The ABS system in the 1990 through 1993 Imperials was somewhat less than something worthy of being associated with the name "Imperial". The system was crude and primitive by today's standards and often failed, leaving the vehicle with no brake boost, and the perception of "no brakes" to many drivers, often resulting in serious front end collisions that would invariably spell the end of the vehicle. This says nothing about the doubtless property damage and human casualties that this poorly designed system has been responsible for over the last 10+ years.

Since the 90-93 Imperial is such a joy to drive, as any owner would attest, I decided to retrofit the failing ABS system on my 1990 Imperial with the same old non-ABS style braking system that is found in the Imperial's sister cars, the New Yorker and Dynasty. This type of braking system has been tried and proven effective and reliable for decades...why mess with something that works! Parts for this retrofit are affordable and readily available new, rebuilt or from a salvage yard.

The project started by removing the massive ABS master cylinder and pump.

There are four 13mm nuts under the dash inside the car that hold the master cylinder in. Three are fairly easy to access and one is next to impossible to get to. There is also a clip that retains the pin that holds the brake pedal to the master cylinder ram. Once the four nuts and the pin were removed, I had to remove all the electrical connectors and four brake lines from the master cylinder. The brake lines are difficult to access and rarely come undone without twisting off the brake line. Since I was not saving the master cylinder and I love using my sawzall, I simply cut off the protrusions form the master cylinder where the brake lines were attached. Had I known what I would have to do later, I would have just cut the brake lines close to the master cylinder instead.

With the master cylinder out, I removed the ABS pump. There is only one small bolt holding the pump in. I bent the shroud up and out of the way, removed the bolt and the pump and shroud both came off easily.

Next I had to go to the salvage yard to get a proportioning valve. The ABS does not use an external proportioning valve but rather controls all that in the ABS master cylinder itself. I think just about any K car proportioning valve will do. Mine came from an earlier K car and it works just fine. I had to buy a couple fittings to adapt two of the proportioning valve ports to the 3/16" brake lines. I bought a flaring tool and some fittings so I could make the Imperial's brake lines fit directly into the proportioning valve and thereby negate the need to replace any of the metal brake lines on the car.

Once I had the brake lines flared, I screwed each one into the proportioning valve and mounted the valve to the frame rail of the car just where it came off the donor car. I left off the two lines going to the master cylinder for the time being.

Next was to install the booster. It is a tight fit to get the booster between the strut tower and the engine's intake system but it can be done. I had to lift a section of large wiring harness so the booster would sit tight against the firewall. I installed the four nuts onto the new booster from under the dash of the car. The climate control system has a small vacuum line going to the intake manifold and this is where the brake booster is to be attached. The climate control line is to be reattached to the check valve on the brake booster.

Next, I test fitted the new master cylinder onto the new power brake booster. I used this test fit to position and bend the new brake lines I bought to go from the master cylinder to the proportioning valve. When I had them bent in an appropriate way, I took the master cylinder out again and attached the brake lines to the proportioning valve. I also connected the electrical sensor wire to the proportioning valve and coiled up the lead wire for future connection to the appropriate circuit.

I installed the master cylinder again and bolted it to the booster. Then I could screw the two brake lines into the master cylinder.

The next step was to change the brake pedal to the non-ABS style (Dynasty, New Yorker etc). This is only needed if you are changing from the Bendix type ABS. If you have the Bosch ABS system, your existing brake pedal will line up just fine.

The brake pedal that is installed on the Bendix type ABS system does not line up with the vacuum booster shaft. The pedal is removed by removing the 15mm nut from a pivot pin (inboard end). The pin is round on the outboard end but has two flat spots in it that will accommodate a 7/16" wrench.

Bleeding the brakes took a long time but I finally got all the air out and the brakes were firm. Be sure to start with the wheel farthest from the master cylinder and work your way to the master cylinder. (right rear, left rear, right front, left front)

At this point, there are a few things to watch for.
Effectiveness of front brakes as compared to the rear. The proportioning valve seems to do a nice job here. I've noticed no adverse braking issues with the system.
Brake fluid leaks, particularly where the old brake lines were flared. This happens often if you don't tighten the brake lines to the proportioning vale, like I did. :-(
Pedal travel to be sure there are no brakes dragging. It's a fine line between having enough pedal travel to have sufficient braking effectiveness and being certain the brakes don't drag at all. To adjust this, you need to pull the master cylinder off the booster (this is why you want to put a couple nice curls in the brake lines on the master cylinder) The little rod that protrudes from the booster is threaded. Turning this rod CW will give you more pedal travel and possibly reduce braking effectiveness. Turning the rod CCW will give you more braking effectiveness but could lead to dragging brakes...a very bad thing!

I did end up adjusting the booster rod length a number of times to get the proper pedal travel. This is extremely important! Too much travel and you will not have enough braking power, too little travel and the brakes will be dragging as you drive. Dragging brakes can cause premature wear or even a wheel fire!