my 86 comanche is stuck in reverse what could be the problem

are you talking about a clutch master cylinder? that might make some sense

if his is a v6, they are a real pain in the rump to get the air out of. Its like the slave cyl. is angled wrong. 4 cyl. not much better. I remove the SLAVE cyl. loosen the line so you can point the pin/rod towards the ground. snug line. then gently push on pedal until piston in slave cyl. butts against snapring. Now, at this point you need to crack open the bleeder on slave cyl. and have someone push down on clutch pedal w/their hand. close bleeder. repete this several times. Ck fluid often so you dont suck in air. when the pedal feels solid, not spongy, reassm. slave cyl.into vehc. be careful to align the plastic tip into clutch fork. This should fix it.

had a few jeeps do the same thing and couple years apart... with the same tramission....AX5 ( japanese)... what i had been told by couple of jeep dealers and tranmission shops... this type of transmission where manufacture to be light and cheap... the problem after four transmissions and traveling round the country different shops... reverse then the other gear(s) will follow or go.... by the time you realized no gear(s) left... these transmission are not rebuildable, because of material and the design of the (1) main bearing doing all the work. my 88 jeep wrangler had the same problem. then replaced with the new designed ax5 with a steel housing holding the main bearing and had it ever since the transmission was replaced 1995 with no problems.