Borg-Warner SR4

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The Borg Warner manufactured SR4 was a four-speed transmission primarily used in 1980 to 1982 Jeep CJ models. The transmission was found behind the 151 Iron Duke 4cyl and the AMC 258 Inline 6. The transmission is considered somewhat light duty, yet the transmission often finds its way behind Chevy V8s do to the Iron Dukes familiar Chevy V8 bolt Pattern. Like many transmissions, the SR4 was not originally designed exclusively for the JEEP. The original SR4 was used in 76-79 mustangs. The SR4 transmission the transmission was commonly referred to as the “RAD” and was ran behind Ford 2.3 4cyl and the Ford 302 V8. The top cover of the SR4 actually even has the Ford Blue Oval Logo stamped on it.(see photo) The SR4 is a top loaded transmission features full synchronization in all forward gear. 1st and 2nd synchros are larger than 3rd and 4th. The SR4 gears are all helically cut. The SR4 consists of an internal single-rail shift linkage. Ball bearings are located on front input shaft and rear main output shaft. The cluster gear consists of a shaft sliding through it and is supported by loose needle bearings.

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The SR4 transmission consists of two sections. The aluminum front case is 9-1/4" long. It also features an aluminum top cover retained by eleven bolts. The rear of the SR4 consists of 5.9” rear tailhousing making an overall length 15.25”. The transmission height is 14” and weighs 61lbs. The shifter does not come out of main section of the transmission; rather it is located in the rear tailhousing section of the transmission. The SR4 and JEEP T4 are commonly confused and misidentified as their dimensions are near exact.  Both the SR4 and T4 have a unique "S" curve bend on the handle differentiating them from the 45 degree angle of the T176 shifter . Beside overall dimensions, the SR4 can further be identified by casting #'s of “13-32” and “13-40”. The “13-32” were typically found on AMC 258 inline 6 engines while the “13-40” casting # were for Iron Duke four-cylinder Jeeps.

The Jeep SR4 has a 23 spline rear output shaft for mating to the Dana 300 transfer case. The transmission input shaft has a 7-1/2" input shaft stickout with 1-1/8" x 10 splines. The SR4 does not have a compound low gear but does have all around good gearing. The SR4 was available with two different gear options. The gear ratios were differentiated based on the engine mated to the transmission. The gearing options were:

  • 4 Cylinder Applications

First Gear - 4.07:1

Second Gear - 2.39:1

Thrid Gear - 1.49:1

Forth Gear - 1.00:1

Reverse - 3.95:1

  • 6 Cylinder Applications

First gear - 3.50:1

Second Gear - 2.21:1

Third Gear - 1.43:1

Forth Gear - 1.00:1

Reverse - 3.39:1

 

 

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The strength of the SR4 has often been debated. It is usually a one sided debate as the SR4 clearly is not known for handling heavy V8 horsepower. So what explains the high amount of Chevy V8’s behind the SR4? This can easily be explained by the commonality of the Iron Duke Engine bolt pattern. Since the Iron Duke shares the same 90 degree bolt pattern as the Chevy V8, the Chevy V8 will bolt up to the factory Iron Duke bellhousing. The conversion does require the smaller GM flywheel, mini high torque starter, and modifications to the bellhousing. If replacing the 258 inline 6 engines, Advance Adapters does offer a multi drilled bellhousing to mate to the SR4. The 712548 bellhousing allows for the retention of the factory clutch pedal configuration. Since we use the same bell housing for Chevy to Ford applications, customers who choose to use this bellhousing for the SR4 have the opportunity to upgrade to other transmissions. This bellhousing will also bolt up to popular heavy duty truck transmissions like the Ford T18 and NP435. The SR4 was only used for a short 3 year period. The T176, T4 and T5 would eventually replace the SR4 transmission entirely by 1984.