ST300 /TH350 swap in 1968 GS 350.

I got a great deal on a TH350 tranny for my GS and plan on installing it in the next few weeks. I have not seen any easy way to connect the kickdown switch and am looking for suggestions. I am currently using the original intake and 4bbl Quadrajet (which will need a rebuild). I am also wondering if the trans dip stick tube will need to be replaced as well as the speedo gears.

Also i believe the tranny I got is from a 1970 buick, but I haven't found any type of BOP trans decoder. Its stamped near the tailshaft and bell housing, but I don't know what any of it means.

Any help would be appreciated.

 

The TH350 ought to go in without much trouble, same driveshaft, etc. A little
calibration of the shift linkage is in order, probably the indictor just won't
read out 2nd gear. Sometimes the length and angle of the arm need change.

Check the speedo gears in your trans and put a set with the
same ratio in the TH350, its easier before it goes in the car. There are 2 style
short tail pieces, one for thumb size speedo gears, and one for TH400 size
(driven is the same, drive has a smaller hole for the TH350 drive shaft). Better
yet if the speedo is wrong, note the error and make an adjustment at this time.

When I got a TH350, I tried to get the mechanical kickdown with it. A bracket
for the top end isn't hard to make. Finally got rid of them, only TH400s here.
Bruce Roe

 

Hey golfnstuff, I agree with everything Bruce said. I put a turbo350 in my 68 GS350. Everything transfers over just fine. You didn't say if you had a shifter on the column or the floor. Mine was in the floor. It barely would "shift and hold" 1st gear. I never hooked the down shift cable up. The speedometer gears must have luckily been the right one because it was pretty accurate. Eventually my shifter broke. So I massaged a B&M shifter to fit in the PRNDL slot on the console. Works great and now I can manually downshift. Welcome to the V8 forum. Where are you located?

 

My method would be to use a TH350 kickdown cable setup connecting to the
carb, those were pretty common. The one to the gas pedal harder to get done.
Bruce Roe

 

Thanks for the replies. I am in Southern California. My 68 is a column shift. I a few years ago before I really knew what I was getting into, I found a 69 speedometer console for a three speed and it fit perfect in the dash, just silver instead of black, so I will have D L L.

Besides the bracket to hold the kickdown cable on the intake, do I need to buy or fabricate an addition bracket to the throttle assembly on the carb?

I do appreciate the help.

 

Try seeing what you can find at the junk yard. The Buick setup looks like another
hole, square, needs to be in the firewall, unless you already have it, currently
plugged. Any cable connected to the same type carb you have should be a direct
bolt on. Bruce Roe

 

Thanks all for the replies. I will try and post some before and after picks however it gets set up...