I have a ’53 M38A1 and have a problem with it. When I shift it into four-wheel drive, it will not shift back to two-wheel drive unless I raise the Jeep up off of its wheels. On the lift you can run through all the gears and in and out of four-wheel drive and the transfer case high and low range. If the Jeep is on the ground,
I can use all gears and high and low in two-wheel drive, but when I engage the front axle, I can go through all of the gears in high or low, but it will not let me disengage the front axle unless I pick up the wheels off the ground. The tires are the same size and the gear ratio is the same in the front and rear axles. Do you have any ideas what could cause this?
As you have noted, it’s important to make sure that all of the tires are the same diameter and that the front and rear axles have the same gear ratio. Any significant variance could cause the driveline binding you are describing.
It’s not at all uncommon for a Jeep transfer case to become bound up. Even some late-model modern transfer cases can become bound up when put into the wrong scenario. The Spicer 18 in your M38A1 is not at all a complex transfer case. There really isn’t anything inside of it that could be causing the problem you are having, as long as the transfer case gear oil is clean and not glittered with metal shavings. Keep in mind that the M38A1 four-wheel-drive system is designed to operate on a dirt surface. There is no differential inside the transfer case, so the system requires that the tires slip at least a little when cornering. If you are engaging the four-wheel drive and operating the Jeep on a hard-paved surface, you could be causing the driveline bind.
If you end up with a bound-up transfer case, never force the transfer case shifter. It can cause damage to the shift linkage, the shift fork inside the transfer case, along with other components. To unbind a transfer case, pull the Jeep forward and back in a straight line once or twice on a loose surface and stop prior to attempting to shift the transfer case out of four-wheel drive. If it’s still bound up, drive a short distance forward in a straight line, stop, and try again. Repeat the process until the transfer case can be shifted without forcing the shifter to the point that the shift lever is flexing. Shifting in and out of low range generally requires the Jeep to be stopped, but you should be able to shift the transfer case in and out of four-wheel drive high range with the Jeep moving at a slow speed. The only way you should be able to shift the Spicer 18 in and out of two-wheel-drive low range and four-wheel-drive low range is if the interlock pill inside the transfer case is removed. Two-wheel-drive low range is not a shifting option if the interlock pill is retained. Partial disassembly of the transfer case is required to remove the interlock pill.