Enzo_Guy

I bought a '78 Trans Am (no, it's not black) with a Pontiac 400 motor and a TH350 transmission. I'm investigating throwing in a Doug Nash 4+3 transmission to obtain the 4-speed goodness (and to avoid the complications of a 5-speed or 6-speed swap) but still have functioning overdrive. I plan on running a relay swithc for the overdrive unit, I can turn it on for the highway but sitch it off for racing. I know that these transmissions have a bad reputation, so I am inquiring as to where I can obtain a rebuild kit that will make the transmission decent to use. What rebuild kit would you guys suggest?

c4cruiser

The 4+3 does not have a tranny mount pad like the standard Super T-10 does nor does it have any way to mount a shifter like the Super T-10. The Corvette shifter bolts to the body under the console. These two issues would have to be solved to hold up the motor in the F-body and to shift the tranny.

For a rebuild kit, contact SKSpeed in upstate New York.

You would probably be better off with a Keisler unit or a Richmond Gear 5 or 6 speed. Either one should be available as a direct bolt-in for the F-body cars.

They are pricey ($3000 and up) but will work much better in terms of fitment and no wiring hassles.

Enzo_Guy

Actually, with all of the modifcations I have to do for that Keisler unit, I might as well just get an LT1 T56. And if I'm going that far I've pretty much blown my budget wide open and I'll end paying more for the transmission than I did for the car and motor rebuild combined. By saying the tranny has no mount pad, are you saying that there is no place to hook a crossmember to the it (perhaps a picture of what you're explaining)? And I am aware of the shifter, my grandfather and uncle run a metal fabrication shop, so I'm sure they devise something to hook it up (that's also where I could get a crossmember from).

c4cruiser

Because the Corvettes use a C-beam (like the 82 and later F-bodies, there is no tranny crossmember. So yes, some fabrication would have to be done to attach a pad to the tranny case so the crossmember could be used.

Here's a pic of a 4+3 with headers. Note that the OD oil pan is right where a "typical" T-10 tailshaft with a crossmember mount would be.

You can't see it in this pic, but the C-beam mounts to the far side of the tailshaft behind the Y-connection. The shifter is above the OD oil pan on the near side.

I guess, you could fabricate a mount to the body to attach the shifter, but the Corvette shifter IMHO is nowhere near as strong as the typical Hurst Competition Plus shifter.

The 4+3 wil handle about 460 ft-lbs of torque but if you are planning mods to get the motor to 375HP or so, the OD unit may not be able to handle that power level. Callaway did use them behind their twin-turbo motors in the 87 and 88 B2P Callaway C4's but that would have been about all the OD unit could handle.

I know that Pontiac motors can generate tons of torque so that could be a factor in your tranny selection. SKSpeed can build a stout OD unit, but even a plain rebuild will run $1200 or more for the OD.

rj8806

Just to clarify something here for you, there is NO modification needed to a '78 T/A in order to get one of our TKO units in it. They fit right in the tunnel with no cutting, no beating of the tunnel, no re-location of the shifter....no nothing.


Richard
Tech Support

Enzo_Guy

Ah, you are correct, I was thinking of the '67 Chevelle. I had just been talking with my uncle last week about one of your units going in his car so we looked up on the website and found out about the driveline angle problems some people were having.:o

Also I'm not sure I'm going to be able to afford either option as the budget just got a good bit tighter for personal reasons. I think rebuilding the TH350 and installing a full manual valve body and Hurst t-handle shifter is probably going to give me the best bang-for-the-buck with this car.