Topic: HYDROMATIC GUYS...what do I have, Thanks!!
in Forum: C3 Driveline Components
Already a Member?
Click Here to Login
Not yet a Member?
Click Here to Register for Free!
Former Member
Send PM
Easthampton, MA - USA
Joined: 5/27/2007
Posts: 114
Vette(s): 1970 corvette conv, 350 auto.
Well Guy's...and Gal's, looks like my engine #'s match the VIN, but, The tranny is not the correct one. Runs great and seam's to shift nice and crisp, so , I realy cant complain...BUT....I realy what to know if it is even the correct type of transmission...and if the gearing would be diffrent than it is supposed to be. SO...looking to find out the following if possible, and I took some pictures that I hope will help.
1) is it in fact a THM400 like it is supposed to have, or something else
2) if it is...or is not a 400, is the gearing difrent and going to make issues for the drivetrain
3)the following #'s are on the tag...can anyone tell me what vehicle the tranny is from....and how it would be diffrent from the one that is supposed to be in there 75P480 75CP 40309
Thanks for your help...then I think I will stop searching out #'s and torchuring myself!!

SPONSOR AD:: (Our Sponsors help support C3VR)
Former Member
Send PM
Easthampton, MA - USA
Joined: 5/27/2007
Posts: 114
Vette(s): 1970 corvette conv, 350 auto.
Former Member
Send PM
Easthampton, MA - USA
Joined: 5/27/2007
Posts: 114
Vette(s): 1970 corvette conv, 350 auto.
If you have a fairly square pan with a corner cut off, it's a THM350. If it's a rectangle with notches in two corners, it's a THM400
The 400 uses a 2.5:1 first gear ratio
The 350 uses a 2.75:1 first gear
I don't have a book for the numbers. Someone??

Moderator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20219
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
I consolidated three threads into this one.
It is a 400 trans.
Adams' Apple 2008-06-21 18:44:31

It is a 400 trans.

Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
Former Member
Send PM
Easthampton, MA - USA
Joined: 5/27/2007
Posts: 114
Vette(s): 1970 corvette conv, 350 auto.
Thanks KSTYER, and Joel...sorry I made it a couple posts..........GLAD AT LEAST IT IS A THM400......little bit of seapage around gasket so I am gonna change the gasket and filter. The parts where ordered as for a 1970...will they fit if tranny is a '75 


Moderator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20219
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
All 400s are the same...there are no differences in anything but the calibrations of the valve body, and a (very)few internal parts differences. As long as you order/request parts for a 400, they'll work just fine.


Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
in Forum: C3 Driveline Components
SPONSOR AD: (Our Sponsors help support C3VR)