The Stovebolt Site Forums The Shop Area Engine Shop 1959 3100 short transmission swap

i have a 59 3100 short fleet with the straight 6 and the original automatic trans.
i would like to install a more modern standard shift tranny. is this transmission conversion difficult and what special parts will i need to fit it to the original motor, and most important what type of donor vehicle should i look for?
i would also like to have it geared for more practicle highway driving.

thanks

Well, start with a bellhousing from a 55-59 chevy or gmc 6 cylinder. Get the clutch pedal, clutch fork, clutch linkage, starter, starter pedal and linkage, flywheel from a 55-59 chevy 235... then decide on a transmission. There are plenty of transmissions that will work. Even Money says you will have to find a new driveshaft, or have one built. Don't forget you will need 2 new rear motor mounts. You might also need a new bellhousing crossmember to get everything else to bolt in.

For better gearing, you could swap out the gears in the rear to 3.38:1. You likely have 3.90:1 now, or you could swap the rear altogether. Of course if you find an OD transmission, you would not have to touch the rear.

The Hydramatic transmissions are highly sought after. If it were my truck I would makes sure the linkages are adjusted properly, and change the rear gears to something more highway friendly.

i am still learning and have never even seen one of these transmissions dropped so some of the concepts are still a bit abstract. my objective is to just get the vehicle up and running as a "practical" daily driver of sorts, not looking to go show/restoration quality or too fancy. it still has the original 235 straight 6 with the automatic transmission (is the automatic version the "Hydramatic" you were referring to?) all of my every day vehicles are automatic and the thing that appeals to me about these old trucks is a good old floor shift.

sounds like a very involved swap. is the "bellhousing from a 55-59 chevy or gmc 6 cylinder and the flywheel from a 55-59 chevy 235" still needed even if i am using the existing original motor? i am guessing that the two new rear motor mounts are for the additional torque issues? is this rear motor mount issue complicated?

how much easier would it be to just find a standard original transmission from a 55-59 and drop that in and that have that geared for practical driving and how satisfying do you think the results will be as opposed to doing a the new tranny swap?

i found an "old school" hot rod mechanic who might be willing to do the work. i just do not know how to proceed. would the old automatic transmission be worth selling to defray some of this cost? what do you think it would be worth?

thank you for your help

yes, the hydramatic is what the era automatic is called
- the original floor shift trans is the sm420 4 speed - has a useless granny low gear
- the original 3 speed is a column shift, requiring different linkage and column components than the automatic
either IS a pretty involved swap, won't be cheap and you'll be searching for awhile to find all the necessary parts
- the bellhousing with mounts [and crossmember] was used for the standard trans, a different bellhousing was used for the auto and mounts the back of the engine on a trans crossmember, just a different setup
- gearing for "practical driving" has nothing to do with the trans, any one will have the same 1:1 high gear, standard or auto unless you get an overdrive trans, which is a similar but different can of worms, otherwise the rear gearing is the only way to get higher road speed at lower RPM
- yes, the hydramatic will be worth serious money

you might find the 55-59 assembly manual very useful in figuring out your choices

also, if you were to go to a 'modern' trans, like the T5 [OD], all the same changes to the driveline would be needed, + you'd have to find a new floor pan ["high hump" for 4 speed] and rig your own shift setup that would clear the seat

Bill