TH350 to TH400 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

ramz · 10-07-2011, 07:42 PM

I'm looking to switch the tranny from a TH350 (3 speed) to a TH400. Has anyone done this before and if so any pointers? New drive shaft? ??

Thanks

**old Rusty C10** · 10-08-2011, 07:54 AM

I belivee there is a difference in the driveshaft.. as i believe that the th400 is a little longer and im not sure if the yoke fits both models ( its been a long while. Other than that youll have to re arrange the vacuum on the motor and eliminate the one going to the trans as a 400 does not have a vacuum modulator.. IIRC the kickdownn cable works the same way. Make sure you use the correct torque convertor.
I do know that most of the pickups with 400s had the long tail trans (9 inches) as opposed to the short tail (6 inches) whereas the vans had the short tails

80SPORT · 10-08-2011, 12:35 PM

Both use vacuum modulators

TH400 uses electric kickdown;you will need the switch(mounted under dash) and wiring from a th400 truck;th350 used cable

TH400 used a different yoke and in the truck app uses a 2 pc driveshaft;many trucks came with TH400 ...even small blocks w tlr pkg so your best bet is to find/buy a parts truck as you will need the extra crossmember to hang the steady brg on;if you have a car app th400 that uses a slip yoke rather than the truck app bolt on yoke you could use your original driveshaft but you would need to modify length to fit

KQQL IT · 10-08-2011, 01:09 PM

A one piece works just fine,
The X-member needs moved back also, the holes are already there.
A slip yoke will work on either tailshaft.

10-07-2011, 07:42 PM	#1
ramz Registered User Join Date: Jul 2011 Location: Dallas, TX Posts: 205	TH350 to TH400 I'm looking to switch the tranny from a TH350 (3 speed) to a TH400. Has anyone done this before and if so any pointers? New drive shaft? ?? Thanks

10-08-2011, 07:54 AM	#2
old Rusty C10 Robert Olson Transport Join Date: Oct 2002 Location: recent transplant to NC USA Posts: 20,345	Re: TH350 to TH400 I belivee there is a difference in the driveshaft.. as i believe that the th400 is a little longer and im not sure if the yoke fits both models ( its been a long while. Other than that youll have to re arrange the vacuum on the motor and eliminate the one going to the trans as a 400 does not have a vacuum modulator.. IIRC the kickdownn cable works the same way. Make sure you use the correct torque convertor. I do know that most of the pickups with 400s had the long tail trans (9 inches) as opposed to the short tail (6 inches) whereas the vans had the short tails __________________ Bob 1951 International running on a squarebody chassis "If a man's worth is judged by the people he associates himself with, then i am the richest man in the world knowing some of the fine people of this board" http://67-72chevytrucks.com/vboard/a...t.php?f=25&a=9 (you can review the site rules here!) PM Me for your vehicle/parts hauling needs in the North East US or see my Facebook page Robert Olson Transport Live each day to the fullest.. you never know when fate is going to pull the rug out from under you... I hate cancer!!

10-08-2011, 12:35 PM	#3
80SPORT Registered User Join Date: Mar 2008 Location: red deer alberta Posts: 777	Re: TH350 to TH400 Both use vacuum modulators TH400 uses electric kickdown;you will need the switch(mounted under dash) and wiring from a th400 truck;th350 used cable TH400 used a different yoke and in the truck app uses a 2 pc driveshaft;many trucks came with TH400 ...even small blocks w tlr pkg so your best bet is to find/buy a parts truck as you will need the extra crossmember to hang the steady brg on;if you have a car app th400 that uses a slip yoke rather than the truck app bolt on yoke you could use your original driveshaft but you would need to modify length to fit

10-08-2011, 01:09 PM	#4
KQQL IT At the body shop. Join Date: Aug 2009 Location: Land of fruits and nuts. Posts: 5,316	Re: TH350 to TH400 A one piece works just fine, The X-member needs moved back also, the holes are already there. A slip yoke will work on either tailshaft. __________________ " That didnt make it any newer " " Dont antique the equipment "



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