I just replaced the master cylinder and booster on my 91 Ranger. Both were likely original equipment. I bench bled the master cylinder and installed everything without problems. But when I tried to bleed the brakes, rear passenger first, I got almost no pressure, only a little brake fluid oozing out. The same happened on the driver's side rear. The front brakes bled normally, plenty of pressure and plenty of fluid coming out.
rebled the master while it was on the car to be sure I had no air in it. Some bubbles came out but that didn't cure the problem.
I then removed a brake line from a rear wheel cylinder but still nothing came out when I stepped on the pedal.
Before this all happened, the rear brakes worked very well. I could lock 'em up if I really stepped on the pedal. So, I'm mystified about what my problem is.
he reason I replaced the master and booster was I was getting a whoshing sound when I stepped on the brakes. Any help or advice welcome.

 

Is the brake pedal firm when pressing down with engine running or does it slowly sink to the floor?

If its firm then issue is most likely Rear ABS module, article here on it: https://www.therangerstation.com/for...-valve.133050/

You can get a replacement as well

First check that new Master is OK
Engine off
Have some one press down on brake pedal or use a stick against the seat to push down pedal
Loosen the Front brake line on the Master, that's for rear brakes, make sure you get a good squirt of pressure, if not the Master is bad, yes it happens, lol

The front brake line on the Master goes to the ABS unit, so follow it down to the drivers side frame rail
What may have happened is that the rear brakes were working, but barely, and the bleeding shifted some "crude" in the ABS unit so its now blocked

When you remove the brake line from the master, fluid will start to flow out of the master so have something handy to plug that line, its just gravity flow no pressure, unless you press the brake pedal, lol

 

Ron: Thanks for the quick response. The pedal is firm when the engine is running. The master is ok according to your test. When we bled the master, plenty of fluid came out of the front port when the pedal was pressed down. I'll check out the ABS article. Thanks. JXm

 

Ron:D: My problem was and remains no brake pressure to rear of 91 2.3 Ranger. It occurred after I replaced the master cylinder and the booster. I have tested the master cylinder and it is working: Plenty of pressure at both outlets. i just replaced the ABS hydraulic unit and also the sensor that reads the differential, and tried to bleed the brakes again today, but no improvement. Only a tiny amount of fluid comes out of the two rear cylinders when I try to bleed them. The brake pedal is hard and barely moves when the vehicle is not running. When it is running, the pedal goes slowly toward the floor., and drops about an inch when the bleeder values are opened in the rear. Any more ideas? Thanks> Uncle Buck

 

Did you check if you have flow out of the ABS unit, when pedal is pressed?

There is only 1 brake line from ABS unit to the rear and top of rear differential, where there is a "T" and 1 brake line to each wheel cylinder
Remove the Flex line from the "T" OR at its other end, and see if you have flow out that hose/line

 

RonD: I just disconnected the flex brake line where it links with the T junction on top of the differential, with a piece of wood holding the brake pedal down hard. (I was working alone). A little oozing at the place I disconnected occurred, but no burst or pressure detectable. So it appears almost no pressure is getting past the ABS hydraulic valve unit I replaced in the frame near the front of he truck. This was the reason I replaced it, so I'm not sure if this means the ABS valve unit has been bad twice or if there might be another reason. Is there an electrical component to the equation? Anyway, I've got about another week before my return option expires with Rockauto. What do you suggest I do now? Thanks as always for the wise counsel. Uncle Buck

 

Does your ABS light work?
It should come on with key on and then go OFF

With brake pedal held down you will just have gravity flow from master to the open line, no pressure
You could pump the pedal and hold it down, then loosen a connection and you should get a squirt of pressure

I would first test if fluid is getting IN to the ABS unit

And many use a bypass on these units when they break
You can take the old ABS unit to parts store and get matching fittings and short bendable brake line so you can connect the IN and OUT lines together without the ABS unit in between