks.
Take the adjusters out, unthread them the whole way. Clean the threads carefully, oil and reassemble.
Make sure to take the front piece off as well.... clean it out and oil it. Make sure that the whole unit can thread in and out with ease.
If you are uncertain about rear wheel cylinders, replace them.

When I first bought my one truck, it stopped ok.... not great but ok. I decided to replace/rebuild everything in the brake system.
Wheel cylinders are the end of the road for the brake lines......
any crap that may form or break off in the course of the last 20-30 years ends up here.

So far in regards to the brakes all you have done is thrown parts at the problem. You have never ascertained what the real problem is.
Do yourself a favor and jack the entire vehicle up (or at least, front then the rear).
Spin the wheel by hand and have someone gently push the brake, you will learn a lot in a hurry and at least know which direction to go.
The rear wheels also are supposed to have a tiny amount of brake drag when adjusted properly.... if they spin and do not just barely touch, they are too far out.

good luck,
drew