Besides carefully checking all parts that are reused, replacing them when necessary, and undergoing a meticulous assembly process, B&M 700-R4s are toughened up considerably by adding high-performance B&M Racing Red clutch packs. Of course, upgrading to better factory components is only part of the story. As we've noted, however, we could just as well have given up our '84 Z28's earlier box, since all cores are totally dismantled, the hard parts thoroughly cleaned and inspected, and upgrades to the later parts made where necessary. We brought B&M a '92 core-the very 700 we burned up during our Mission 305 engine build and replaced with a T56 ("Trans-Mission 305 Parts 1 and 2," Feb. The manual that comes with this kit provides a comprehensive list of the improvements made to the 700 from 1982 to 1986. For those running pre-'87 units, B&M makes the Super Transkit (PN 70230) for DIYers looking to upgrade the tranny themselves. By that time, GM had beefed up several areas of its primary slushbox, most notably by changing from a 27-spline input shaft to a 30-spline unit they also improved lubrication in several ways, including the improvement of the oil pump and including an auxiliary valve body to provide direct lubrication to low gear. By the time the 11-year-old tranny had to handle this output, it had been substantially improved from the original version, and therein lies the first key to making the 700-R4 into a performance piece.Īll B&M's street/strip 700-R4s are built to '87-and-later specs. The most it had to deal with was the '92 Corvette's 300hp, 330-lb-ft LT1 power-plant. In its stock form, however, the 700 was never really called upon to handle tons of power. The overdrive cog also gives hot rodders the ability to run stiffer rearend gears without unduly affecting fuel mileage at cruising speeds. The combination of lower First and Second gears and an overdrive cog give the 700-R4 the potential to be a good real-world performance transmission, promising the best of both worlds: acceleration and mileage. On the other hand, the 3.06:1 First gear and 1.63:1 Second gear found in the 700 are both lower than their counterparts in the TH350 and TH400, providing increased acceleration. The 700-R4, featured in various '82-92 GM models, was a product of the OEM's still-ongoing search for better gas mileage, featuring an 0.70:1 overdrive Fourth gear that, in stock form, kicks in early and often. With this in mind, we paid a visit to B&M Racing & Performance's transmission rebuilding facility to have a look at the makings of a high-performance 700-R4. On the other hand, a transmission is like any other part of a performance car-it's only as durable as it's built to be. ![]() And our current '84 Z28 project came with an obviously abused, one-speed only, badly leaking 700 backing its 190-horse, 240 lb-ft 305 H.O. ![]() '04) churned out 295 lb-ft of rear-wheel torque, burning up its 700-R4 in the process. Our own experience seemed to bear out this assessment: our "Mission 305" Camaro (June and Sept. Despite the fact that millions of cars left The General's assembly line with 700s in place, including Camaros and Corvettes, many enthusiasts hold the 700 in light regard for performance applications. "The proof is in the pudding," the old saying goes, and it's all the more appropriate when we're talking slushboxes-in this case GM's ubiquitous four-speed automatic, the TH700-R4.
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