The Novak Guide to the
Borg-Warner T98 Transmission
The T98 transmission is a heavy-duty, top loading, truck style four-speed. The Borg-Warner T98 transmission was introduced in 1948 and persisted until 1964 in Ford trucks. It was installed into Jeeps starting in 1955. The Jeep T98 was a desirable, but rare option for Jeeps through 1972, as it was a special order item for civilian versions. It was more common in military versions of the CJ like the M38A1.
|There is a distinction to make between the "T98" and "T98A" transmissions. The T98 was the earlier 1948-1955 transmission, and the T98A was the later, 1955-1972 version. The principal change here was the change in hand of the helically cut gears. For the purpose of this article, we'll refer to both as the T98.|
The Borg Warner T98 was distinctively the first compound-low, four-speed manual transmission to be offered in Jeeps. This transmission was standard in the Kaiser Jeep M715 and M725 military trucks. It was also found in IH, Reo/White, other trucks and industrial applications.
The T98 is a good, tough transmission, and all consumable parts are available as well as most hard parts. Key parts like Jeep version input shafts are difficult to find and interchange, so individuals hoping to mix and match different versions for conversion and adaptation purposes often find it to be a frustratingly long and expensive experience.
The T98 is ~11-7/8" long. It has a deep first gear of 6.39:1 and is direct-drive in fourth gear. It's reverse ratio is 7.82:1.
The T98 is fully synchronized in the second through fourth gears. All gears are helically cut except first and reverse, which are spur gears.
The T98's progeny, the T18, used the same top cover as the T98 up through 1979. Many individuals assume they have found a T98 upon seeing the "T98" cast into the top cover, when in fact, it is a T18.
The only way to rule T98 out from being a T18 is to open the top cover and count gear teeth. The T98 will have a 43 tooth first-reverse sliding gear (the rearmost mainshaft gear, spur cut) and a 17 tooth cluster gear (also spur cut).
The T98's mainshaft features a smaller pilot tip than the T18 and has needle roller bearings under second gear.
Jeep T98's may feature a casting code of 1301-174-6117. Some may have a T18-1P WG Division cast into them.
|The Jeep / IH / industrial style rear bolt pattern|
Ford, Jeep & IH
The T98 transmission is ~11.9" long and features a cast iron top cover that is retained by six bolts. The T98 case is of cast iron. The case itself is unusually narrow for a heavy-duty gearbox. The case and top cover are both cast iron, with the top cover being retained by six bolts.
Jeep and IH T98's typically have 6-spline and threaded end output shafts onto which the Dana transfer case gear installs directly.
The Ford T98 will typically have a 10-spline 1-1/8" diameter input shaft.
The Jeep T98 as found behind the 134 I4 engine will have a 10-spline, 15/16" diameter input shaft. T98's that are found behind the OHC 226 I6 engine (M715/M725 trucks only) featured a 10-spline 1-1/8" diameter input shaft.
Transfer Case Compatability
The Jeep T98 was factory-married to the Jeep Dana Spicer Model 18 transfer case, and only the small input bore versions. All 4wd style T98's used a rear cast iron adapter plate about 1" thick.
The T98 was also available attached to the Dana 20 in the 1962-1965 J Series truck.
The 1967-1969 military M715 and M725 trucks used only the T98 as their transmission. This was essentially a two-wheel-drive style transmission that was married to a New Process 200 transfer case via a jack shaft.
Engine Compatibility and Adaptability
The T98 as found in the M715 / M725 trucks is readily and simply adaptable to GM power through the use of our #C715 adapter assembly. GM conversions to other Jeep T98's are possible, though are usually done on a special order basis, as there are three different versions found in Jeeps. Individuals interested in these conversions should measure the stickout length of the input shaft and relay this information to us.
The T98 and AMC eras are anachronistic and the transmission was never joined to an AMC engine. There are neither factory nor aftermarket provisions nor compelling reasons to do so.
Rebuilding the T98
The T98 is straightforward and enjoyable to rebuild. Many shadetree mechanics do very outstanding rebuilds if they have access to a press, snap ring pliers and bearing pullers. Many choose to do a full rebuild during the adaptation process, and our instruction guides feature all the details, diagrams, pics and tricks required to do professional level work.