I have a 1958 GMC truck with original drivetrain.270engine3spd&3:07rearend. Trans needs rebuilding/replacing. So how inexpensive can I convert to automatic trans?I estimated roughly $2k to do the automatic change over verses $800 to do manual swap out. Any manual trans that would work like Saginaw 3/4 spd? Thanx
You aught to be able to find a good 3-speed for that cheap if you poke around. They don't have a lot of value unless they have an overdrive.
Your bell housing should have the common transmission pattern that will accept later G.M. 3, 4, and 5 speeds, although the 5 speed will require a little modification.
The fully synchromesh Saginaw 3 speeds used from about '65 up would be the least expensive that still offered some gain over the original trans. As others have stated above, the bell housing bolt pattern is the same for a wide variety of GM manual gearboxes. The only difference with trucks of that era is, the lower bolts enter from the clutch side and threads are in the transmission 'ears' and car's are not. A very simple matter to deal with. Any automatic trans, other than the original optional Hydramatic, will require an adapter. They are available from several sources.....Tom Langdon's Stovebolt Engine Co., WilCap or Bendtsens in MN. With the 3.07 rear gears, you could use a non O/D automatic (TH350) and still have relatively low rpms on the highway.
is a Saginaw 3/4 spd a direct swap?how would I know what clutch kit to buy?Do I tell them what truck I have? Or is there a way by reading numbers on the transmission??
The overall length may be different from your stock gearbox, and I'm sure that the spline count on the output shaft will be different; that changed in 1963.
Me, I'd go with a Saginaw FOUR speed; they come in 4 different first gear ratios and gear spreads, AND Patrick's has a modified Hurst shifter they sell that will clear your stock bench seat. It spaces the shifter ***embly more forward, and uses shorter rods. Plus, Saginaws are pretty cheap; I gave the last one I had when I sold my Saginaw 3-speed with O/D to a fellow HAMBER (****gy) for him to build a Saginaw 4-speed with O/D. Or, you could use a Saginaw 3-speed, and modify the shift levers/rods in order to keep your stock column shift, if you still have that feature. You WILL need to change out your slip yoke, the clutch splines are the same. ANY of the "common" Muncie 3 and 4 speeds, Borg Warner 3 and 4 speeds, and Saginaw 3 and 4 speeds will bolt right in. The early Borg Warner's may even have the course output shaft that will work with your current slip yoke. The 3-speed Muncies and Borg Warners meant for GM applications are kind of rare, they did't make a lot of them to start with. You could even use a Dearborn (Ford) 3 speed designed for use in the 66-67 Pontiac's, but same deal about being rare; plus they may bring a good price due to their unique application. GM did't have a HD, full synchro 3-speed at the time, so used the Dearborn (Ford in a GM product!!!). I guess it was "payback" for "Ford (Lincoln) using the GM, cast iron Hydra-Matic in the early 50's. Going to a more late/modern manual trans, you could also use an S-10/Camaro/Firebird T-5; just be sure to get the one with a gear driven speedometer drive and not the electronic one. Butch/56sedandelivery.
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