Corvette Transmission Build - Slip Slidin' Away, Part II

Making The 700-R4 Better, Stronger, And Faster

PJ Rentie Apr 1, 2000 0 Comment(s)
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In last month's issue, we tore into The Blubonic Plague's very tired 700-R4 and showed the catastrophic effects of a bad Throttle Valve (TV) cable. Actually, it was a cheap 10-cent plastic clip that went bad. The TV cable comes from the throttle valve in the transmission and connects to the throttle body on the engine. This cable tells the transmission the position of the throttle. The transmission increases or decreases line pressure according to throttle position. Without this connection, the trans would never raise the line pressure, and the internals would burn up because they couldn't handle the load. Now, we're going to follow Mike Bastio of Toy Shop Transmissions as he re-incarnates The Plague's stricken tranny into a formidable piece of automotive machinery.

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The 700-R4 has been refined and upgraded over the years, and having rebuilt a few thousand of these babies in his career, Mike knows what works and what doesn't. He can tailor each transmission to the needs of the customer. Our needs were easy to address: we wanted a street trans that shifted firmly, delivered good mileage, and could handle a ton of horsepower (eventually). Armed with that information, Mike proceeded to get down to business. He noticed during the teardown that the transmission had already been rebuilt once and had a couple of upgrades. One of the upgrades already present was the replacement of the low/reverse reaction sun gear with a stronger unit. Other areas that Mike concentrates on (by modifications to the valve body) are fluid flow, pressure regulation, and improved shifting. When you think about it, most of Mike's modifications are based on common sense, but without the intimate knowledge of the inner workings of the transmission, they're useless.

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The finished product was, in a word, impressive. The Blubonic Plague has a whole new attitude, and although I know I'm supposed to get better gas mileage, I haven't, because I'm having too much fun sticking my foot in the throttle to get the most out of every tire-barking shift! Once I settle down, I expect my combined mileage to be in the 15-16 mpg range. Before we go any further, I must say that I made a mistake in part one of this article. I referred to a part that I called the 3-4 drum, when it's actually the reverse input drum. The band that holds it is called the 2-4 band, meaning it holds the drum in second and fourth gear. Now that I've gotten my terminology correct, let's get started.

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