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D. Jeep T86

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T86 Transmission

In 1965 Jeep introduced the much welcomed Buick Dauntless V6 engine and with it a new 3 speed transmission known as the T86. The T86 was clearly a revamped T90 with some quality improvements. The transmission would offer similar success as the T90; however, the transmissions’ reign would be short lived only seeing 3 years of service. 

The cast iron T86 transmission is compact at only 8.80” long and 14” in height. It features a cast iron top cover which is retained by six bolts. The case is typically stamped with a “T86AA” on the side of the transmission. T86 transmissions have a 1-3/8", 6 spline output shaft for mounting the transmission to the transfer case input gear. The T86 utilized a 4” bearing retainer to index to the large hole Dana 18. The transmission gear ratios for this transmission are 2.79:1 first gear, 1.68:1 second gear, 1:1 third gear and 3.79:1

The front bolt pattern on the T86 transmission is slightly different than the T90 offering a more square like pattern. The input shaft on this transmission is 10 spline 1-1/8" diameter with a somewhat long 9.5” stickout. The Buick engine was mated to the T86 by a 6.5” deep bellhousing and a 2.5” thick cast iron adapter plate. This adapter plate can be used with a Chevy V8 bellhousing without any modifications. Since Jeep no longer makes this stock adapter, we manufacture our Chevy adapter plate as a direct replacement. We offer a similar adapter for Ford V8 conversions as well.

The T86 transmission is synchronized in the second and third gears much like the T90. Unlike the T90, The T86 utilized an all helical cut, constant mesh, gear configuration. Jeep’s intention was to offer a superior transmission to handle the brawny Buick V6. The T86 certainly offered a better design over the T90; however, it would really take the T-14 transmission to offer significant strength over both the T86 and T90.

The T86 served well behind the Buick V6, but it does lack in comparison with most modern transmissions. The low axle ratios of early jeeps and lack of overdrive limit the drivability of many old Jeeps. Considering the short wheel base of the older Jeeps, Jeep owners are left with little options for better highway speeds. 5 speeds are generally too long to convert for small wheel base vehicles. One of the few overdrive options for the early Jeep is the Saturn Overdrive. It allows the Jeep owner to retain his dependable T86 while also achieving the rpm reduction and higher highway speeds so desperately needed.