So , I'm poking around in the back lot of a war surplus store and there's all these ancient wooden crates full of stuff , just falling apart so I begin poking my nose in ....Hm , rebuilt Dodge M-37 (Power Wagon) trannies.. I schlepp on inside and ask the guy ' Hey , you got any old GM trannies ? ' " Oh , just some brand new Muncie M-420's , I sell them to the Toyota Land Crusier guys...." !! =8-0 !! I knew there -had- to be some of these floating around somewhere but I really gave up expecting to find one in my lifetime.... He wants $450.00 for one (_OUCH_) ~ is this too much for a BRANDY NEW Muncie SM-420 floor shift , four speed , compound low tranny like our trucks ('47 through '67) use ? this is for an open driveline so I'd have to use my old top cover and shifter plus my rear cover and yoke etc. This might be a good thing , how the heck will I pay for it ? . Comments please ? . -Nate
RE: N.O.S. Military Surplus Muncie Nate: Too bad I'm in Texas, I assume you found the 420's somewhere west of the mountains? I have a question for you. I am currently replacing an SM 420 in my 1954 3100 with a open yolk model of the same tranny from a '50 1 ton Chevy. The swap on the yolk has been simple. But I mstill have questions. Why would I need to swap out the top cover and shifter? These look identical, but I haven't set them side by side yet. My '54 is real high miler, but completely restored in my backyard (finished in 2002). I did not rebuild the torque tube, or tranny at that time. The truck is in the air again now, rear end and torque tude removed, low miler tranny being readied. I am waiting on a ring and pinion 355:1 from Patrick's, then reassembly. I believe I have to keep my 12 tooth speedo gear, there is 14 tooth in the one ton tranny. My gear is really worn, on the yolk side as well, but does work. Any suggestions on the tranny gear? I know a jeep builder who would love to find the military surplus 420's. I appreaciate any advice.
RE: Muncie SM-420 There are several different part number lids , all seem to fit O.K. just look at the shift fork and maybe lay a caliper or mike on the shiny parts of the forks , use the thickest ones to improve shifting and reduce shift lever rattle . There are also many different bends available in the shift levers so make sure it's the right bend else it may hit the seat , again the tip wears so use the thickest one possible . Use the longest & strongest spring in the shift tower . The gears were made with a variety of different tooth counts to adjust the speedo to the final drive , do a milage check to see how accurate your speedo is then try the other gear , it may suprise you. -Nate
RE: Muncie SM-420 [updated:LAST EDITED ON Apr-03-06 AT 01:38 PM (CST)]A couple of comments: Nate there is a tranny shop here in Portland (huge tranny rebuider) that wants $750.00 exchange for rebuilt SM 420's. I said fine, if they are worth so much, I got two spares, what they pay for cores? Nothing I was told, they had just purchased a couple hundred as military surplus. I did get a complete rebuild kit from them for $148.00, including syncros, which was less than the kits I saw on the Web. I have seen used SM 420's at the $50 to $75 price pretty regularly in the past. As to switching the top plates, the same tranny shop told me cores had to have their original top plate as the shift forks were set up at the factory to match the gearbox. I have heard this from one other source as well. Don't know if it is true, but also did see a post somewhere where someone complained of shifting problems after switching a top plate. I don't know why you would need to switch them as I believe there is little or no difference between them, other than the setup mentioned here. Steve O
RE: Muncie SM-420 Thanx , Steve ; The deal with the top cover is this : many differant applications so you cannot always just install your old shift lever to the new tranny This place in Portland , does it sell the N.O.S. military units ? or did they just buy some of the crates of used M-420 trannies for cores ? . ,akes a bit of differance IMO . NO ONE ever wants to buy cores no matter how much they may b*tch & complain about lack of suitable cores ~ were I rich , I'd have allready bought one of these trannies just to stash in my house . -Nate
RE: Muncie SM-420 Nate; My Chevy shop manual explains in detail that the speedo gears are machine mathed to the indivual yolk (the worm drive). It recommends replacing both parts. I would use the better 14 tooth speedo gear if I were not concerned with this. I can always put a speedo adapter on the cable side to correct the meter. The 14 tooth gear is mated to an open yolk with at least one more row of worm drive than found on the closed (torque tube)yolk. If you want to get rid of old sm420's I bet you'll find the folks at NOVAK SM420 interested. These folks specialize in adapting sm420's to all kinds of jeeps for rock climbing. They really like the short, strong tranny, especially the low first gear. Do a google for them, I have acqured a gasket set for my 420 recently. They are on your side of the big mountains.
