Hi guys, trying to figure what this transmission is in my 1968 Skylark. I know it's not original to the car. The tag says BU-68 which leads me to believe it's from a Le Sabre 68 as per this site :Buick 400 Automatic Transmission Codes (teambuick.com). However, it's a TH375 and I can't find any info saying 68 Le Sabre came with a TH375. Before investing into a better torque converter and shift kit, I'd like to know if this is a "good" transmission or should I start shopping for a TH350 or TH400... I read conflicting things on TH-375 , is this a good transmission?
That's a THM375. the 27 spline output shaft/housing (and can be replaced) one less friction in the direct and forward clutches and a roller rather than a sprag, but you can always get a better 4L80 direct drum, 36 element sprag and piston and have more frictions/plates in the direct. And you could get a different forward piston (lower profile) and add extra friction. The Trans-Go shift kit would likely be your best bet for the valve body plate mods. There are a lot of good things (and some bad things) you can do to massage the THM375, but unless you are pushing a lot of HP, is would be fine with only the direct drum/sprag upgrades. If you do it yourself, "rollerizing" the gear train and getting the stack up clearances and end play will benefit life. It's complex, but not complicated. (lots of little details to getting everything right). Inspection, for wear, on pump/gears, and the planets/rings are also important, as well as the governor shaft bore in the case for galling or wear, and can be repaired with a bushing and reamer kit, and a new "higher shift RPM" governor can be had if yours is scored or worn.
Ron Sessions 'Turbo Hydra-Matic 400' book states the THM375 was only used in '72-76. On the underside of the tail housing it has raised, cast lettering, pretty bold, stating '375-THM'. The '2 dimple' pan above is correct for 67.5 and later.
The OP's trans may have been a rebuilt TH400 and the shop swapped the tailshaft/housing to accommodate a 27 spline driveshaft, or someone "DIY" swapped for same reason. Would explain the "68" case tag. (if the tailshaft housing is cast with the "THM375").
