Th400 Question For Joe Lucia

[Brad H.]

Hi Joe,
Any idea if a 69 CY code THM400 will fit a 69 350/300 auto car? Were there any external differences or is the CY just a heavier duty internal model for BB engines?
Thanks so much for your thoughts!
Brad

[Joe L.]

Re: Th400 Question For Joe Lucia

Hi Joe,
Any idea if a 69 CY code THM400 will fit a 69 350/300 auto car? Were there any external differences or is the CY just a heavier duty internal model for BB engines?
Thanks so much for your thoughts!
Brad

Brad------

A "CY" coded 1969 THM-400 will fit a 1969 350/300 application with no fitment problems, at all. However, the operational characteristics of the transmission might not be well-suited to the 350/300 application.

A "CY" coded THM-400 is a very rare bird. It was used in other applications besides Corvette but those applications are not too likely to produce many donors (i.e. 1969 passenger cars, Chevelles and Camaros with SHP, mechanical lifter big blocks). Have you located such a transmission for sale?

[Terry M.]

Re: Th400 Question For Joe Lucia

Joe,
Won't he need a different flywheel? The CY has six mounting ears on the torque converter, and the standard torque converter has only three mounting ears. I suppose, however, one could use the standard flywheel and only three of the six torque convertor ears since the 300 hp engine will barely register on the CY trans power scale.

As for other CY applications: I once owned a 1967 GMC 3/4 -ton pick up with a V6 that had, I think, a CY trans in it. That thing was a beast.

[Joe L.]

Re: Th400 Question For Joe Lucia

Joe,
Won't he need a different flywheel? The CY has six mounting ears on the torque converter, and the standard torque converter has only three mounting ears. I suppose, however, one could use the standard flywheel and only three of the six torque convertor ears since the 300 hp engine will barely register on the CY trans power scale.

As for other CY applications: I once owned a 1967 GMC 3/4 -ton pick up with a V6 that had, I think, a CY trans in it. That thing was a beast.

Terry------


Some original flexplates will have provisions for 3 or 6 converter attachment bolts. If not, he could either just use 3 attachment bolts or obtain a new flexplate. I would highly recommend doing the latter. Virtually all, if not all, currently available flexplates for the THM-400 application have 6 converter bolt attachment holes. These things are quite inexpensive---about 50 bucks, or so.

As far as the 1967 GMC pick-up goes, if it had a "CY" coded transmission, I think some previous owner must have installed it. I can't find that the "CY" code was used prior to the 1969 model year.

[Clem Z.]

Re: Th400 Question For Joe Lucia

the only thing we ever changed when using a THM 400 between a SBC and a BBC was the torque converter and the governor

[Brad H.]

Re: Th400 Question For Joe Lucia

Joe and all,
Thanks for the input. I am going to look a some 69 THM40s and the guy really does not know what he has other than they are 69 models...we'll see. I didn't realize the CY was so rare. I thought that if I got there and he had no CK 400s I might snag a CY if he had that. After this information, I'm sure that isn't the case. I really appreciate everyone's input. If I run across a CY, I'll post it.
Thanks again,
Brad

[Clem Z.]

Re: Th400 Question For Joe Lucia

here is a website about the THM 400. http://www.chevellestuff.com/qd/th400.htm

[Terry M.]

Re: Th400 Question For Joe Lucia

Terry------
As far as the 1967 GMC pick-up goes, if it had a "CY" coded transmission, I think some previous owner must have installed it. I can't find that the "CY" code was used prior to the 1969 model year.

I am pretty sure the trans was original to the vehicle. I am not sure what the code was, but that sucker had a thicker case than usual, and reinforcing rods running between the pan bolts for the trans and engine. Those rods were because the engine weighed so much. That engine was a monster. When I overhauled it the ring package was the same as that for a 427 -- just two less cylinders. I think the coolant capacity was on the order of six gallons. I just couldn't keep the tin worm in check.

[Clem Z.]

Re: Th400 Question For Joe Lucia

looks like i had a CJ model behind my 482 cu in BBC i had installed in my pick up because it was the original 396 pick up trans. i had no trouble with the trans and it was abused.