Installed 455 with th400 into '66 Lemans convertible. (originally had 326 w/st300). Used original motor mounts, and location is perfect. Used original shift cable and bracket, re-drilled bracket at transmission- detents at shifter still line up-will even go into first if you press the button on shifter. Installed th400 yoke onto original driveshaft. Fit like a glove. Installed driveshaft (previously shortened 5/8") onto short output on trans., there is 3/4" between output and shoulder of yoke, (should be o.k., yes?). Only real problem seems to be the crossmember to frame mounts. Installed center bolts on trans. to crossmember, and mounting holes are 6 1/4" away on both sides from frame mount holes. Am I relegated to having to weld the frame mounts to the new location, or is it possible to use a piece of say, 1/4" plate steel on either side and use the existing holes to attach, to make up the difference? Or, is there a different crossmember I can use? I'm pretty excited about this, and need to go CRUISING SOON,!!!!!!!!!! (or I shall surely perish). THANKS!!!!!
The '67 GTO was the only A body Pontiac to use the TH400 trans. And '67 was the first year. The transmission cross member and its location is unique. A '67 GTO cross member is pretty tough to find, and even then, your mounting holes on the frame will be off, as you discovered. To convert your '66, you will need to fab up your own mounting system, or fab up a custom cross member. It's about the only PITA part of the entire conversion.
I forgot to mention, the '67 GTO CONVERTIBLE cross member is entirely different from the hardtop and post cars. Very rare, as it's a one-year, one-model application.
Thanks geeteeohguy, I pretty much assumed that was the answer. I really hate to butcher up a beautiful original piece like that crossmember (it made me kind of ill to bend & drill that little shift bracket at the transmission pan, as it was in excellent shape. But it works). Do you have any ideas as to whether or not my plate steel method will work? From frame brackets to crossmember, I'll use a piece of steel 3" wide x 9 1/4 long, line up the holes and bolt it together with case hardened bolts & washers. Then maybe weld an angle iron under that at the frame. Also, is that 3/4" clearance at the yoke to tailpiece o.k.? Cranked the 455 up today- SMOOTH AS SILK !!! I'm getting pretty antsy to drive 'er.
I'm no engineer, but I know that whenever you divert a load from the straight line, the support system must be much stronger....a straight span is much stiffer/stronger than a U-shaped one. You'd be putting all the load on the bottm of the "U", and it would want to bend and sag. I think the best plan would be to bite the bullet and drill mounting holes in the frame where they need to be and do a straight forward install. Realistically, it's never going back to stock.
Rule of thumb for yoke insertion insert fully in than back it out 1" . That allows for travel for rear to move with suspension . Also rule of thumb for drive-shaft measurement as well .
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