[ryan389]

HI
I HAVE A 64 LEMANS CONV. WITH A 73 400 GRAND PRIX MOTOR.
I JUST BOUGHT A 73 TURBO 400 TRANS, IM RUNNING A STOCK REAR (308 POSI)
WHAT MODIFICATION DO I HAVE TO DO TO MAKE THIS WORK, ID LIKE TO KEEP THE AUTOMATIC ON THE COLUMN.
TRANS CROSS MEMBER, U JOINT SIZE, ETC.
THANKS!!

[Tom Vaught]

If you use the early Pontiac Frame Mounts and early engine mounts that will bolt to the 5 bolt boss block you can drop the engine right in the 64 chassis. I have done the same with a 70 455 block and those mounts.

The turbo 400 trans will work in the 64 chassis with little effort. A friend had one in his 64 GTO. 308 Posi is fine if you are not drag racing and do not put a sticky tire on the back. It will love the 3.08 gear. You probably will have to move the trans cross-member backwards so that the Turbo 400 trans mount is in the right spot.

I run a Doug Nash 5 speed with the trans mount in the same spot as a 1967 GTO with a Turbo 400 trans. I have a convertible too. What I did was cut the frame mounts for the Trans crossmember right in the middle of the frame mount and reweld the back portion a couple of inches rearward. This lets you now add a piece of metal on top of crossmember frame mount (1/8" thick is fine) and tie the two frame mount pieces back together again.
Then you mount the engine and trans (and the trans crossmember and find out where the new biscuit retention brackets need to be and drill the holes. Now the installation will look totally stock and you could go back to a different trans: Turbo 350 or a 4 speed Muncie, as well as the factory 64 auto trans if you wanted to.

Hope this helps Ryan. Have done all of the steps you need to have done.

Tom V.

[b-man]

The transmission crossmember needs to be moved back by 6" to accommodate the TH400.

You're going to have to either move/modify the mounting brackets on the frame (like Tom described above) so you can use the original crossmember or buy an aftermarket crossmember that's made specifically for the early convertible A-body to TH400 conversion:https://crossmembers.com/product/196...r-boxed-frame/

The factory 2-speed column shift linkage pieces will bolt right up to the TH400. You won't be able to manually select low gear, but other than that it works fine with no mods whatsoever.

The trans cooling lines and fittings from the 2-speed also directly interchange with no mods.

The driveshaft typically needs to be shortened by about an inch and a TH400 yoke and appropriate U-joint will be needed. The dipstick tube from the GP should work, I used one from a '69 GP.

With all that said, it's so much easier to go with a TH350 that you should seriously consider going that route, with the car being a convertible this is really the best way to go. Everything bolts right up, crossmember can stay where it is and driveshaft bolts right up with no mods needed.

[ryan389]

THANKS GUYS!!
I WENT WITH WHAT B-MAN SUGGESTED, JUST A SIMPLER MODIFICATIONS I WANTED.
THANKS!

[Singleton]

Just as an FYI, you can save a little money, (shipping charges), on those G-Force Crossmembers by buying them from Summit Racing. The crossmembers are listed as a Summit brand, but are actually G-Force units, sold at the same price, but Summit has free shipping

[b-man]

Did you decide to go with the TH350 trans?

The cooling lines and linkage interchange on it as well.

[ryan389]

YES, I WENT WITH THE 350.
AND THANKS FOR ALL THE HELP!!
AND REALLY GLAD THE LINKAGE WORKS OUT AND THE COOLING LINES

[Tom Vaught]

Smart move with the 350 Trans and making your life easier.

The 350 Trans will work great in a Le Mans Vert.

A Co-workers Dad has a 64 Original Tri-Power 4-Speed GTO.
They swapped in a 350 Auto Trans so he could still drive the car.
He is over 75 years old now.

Tom V.