General Discussion > Buick Interchange
1965 gran sport 400 tranny upgrade
Robin Cook:
What is required to upgrade stock th300 to a 65 th400? My first roadblock was stock floor shifter does not fit!
WkillGS:
Shiftworks has a cable operated kit to adapt the stock 2 speed shifter to the 3 speed ST400.
The 400 trans is longer, so you will need to add some brackets to the frame to mount the crossmember to. The extra length will also require a shorter driveshaft. The smaller ST300 converter will fit the ST400. Some big-car flexplates are only drilled for the big converters, but most have the dual pattern by 1966.
Trans cooler lines need to be changed too.
Dr Frankenbuick:
Also, the 400 has a larger yoke and the trans mount is different. You can modify the mount to work or get one for a 400.
GreatScat1965:
A stock 1967 shifter will work if you can find one. Minor floor cutting would be required.
GreatScat1965:
A 67 PRNDL will fit as well
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