I'm new to this site so here goes. I have a 1992 Dodge 3/4 ton 4X4 diesel. I lost all brakes the other day in town. It felt like the master cylinder so I replaced it. The pedal goes down and stops but then slowly goes past all the way to the floor. I have had 4 master cylinders and the all do the same thing. I replaced the front pads, rotors, calipers. rear shoes, drums, wheel cylinders and all the brake hoses and it still does. Any suggestions

 

i'd say just keep throwing parts at it until it's fixed.

before i start, what have you done diagnostically?

 

There are about 1000 threads about this issue with these trucks.

In short, you have air in the hydraulic system. 99% of the time it's in the rear brake circuit with the abs valve.

Bleeding these trucks is sometimes difficult, and can have a significant learning curve if you just wing it. Search my screen name, and my threads, as I give a good education on how to do it, as I learned the hard way myself.

 

First thing is adjust your rear drums. This is a common problem on these trucks and there are many threads about it. NJTman on this site has a good thread on how to correctly adjust the rear drums, just search his posts. When the rears are adjusted correctly and they still go to the floor, then move on to other stuff...Mark

 

Update on 1992 Dodge W-250. I forgot to mention that the rear anti lock has been bypassed many years ago and it has worked fine until I lost my brakes a few weeks ago. The rear brakes, drums, and wheel cylinders are new and adjusted to drag a little on both sides.

 

Where are you getting your master cylinders from?

Rebuilds are not what they used to be...........Do a search here and you will see multiple replacements of rebuilds until the owner got irritated and put a new Raybestos or bendix ( or other top quality ) MC on.

 

Did you bench bleed the master ?

Do you know that you can damage the seals in the master if you bench bleed it incorrectly ?

Have you 100% confidence there is no air in the system, and if so, how do you know ? What did you do to confirm ?

I will simply refer back to my original post from here out.

 

My right rear was a real PITA to get bled. for some reason these trucks are more dificalt to get all the air out of than most others I have owned.

 

I will agree with everyone that bleeding the brakes on this truck is a real PITA. I found a good thread on this site that used a gravity method. That was the only method that worked. I think I still ran an entire bottle of fluid thru the system.


I keep the rear drums tight. My first bench bleed did in fact damage the seals. I also only purchase new cylinders.


There is another excellent thread that shows a technique on adjusting the rear brakes. This method requires removing the rear shafts just enough so you can freely rotate the drum. I have the limited slip and trying to get a feel on the drums is impossible.


cheers
Doug

 

I have replaced the master cylinder with new ones. 2 from O'reillys auto parts and 2 from Car Quest. They have all been new. Can't find another manufacturer that builds master cylinder for this old of a truck. I bench bled them installed them. The pedal goes down and stops but slowly bleeds by and goes to the floor. I am a retired mechanic and have replaced hundreds of sets of brakes in my career but I've never ran into something like this.

 

And unfortunately, you're not listening to us either.

There's a design flaw in the master that if you bench bleed them wrong by depressing or inserting the piston in too deep, you tear the seals in the master. The rear brakes need to be bled with a reservior capture system that allows you to "see" what is coming out of the cylinders bleeder screw, keeping vertical backpressure on the fluid while opening the bleeder. Vaccu-bleeders DO NOT WORK on these trucks.. Period. Been there done that.


Every one of us who have these trucks (almost) has had this particular problem. It's somewhere in it's design, although it may seem simplistic, that's what this comes down to.

There are even a few guys here who opted to forgo dealing with this issue, and swapped out the rear brakes for a disc conversion.

Not doubting your experience. These trucks are just different. Can't tell you why, but I can tell you that there are fixes to it, but they just aren't conventional.

You want help. I've given it to you and told you where to find the answer. If not, that's okay too, because I too didn't believe it at first, until I spent hours struggling with these brakes until I figured out for myself.

I wish you the best.

 

Pretty sure that's my thread as well..

 

For all you stubborn pineapple headed guys out there who don't want to spend the time looking for yourselves, I'll post it here:

Post #11

https://www.dieseltruckresource.com/...8/#post3036738

Read the entire thread. It tells you in engrish exactly how to bleed the rear brakes further into the thread. You can use the tool on the front brakes as well to see if you have air in the system up there as well. Without being able to physically "SEE" the bubbles in the vertical tube, you will never know if you got all the air out or not.

BTW,

Either have a second person continue filling the master while doing this, or be like me and keep going back and filling it up by yourself. Much easier if you have a helper, though...

The connections need to be tight. Not so tight you snap off the bleeder screw, caliper hose bolt or whatever, but tight. If you do this process with old brake hoses you're asking for trouble.

BTW, Replace all 4 brake hoses if they're older than 5 years, as they are JUNK aftermarket now, and the original ones are too old to keep (collapse internally) if still in existence on the truck. New hoses are cheap, and unfortunately new ones are made no longer to last. I replace mine every few years just because of this fact.


Have fun.....

 

Another cure is the hydroboost swap. som of us have done it and used GM parts with great success.

 

I have a simple device which I got many years ago. It is a check valve in a short length of hose. One end goes over the bleed screw and the other end goes in a jar. I just slip it on. Open the bleeder and slowly pump the brakes until I get the air out. I keep the MC full between going wheel to wheel. It works fine for a one man operation. The check valve stops air from being sucked back into the system when you pump the pedal. Look around. If you can find one it may work for you.

Edwin