Well this weekend I had a stroke of luck. I’ve been reading about a second VIN plate located in the engine compartment with important information including the paint, trim, axle and transmission codes. I kept looking in the engine compartment but could not find it. I figured someone must have removed it at some point and that had me a little worried. Besides that, I wasn’t sure about the original gearing or the paint code. It turns out someone did remove the plate and that someone was me! I was going through all the parts and I found it! I must have removed it back when I took the engine out of the truck 10 years or so ago.
I’ve read that 1981 was the one and only year they used 3.90 differential gears but I couldn’t verify this since I didn’t keep the old gears when I had them swapped out for 4.56. The G072 axle code does verify that the gearing is 3.90 where G indicates an 8″ ring, 07 means a 3.90 gear ratio, and 2 means two pinon open differential (http://old.lcengineering.com/LCTechPages/TECHGEARJANUARY.html). Below is a comparison of the original setup and the new set up using the awseome http://www.grimmjeeper.com/gears.html tool. At some point the transmission in the truck was replaced with a four speed since the transmission code states L52 which is a five speed but when I got the truck there was a four speed (I’m assuming an L45, https://www.marlincrawler.com/tech/transmission/transmission-gear-ratio-chart) in her. It is interesting that Marlin lists L52 as a 1983 transmission while my transmission code from the engine compartment plate states that Bessie got an L52 in November of 1980. The VIN on the engine compartment plate does match the VIN on the dash. There are other case of this reported (https://www.yotatech.com/forums/f114/1981-came-l52-307798/). I’m also assuming that we put in a 4.7 Marlin Crawl Box in this scenario.
