65 LeSabre 455/ST400 swap possible?

[mcdermott716]

I am currently rebuilding a 65 LeSabre Convertible with the 400 package (ST400 and 300 CI w/ 4 barrel) but was wondering if it is possible to mount a 455 from a 70-72 riviera to the Switchpitch 400 currently residing in the car. I am hearing multiple answers saying it is possible cause of the BOP bolt pattern on the ST400 but others are saying not wtih that year tranny. Can any1 validate these rumors cause I want to stay Buick/ Buick combo and the 300 is harder to find parts for than the 455 and theres no replacement for displacement. :Brow:

[tomthacher]

I believe that the trans from 64 to 76 have the same bolt patern. I am not sure about the flex plate but think they are the same also. I think the st400 is a great and durable trans but the t400 has more direct power to the wheels. The other problem you will encounter is the crossmember and motor mounts. I put the 455 into A body(skylark) with motormount transition pads purchased from Poston Enterprises. I think your LeSabre has the same location holes. Good luck.

[DaWildcat]

We need to hear from the experts regarding the bellhousing bolt patterns on the 300 engine. if it's BOP you're in good shape, but if it has the nailhead bolt pattern, no go.

Regarding the differences between the ST400 and TH400, there are few from a durability standpoint, other than the case ring added in the later transmissions for the center support.

I don't understand the "more direct power to the wheels" thing, they both have the same gear ratios and in general have most design features and parts in common. My 400 trans is a hodge-podge of parts, using a later case with 1967 variable pitch parts.


Devon

[buickbeast]

ive worked on transmissions since i was 14 years old.though i havent worked on too many older ones except the 4 speed hydro the powerglide cast iron and aluminum the turboglide the powerglide the cast iron torqueflight and the fordomatic,fmx.most 400 ive worked one were later model but i do know most older gm cars tend to have odd bolt patters usually specific to the brand.in the 60's every branch of gm made their own engines unlike now where they all share the same drive and power trains.


best bet would be to get an alder car guy whos dealt with alot of older cars or to measure the bolt patter yourself to see if it matches.the tranny belousing shouldnt matter at all on the year but by the engine used.as far as ive seen most gm models use the same flywheel to torque converter bolt pattern but i may be wrong.


you can see if it fits but if you have the funds youd be better off with a th400

[SpecialWagon65]

Simple: the 300 and 455 share bellhousing pattern. 455 will bolt right on to the LeSabre 400 trans.
the thing to figure out is if you have enough room in the front of the engine compartment. I would guess(??!!) it will fit, since the 455 fits in a 65 Skylark engine compartment just fine.