Introduction
You can improve breaking by increasing the flow of the brake fluid to the brakes. If you’ve swapped to rear discs you may have found that your stock master cylinder doesn’t flow enough fluid to enable your brakes to work. This article discusses swapping to a Ford F-350 brake master cylinder for increased fluid flow.
Comparing Master Cylinders
Some Ford Ranger owners have installed the 1985 Ford F-350 master cylinder (Dorman M39445) on their earlier Ranger’s. The stock Ranger master cylinder is on the left, and the F-350 master cylinder is on the right.
The stock master cylinder has a 7/8 inch piston, and the F-350 master cylinder has a 1-1/8 inch piston. The mounting bolts on the Ford Ranger’s booster are actually spaced 1/8 inch wider than the F-350, so you’ll have to use a carbide bit in an electric drill to widen the mounting hole a little on the F-350 master cylinder.
Connecting / Adapting The Brake Lines:
One of the important things to note is that the rear reservoir on the F-350 master cylinder goes to the rear brakes, and the front reservoir goes to the front brakes. It’s opposite on the Ranger. Make sure when you connect your brake lines to the new master cylinder that you’re connecting the correct line to the correct port.
You’ll likely need an adapter so that your brake line fittings will connect to the F-350 master cylinder.
The 1985 Ford F-350 master cylinder is listed as having:
- Port 1 Thread Size (Forward) (In): 7/16-24 Inch
- Port 2 Thread Size (In): 3/8-24 Inch
A 1988 Ranger / 1996 Ranger (checked random year range span):
- Port 1 Thread Size (Forward) (In): 9/16-18 Inch
- Port 2 Thread Size (In): 7/16-24 Inch
The Ranger Port 2 needs to go to the F-350 Port 1 which should both be 7/16-24 inch
The Ranger Port 1 is 9/16-18 inch and has to go to the F-350 Port 2 which is 3/8-24 inch. Therefore, you need an adapter to take the 9/16-18 inch male thread and install it into a 3/8-24 inch female thread.
Dorman 490-543.1 (3/16 In. Female to 9/16-18 Male Inverted Flare Dual Brake Line Adapter) should do the job.
When installed, it would look similar to this:
It’s also important to note that all the master cylinder does is push fluid. The proportioning valve (on the frame) is what determines how much fluid goes where.
Also, if you do this swap and your brakes feel squishy, it’s likely because you have the wrong brake lines hooked to the wrong port. If you look at the F-350 master cylinder, you can see that the rear port is much larger than the front port.
Links:
Ford F-350 Master Cylinder Swap Discussion #1
Ford F-350 Master Cylinder Swap Discussion #2
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About The Author
Jim Oaks is the founder of The Ranger Station, one of the longest-running Ford Ranger enthusiast communities on the web. He has spent over three decades owning, modifying, repairing, and driving Ford Rangers on the street, trail, and cross-country routes.
Since launching TheRangerStation.com in 1999, Jim has documented thousands of real-world Ranger builds, technical repairs, drivetrain swaps, suspension modifications, and off-road tests contributed by owners worldwide. His work has been referenced by enthusiasts, mechanics, and off-road builders looking for practical, experience-based information rather than theoretical advice.
Jim’s hands-on experience includes long-distance overland travel, trail use, drivetrain and axle upgrades, suspension tuning, and platform comparisons across multiple Ranger generations. The content published on The Ranger Station is grounded in first-hand experience and community-verified data, not marketing claims or generic specifications.