1990 YJ, Manual Transmission, 4.2 6cyl. - After 30 years and 397,000 miles, I finally removed the factory-installed 231J Transfer Gearbox. The new "rebuilt" Gearbox was supplied by TheGearShop1945.com. The Gear Shop needed to know if the front axle 4WD was vacuum controlled or electric, and if the front yolk was threaded for "bolt & strap" u-joint attachment or U-Bolt style so they could supply the proper yolk. Oh, and they wanted to confirm that the speedometer was the manual cable type. They sent a good-looking unit that was "tight" when compared to the sloppy gearing in the old gearbox. It went straight in, no modifications required. I've kept my Jeep drive train "stock"... no lifts and standard tire size.
So this is NOT an exceptional story, and I have no questions to ask, but there was one interesting requirement from The Gear Shop that I wanted to mention in the forum.
They insist that the gearbox be filled with 5W30 Motor Oil. For 30 years I have followed the Jeep Maintenance Manual recommendation that Automatic Transmission Fluid (ATF) be used. The Gear Shop will not honor the warranty if the gearbox is not filled 5W30.
Naturally, I called them for an explanation and they convinced me to use the motor oil. The ATF is thinner, cavitates easier and creates a fine mist that vents overboard. Unless you regularly check and fill the gearbox, you can lose half the fluid over an extended time period. The motor oil has plenty of lubricity for the gearbox, does not vent away, and is compatible with the seals. Since they issue the warranty with this condition, I complied. So far, it works great!
The only "new" gearbox problem that had me under the Jeep for an afternoon was related to the speedometer not working. This turned out to be an issue with installing the 30 tooth speedometer gear in the proper orientation so as to engage the worm gear in the new Transfer Case. This was NOT a gearbox issue, and I'm sure there has been many discussions concerning speedometer gear installation, so I won't go into it here. I will say that The Gear Shop (near Baltimore, Maryland) was a pleasure to deal with, provided a quality rebuilt product, is family owned, and made the core return (via UPS) very easy. I paid them $695 for the Gearbox plus $125 shipping (both ways to/from Southern California). The complete shipping weight with their special container was 93 lbs.
So this is NOT an exceptional story, and I have no questions to ask, but there was one interesting requirement from The Gear Shop that I wanted to mention in the forum.
They insist that the gearbox be filled with 5W30 Motor Oil. For 30 years I have followed the Jeep Maintenance Manual recommendation that Automatic Transmission Fluid (ATF) be used. The Gear Shop will not honor the warranty if the gearbox is not filled 5W30.
Naturally, I called them for an explanation and they convinced me to use the motor oil. The ATF is thinner, cavitates easier and creates a fine mist that vents overboard. Unless you regularly check and fill the gearbox, you can lose half the fluid over an extended time period. The motor oil has plenty of lubricity for the gearbox, does not vent away, and is compatible with the seals. Since they issue the warranty with this condition, I complied. So far, it works great!
The only "new" gearbox problem that had me under the Jeep for an afternoon was related to the speedometer not working. This turned out to be an issue with installing the 30 tooth speedometer gear in the proper orientation so as to engage the worm gear in the new Transfer Case. This was NOT a gearbox issue, and I'm sure there has been many discussions concerning speedometer gear installation, so I won't go into it here. I will say that The Gear Shop (near Baltimore, Maryland) was a pleasure to deal with, provided a quality rebuilt product, is family owned, and made the core return (via UPS) very easy. I paid them $695 for the Gearbox plus $125 shipping (both ways to/from Southern California). The complete shipping weight with their special container was 93 lbs.
