By using hydraulic pressure to operate a clutch inside the torque converter, the fluid coupling could be bypassed, and the losses in churning the automatic transmission fluid inside the converter could be avoided. The lockup torque converter, along with the overdrive fourth gear, was a brainchild of the oil crisis in the 1970's. (The TH350 three speed offers a 2.52 to 1 low gear, and the TH400 low gear ratio is 2.48 to 1.) So getting a heavy load started is easier with the 700R4 due to the lower first gear. First gear is also deeper, with a 3.06 to 1 ratio in the 700R4. The overdrive fourth gear, at a ratio 0.71 to 1, allows the engine in a car or truck to loaf along at 30% lower RPM when cruising on the highway, without changing the axle ratio.
Historically, the new-for-1982 700R4 grew out of the venerable Turbohydramatic 350, with the addition of a fourth overdrive gear and a lock-up Torque Converter Clutch (TCC). as they build me a new high-performance upgraded 700R4 transmission.
Next month, in Part Two, we'll follow Fourth Gear Inc. This month in Part One, I will discuss the operation of the 700R4 and highlight some of the upgrades that are currently available to improve both performance and durability. If you cannot locate the information you need by forum keyword search, just post your question and watch the opinions come pouring in. The Diesel Page Forums are a good place to start. Further research is necessary on the reputation of any given supplier. One caveat, however the person publishing the information on any given website is probably NOT the technician who will actually be building your transmission. There is a wealth of 700R4 information available on the Internet, and the links at the end of this article are the most useful ones I found. So I began researching what 700R4 upgrades were needed and what companies offered them before selecting a replacement transmission.
#BUILT 700R4 TRANSMISSION UPGRADE#
My planned Nitrous Oxide upgrade in the future would only make the situation worse, like scattering tranny parts all over the secret " 2Fast, 2Furious" dragstrip I had stumbled across just outside of Miami. This hot new engine, pushing around 180 non-turbo horsepower out the flexplate, only emphasized the flare (slippage) I was experiencing on the 2-3 shift.
These two opinions can't both be right, or can they? My trusty '84 C-10 was still running its original 700R4 after 150,000 miles, and now was subject to the increased torque from my customized naturally aspirated 6.5L diesel engine. It overheats and can't survive in a diesel truck." or " The 700R4 is the ideal transmission for a truck - having a deep first gear ratio for more available torque when getting things rolling, and a generous overdrive and lock-up torque converter for improved fuel economy." Strike up a conversation about automatic transmissions for our GMC and Chevy diesel trucks, particularly the '82 - '89 6.2L trucks, and you will hear one of two opinions: " That 700R4 is a piece of garbage. Lee's Performance 700R4 Automatic Transmissions
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