Borg-Warner T98 Transmission
The T98 transmission was a heavy-duty 4 speed transmission designed by Borg-Warner in the late 1940's. The transmission was Borg-Warner's first 4 speed transmission to be introduced into mainstream production. It was used by numerous automobile manufacturers including Ford, International Harvester and Jeep. The introduction of the Jeep T98 was intended to meet the demands of industrial and military applications. It is these attributes which make this heavy duty transmission so desirable for the 4x4 community today. The Borg-Warner T98 was first utilized by Jeep in 1955. The transmission was obviously advantageous for both its strength and ultra low gearing. CJ Jeeps equipped with T98s were not your typical showroom floor Jeep. During this time period, most civilian Jeeps were factory equipped with standard 3 speed transmissions. The T98 transmission was mostly available by special order only. Besides military jeeps like the M38A1, M715 and M725 trucks; The T98 was commonly special ordered by industrial and agricultural customers.
The cast iron T98 transmission case measures 11.87" long, 17.45" height and weighs approximately 145lbs. The T98 utilizes a cast iron top cover which is retained by six bolts. The top cover has a T98 stamped on it. The case may also have a casting # of 1301 or 1309. The transmission input shafts varied in both length and diameter. The transmissions found behind the Hurricane 134 4cyl engine have a 10-spline, 15/16" diameter input shaft. While input shafts found behind 6cyl engines use a 10 spline1-1/8" diameter input shaft. The stickout lengths of these 6cyl inputs varied extensively. Although spare parts for the T98 are commonly available, some of these odd length input shafts are becoming increasingly difficult to locate.
The T98 utilized helically cut gears in 2nd through 4th gears, while 1st and reverse were non-synchronized spur gears. The T98 has an impressively low first gear of 6.40:1. This in itself makes this transmission desirable for offroad enthusiasts. It is probably safe to say the T98 was one of the first rock crawling transmissions. The complete gearing is as followed:
| 1st | 2nd | 3rd | 4th | Rev |
|---|---|---|---|---|
| 6.40 | 3.09 | 1.69 | 1.00 | 7.82 |
The rear of the Jeep T98 was always a 1-3/8" x 6 spline output shaft for mounting to the input gear of the Dana 18/20 transfer case. The transmission was connected to the small hole Dana 18 via a 1" thick cast iron adapter plate. Jeep would also offer the T98 behind the Dana 20 in a very limited run of 1962-1965 J series trucks. The transmission was also largely used in M715 and M725 military trucks during the Vietnam conflict. These setups were actually 2wd transmissions offered with a divorced Np200 transfer case. The transmission was then attached to the transfer case with a small driveshaft.
The T98 transmission would slowly be phased out in favor of the improved T18 transmission. The T18 transmission would offer a number of upgrades over the T98. There is often much confusion and misidentification among the T98 and the T18. It would seem logical that a transmission stamped with T98 be a T98; however, this is not necessarily true. Some Jeep T18 transmissions used the exact same top covers as the T98. The stamped T98 top cover is where most misidentification occurs. It can pose confusion for those seeking specific gearing options and spare parts. Identification is also imperative when using one of our adapters do to input shaft and output shaft differences. We have put together a more detailed technical section on conversions with the T18 and T98. Please review this section for a better explanation on the differences, commonalities, and adaption options for these often misidentified and misunderstood transmissions.