Summary; Using a 4 speed in your 1/2 ton truck? X-Mass has given me some spare time to study the functional durabillety and technicall differences of these spesific gearbox alternatives, and i think it is great to know that there are quite some differences between these? The Saginaw tranny seems to have some weaknesses compared to the Muncie M20 and M21? The main difference is the way how they are build up and the way the gears are placed in the cases. The outher case sizes are allmost the same but i am not shore if the mounting holes in the ears towards the bellhouse fits directly when using the Muncie, maybe one has to use an adaptor plate? Maybe some of you knows more about this issue? Both cases are bolt in solutions and you dont have to do any spesial changes to get it work. No cutting or replacing or changing is needed. The Saginaw version have the 4. gear placed in the lock versus the Muncie wich has placed the 4.gear inside the case and this solution is more durable. The Muncie transmission is synchronized in a better way and shifts smoother to. The saginaw is made of cast iron and pretty heavy versus the Muncie that is made of aluminium. Muncie M20 and M 21 is propably a better alternative and more durable. The M 22 the "Rock crusher" it is not really the best alternative to use because of the wining noice they make. Differences are also in the ratio; Transmission First Second Third Fourth GM Saginaw 2.54 1.50 1.00 -- GM Saginaw 2.84 1.68 1.00 -- GM Saginaw 3.11 2.20 1.47 1.00 GM Saginaw 2.85 2.02 1.35 1.00 The best option here is to use the Sagianaw case with the 3.11 first gear combined with 3.55 rearend ratio if you want to use the original axle ofcourse. 10 splines and 2 grooves on the inputshaft and 27 on the outputshaft. MUNCIE MODEL/YEAR MAIN DRIVE GEAR (TEETH) MUNCIE MODEL/YEAR COUNTERGEAR (TEETH) M20 1963-65 Wide Ratio 24 M20 1963-65 Wide Ratio 17 19 22 29 M20 1966-70 Wide Ratio 21 M20 1966-74 Wide Ratio 17 19 22 25 M21 1963-70 Close Ratio 26 M21 1963-74 Close Ratio 17 19 22 27 M22 1965-70 26 M22 1965-72 17 19 22 27 The best option here is to use is the Muncie model M20 with the wide ratio made between 63-65 with the 10 splines on the inputshaft and 27 on the outputshaft. http://www3.sympatico.ca/atkinsom/history.html http://www.yearone.com/updatedsinglepages/Id_info/muncie.htm To save money it would not be to hard to get hold on either a Muncie or a Saginaw at your locall wreckyard. Camaro,Chevelle and Nova cars between 65 and 80 used these tranny solutions. Cleaning and remanufacturing is not a difficult work and with the support by using a working manual this gives no problems ? At Ebay they sell complete rebuild kits for both transmissions for a 75 US dollars. Good luck hunting Martinius.
Vegas had the Saginaw 4-speed transmissions. Back in the 60s everything would bolt up they chevy made. You could get the whole Vega with 40,000 miles on it for 75$ or less. I had the Saginaw with the lo speed 1st gear and 3.73 rear gear in a 57 belair with 350 engine. It was to low of a first gear and I changed it out for an automatic.
