I've got a 1990 Ranger 4x4 with the 2.9 and it's a 5 speed if that matters. I've replaced the master cylinder after I did a complete bench bleed on it. I've also bypassed the RABS valve on the truck so as to see if that was my problem. I've gone through all four wheels bleeding them to make sure all the air is out of the system. I also replaced both rear wheel cylinders and both front calipers before I did the bleeding of the system. It has brakes when the truck isn't running but as soon as you start it the pedal goes to the floor and doesn't get any better if you try to pump it. There is no sign of a fluid leak anywhere I can find so now I'm totally stumped. Any help is greatly appreciated.

 

Welcome to the forum

So you were able to bleed the system by pumping the brake pedal engine off?

But when engine is running when you pump the brakes it doesn't BLEED?
(don't care about brakes right now)


The Power booster has 2 rods inside, brake pedal rod and master push rod, they are not connected but can't see them only working with no vacuum pressure

You can unbolt and pull the master forward, start the engine and have some one press down on pedal, make sure push rod is moving out, try pushing it back while pedal is down

 

I removed the master cylinder from the booster and started the truck and let it idle for about 3 or 4 min so I knew it had vac pressure then had my son push the pedal and hold it. The rod that pushes the master cylinder came out like it's supposed to and with it fully extended I couldn't make it go any further out. When he released the pedal the rod that hooks to the brake pedal came all the way back to where it should be but the master cylinder rod only returned half way and then I had to push on it for it to go the rest of the way back. Is that normal?

 

Yes, thats normal, it relies on Master to push it back into the booster

All I can think of is you got a bad master then.

As you suspect its not all that complicated of a system

 

could be you got the wrong master cylinder and the stroke of the rods are different on different ones. Do you have your old one? Put it in to see if things change.

 

I've now gone thru and replaced both front calipers and both front rubber brake lines. I've also replaced both rear wheel cylinders and I am getting new clean fluid everywhere after bleeding the brakes and am not getting any air out anymore at all. I still can't get the pedal to do anything but go to the floor and can't find anywhere that is leaking. The only thing that has not been replaced is the booster and I don't think it would be causing my issue. Any help with this would be greatly appreciated because I'm at the point of just cutting my losses and getting rid of the truck.

 

Get rid of the truck

Brakes are not that complicated
Simple hydraulics

Master pushes fluid out to a closed system, when pressure builds up in the closed system then you can't push on master any more

So either Master is not pushing out fluid or closed system is not closed, it leaks

Really doesn't matter whats "new", new just means NEVER TESTED now-a-days