Sun Aug 23 2020

Master cylinder attach hardware

When putting together the rudder and brake pedals the other day, I found myself unsatisfied with Van's approach for attaching the brake pedals to the master cylinder. Here is an FEA of Van's design. Note how the bolt attaching the master cylinder to the brake pedal experiences significant bending when a large load is applied. This load case will definitely lead to bent hardware. Although this analysis is a linear, static analysis, it predicts .015 deflection. However, the bolt will almost certainly yield, resulting in substantially higher deflection. Also, I have a strong suspicion that there will be increasing free play in the brake pedal over time due to this single shear application wearing out the holes in the brake pedal and the master cylinder over time.

I put a lot of though into how to tackle this (percieved) problem over the past few days. I decided that making a custom attachment hardware would give the desired improvement. Essentially, I'm going to build a custom spacer which will contour to the rounded mounting boss of the master cylinder. This spacer will be silver soldered to the bolt. The contour will prevent rotation of the custom hardware relative to the master cylinder, so a regular fiber locknut can be used on the end going through the master cylinder. A castle nut will be used for the end protruding through the brake pedal tab. Deflection for the same load as above should be about .0025.

Here is a drawing of the custom spacer.