Overdrive th400

[Racincc85]

I was thinking of getting a 75' vette with the Th400 tranny. I want to use it as a daily driver in the summer and don't like the idea of driving around everywhere with no overdrive killing my gas mileage and wearing the engine out faster. Is it possible to add an overdrive kit to the th400? ( i have seen this done with torqueflite 727's) I could probably just switch the tranny out to a th700r4 but i want the th400 for durability reasons as i plan on tuning the motor up to 400~500 hp.

[383PhoenixAm]

I'm not sure how well an overdrive kit would do on a Th400. I've seen people add modules of some sort to the tailshafts and get an overdrive from that. I'm not sure how it works or where they're from though.
700r4s are extremely easy to come by and should be really cheap. I'm not sure what power they are rated at in stock form, though I have seen them in stock form placed in a lot of 500+ horsepower cars. I know that modded 700r4s can be trusted with a lot more, too.
If you want to go technical go to thirdgen.org message boards and ask around the transmission/drivetrain forum. They have a sort of speciality with them.

[crxlvr]

check out www.tciauto.com or www.levelten.com they sell od kits.

[Racincc85]

I was looking around earlier and i found this http://www.transmissioncenter.net/Ge...0Overdrive.htm

I also found a company that makes a lockup converter for the th400 as well. I mostly want to stay with the th400 because it's what originally came with the vette. if i do decide to go with the 700r4, how would i go about hooking it up to the vette's 3 speed shifter and hooking up the lockup converter?

[MagicRat]

I think that a properly built 700 is a better bet. They can be modified to take the power you are planning on. They also had a lower 1st gear for more revs off the line than a 400.

Try to get a late-1986 or later version. They had internal mods which made them better than the early ones.

The lock up converter uses a simple 2 wire solinoid. You can just hook this up to a dashboard switch. Flick the switch and it locks up.
But you must remember to unlock or the engine will stall as you come to a stop.
There are simple aftermarket controllers to allow for automatic lock and unlock, depending on throttle position etc.

[Racincc85]

will the 350 engine bolt right up to the th700r4 without major modification?

[TechX]

I think a 4L80E tranny is a 400 with OD. A 700R4 has a better first gear than the 400/4L80E but not as tough for sure. You should call around and see if a junkyard wants to trade.

[383PhoenixAm]

Originally Posted by Racincc85

will the 350 engine bolt right up to the th700r4 without major modification?

Yes. A lot of th700r4s came stock mated to 350s.

[MagicRat]

Originally Posted by TechX

I think a 4L80E tranny is a 400 with OD. A 700R4 has a better first gear than the 400/4L80E but not as tough for sure. You should call around and see if a junkyard wants to trade.

Sure, but the 700 can be built to do anything you want and it's MUCH easier than adapting an aftermarket shift computer to make the 4L80E function in a non computer car.

[TechX]

Yeah it probably would be much easier. Just a thought though. :-)