The ∧1 M20 wide-ratio transmission has a 2.54:1 First gear ratio and the M21 close-ratio has a 2.20. The primary difference between the M20 and M21 models is their gear ratios. Because owners of these cars rarely part them out, the likely available transmissions will be the M20 and M21. The M22 was a rare model offered in supercars like the ∦7 427/430hp Corvette. After 1971, all Muncies were fine splined. Many think all fine-spline Muncies are Rock Crushers, which is not the case. The Muncie came in three flavors: the M20, M21, and M22 (the Rock Crusher). With a 10-spline input shaft and a 27-spline output shaft, the early Muncie was less durable than the ∧1-and-later models with its 26-spline input and 32-spline output shaft. Interestingly, there are two distinct versions of the Muncie that many Bow Tie enthusiasts may not be aware of. The Muncie is an aluminum case four-speed transmission introduced in 1963. The Saginaw four-speed is essentially a cast-iron three-speed design with an extra gear designed for applications under 300 hp. Well briefly outline the group and leave the final decision to you. There are five manuals worth installing in a Chevelle, and for each type of gearbox there are variations that may or may not be worth the time and money to install. The crossmember will need to be moved almost 9 inches toward the rear of the Chevelle. To swap in the 4L80E, the driveshaft will have to be shortened 3-¼ inches and a 32-spline slip-yolk must be used. The 4L60E is exactly the same swap as the 700-R4/4L60. With its equally huge 29.625-inch mounting location, the 4L80 is a behemoth best left to the big-block crowd. The down side is its size, at 225 pounds with converter and 31-inch overall length. The 4L80E uses the larger 32-spline output shaft and offers the highest torque capacity (over 700 ft-lbs in the aftermarket JET model). Its overall length is the same as the 700-R4/4L60. The 4L60E is an electronically controlled version of the 4L60 that retains the 27-spline output shaft and has a 30-percent overdrive. The final two automatic transmissions are the 4L60E and the 4L80E. To switch a Powerglide to a 700-R4, use the Glides 27-spline output shaft, shorten the driveshaft 2.75 inches, and slide the crossmember back 1-¼ inches. Corvette versions have no provisions for a crossmember mount because of their driveline torque tube design, but can be exchanged for a different extension housing that has a mount provision. This trans is a four-speed O/D unit with a 27-spline output shaft. It changed its name in the early ∩0s to 4L60, but the internals remained the same. The 700-R4 is the larger cousin of the 200-4R. The good news is that the driveshaft will not have to be shortened. To swap with the Glide, the crossmember must be moved back 6 inches. The 200-4R measures 27.75 inches, with a 26.81-inch mount position. These transmissions are durable enough to withstand the punishment of the legendary turbo Buick Grand National from the factory. The 200-4R overdrive trans has a 27-spline TH-350-style output shaft and is commonly found in ∨1-∩0 Chevy Monte Carlos, Malibus, El Caminos and Impalas. If a four-speed overdrive automatic is more to your liking, there are four available: the 200-4R, 700-R4/4L60, the 4L60E, and the 4L80E. Since the TH-400 is a little more than ½-inch longer than the Powerglide, you will have to shorten the driveshaft. To install a TH-400, use a TH-400 32-spline slip-yolk and move the crossmember back 6 inches. The TH-350 is a direct swap for the Powerglide both share transmission mounting positions, overall length, and spline count. The TH-400 uses a larger 32-spline output shaft. The TH-350 has a 27-spline output shaft and is half an inch shorter overall than the TH-400. The TH-350 was released in 1969 as a smaller economical version of the TH-400, which was introduced in 1965. It has two versions: the early cast iron, which is universally ignored, and the later aluminum case. The Powerglide is a 27.75-inch-long two-speed transmission with a 27-spline output shaft. There are three non-overdrive transmissions. Using the Powerglide as a baseline, CHP will explore how many of these transmissions can be simply bolted in using the same transmission crossmember mount and driveshaft length. Models range from the classic lightweight two-speed Powerglide to the 225-pound monster 4L80E. If automatics are your passion, there are several that will bolt into a Chevelle with little effort. Follow along as CHP bench-swaps a myriad of different transmissions. With the proliferation of overdrive transmissions, a steep First gear, and stump-pulling torque, multiplication can be combined with mellow tones and gas mileage on the interstate. Wide floor pans and ample transmission tunnels makes installing any gearbox possible. The beauty of ∦4-∧2 Chevelles is in their versatility.
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