The Stovebolt Site Forums The Shop Area Driveline modern transmission into a stock 58

i have a stock 58 short fleet with a rare option automatic transmission(straight 6 motor). I would like to install a modern type standard transmission with practical gearing in the rear end to make daily driving/highway driving more practical. i will inlist the help of an experienced mechanic to do this job.

what type transmission will i need to look for as a donar transmission and what adaptors/parts will i need to make the swap. is this type of swap routine? anything in particular i need to know or be aware of?

thanks

I'd suggest an overdrive trans, either the original style OD 3 speed [post 68 is all syncro] or a modern OD 4 speed, then the rear gear change won't be needed, it's quite spendy ... you'll need the flywheel and clutch package to fit the 235, along with the clutch pedal and linkage [and a hole in the floor], and all the shifting bits, which with the OD 3 speed could be the original column shift parts that might be found with a post in the parts wanted here, or another hole in the floor for a floor shift ... might also need to modify the drive shaft, not sure if there was a length difference

Bill

I believe the 4-speed Hydra-Matic was the only automatic transmission option in 58, and it's a huge job to convert to a standard transmission. Be sure to save all the automatic-specific parts you take off, as there are plenty of people wanting to go the other way and those parts are very scarce. Unless you plan to do a butcher job with a floor shifter, you're going to need a different steering column, shift linkage, clutch pedal, and possibly the crossmember under the bellhousing, bellhousing, flywheel, clutch, pressure plate, shift linkage, etc.

It would be best to try to find a complete donor truck with a trashed-out body to be sure to get all the bits and pieces you'll need, or just try to find a stick shift truck in running condition, and sell the automatic truck.
Jerry

Put a set of 3.38 gears in the rear and call it done. Any newer automatic will be a dog in comparrison to the 4 speed hydramatic you have in there.

IIRC, the 3.38 gear was part of the Hydramatic option for that year.

thanks for the info.
just to detail a few points:
>if i did decide to convert to a modern type "standard" it would definitely be a floor shifter, not column.
>specifically what type of a junker donar truck/or (year/model)transmission type would i want to focus on for the swap
>are all of the additional misc. parts needed to change over available as some sort of kit or will i need to piece them together?

All that being said......as swing daddy had suggested i could consider letting the original transmission be so long as the gearing and ride was suitable for a highway/daily driver type of vehicle. as practical driving is my bottom line objective.

thanks

if i were to leave the original 4-speed Hydra-Matic intact is there any way to make the drive more practical for a daily driver?
the trans really seems to be screaming on the highway at about 45mph. i am not sure of the gear combo, would a gear switch make the situation better?

practical driving is my bottom line objective.
thanks

Is the transmission shifting into Fourth gear? A simple adjustment may be needed to ensure all 4 gears are being used.

Depending on gears and tire size, 65 mph should be around 3000 rpm. Using an online calculator I punched in 3.9 rear gears and 28 inch tall tires and came up with 3042rpm. if your truck had 3.38 gears 65 mph would be 2636rpm. put some 31 inch tall tires and you are down to 2381 rpm

There are many rear ends and tire combinations you can use to drop the rpm further. 1957-1959 gmc 1/2 tons had a 3.08 spicer rearend available. This rear would be a near drop in replacement, however brake parts for the spicer rear tend to be challenging to find. Chevy 10 and 12 bolt rears can also be made to work with a little help from an electric glue gun. The 10 and 12 bolts have gear sets available from 2.73:1 through 4.11:1.

I have an IMCA modified 9 inch in my 59 gmc with 3.70:1 posi. I also have an OD transmission which makes the final drive about 2.70:1. I have a big V8 and needed more rearend because the rebuilt eaton HO33 rear with 3.38 gears was literally ripped apart by my new engine. You shouldn't need to go crazy with a 235 6 cylinder.

if the trans is 'screaming' the trans needs some attention
if the engine is screaming at 45, you're not getting into 4th, especially if it does have the 3.38 rear as Longbox suggests .... and no, there isn't a 'kit' for a trans conversion

Bill