Th350 vs th400 swap from st300

Kingadri

Newbie
So I've removed the st300 from my 68 skylark, now I've come down to swapping it out for either a th350 or th400 , this car has an inline six in it already, I'd just like to use it as a nice cruiser. Also does anyone know the driveshaft length I will need for the swap , thank you.
 
Th350 fits directly in place of the St300. No change in mounting, driveshaft or driveshaft length. The Th400 requires shortening the driveshaft by about 5/8”, a 400 mount, a different yoke and moving the crossmember back.


Sent from my iPhone using Tapatalk
 
Since you have a six cylinder, the turbo 350 will handle all the power plus the turbo 350 is lighter and more fuel efficient.
 
The TH400 would be overkill and not worth the effort for your application. TH350 is plenty stout...good luck with the swap.
 
You may want to consider a 2004R instead of the TH350. It is a close ratio transmission with a lock-up converter and overdrive. I put one in my ‘68 Skylark. Everything fit well, same driveshaft length but had to move the crossmember back to the TH400 position. The holes are already there. It is a metric transmission so be aware of the tail shaft mount bolts and the nut on the shifter linkage.
 
You may want to consider a 2004R instead of the TH350. It is a close ratio transmission with a lock-up converter and overdrive. I put one in my ‘68 Skylark. Everything fit well, same driveshaft length but had to move the crossmember back to the TH400 position. The holes are already there. It is a metric transmission so be aware of the tail shaft mount bolts and the nut on the shifter linkage.
Hey

what did you use for the lockup
 
TCI makes a kit. It requires some minor rewiring inside the transmission. It blocks out the lock-up except when you are in 4th gear with highish manifold vacuum and provides for a kick out when you tap the brakes. My Skylark does not have cruise so I used a double pole brake light switch to do that. The vacuum switch took some fiddling to get it dialed in but has worked well since. I found some pics I took when I wired the transmission.
 

Attachments

  • IMG_0097.jpeg
    IMG_0097.jpeg
    512.7 KB · Views: 6
  • IMG_0080.jpeg
    IMG_0080.jpeg
    565.1 KB · Views: 6
  • IMG_0046.jpeg
    IMG_0046.jpeg
    347.6 KB · Views: 6
  • IMG_0030.jpeg
    IMG_0030.jpeg
    332.8 KB · Views: 6
Last edited:
Just another note as if you weren't convinced of the impractacality of the turbo 400 already. When I changed over my 69 Cutlass from the jetaway 2 speed (same transmission as the ST300) to a Turbo 400 (I had a V8) I had to replace the parking brake cable that ran from the pedal to the shoe cables for reasons I don't remember. It was not an easy or pleasant job to do and seeing as it was 30+ years ago I wouldn't be able to do it today.
 
Back
Top