About the only thing left that I have not removed at least once on this van is the vacuum power brake booster. The Ford shop manual simplistically says to just unbolt the master cylinder, prop it up, remove the 4 bolts holding the booster to firewall and, ta dah! remove it. Given the limited available space, I have my doubts this will be as easy and straightforward as the manual insinuates. Can the brake lines be left attached to the master cylinder as the manual seems to imply? Anyone with experience or tips for removing the booster please reply.

 

I've removed the boosters from my 69 and 87 Mustangs, and in both cases, there would have been no way to remove the MC without first unhooking the lines. The hard lines will not flex enough to allow the MC to be pulled off the studs on the booster. I doubt that you can remove the MC from the Aerostar without first uncoupling the lines.

Is there something wrong with your booster that you have to remove it?

 

I've been plagued by a mysterious soft brake pedal that cannot be made to firm up. No amount of bleeding, bypassing the RABS valve, running up the rear shoes to total lock will solve this. I replaced the master cylinder to no avail, put new drums on the rears and in frustration, took it to brake shop to power bleed the lines. After an hour they admitted they could not find a reason for the soft pedal that goes almost to the floor on start up.

All the websites say a bad booster causes a hard pedal not soft and my booster passes the vacuum test and pumps up hard with the engine off.

However, I found a small notation in my Ford shop manual regarding the internal rubber reaction disc. "NOTE: Make sure the booster rubber reaction disc is properly installed.... A dislodged disc may cause excessive pedal travel and extreme operation sensitivity......"

With over 300,000 miles of service any rubber piece is bound to have some wear or deterioration. This is my final attempt to solve the problem.

 

Funny you should mention that.

My 1990 4wd van has always had what I feel is a spongy pedal. I can stomp on it, and the van will not stop as hard as say, my 1991 2wd van. I've carefully bled it many times, and adjusted the rear shoes to no avail. I had an assistant push the pedal (with boost) while I checked for weak flex lines, but did not find anything obvious. I suspect it's air trapped in the lines or RABS valve, but have not tried to get a professional bleed yet.

When I was replacing the MC on my 69 Mustang (it was leaking), I accidentally dropped the rubber disk into the vacuum booster. I thought I would just adjust the pushrod out to take up its slack. Boy, the booster became so sensitive that it was impossible to get a smooth stop. It was like as gently as possible, push the pedal 1/8" at a time, and get nothing for most of the travel and then suddenly full lock-up. This was why I had to remove the booster on that car, to retrieve the little disk. My feeling is that if it had completely disintegrated and fallen away, the booster will behave abruptly like that. This is not the feeling I'm getting from my van right now; it's smooth and consistent, but it just doesn't feel very solid.

Please keep us posted on what you find, as I'd like to know if there is a fix for this, or something I have to live with.

 

removing the master cylinder and disturbing the pushrod often unseats the rubber reaction disc. Only one way to get it back in correctly, disassemble the booster.

 

To answer my own question. No, you cannot simply unbolt the master cylinder, pull it forward with brake lines attached and drop out the power booster.

The following applies to a 1991 model. Later models may be different configuration. In a nutshell, you will need to remove the battery, disconnect the wiring harness to the cruise control along with the two vacuum hoses, unbolt the cruise control unit (3 x 10mm bolts) and set to the left side. Disconnect the brake lines from master cylinder. May need to place a suitable container below to catch dripping brake fluid.

Inside, remove the latch pin from the brake pedal and withdraw the nylon washer, bushing, switch assembly and the plastic stop for the brake light switch. May be good idea to remove these one at a time and make notes of the order of re-assembly.

TiP: On re-assembly the tendency is to pull the brake pedal upwards for better access. If you pull to far up, you will hear a ratcheting sound of the brake light switch being pushed back in it's retainer. (Its a notched plastic retainer) This will mess up the switch function. Make sure you mark the position of the brake switch beforehand.

There are four bolts holding the booster to firewall with 14mm nuts. 3 are reasonably easy to access using a universal coupler. The fourth can accessed easier if you remove the cover plate on the fuse box and go in through the side of the fuse box opening.

Some minor wiggling around in the engine compartment will eventually free the vacuum booster. Check inside to see if you have any fluid collected in the bottom.