David M Posted August 20, 2020 Report Share Posted August 20, 2020 I've got a 1955 Dodge C-1-B6 with a NP420 4-speed. The guy who sold it to my Dad (in 1973!) said it was late in the model year and maybe got some '56 parts, but who knows. In any case, it's got a casting number C-88221 with a top cover C89988. The pictures below are from another post, but mine looks the same, with e-brake and all. (Not sure about the tower though.) It's being rebuilt, but the synchronizer is blown and I can't find a replacement. Any ideas? I've asked D. Cirillo and Vintage Power Wagons, no luck. Quote Link to comment Share on other sites More sharing options...
Dodgeb4ya Posted August 20, 2020 Report Share Posted August 20, 2020 If you have the OE part # try AMS Obsolete...AKA Mitchell Motor Parts. Not cheap but have lots of NOS MoPar. The trans data of manufacture is usually cast on the shifter cover..day/month and year. 1 Quote Link to comment Share on other sites More sharing options...
David M Posted August 20, 2020 Author Report Share Posted August 20, 2020 Thank you, Dodgeb4ya. I'll check there. Dennis Maroudas tells me I'm looking for synchro assembly AWT262-2.5 The casting has date 1/6/55 (or maybe 7/6/55, it's not super clear). The top cover date is 1/31/55. Quote Link to comment Share on other sites More sharing options...
Dodgeb4ya Posted August 20, 2020 Report Share Posted August 20, 2020 (edited) The AWT# is an after market synco assembly kit I suppose. Original MoPar syncro parts are generally sold separately .... The 1954-56 DT parts book shows only separate synco parts except for the M-6 Truck-O-Matic trans. Usually the ring and ring assembly wear out. Seen one with broken pins too. Edited August 20, 2020 by Dodgeb4ya Quote Link to comment Share on other sites More sharing options...
David M Posted August 20, 2020 Author Report Share Posted August 20, 2020 Wow, that is really helpful. I have the shop manual for the truck, but not a parts manual. This is great info. I know the tranny tech mentioned broken pins, but I'll take this info to him and see if I can narrow down what I need. Thank you for taking the time to look it up! 1 Quote Link to comment Share on other sites More sharing options...
David M Posted August 25, 2020 Author Report Share Posted August 25, 2020 Parts for the later NP420 transmission (1956-) seem to be easier to find than the early version. I can find synchro rings (inner and outer) for the later version (1669891 and 1669893), but not for the early. They certainly look identical to the casual observer though. Does anyone know if they would work? Quote Link to comment Share on other sites More sharing options...
bkahler Posted August 25, 2020 Report Share Posted August 25, 2020 I may have missed it but does anyone know how to tell the differences in the NP420? I have a NP420 installed in my truck that I bought many years ago. I don't remember if I was told what model year truck it was from. Knowing what syncros would work as replacements if needed would be nice to know. Quote Link to comment Share on other sites More sharing options...
CO54 Posted August 28, 2020 Report Share Posted August 28, 2020 That is an NP420, It should be syncro'd. like my '54 C1C based on the info I found with the drain and fill plug locations. Your casting # matches mine with a date stamp of 6-16-53, my cover casting # is C-89989, date stamp 7-24-53. I was able to find some parts for it through Vintage Power Wagons (listed in the Vendors Posting) . You just have to read into it their breakdown on vehicles. Also extremely helpful on the phone with getting you the right stuff. Quote Link to comment Share on other sites More sharing options...
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