1987-1991 Ford F-Series Brake Master Cylinder

Ford F-150, F-250, F-350 Brake Master Cylinder Replacement Procedures

The master cylinder is the heart of the vehicle braking system; without it, there's no way to activate the brake calipers/wheel cylinders at each wheel. Master cylinders typically require replacement do to the development of leaks within the internal piston assembly, which allows brake pressure to bleed off slowly and reduces overall brake performance. It's also quite common for a worn master cylinder to develop an external leak at the rear of the assembly where it mounts to the brake booster.

Applicable model years: 1987 - 1991 Ford F-150, F-250, F-350
Brake master cylinder: See parts list below w/ model breakdown
Brake fluid spec: DOT 3, Motorcraft PM-1-C
Brake bleeder: Mity-Vac MITMV8500 vacuum/pressure pump

 

Caution - Do not attempt to service/repair the master cylinder if you lack experience with and/or knowledge of vehicle braking systems. Improperly repaired items may result in vehicle damage, personal injury, or death. Seek the help of a professional if you lack the tools or do not fully understand the procedures for bleeding a typical automotive brake system.

1987-1991 Ford F-Series Master Cylinder Parts List

Model Years

Model(s)

Wagner P/N

Raybestos P/N

ACDelco P/N

1987 - 1991 (4/1987+)

Ford F-150

MC120369

MC39634

18M1755

1987 - 1991 (4/1987+)

Ford F-250 under 7,000 lbs GVWR

MC120369

MC39634

18M1755

1987 - 1991

Ford F-250 over 7,000 lbs GVWR

N/A

MC39636

18M1753

1987 - 1991

Ford F-350 SRW (single rear wheel)

MC120368

MC39635

18M353

1987 - 1991

Ford F-350 DRW (dual rear wheel)

MC120368

MC39635

18M353

How to Replace the Brake Master Cylinder

Note that nut/bolt sizes may differ slightly from those listed depending on vehicle model/year; featured truck is a 1991 Ford F-250.

Click any thumbnail to view fullsize, detailed image

brake master cylinder

• Disconnect the negative battery cable(s).

• The new cylinder [hopefully] included a replacement seal for the master cylinder check valve in addition to a series of plugs, which will reduce spillage of brake fluid when the brake lines are removed (ACDelco replacement cylinder shown).

brake line bracket

• Remove the nut for the brake line bracket on the brake booster stud (9/16" socket/wrench). Position it so that the brake lines will float loosely once they are disconnected from the brake master cylinder.

• Optional - use a suction gun or similar tool to drain the master cylinder reservoir as much as possible.

master cylinder reservoir connector

• Disconnect the electrical connector from the sensor on the brake fluid reservoir. The detent is located on the bottom of the connector and must be released before the connector can be unplugged.

removing brake lines

• Place several shop rags/towels below the master cylinder.

• Remove the large brake line from the master cylinder using a 5/8" flare nut wrench. Plug the line using a vacuum line plug or equivalent. Plug the master cylinder port using one of the supplied plugs.

brake lines and master cylinder ports plugged

• Remove the small brake line from the master cylinder using a 7/16" flare nut wrench. Plug the line using a vacuum line plug or equivalent. Plug the master cylinder port using on the supplied plugs.

• Be cautious not to kink the brake lines when handling them.

brake master cylinder removed

• Once the brake lines have been disconnected and plugged, remove the master cylinder. It is secured on two studs attached to the brake booster; (1) on the driver side and (1) on the passenger side. A 9/16" socket/wrench is required to remove the (2) nuts.

check valve for master cylinder

• Remove the check valve from the old master cylinder using a 7/8" wrench. Remove and discard the o-ring seal, then install the replacement seal.

• Install the check valve on the replacement master cylinder after lightly coating the o-ring seal with clean brake fluid.

new brake master cylinder installed

• Install the replacement master cylinder to the brake booster. It is recommended, but entirely optional to use anti-seize lubricant on these bolts. Secure nuts down tightly.

Mity-Vac MV8500 brake bleeder

You're going to need a brake bleeding tool for subsequent procedures. We highly recommend the Mity-Vac MV8500, which comes complete with various fittings, hoses, accessories, and is packaged neatly in its own molded storage case. It is selectable between pressure and vacuum, making it suitable for a wide range of diagnostic and repair functions (brake systems, wastegate actuator tests, vacuum system troubleshooting, etc).

Note - this is NOT a paid product placement or advertisement; we're endorsing this tool because it works well.

bleeding master cylinder

• Fill the master cylinder reservoir to the fill line, then use a vacuum pump/brake bleed tool to bleed each master cylinder port. This is done by using the appropriate fitting(s) and drawing brake fluid through each port of the master cylinder. During the process, do NOT allow the reservoir to empty completely; add brake fluid as necessary.

Note - there are alternative methods for bench bleeding the master cylinder.

air in lines of brake bleeding tool

• Large bubbles in the bleed line represents air that is being drawn from the system. Continue to bleed each port until no air bubbles or only extremely small bubbles are present. Re-plug the ports once they are bled.

master cylinder replaced

• Once the master cylinder is bled, reconnect the brake lines and master cylinder sensor connector. Reinstall the brake line bracket over the brake booster stud.

• Bleed the entire brake system in the following sequence: 1) passenger side rear brake, 2) driver side rear brake, 3) passenger side front brake, 4) driver side front brake. This can be performed by using the vacuum/bleed tool mentioned above, or with the help of a colleague. Monitor the brake fluid reservoir level during this process, as you will need to start over from step 1 if the reservoir is allowed to drain completely.

• Test brake system for proper operation. Bleed brake system again if necessary. Do not drive on public roads until the brake system is properly bled.