Another low-buck automatic conversion that could very well pay for itself
Several months ago we highlighted the Turbo Hydra-Matic 200-4R transmission as an automatic overdrive transmission for the economy-minded. The addition of an overdrive gear to any three-speed transmission, be it an automatic or manual shift, can improve fuel mileage and help decrease the wear and tear on your engine.
This month we will discuss the big brother to the TH200-4R referred to by General Motors as either the TH700R-4 or their later designation for it, which was the 4L60 transmission. Although some transmission installers feel that the low first-gear ratio and high second-gear ratio do not make the TH700R-4 the best racing transmission, there are quite a few adaptations you can perform to make it a race-ready drivetrain component. Weighing 184 lbs. this transmission can easily handle power torque ratings up to 650-lbs.ft. of torque, while propelling as much as 8,500 lbs. of payload down the pavement. This makes the TH700R-4 a prime candidate for a swap into any GM rear-wheel driver as a replacement for a TH350, Powerglide, TH400, or TH200-4R.
The TH700R-4 was the first overdrive automatic transmission used in GM cars and trucks in 1982, designated as a Hydra-Matic MD-8 transmission according to GM’s RPO codes. The quickest way to identify one of these units in a vehicle is by the square 16-bolt oil pan. The governor and speedometer drive are both located on the driver’s side of the transmission, the sleeve for the speedometer gear can be found in the tailhousing of the unit. TH700R-4 transmissions use a lock-up torque converter, and they use an electric control solenoid to operate the lock-up function. The electrical connector for this solenoid connector is also on the driver’s side of the transmission case.
Initially, the TH700R-4 came with a 27-spline input shaft from 1982-1984. Later production units were equipped with a 30-spline input shaft. Although the later 30-spline version is more desirable, both units can be interchanged if a torque converter with the proper spline count is also used. For the most part, you will find TH700R-4 models using the standard 153-tooth GM small-block flexplate; however, there are 168-tooth Chevy big-block and 166-tooth Pontiac flexplates available in the aftermarket. A detent or TV cable controlled the passing gearshifts. Several different detent cables were used depending on the vehicle the donor transmission came from. Later versions of this transmission, referred to as the 4L60E (1993 and up), used an additional electric kickdown solenoid to engage the passing gear; however, for this article we will be focusing on the earlier TH700R-4 and the 1990-’93 4L60 units.
TH700R-4/4L60 transmission shift ratios are: First, 3.06:1; Second, 1.625:1; Third, 1.00:1; OD, 0.69:1; Reverse, 2.29:1.
Both the TH700R-4 and the 4L60 versions have an overall length of 30-3/4 inches except in the Corvettes, which measure 29-7/8 inches overall. All other important dimensions such as bellhousing bolt circle and location of the transmission mount are listed in the parts locator section of our website at http://www.hemmings.com/parts-locator/transmissions.html.
You can find a donor transmission from one of these General Motors vehicles:
o 1984-’91 Buick Electra, LeSabre and Estate Wagon
o 1991-’92 Buick Roadmaster
o 1990-’92 Cadillac Fleetwood Brougham
o 1982-’92 Chevrolet Impala and Caprice
o 1983-’93 Chevrolet Camaro and Pontiac Firebird
o 1983 Chevelle
o 1982-’92 Corvette
o 1985-’91 Chevy Astro Van
o 1982-’93 S-10, T-10 and Sonoma small pickups and Blazers
o 1991 R and V series Suburbans up to 3/4 ton
o 1982-’93 C and K series pickups up to 3/4 ton
o 1982-’93 G series vans up to 3/4 ton and full-size Blazers
o 1991-’92 Olds Custom Cruiser station wagon
o 1991-’93 Olds Bravada
o 1986-’88 Pontiac Bonneville
o 1987-’88 Pontiac Grand Prix
o 1983-’86 Pontiac Parisienne