Verus Forged 4130 Clutch Fork

Verus Forged 4130 Clutch Fork

Increase strength and longevity of the clutch fork by using our forged 4130 clutch fork for the FR-S, BRZ, and GT86. The ZN6/ZC6 chassis has a weak clutch fork that tends to break or bend when used with heavier pressure plates. This fork fixes those issues and can be used with extremely heavily sprung pressure plates. These are heat treated to a hardness of 26-32 HRC and then cyro treated for improved physical properties. The unit is black oxide coated for rust resistance.

Note:

Material Properties, Yield Strength, and Deformation

To conclude our crash course, the factory clutch forks are being stressed over yield strength and are being plastically deformed. We must create a clutch fork that keeps maximum stress under yield strength with minimal deformation.

What the fork Subaru?

Let's Look at What We Are Dealing With

For complex situations like this, Velox practices Computer Aided Engineering (CAE). In this case, that would be using Finite Element Analysis (FEA). Our analysis software of choice is ANSYS. ANSYS is at the top tier of analysis softwares and is used in over 90% of the top 100 fortune 500 companies, F1, NASCAR, etc. It’s very powerful software.

So with all the inputs plugged in like material properties, loading, and fixturing, after running mesh sensitivity studies, and setting up the legend correctly, below are some photos of the of the von-mises stress analysis on the OEM clutch forks. The color red is set to yield strength, anything in pink is above yield strength, cooler colors (green/blue) are lower stresses.

What Are We Looking At and Why Did We Do This

First things first, what we are looking at are graphical representations of the stress the clutch fork sees in a highly loaded pressure plate situation. What is of most importance to us, is viewing the areas near, at, and above yield strength. Typical analysis set the legend from minimum to maximum stress the unit sees; but this doesn’t give us an easy to read indication of problematic areas. Simple solution, change the legend so that the max legend value is yield strength and we can quickly and easily view what is happening.

We did this initial analysis to visualize trouble areas and give us a starting point to compare our upgraded design to. Without this visualized data, we would be guessing where and how to make the design stronger. Ultimately, this allows us to quantifiably improve the design faster as well as design a better product at the end of the day.

Time to Fix This Issue!

Using the information gathered from the OEM FEA analysis, we are able to methodically improve the design. First, we wanted to machine this from a stronger material than stamped sheet steel, so we chose 4140 Chromoly steel. In the annealed state, 4140 is 12% stronger in yield strength than typical sheet steels. We then increased the wall thickness by 25% minimum throughout. Finally, we removed the major stress rising locations found in the initial analysis.

Results From Improvements

Time to Up-Shift into Prototypes

Knowing what we can expect from a machined part using CAE, we can build a rapid prototype from plastic to test fitment knowing full well our improved design will withstand the loads. Rapid prototypes save time, reduce costs, and improve part fitment before ever cutting into a piece of metal. This technology is absolutely game changing for manufacturing!

Production Ready, Clutch Out, and Back on the Gas

Production pieces are below. We have heard nothing but glowing reviews from this modification; from clutches that operate again to a much more consistent clutch feel. If you own a Subaru and are upgrading your clutch, we highly recommend looking into our clutch fork as well. The FRS/BRZ/GT86 clutch fork shares the same clutch fork as 278 vehicle variants in the Subaru line up and the 2015+ WRX clutch fork shares its clutch fork with 72 other vehicle variants. We were also asked to accompany the clutch fork with an improved pivot, which is also available.