April 8-21, 2018: First MarRack Prototype finally finished! (continued)(2) Restore proper steering geometryFirst, for anyone wondering, I'd like to specify why this is needed. Because the MarRack is larger than the Tacoma rack, we cannot simply "make it fit" and connect tie rods. We have to ('A') maintain the original tie rod length, and ('B') maintain the original tie rod horizontal angle. If either are ignored, the result will be an unwanted progressive rate of toe angle change with suspension movement. This was how I had been driving the truck since March 2nd and it was horrible. (I did so because I needed to get miles on the MarRack to ensure things were stable, no leaks, etc.) Any bump in the road that only affected one side of my IFS would instantly cause the truck to pull one way or the other. I even took different roads to get home just to avoid certain corners and dips. So for the MarRack to be a success, obviously I need to get the geometry worked out.
This was the most time consuming aspect. I made a ton of CAD drawings and 3D printed parts. During a 6 or 7 night stretch I made improvement after improvement ultimately deciding not to do any production CNC work as it had become crystal clear that this prototype will only need to get me through a three or four month stretch.
What we came up with for my prototype was to use our Marlin Crawler forged steel High Steer pitman arm (we use this on live axle cross-over steering systems), flipped upside down and modified in a double-support arrangement against the factory forged steel spindle steering arm. I told our machinist to stop on everything and after making multiple jigs I had the geometry figured out to a 2-degree of toe change through-out the range of suspension articulation. This was difficult to achieve due to reasons explained below but for now and without any computer aid I am very, very pleased with how my measurements turned out!!
Here is the precise location that is required for the limitations of the first prototype
Below is what it looks like as a whole
What we've got going on is that we must make a stronger and wider than stock component (the MarRack) fit within a space constrained by the brake rotors. Because we cannot maintain original tie rod length due to rotor interference (see above reference 'A'), one solution could be to move them forward. I chose this route for my first prototype, however, I will be using an incredibly unique approach on version 2.0 that I have yet to see any aftermarket company do that I believe will solve this problem entirely while maintaining original rotor size and location.
Don't be thrown off by comparing steering arm placement: Remember, the factory TRE mounted upside down. While my placement appears to be lower than stock, it's actually higher, and thus satisfies above reference 'B'. There is, however, a highly critical Rock Crawling design advantage that at this time does not make geometric sense. Minds will be blown once I get the next prototype built I promise you!
