Should I install an overdrive transmission in my older vehicle??

I have been receiving, on the average, about 25-30 e-mail messages a day, and, by far, the most popular subject has been information regarding the 700R4. Some people want information concerning their vehicle, that already has a 700R4, and some are planning to put a 700R4 in place of their existing transmission.

Many people want to install the 700R4 (there have been similar inquiries, involving the Ford E40D, and AOD, and Chrysler 500, and 518 transmissions), simply because they are interested in better gas mileage. While it is possible to get better mileage with a taller gear ratio, and a lock-up torque converter, it is not usually the recommendation of the author, to go through the trouble, and the expense. Consider the story with a certain suburban that I put a 700 in, a few years ago. (there have been countless examples, but this one is very typical). I was contracted to put a 700 transmission in an early model Chevy Suburban (350 engine, and TH350). The owner was getting around 10 mpg before the conversion, and after the 700 installation, brought the mileage up to 12 mpg. Now, at 10 mpg, a vehicle would burn around 10,000 gallons of gasoline to go 100,000 miles, at a cost of about $14,000 (assuming cost of gas at $1.40), while the vehicle would burn only 8333 gallons of gasoline at a cost of $11666.20, thus having a gross savings of $2333.80. He spent $2000.00 for the installation. The transmission did not last as long as the 350, so, over a 100,000 mile lifetime, he will probably spend an extra $500-$700 to overhaul the transmission, and, if he keeps the Suburban for a long time, will have to have the transmission overhauled more often than a comparable 350. So, if your only reason to install a 700 is gas mileage, invest your money in something else....you will probably get a much higher return.

There are several reasons, other than gas mileage, to install a 700R4 in your vehicle:

The 700 has a lower 1st gear ratio than a 350 or a 400

The 700 has an overdrive ratio (around 20%) that will lower engine cruising speeds, and cut down on engine noise

A higher stall speed torque converter can be utilized, without the drawbacks of the higher heat generated by conventional higher stall speed non-lockup torque converters