I'm not sure which transmission is in my car but it is a 3 speed automatic. I had to shorten my driveshaft because it was jammed up against the tail housing of the transmission. Prior to shortening the driveshaft I measured it and it was at factory stock specs. It is now 1 1/2" shorter than original. Could it be that the tail housing on my transmission is incorrect? How do I identify what I have? I read a post where George said that if the transmission tail shaft is too long it messes up the harmonics. I am in the process of chasing a high speed vibration (above 65 mph) and am wondering if this could be the source. 1971 Skylark Custom Convertible. 350/4 bbl.
The TH350 has 5 sides, (looks like a square with a corner cut off). TheTH400 is very odd shaped. Both have 13 bolts. http://www.truckforum.org/attachments/trans-reference-jpg.5395/
I believe that the universal one just has extra holes in the bell housing to fit a Chevy, I'm not sure if the oil pan is different. As far as the length being different that could be possible.
I'm going to have to get under there and take a look at the pan. Comparing overall dimensions between the BOP 350 and the Universal 350 there is minimal difference. Now I'm wondering if it isn't a TH400 which is 2 inches longer. There's only one way to find out! Thanks for your help with identifying these transmissions! Lee
The THM 350 came with different length tail shafts. Measure the extension housing on yours. The vacuum modulator comes out the back of the trans on a 350, it comes out the passenger side on a 400. The governor is behind a round cover on the driver's side on a 350, it's behind a square cover with 4 bolts on the passenger side of the 400.
I'm pretty sure, from your description of the round governor cover on the driver's side, that I have a 350. How long should the tail shaft be on a 71 Skylark? Apparently mine is too long.
Measure the extension housing. I believe the lengths were 6 1/4", 9 1/4", and 12 1/4". Pretty sure it should be the short one.
The T400 would use a large diameter slip yoke(1 7/8") going into the trans while the T350 uses a smaller slip joint(1.5"). A 350 Skylark would normally come with a T350 with the shortest tail housing. Obviously there is a 3" difference between housings so that doesn't seem to indicate a problem there. I don't know how your car would have been drivable if you needed to take 1.5" off the driveshaft for it to work. It should have been slammed against the tail housing. If it did slam against the tail housing there is a good chance it is bent and you are lucky the trans didn't crack. You should have about 3/4" to 1" of slip joint showing behind the trans seal to the front of the yoke while the car is at ride height while sitting on the ground. Another possibility is the rear end was changed. I believe the corporate 8.5" rear end has a different pinion length than the earlier Buick 10 bolt. I'm not sure which is which but I'd say there is a good chance the corporate 10 bolt is longer because of the beefier pinion diameter.
