472 and 425 tranny differences

[ardisorn]

I'm going to swap a 472 into my down sizing 78 fleetwood.
I have a few question about tranny.
As I know both 472 and 425 will come with THM400 tranny (for RWD)
But the THM400 that come with 472 (from a 74 fleetwood) look obviously longer than the one in my car.
At first I thought that i will use my old tranny.
But i just wondering if there are different version of THM400 in 472 and 425.
Should i use my old tranny or use the one that come with a 472?
Anybody have a clue about this?

[BRUCE ROE]

The 472 trans would be best, because its set up for the bigger engine, but it has a 9" tail section. A 4" tail section can be swapped in, by completely dis assembling the trans. Otherwise, the 2 transmissions are interchangeable. Bruce Roe

CLC advisro # 14630

[cadillac_al]

The 400's are all the same on the inside. It will be easier for you to use the 78 trans since it is already the correct length. I have some long shaft trannys around my shop that I plan to use someday and I plan to find a shorter driveshaft to make it work.

[BRUCE ROE]

The parts inside most TH400s interchange, but aren't quite identical. A 425 engine likely has the weak 9 element sprag instead of the stronger 16 element with a 472, and fewer direct clutch plates. The plastic spring guide in the later may be curling up, but not the earlier aluminum guide. I have a description of some of the best (or NOT) internals on PHOTOBUCKET (search user bcroe), or email bcroe@juno.com for a direct link. Bruce Roe

[ardisorn]

Thank you for your information.
Anyway, Does it need to be total disassembly or can I just swaping the tail section?
I just don't want to disassembly it unless it need to be repair.
Do you think if I shorten the drive shaft and use The TH400 from 472, would this be OK?
Thanks,

[BRUCE ROE]

You must completely disassemble a TH400 to change the output shaft. At this age it could use new rubber piston seals, even if not worn much. Using the long tail means moving the trans support back, as well as shortening the drive shaft, check your frame. See differences between years at album BUILD A SWITCH PITCH, even though yours isn't SWP, at:

http://s93.photobucket.com/albums/l71/bcroe/
(that is a lower case "L"71, not an upper case "i"71)

[ardisorn]

Thanks BRUCE ROE
I just wondering that what is SWP?
Is it like a torque converter lock up?

[BRUCE ROE]

Many TH400s built before 1968 were SWitch Pitch. The beauty of a SWP is ability to give a little more performance, a little more smoothness, and a touch more economy. Only the torque converter is different, with ability to change between high stall (performance) and low stall (economy) to improve driveability. It reduced my 0-60 by 10%, and brought complements on how smooth the car was. Its just a little like a lockup torque converter.
Bruce Roe

[ardisorn]

Thanks BRUCE ROE

That's great! I love it.
Do you have some more information about how it work.

If I have a non SWP TH-400, Can I just replace the torque converter with a SWP one.
Or does it need the other parts too.
Just wonder why GM drop this beautiful feature since 1968. Is it kind of cost reduction?

Cheers, Art

[BRUCE ROE]

Art, Yes it was cost cutting; in 68 472 & 455 engines came out to compensate. You need a different front pump, converter, stator passage oil restrictor, another wire, & some means to control it. Send me email & I'll forward more info & links. bcroe@juno.com Bruce Roe Cad-Lasalle #14630