Under floor Master Cylinder Brake Bleeding

[Drbrown]

Be sure to bench-bleed the master cylinder before installation (some come that way) and adjust your brake pedal play as necessary. My '47 has an access hole in the floor pan - just need to lift the carpet. I have Speed Bleaders and like that they allow one person to bleed the system. Regarding brake fluid, over time DOT 3 and 4 brake fluid absorb moisture which can damage the master and wheel cylinders. I have not converted the system for use of low-absorption DOT 5 because of concerns its more easily may "leak". So I have my brake fluid changed every three years. For my '47 the shops can remove the master cylinder cap from beneath the car. Then they open all the wheel cylinders and suction the old fluid out. They pump new fluid in from below. The cost is minimal given the benefits.

[glennpm]

Originally Posted by Drbrown

Be sure to bench-bleed the master cylinder before installation

This is required for dual bowl master cylinders but not required and a waste of effort for the original single bowl masters.

[mcgarrett]

Keeping the master cylinder full while bleeding was one of the biggest challenges with the MC under the floor, especially if you're working alone. This kit worked reasonable well and wasn't expensive.

https://www.harborfreight.com/brake-...der-92924.html