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The Novak Guide to the

Borg-Warner T15 Transmission

t15_transmissionThe Borg-Warner T15 is a medium-to-heavy-duty, three-speed transmission, introduced in the 1971 Jeeps. It was offered in CJ Jeeps up through 1975 and in Full-Size Jeeps through 1979. The T15 was primarily found behind the AMC V8 engines as the base transmission, but was also found behind the AMC 232 and 258 I6 engines as an upgrade option over the T14. The upgrade to the T15 transmission was the Jeep T18 four-speed.

Features

The T15 is a top loaded, top shifting transmission using a cane shift lever.

The T15 is synchronized in all forward gears and all gears are helically cut. It uses sliding clutch collars in lieu of sliding gears as found in other, earlier Borg Warner three-speeds.

Identification

The T15 transmission is 10" long and features a cast iron top cover that is retained by 8 bolts. The main case is of cast iron. The case itself has two protruding bosses as provisions for side-shifting actuators, however, no known Jeep side-shift applications are known.

The T15 transmissions as found in Jeeps has a 1-3/8" x 6 spline output shaft for mounting the transfer case input gear.

The Jeep T15 may have the following casting numbers: T15 or 1307, or 13-07-065-901 and these are typically found on the passenger's side.

t15_specs_gasketIH featured a T15 in both top-shift and side-shift versions, the latter having the following casting number: 13-07-065-903. Transfer case compatability for IH T15's was the same as for the Jeep versions, marrying directly to the Dana 20 "Texas" bolt pattern and six-spline input gear.

The Borg Warner T14 and T15 transmission are similar in designation, and visually somewhat similar. However, the T14 did use a three-bolt front bearing retainer whereas the T15 used a four-bolt front bearing retainer.

Transfer Case Compatibility 

T15 was available attached to the Jeep Dana Spicer Model 20 transfer case in the 1971-1979 Jeeps.

The T15 always used a 6-spline transfer input gear. An informative chart of these gears can be found here.

 

Engine Compatibility and Adaptability

t15_front_passenger_isometricThe Jeep CJ T15 had a 1-1/8" x 10 spline input shaft (or "clutch shaft") with an ~8-1/2" stick-out length and its pilot tip is ~3/4" in diameter.

The Jeep FSJ T15 from 1971-1979 had a 1-1/8" x 10 spline input shaft with an ~11" stick-out length and its pilot tip is ~3/4" in diameter, and was factory installed using a cast spacer to place the trans closer to the driver.

GM 

The T15 was never natively married to any GM engines, but it is popular to adapt the 1971-1975 CJ version of the T15 to a variety of GM bellhousings with our T15 adapter assembly.

1971-1979 FSJ T15's are not readily adaptable to GM engines.

AMC 232 & 258, 304 & 360 

The 1971-1975 Jeeps with the AMC I6 & V8 had a bellhousing that married directly to the T15. This was a deeper bellhousing (~9") than the standard AMC bellhousings that would be released in 1976.

Rebuilding the T15 

t15_rebuild_kitThe T15 is quite easy and enjoyable to rebuild. Many shadetree mechanics do very outstanding rebuilds if they have access to a press, snap ring pliers and bearing pullers.

See Novak's T15 master rebuild kit.

 

Summary

When filling your T15 with gear oil, we recommend that you select a conventional mineral oil or a para-synthetic in lieu of a full synthetic oil. Properly assembled manual gearboxes do not have the thermal strains seen by combustion engines or hypoid gears. Synthetic fluid in these gearboxes, while not harmful, is probably an economic waste.

Hypoid gear oil is sulphurized higher than transmission oil and can be mildly corrosive to the non-ferrous alloys used for synchros, bushings and thrust washers in these transmissions.

An 80W-90, API-GL5 or MT-1 rated fluid is very good. Some claim faster shifts from using a 50W engine oil in their transmission and we do not consider this to be contraindicated unless you operate your vehicle in a very warm environment.

The T15 is among the strongest of American made three-speed transmissions. They had a relatively short run in Jeeps, but offered good service, even if the gearing was not as broad as the available T18. The T15 was replaced in Jeeps by the T150 transmission in 1976.

t15_top_rear_view

 

Sources

  • The Novak archives and our customer's input
  • Jeep Technical Service Manuals
  • Jeeptech.com & Terry Howe 
  • Jeen at Stork's Jeep

We welcome any contributions or clarifications to this article. Contact us here.