Finally started working on installing a backup light switch into my SM420 this weekend. Using the following article (Thank you June of Toy4x4s) as a guide as well as emailing the author with various questions, I felt comfortable enough to give it a try.
http://members.aol.com/toy4x4s/hole.htm Since I have a spare tranny, I removed it's top plate (tower) for this project. Nice to still be able to drive the truck while working on such a project. I think the following folder will give most of you an idea of what I'm doing with a few additional comments.
A few measurements of interest using digital calipers:
Reverse Rod diameter: .623"
Wall thickness: .275"
Space between rod and wall: .152"
A. Take your time in setting up where and how you are going to drill the hole. I also chose the angle approach because there is a little more meat at the upper corner as compared to the top. Also it will be easier to attach the wires from underneath. Besides your tranny cab cover might not allow a switch and wires to extend vertically.
My handy bench drill press was the way to go. Once I set up the jig to firmly hold the tower at the right angle, I was able to quickly drill the hole required for the tap ( 9/16 -18). Lots of cutting oil.
B. Though the original article said that any generic switch from NAPA would work, the switch I bought (Napa #NS119) has made an exception for it is too long. Meaning the threaded portion goes too far into the tranny causing the threaded portion to make contact with the reverse rod in the tower, thus for this switch I had to add some spacers to back it out so the reverse rod makes contact with the switch's button made out of delrin. I could not find a store which had a switch in stock so I've been forced to order something somewhat blindly.
B. This switch's button came factory stock with almost a perfectly squared off end. For this application, you want the button to be either well chamfered or rounded (pic 3). The rod makes a side contact with the switches button, not an end contact. My pic (sketch) #12 helps explain this. Anyway I had to round the end of the button so the rod could activate the switch easier. If it was easy enough, I would love to remove the reverse rod and round the edge of it also so the contact between the two (pic 9) would be smoother and less harsh? Because the button is made of delrin I can imagine that in time, the steel rod's edge is going to wear the button material away. Does anyone have experience in removing and reinstalling the reverse rod? I see that it must come out through the front freeze plug (can't think of a better name looking at it).
C. The space between the rod and wall is very limited so the travel of the button before it activates much be very minimal.
Because the first switch is too long, I have ordered another couple switches to experiment with (all having the same threads) and will pick the least of all evil to do the permanent install.
Stay tuned.
http://community.webshots.com/album/141689703NurJLp?280
