i have the exact same problem with my truck. it is a scary situation to be in when you are on a hill and try stopping and the rears lock up. i have had weight in rear and did`nt notice it to be so bad. i need this fixed in a bad way.

 

i would look at the perportioning valve, also i saw some forum where guys were putting 1ton chevy wheel cylenders in dodges to "improve braking" i think it was 1500s they were doing it to tho. it was quite an old thread that just sort of ended so i suspect they must have all died in tragic motor vehicle accidents

 

a proportioning valve works by limiting the pressure to the rear end. It apply's the front brake pressure on the valve which restricts the flow to the rear brakes until the pressure from the master cylinder to the rear brakes over comes the valve and flows to the rear brakes and as soon as it overcomes and flows past the valve the pressure drops and the front brakes closes the valve again just to repeat the cycle. so the more pressure to the front brakes then the less pressure to the rears, There is a reason the rear brakes can last three to four times times longer then the fronts. If the rears are out of adjustment and the hydraulic systems are working properly then the front brakes pressure will be greater then normal thus causing the rears to have less pressure then they should. The reason they are grabby when loose and cold is because when they move that much and are cold they want to grab, it really is that simple. As a shop foreman I have never replaced a proportioning valve but we are talking about dodge ... I would check the front brake pressure first

 

I have not fixed the problem yet, my fronts are working but just not as hard as my back brakes, I already put bigger wheel cylinders in the back as well it did the same thing before with stock ones as well, my brake pedal is still spungy but only when the truck is running when its off they are nice in hard even when i first hit em. But while its on they go almost to the floor before engaging the brakes. Its all adjusted, I cant seem to find the problem what seems wierd to me is if i hit the pedal repeatdly very fast I lose vaccum pressure and therefore power brakes but I normaly never hit it like that but could this indicate something? or is this normal? Maybe my drums are bad? I cant figure this out its frustrating seems like a common problem no one can figure out Nothing is leaking and im getting no air everytime i bleed them. Im lost with this one

 

You need a pressure gauge on the front calipers, like my description said about the proportioning valve, if the hydraulic pressure to the front is weak and the rears are normal then the rear pressure will over come the valve and appy more then desired rear brakes. 80% of the pedal stiffness is dictated by the front brakes. If you had a vacuum leak at the hydroboost your pedal would be almost as stiff as when the truck is off. If you open the front brake hard line at the master cylinder does brake fluid easy drip out?

 

actually its funny apperantly i have the same problem, i almost ate it this morning on my way home from work. guy pulled from slow traffic right in front of me in the rain. when i got on the brakes my rears locked up on me too and the *** end started to come around on me. thats my first panic stop in this truck since i bought it a little while ago and it didnt go too well.

 

Last time I checked it was a pretty good stream from the front brakes portion of the master cylinder. This sucks dont want to just replace everything but seems like its my only way out this time

 

Buy a brake pressure kit first Like this one. if your calipers are the same pressure or less then the drums you have a pressure problem, leak or master cylinder. You never mention abs, do you have it?

 

that kit looks pretty cool, does it just thread in where the bleeder is? i wonder if you could drill out a bleeder screw and braze a fitting on it and attach to a gauge to make your own tester

 

It does thread to bleeder, gauge has to be up to 1500 psi, fronts should hit 900-1200, rears 500-800

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We have a web site that is for mechanics to ask other mechanics about problems, There are a lot of brake problems for this truck, DOH!!! here is one summary...

We replaced abs control module, dealer brake master cylinder, arched rear shoes to match drums, replaced brake calipers with 3 different brands, bleed system with scan tool activating abs system, pressure bleed system & gravity bleed system. After all said & done, found pedal is designed to drop down at a stop sign under heavy brake pedal pressure. Brake pedal is only used as a brake switch at this time. The abs system will dump what ever is not needed at a stop. Vehicle will not move or roll with pedal down but just does not feel correct. Test drove many times & brakes are good & solid. Test drove in gravel & abs system works good also. We stopped working on the TRUCK.

Here's another one

Well this one is fixed, I recieved some good info on larger bore wheel cylinders, different braks shoe linings etc. There are larger bore wheel cylinders, the application is 13 by 3and a half shoes instead of 13 by 2 and a half. So that is good to know, I tried both things and the problem was still there. The ultimate fix was the system ground wire at the abs control module which is the black wire with an orange stripe, it was broken. The odd thing is that there were no codes and the abs light was off. The customer had worn all of the brakes metal to metal so the mechanical problem had to be solved first, after all of this he said that the brakes had been locking for along time, that piece of info sure could have helpful earlier in the game. Anyway all is good, one helpful tip for the future would be to get more history from the customer. Thanks to all who responded. Rick

You need to use hose clamps and clamp off the rear, Brake pedal feel the same? clamp off front, Brake pedal feel the same? They also had one that was a bad booster, the brakes were fine until they heard a loud pop. They replaced the master cylinder twice for a soft pedal but it ended up being the booster. They also never said anything about rear brakes locking or grabbing.