At current I have a turbo 400 transmission behind my big block 455. The engine is built to Around 400 hp. I’m looking to install an overdrive transmission and was thinking of either a 700r4 or a gear vendors under an overdrive unit on my present transmission. Does anyone have any experience with these units and the pros and cons?

 

The 700R4 needs about as much internal work as the 200-4R to live behind a 455, but at least it requires more floorpan mods, crossmember movement, and a custom driveshaft. Ironically, the 4L80E is significantly stronger than a 700R4 and is a slightly easier fit in the A-body tunnel. That humongous servo wart on the passenger side of the 700R4 is what makes it a tough fit in the A-body. The 4L80E is literally a TH400 with an extra overdrive stage between the front pump and the rest of the trans (thus the longer case). Many of the internal hard parts are the same between the 4L80E and the TH400. You need the aftermarket banjo fittings for the cooler lines to simplify tunnel fit, and yeah it's still tight, but it really only requires a slight massaging with a hammer to clear.

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As joe said, either trans can be built to handle the torque of a stout engine, but those upgrades are expensive. It’s been my experience a 700R4-2004R becomes a maintenance item around 600hp, and that after all expensive parts are bought.

in my opinion, the money spent on upgrades is better spent on the controller for a 4L80. Any junkyard 4L80 on good used condition will yawn at 700hp with nothing more than a good shift kit. If your willing to go into the trans a little more than required for a shift kit, 900-1000 is no big deal.

Granted, 4L80 transmissions and converters are more expensive. But tear up a couple lesser transmissions, the repairs will far exceed the initial cost.

 

What exactly are you wanting it to do. Racing, or an occasional tire burnout on regular tires, or just easy street cruising once in a great while, or just maybe a quieter ride with better gas mileage.

 

If you are absolutely positive you won’t be adding more power, either trans will live with 400hp and the usual BBO torque, if built correctly.

The 700 has the advantage better strength straight from the factory. The 2004R can be built to handle power that will shatter a built 700, assuming your pockets are deep enough. The internal parts of a 200 are all steel, they can be upgraded to aftermarket to handle big power. The 700 biggest weakness is the cast aluminum input housing, enough power will tear the shaft out of the housing, resulting in 7 neutrals and a park. The 700 has a lower 1st gear ratio, and a huge gear spread between 1-2 gear. Overdrive is basically the same. The 700 trans is also much easier to source, the best ones have a large St Louis Arch shaped casting line above the servo cover. Just make sure it doesn’t have the large round electrical plug, that is a 4L60E, basically the same trans internally, except it’s electronic. It will require a aftermarket controller to run the trans.

Any transmission shop that has been in business more than 10 years should be able to build a 700, the 2004R doesn’t have nearly the aftermarket support. You will need to source aftermarket parts from specialty builders. Dace Husek, CK Performance, Extreme Automatic, and Jakes Performance all have performance parts.

Lots to consider!!

If you have zero desire to ever go beyond 400hp, use a 700. With the right friction and cheap upgrades, it will live just fine. Have the shop build it with the Sonnax Smart shell, a hood wide band, upgraded 3-4 clutches, corvette servo, and a hood shift kit. Make absolutely SURE the TV cable is installed and adjusted correctly. There are a ton of options for the lockup converter clutch control.

 

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I like the way the car is handling at present but I’m running a 373 gear ratio in the rear end. Trying to drive a long distance from one town to the next is a bit of a killer. I’m not really looking for gas Gas mileage with a 373 gear ratio, but it would be nice to be able to drive it on the highway without working the engine so hard.

 

I know what you mean, after installing a 2004R at a shop. It was not why I wanted to do the swap, but it was a nice benefit and the transmission itself was even quieter and smoother than my old TH400, to me. I did not expect that benefit. To me the shifts were greatly improved being very fast and firm, but they were barely felt at lower speeds normal driving. Over drive on the 700 will bring you down from the 3.73 to an overall 2.611 ratio, on the highway in over drive.