Working on a transmission swap project to replace a munched G54. Info and parts are getting scarce for the mini trucks so I’d figure share what I find. The goal is a stronger R series transmission behind a 22R while maintaining the shifter positions on the floor. I’m keeping the factory bench seat of my 87 Pickup, and have little interest in majorly modify the floor pan.
I have a R156F from a 2017-2018 2TR 4WD Tacoma, plus a 22RTE bell housing and R151F turbo extension housing to bolt up a gear drive RF1A transfer case.
The R156F uses the short 6.5 input shaft and the 22RTE bell housing bolts up no issues. So the input side of the transmission is taken care of.
The issue lies in the larger output shaft bearing diameter of the R151F interfering with the 5th gear spline gear of the R156F. The R151F uses a 70x20mm bearing and the R156F uses a 60x22mm bearing. It appears there’s about 3mm of contact between the R151F extension housing bearing support and the R156F spline gear. I don’t have an early R150F to measure, but I suspect the newer design synchro pack is a larger diameter than older design, hence the reduced bearing diameter in the late model R15x transmissions.
Here you can see how the transmission side of the R156F (left) and the R151F (right) extension housing differs.
From my measurements there appears to be no appreciable difference in the major dimensions. However the R151F has a provision for the shift rail to pass into the rear of the housing, while the R156F doesn’t.
Here’s the 5th gear side of the R156F with a highlight of where the contact is:
Moving forward I may clearance the R151F extension housing for the R156F spline gear, and then use the larger 151F bearing with a larger 5th gear spacer on the output shaft to make up for the differences in bearing thicknesses.
I know souring an early gen R150 would have made this a more simple endeavor, but the updated internals and gear ratios of the R156f made it an attractive option. Still brainstorming on the way forward.
I have a R156F from a 2017-2018 2TR 4WD Tacoma, plus a 22RTE bell housing and R151F turbo extension housing to bolt up a gear drive RF1A transfer case.
The R156F uses the short 6.5 input shaft and the 22RTE bell housing bolts up no issues. So the input side of the transmission is taken care of.
The issue lies in the larger output shaft bearing diameter of the R151F interfering with the 5th gear spline gear of the R156F. The R151F uses a 70x20mm bearing and the R156F uses a 60x22mm bearing. It appears there’s about 3mm of contact between the R151F extension housing bearing support and the R156F spline gear. I don’t have an early R150F to measure, but I suspect the newer design synchro pack is a larger diameter than older design, hence the reduced bearing diameter in the late model R15x transmissions.
Here you can see how the transmission side of the R156F (left) and the R151F (right) extension housing differs.
From my measurements there appears to be no appreciable difference in the major dimensions. However the R151F has a provision for the shift rail to pass into the rear of the housing, while the R156F doesn’t.
Here’s the 5th gear side of the R156F with a highlight of where the contact is:
Moving forward I may clearance the R151F extension housing for the R156F spline gear, and then use the larger 151F bearing with a larger 5th gear spacer on the output shaft to make up for the differences in bearing thicknesses.
I know souring an early gen R150 would have made this a more simple endeavor, but the updated internals and gear ratios of the R156f made it an attractive option. Still brainstorming on the way forward.
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