72GoldOlds350

Hello,

I currently have a TH350 in my 1972 Cutlass, and Mark R just built me a stout SBO 350, and I'm installing a TH400 to go with it. So far, I've only purchased the new trans mount and new parking brake cables, but is there anything else I'd need to make the installation work? Any other oem-style cabling, brackets, etc.?

Much appreciated!

matt69olds

The transmission yoke is different, the TH400 uses an electric kick down solenoid. I think all the 68-72 A-body cars have the wiring already under the dash, you need the switch, mounting bracket, and add the wire to the existing engine harness under hood. The dipstick and trans fill tubes are different, the vacuum modulator is in a different location. That’s all the differences I can think of.

69 Hurst

Its been a while since I did this conversion myself. If I remember correctly, the "pad" on the cross member for the trans mount needs to be cut off the front side and welded to the back side if going from a TH350 to TH400. This will not be an issue if you are replacing your existing cross member with one from a TH400 car.

oldcutlass

A drive shaft and a new yoke. The xmember is the same it just needs to be moved back a couple of holes.

72GoldOlds350

Thanks, everyone! Yes, I have a new driveshalf being made once the engine and trans is installed.

So far I have:

-kick down solenoid
-switch
-mounting bracket

69 Hurst

Ah, I did the conversion on a '78 Trans Am. We did not have the option of using other holes as there weren't any.

72GoldOlds350

Hello all,

below is a screenshot of the itemized parts list - I think I have them all. Let me know if I'm forgetting anything!

svnt442

You don't need to do anything with your crossmember except to move it back. They are the same for all transmissions in the 68-72 A bodies.

droptopron

On my 70 I had to cut the tab off the gas pedal that the Turbo 350 kickdown cable connected to. It interfered with the switch. On my car the wiring was already part of the harness. I just hooked it up.

http://www.buickperformanceclub.com/conversi.htm

72GoldOlds350

I've heard this before, but then others (see below) say they had to alter the crossmember. I guess I could always find out and order the part if I indeed need it.

Also, even if the stock crossmember does work, considering the new amounts of power the engine is going to produce, is that aftermarket crossmember any stronger?

Thanks for the link! I wonder if that is the same for Olds.

oldcutlass

You can modify your old modulator line to work on the T400 and as stated above you just need to move your current cross member back a bit.

72GoldOlds350

Is the aftermarket crossmember any stronger that stock?

matt69olds

I’m sure the boxed crossmember is stronger than stock, they are also much heavier. The G-Force crossmember I used in my 87 442 years ago was a beast.

svnt442

You're not putting down enough power to worry about it. You'll crack the transmission case before you hurt the crossmember.

matt69olds

I don’t think the trans crossmember is ever really under serious stress. I’m guessing chassis flex would be a issue long before the trans crossmember causes problems

72GoldOlds350

Any other parts I may need that are not listen on the parts list I supplied? Just hope I'm not missing anything.

72GoldOlds350

I'll take that as a negative. I do appreciate all the help, everyone! Love the community on this site. I'll keep everyone posted if I run into anything specific or if there's any updates.

joe_padavano

There is no difference in factory crossmembers from TH350 to TH400. Use your old one. And yes, the accelerator pedal for a TH350 needs to have the tab cut off.