A 401 has a bore of 4.1875 which equals 4 3/16ths. A 425 has a bore of 4.3125 which equals 4 5/16ths.
When I got my 65 GS already had the wrong 66 401 so I found a 64 425 with tranny from a Riviera to rebuild. Is there any difference between the years of the 425s?
the 1963 425 will have a crank setup for a dynaflow transmission. you can swap cranks or get an adapter assy
The engine will work but just so you know, the '64 ST400 is a one year only the first year it was built its different than all the newer versions of that trans. The shifter is weird it had only 2 forward gear selections but it is a 3 speed! To get it in first gear there's a certain way you have to shift it back and forth IIRC? In the Riv it came out of the shifter selector for the forward gears would of been D L in that order I think? Maybe Tom T. can chime in, he forgot more about that trans than I ever knew or will know! Anyway, seeing how it has the same amount of shiftable gears in it as the car its going in will have at least that will be an easy install for your car, shifter wise anyway.
Thanks 300sbb I’ve been running the 425 for awhile with the ST300. Recently picked up BS code ST400 in the process of gathering parts for the swap.
I believe in the 64 if you banged the shifter hard into low you would get first gear. It’s been more than a few years though since I’ve had that car. Cliff
In senior series cars with the 400 (at least in 1964), if you start from a start with the shift lever in "L" and hold it until the car won't go any faster, slam the shift lever into "D" and then immediately back into "L", the car will hit second and chirp the rear tires. So I've been told. Also, if you are above 20 mph and move shift lever to "L", the transmission will go into second gear. Keep in "L" and as soon as the vehicle speed reaches 20 mph, the transmission will move to 1st gear. Again, so I've been told....
Tom Telesco did my 425 and I assume that he had the block checked fore core shift. In any event, it has always run great (since he rebuilt it - it ran crappy after it's first rebuild by someone else). I love the engine.
That's mostly right! Start in (1st) Low, move to 'D' to shift into second gear then back to 'L' to keep it in second. Then shift to 'D' to shift into third. This did cause a hard 1-2 shift, which was fun! No idea if was good/bad for the trans. Downshifting from 3 to 2 was fine, but you couldn't control exactly when it would downshift into 1st. The '64 ST400 did NOT have the switch pitch converter, it had a fixed stall. IMO that's the biggest downside to this trans.
The fixed stall isn't an issue anymore with the new converter technology that is available now. They changed the trans because when people's teenagers drove the cars with that trans, they soon figured out when it was in first gear it would stay there until it was shifted out of 1st! I can imagine there were a lot of engine warranties happening with that trans.
That is true Derek. Lots of warranty repairs on Monday mornings for Buick & Cadillac. My original trans. with converter stalls at approx. 2K RPM's.
Well Walt, I'm pretty sure it did not increase the life of the transmission but my grandmothers 64 Electra won many races abusing the transmission that way. I think it scared the other car more than physically out performing them! Most had never seen a green giant boat of a car bark the tires (with posi no less). Scared them enough that they lifted the throttle! Like I said, no idea of the RPM just that it wouldn't go any faster (Tach? Who needs a Tach!!). My 401 held together in the hands of a 16 year old for many miles. Tough old bird... With mine, if you were in 3rd gear and pulled it down to low, it would downshift to second. Just leave it in low and at 20 mph it would drop to 1st all by itself.
401 - forged crank . 425 - cast crank Correct ? And someone mentioned that they were swappable . I've always liked the 401's . Had a couple . Tough motor .
