Ball Hones for Hydraulic Valve Rebuilds

In automotive applications, metering valves promote balanced braking between a car’s front and rear wheels. Typically, these hydraulic components are used in rear-wheel drive (RWD) vehicles with front disc and rear drum brakes. In classic cars such as the 1970 Chevrolet Camaro, a metering valve is located in the brake line between the master cylinder and the front discs. By regulating the flow rate and fluid pressure, this hydraulic valve keeps the front brakes from operating until the rear brakes start working.

Disc brakes are fast-acting. Drum brakes take longer to engage because of spring tension and linkage clearance. By delaying the application of the front disc brakes, hydraulic pressure can build in the rear drum brake wheel cylinders. In addition to brake line connections, metering valves have a main bore with a piston that closes. To ensure proper braking action then, metering valves in older vehicles may need to be replaced. With the right tools and parts, however, these hydraulic valves can also be rebuilt.

How to Surface Finish Hydraulic Valves

At Muscle Car Research, an on-line forum for a family-owned business that provides auto parts and repair services, hobbyists ask questions and get answers about restoring muscle cars. For one mechanic, rebuilding an old General Motors (GM) metering valve was a project worth documenting in detail. Step-by-step, the user explained how to rebuild the hydraulic valve by using a seal kit along with tools and cleaners.

For improving the surface finish of the valve bore, the mechanic used a 1” ball hone. The Flex-Hone® tool from Brush Research Manufacturing (BRM) has its share of nicknames, but ball hone is actually a trademarked name for BRM’s flexible honing tool. Built with a double-wire metal stem and flexible nylon abrasive filaments, the Flex-Hone® features abrasive globules (balls) that give the cylinder hone its unique appearance. For ball hone users, however, it’s the tool’s performance that matters most.  

When to Choose and How to Use Flexible Honing Tools

Flex-Hone® tools aren’t designed for use with bores that are out-of-round, or that require heavy-duty material removal. That’s why the user advised hobbyists to inspect the bore first for problems such as pitting, which can cause leakage. The valve bore for the 1970 Chevrolet Camaro wasn’t pitted, however, and a 1” ball hone from BRM imparted a surface finish that promoted proper sealing and seating.  

After chucking the Flex-Hone® in a handheld electric drill, the muscle car mechanic followed BRM’s recommendations for revolutions per minute (RPM). As a rule, smaller ball hones require faster speeds. For a 1” cylinder hone, 800 RPM is a good guideline. The Flex-Hone® Resource Guide provides general speed ranges, but machine trials may be needed to verify parameters. This free, downloadable resource also explains the importance of using ball hones with a high-quality lubricant such as Flex-Hone® oil.

BRM cylinder hones are self-centering, self-aligning to the bore, and self-compensating for wear. Using a low-temperature, low-pressure abrading process, flexible honing tools impart a plateau finish with oil-retaining grooves for optimum lubrication. This cross-hatch pattern also reduces seepage in hydraulic and pneumatic applications while promoting longer seal life. In addition to metering valves, automotive applications for Flex-Hone® tools include deglazing engine cylinders.