I bought a 4 speed SM420 transmission without knowing the year but had some idea. I found out thru other postings that a 7 digit casting number beginning with 37,38 or 39 fall in the 1964-67 year time frame. You could also tell the year by the code above the casting number. For ex: B1060 means it was feb 10, 1960.. I thought I was all set to identify any SM420 but what i have seen in looking at SM420's is that there are some that have the 1st letter followed by only 3 numbers instead of 4. Mine is L184.. So does anyone know how to decode this to figure out what year this is? here is a picture.. thanks
I'm not positive and cant find the book I was looking for to confirm it, but I think that L=december, 18=day and the 4=would make it decade plus four(ie.1934, 1944, 1954, 1964 ), SM420 have been around along time and although it my not be the oldest of the top loader 4spd tranny's, I belive it's the longest model ever used and if it isnt it sure is one of. from its inception to its end it went through a few changes internally and some externally visable diffrences. some of the changes where made to eliminate proublems, but most where to incorporate new casting and mechining techniques by the manufacture. one of the visable external changes occured in the late 50's or early 60's and that was the elimination of the reverse excentric nut and bolt visiable on the right side( oppisite of the pto cover ) of the case just below the lid mounting flang, the other occured around the same time and that was the elimination of the mounting stud in the lid on the right hand side for the hand brake lever.
this what I found on the net The last year of the SM420 (1967) had a backup light switch installed in the top cover to meet that year's federal mandates. * 1947-1953: 1. No ribs on the case 2. Grooved worm on the input shaft instead of neoprene seal 3. Synchro rings all differ from each other. 1st-2nd synchro ring is bronze 4. Weep hole at 6 o'clock on the bearing retainer snout 5. Six digit casting number on the case, usually like "59xxxx" e.g., 591665. * 1954-1963: 1. Same as previous but uses a neoprene input oil seal 2. No weep hole at 6 o'clock on the bearing retainer snout * 1964-1967: Same as previous except 1. 1st-2nd synchro ring is aluminum and 3rd-4th synchro rings are identical to each other 2. Seven digit casting number usually like "37xxxxx", "38xxxxx" or "39xxxxx" * 1968-1981: Military Con-Diesel version. Features the strongest case and optimized internals. Usually equipped with unique top cover, but can be converted to standard top-shift control. Seems to be a 1964 transmission
Hey guys, found your site surfing the web. I installed an SM420 in my 1973 Toyota FJ 40 and my top cover is worn out (got stuck between gears. Without the clutch, the engine would lug out because the tranny was bound). I need to track down a new top cover. Hope the original poster doesn’t mind if I piggy back off his post. I am trying to identify which top cover I can replace mine with. It has the plastic shifter interlock plate. I believe the top cover I have is not the original. But I am having trouble figuring out the build date of the tranny and the build date of the top cover. Top cover: K2362 (passenger side markings) and 591568 (driver side marking) I believe this that K is for the 11th month so November 23, 1062. The tranny is K295 and 3837334. Would that be November 29, 19?5? But Novak’s page says that numbers starting in 38 would be 1964-67 so that doesn’t make sense. Also, what year’s top covers are compatible with what year tranny? I know there are two top covers made and each works with only specific years. Thanks for all the help and thanks to the OP for posting the first post. Dan
