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I had mentioned some time back that once we got this '74 in running shape (I didn't put the drive train in it), I was really surprised to find that this tranny only has two forward positions on the shifter and only shifts once - from low to drive - in other words - a powerglide. It otherwise seems to run and shift fine.
When I posted about it on this site, someone surmised that the builder may have put that in for racing purposes (which wouldn't surprise me). Anyway, I was likewise surprised when I looked at the pan and it's stamped "hydromatic." So I snapped a photo and am sharing it below. Guess I always thought a GM hydromatic was a 3-speed. I don't see any other ID numbers on it to share.
So was wondering what current thoughts any of you might have on it. Thanks in advance!!
Yep, its a TH400 and it'll make 2 upshifts because it starts out in 1st gear. The 1st upshift being 2nd gear and the 2nd upshift being 3rd gear. In some transmissions putting it into 2nd it'll start off in 2nd but I don't remember if the TH400's will do that. It was for better traction control in sand or snow.
Last edited by toobroketoretire; Aug 6, 2015 at 12:49 AM.
Thanks for your response . . . guessing you can confirm the TH400 by looking at the pan?? However if it IS a TH400, how come there are only two detents/positions on the shifter behind neutral instead of three? (and it still seems to only shift just ONE time when driving).
as for the shifting, maybe check the linkages for propper throw.
disconnect the cable at the trans and move the shifter to check movement.
drain and drop the pan and check the detent positions when shifter moved.
does it have the std corvette shifter still or some aftermarket unit?
has it had a manual valve body installed for racing?
Thanks for your response . . . guessing you can confirm the TH400 by looking at the pan?? However if it IS a TH400, how come there are only two detents/positions on the shifter behind neutral instead of three? (and it still seems to only shift just ONE time when driving).
as for the shifting, maybe check the linkages for propper throw.
disconnect the cable at the trans and move the shifter to check movement.
drain and drop the pan and check the detent positions when shifter moved.
does it have the std corvette shifter still or some aftermarket unit?
has it had a manual valve body installed for racing?
just random thoughts.....
Although initially doubtful that the linkage could be holding us up, I did go ahead and disconnect it at the tranny, and sure enough, there ARE three detents "south of neutral". I then moved the stock shifter to the rear of the car as far as it would go (s/b low gear), and then checked at the tranny to see if the cable would line up with the actual tranny shifter would line up - and it would not. It's about 1/2" shy of lining up. So how do I adjust/extend the cable length. PLEASE don't tell me I need to take the console apart again :-(
And yes, the shifter plate does show three gear positions - that's why I was confused to begin with.
Can't tell by your photo, but the lock-out cable is to the front and
the shifter cable is to the rear. This the the cable connected on my
73 TH400. Hope it helps.
'74 Auto Trans Identification
