TH350 to 400
Melting Slicks
Joined: Mar 2006
Posts: 3,456
Likes: 102
From: Piedmont Va
St. Jude Donor '11-'12-'13,'19-'20
I did this change in a Pontiac years ago..lot's was different. Yoke, drive shaft length, crossmember/transmount, shifter cable...
If your gonna change it, put in OD...200R4 or 700R4..
If your gonna change it, put in OD...200R4 or 700R4..
Melting Slicks
Joined: Jul 2005
Posts: 2,545
Likes: 3
From: 406ci SB, AFR 180 Heads - 490 HP @5,600 RPM 529 lb-ft @ 4,100 RPM
The Th400 maybe stronger of the two, but is becoming obsolete with the overdrive transmission becoming more popular with strengh and reliability (200r4 or 700r4) for the same money as rebuilding a TH400.
Drifting
Joined: Jul 2002
Posts: 1,944
Likes: 20
From: The only Corvettes in Highett Victoria
don't do it!
seasond,
The T400 was the only auto trans available when they replaced the Powerglide in 1969, and there's nothing wrong with them, but when all is said and done, they're just a 3 speed auto. Plenty of drag cars with lots more hp than you run (modified) T350's without a problem, so the cheapest way out is to go to a reputable transmission rebuilder and have a rebuild done on yours with a shift kit and stronger clutches etc. But you're still stuck with a 3 speed and no fuel saving lock up converter.
Take the advice of the other two and put in a 4 speed. If you fit a T400, you will have to modify your trans mount, as the mounts are in a different location, the tail shaft is a different length and I think the yoke's different. You would have to do all of the above if you fit a T700 or 200, but would have four speeds, including a petrol saving O/D fourth gear.
In other words, there would be little if no difference in cost between fitting a T400 or T700/200, but with the latter you will have a 4 speed O/D trans with a lock up converter.
Regards from Down Under
aussiejohn
The T400 was the only auto trans available when they replaced the Powerglide in 1969, and there's nothing wrong with them, but when all is said and done, they're just a 3 speed auto. Plenty of drag cars with lots more hp than you run (modified) T350's without a problem, so the cheapest way out is to go to a reputable transmission rebuilder and have a rebuild done on yours with a shift kit and stronger clutches etc. But you're still stuck with a 3 speed and no fuel saving lock up converter.
Take the advice of the other two and put in a 4 speed. If you fit a T400, you will have to modify your trans mount, as the mounts are in a different location, the tail shaft is a different length and I think the yoke's different. You would have to do all of the above if you fit a T700 or 200, but would have four speeds, including a petrol saving O/D fourth gear.
In other words, there would be little if no difference in cost between fitting a T400 or T700/200, but with the latter you will have a 4 speed O/D trans with a lock up converter.
Regards from Down Under
aussiejohn
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I had a Turbo 350 in a 70 Chevelle with a 427 putting out almost 500 hp. It handled it with no problems. I wouldn't waste the time or money on the change. I would just make sure the TH350 was in good shape. Maybe put a shift kit in it if it needs a rebuild.
NCM Grand Opening Veteran
Joined: Sep 2005
Posts: 20,979
Likes: 384
From: South of giving a damn
St. Jude Donor '11, '17
IMO there are only 2 reasons to go to a 4-speed auto, either you drive your car a lot and will be able to recoup the switchover price in a reasonable amount of time or you are wanting to run a real stiff rearend gear. Any other reason falls under 'cause I wanted to', which is a fine reason, but not an overriding one.
