The Flex-Hone® for Porsche Brake Cylinders

The Porsche 356B is a classic sports car with a distinctive streamlined design and a rear-mounted, 1.6-L flat-four engine. Manufactured from 1960 to 1963, this collectible automobile succeeded the popular Porsche 356A that won races at places like Le Mans, Sebring, and the Mille Migilia. With top speeds of just over 100 mph, the 356B isn’t speedy by today’s racing standards. Nevertheless, its redesigned valve guides, transmission mounts, shift forks, and brake drums refined the Porsche driving experience in a way that set the stage not just for the 356C, but for the legendary Porsche 911.

How to Hone Wheel Cylinders

For classic car collectors, the Porsche 356 Registry is the place to talk shop about 356 coupes and cabs in body styles ranging from the T1 to the T6, as well as the short-lived SC. So when a Porsche owner named Gus Borner wanted to hone the wheel cylinders on his 356B, the do-it-yourselfer asked for advice about choosing the best honing tool. Although a few users suggested other brake hones and even honing stones, experienced mechanics recommended the Flex-Hone® tool from Brush Research Manufacturing (BRM). “I use this tool,” a German mechanic explained. “This works better than all others.”

When to Hone Cylinder Walls

Built with a stiff metal stem and abrasive nylon filaments, the Flex-Hone® tool uses abrasive globules for a soft cutting action. With their independent suspension, these “dingleberries” ensure that BRM’s cylinder hone is self-centering, self-aligning to the bore, and self-compensating for wear. Although the Flex-Hone® is not designed for heavy-duty material removal, its proprietary surface finishing technology is ideal for restoring brake cylinders that don’t have deep pitting or grooves. “If they’re pitted, they’ll need to be machined and re-sleeved,” a forum user named Joel Jensen explains.

Plateau Finishing for Brake Fluid Retention

Unlike rigid honing stones, BRM’s flexible honing tool produces a uniform pattern of peaks and valleys for optimum brake fluid retention. By removing just the right amount of material, the Flex-Hone® tool produces a surface finish with tiny 45-degree angles. Known as plateau finishing, this technique removes peaks produced by prior honing and machining operations to create a flat, smooth, cross-hatch surface that’s free of rough, torn, jagged, and folded metal. As a forum guest named Allen said confidently, “I will say 99% of cylinders can be honed and rebuilt”.

Have you used the Flex-Hone® tool to improve the surface finish of your brake cylinders? If so, please let us know by commenting on this blog entry.