well i have got a good pickle here or a really bad one as the case may be. I am currently having a brake problem.
Here are the symptoms:
1. Pedal falls through about 3/4 of travel before engagement. When I say falls I mean it, only spring pressure going against.
2. When brakes apply they are strong enough to lock the front wheels, but they fade fast probably after two or three 40-0 stops and then hardly any brakes at all.
3. They can be pumped up to the top of the pedal travel but the brakes aren't worth crap like this takes for ever to stop and thats with me standing on them.

Here is what i have done to fix this problem but hasn't worked yet.
1. Replaced master cylinder several times.
2. Replaced both wheel cylinders.
3. Replaced booster.
4. Bleed the system several times, brought new fluid to all four corners bleed at all junctions, took it to the dealer and they couldn't get anymore air out of it.

Couple of questions?
Would adjusting the push rod on the booster get some of the play out of the pedal. I made sure to adjust it the same length as the booster that came off of it. To tell the truth the brakes were better before the booster or at least engaged before halfway.

would it be the vacume pump be the problem. before i replace that i would rather go to hydroboost.

It still could be a leak but i haven't found one and i have been all over the system, but still could have missed it.

Thanx, Ryan

 

i think a bad vacuum pump would make your pedal hard to push-like you had "manual" brakes

 

thats what i thought but the dodge dealer said that it was either the vacuum pump or the booster but the booster mad it worse. I am usually very good on brake systems but this one has got me stumped. o yeah the dealer also wanted 2000 for a vacuum pump without putting it on, i just laughed at them and left.

 

If its fading then its leaking vac or the vac pump is weak. try blocking off all vac lines cept the booster, it may have one off under the dash.

 

Maybe you have trapped air in the system, try pressure bleeding.

Here is a link for a brake system pressure bleeding tool you can make.

https://www.dieseltruckresource.com/...+bleeding+tool

 

If you need to get a new Vacuum pump these guys have em the cheapest in town

http://www.usdieselparts.com/moreinf...am_Vacuum_Pump

$295, thats alot better then the dealer.

 

in the area i live in there is a local rebuilder . they have rebuilt f600 hydroboost units cheap. so look in your major city for a truck brake rebuilder. ask at truck shop. plug off the lines at the mcylinder and see what happens when you press on the pedal. if big change then move plugs on down the system. make sure your shoes are adjusted up tight i know it sounds simple but i have seen it happen.

 

X2 on the make sure your rear brakes are adjusted out. If the pedal drops at with constant pressure and your sure it's not leaking it sounds like an internal leak in the master to me. did you do a good bench bleed on the master before you hooked it up to the rest of the system if not try that by just running some lines from the ports up into the res and pump slowly until no air. I don't know if that will help or not but what the heck.

 

I adjusted the shoes when i replaced the wheel cylinders, the master cylinder is brand new i put it on last week which would make it the third one in less than a year and they all acted the same, i bench bleed it and then bleed it on the truck and then bleed new fluid to the wheels. i do the bleeding with a catch bottle at the wheels and make sure no air gets back in. any more ideas.

 

well she brakes great at the bottom of the pedal but i am still not happy. i am pretty sure that it is the vacuum pump because on my way home cruise control wouldn't stay engaged. The next problem is figuring out if i should just replace the vacuum pump or go hydroboost. I am thinking that i should just replace it since it cant keep the cruise going, then after awhile go to hydroboost.
I priced it out with parts from car quest and no cores (for conversion), about 550.00 but then i have to add in lines and what not. its the what nots that kill ya.

 

Could it be the infamous RWAL device. I replaced mine and it made things significantly better. I think I will bypass it and put a proportioning valve in place of it when I switch to disks in the rear.

 

If you have good power assist (it sure sounds like it) then the vacuum pump and booster are fine.

Like Mike said, I suspect the RWAL dump valve.

 

For me hydroboost has been the best modification on my truck. I can get the RWAL to chirp 35"x12.5" tires with it.

 

What's the RWAL valve and what does it do. I'm having the same problem with my '93 dually.

 

The RWAL dump valve is located on the frame near the axle. It dumps rear brake pressure into an accumulator on a signal from the RWAL controller. Sometimes they fail "open" so when you hit the brakes you are just filling the accumulator instead of pressurizing the wheel cylinders.