[57GMC-347]

hello got engine rebuilt - nervous about the hydramatic

how straight forward is it to convert to muncie 4 speed ?

worth pursuing ?

thanks
mike

[67drake]

I can’t answer, but your post might get more attention in the “Street” section

[b-man]

Originally Posted by 67drake

I can’t answer, but your post might get more attention in the “Street” section

Let’s try the 1960 and earlier forum first for this somewhat rare pursuit.

At the very least you’ll likely need a 1957 manual transmission bellhousing and flywheel to get started.

[Safari Larry]

You need a 1958-60 std transmission bell housing (same for those three years). It will bolt up to your 57 engine and the 4-speed will bolt up to the bell housing. You need the associated parts such as flywheel, clutch fork, clutch, throughout bearing, clutch pedal/linkage, etc. Driveshaft will likely need to be modified. You'll probably need std transmission rear crossmember for motor mounts.

[57GMC-347]

Originally Posted by Safari Larry

You need a 1958-60 std transmission bell housing (same for those three years). It will bolt up to your 57 engine and the 4-speed will bolt up to the bell housing. You need the associated parts such as flywheel, clutch fork, clutch, throughout bearing, clutch pedal/linkage, etc. Driveshaft will likely need to be modified. You'll probably need std transmission rear crossmember for motor mounts.

thanks for the direction - currently with the hydramatic it also is for the rear engine mounts - location

you think the std transmision bell housing will have those same locations

i will begin searching for that year of bell housing

i just dont think the hydromatic - throttle linkage will work with tri power set up

thanks again -

[57GMC-347]

Originally Posted by b-man

Let’s try the 1960 and earlier forum first for this somewhat rare pursuit.

At the very least you’ll likely need a 1957 manual transmission bellhousing and flywheel to get started.

thanks b-man new to the forum - assist is appreacted

[Bill Hanlon]

I think (no practical experience) that the Muncie will be far enough below the floorboard that regular 4 speed shift linkage would need a BIG hole to allow movement to all 5 gears.

The HM throttle linkage has a spring gizmo on the carb end that lets the carb go to full open without pressing the gas pedal all the way down. When you do press it to the floor they carb stays wide open, but linkage to the HydraMatic kicks the tranny down into "passing gear".

[57GMC-347]

Originally Posted by Bill Hanlon

I think (no practical experience) that the Muncie will be far enough below the floorboard that regular 4 speed shift linkage would need a BIG hole to allow movement to all 5 gears.

The HM throttle linkage has a spring gizmo on the carb end that lets the carb go to full open without pressing the gas pedal all the way down. When you do press it to the floor they carb stays wide open, but linkage to the HydraMatic kicks the tranny down into "passing gear".

Hello Bill

with the tri power - i added (had to have) haha im just not seeing that spring gizmo and rod working with the progessive linkage


you know of any hydratic tricks - to try -

[blueghoast]

Originally Posted by 57GMC-347

Hello Bill

with the tri power - i added (had to have) haha im just not seeing that spring gizmo and rod working with the progessive linkage


you know of any hydratic tricks - to try -

I have a tri-power on my 57-347 and it works fine.
The linkage on the firewall has the return spring and the original linkage
hooks right up to the center carb like the original one does. you might have
to adjust it some as I did on mine. do you have the correct TP linkage ?
hope this helps.

GT

[Safari Larry]

Originally Posted by 57GMC-347

you think the std transmision bell housing will have those same locations
i will begin searching for that year of bell housing

Your GMC has the dual-range hydramatic and used it up though 59. 1956 was the last year Pontiac used the dual-range hydramatic (often called the "slant pan"). During that year, Pontiac had 3 different crossmembers, one for std trans, one for dual-range (same as 55), and one for the new Strato-Flight (same as 57) hydramatic. Different crossmembers were needed for different trans mount locations. Motor mounts are attached to the bell housing and crossmember. Using the 1958-60 bell housing on a tri-five Pontiac required using the 1956-57 Strato-Flight crossmember (with minor adaption). I'm attaching photo of 1956 Pontiac dual range hydramatic cross member (top) and std trans crossmember. Note that the dual-range motor mounts are offset to the passenger's side.

That's Pontiac. I don't know about your '57 GMC crossmember with the dual-range hydramatic. I don't know if the transmission mounting is same as the 1955-56 Pontiac dual-range transmission. If it is, then that offset of motor mounts won't work with the 1958-60 bell housing.

I have a 1958-60 std trans bell housing that I'm willing to sell. They are hard to find because they were commonly used for adapting 1955-60 Pontiac engines to later 4-speed and Tremac 5-speed.

The easy route for you is to use your hydramatic. It is a very good transmission when adjusted properly. But if something goes wrong, you need an "expert" to work on it. I've overhauled a few but that was 62 years ago.

[Bill Hanlon]

Just checked and none of the part numbers for the 2 piece HydraMatic "clutch housing" (Pontiac) or "flywheel housing" (GMC) are the same, so the chances of the mounts interchanging are low. Same for the housing rubber mounts.

[Goatracer1]

I installed a 1957 Tripower on my 1955 Chieftain many years ago. The car had the Hydramatic trans and I didn't have any trouble making up a throttle CABLE to work the trans and carbs. Just a suggestion.