My buddy has an older Jeep wrangler with a 5 speed manual. Yesterday he was cruising down the highway at about 70 and the rpms started to creep up but his speed was slowing. Pulled off the highway and found that he had lost all gears (including reverse) EXCEPT for 4th. No noise etc before it happened.

Any idea's???

J-

Any recent work to the vehicle, including lift, etc?

I would say he needs to replace his clutch. Probably worn and slipping, or something happened down there.

First part sounds like clutch, second like shift mechanism.

Is it that 4th is the only gear that will engage, or that all gears engage but only 4th drives? More details needed.

I would lean toward clutch failure.

Sounds more like a broken shifter. It would make a racket if a shaft or other component failed enough to do that. I just don't see how you could only have 4th gear.

Look up how manual transmissions work.

No recent work, its stock ride height/tire size.

He said that only fourth would make the vehicle move. He was able to feather the clutch and get rolling in fourth. All other gears he could shift into them like normal and let the clutch out and there was no engagement of the gears/movement of the jeep.

J-

I did some googling and this seems to be a somewhat common happening w/ AX series trans. A clip holds 5th gear as it's not sandwiched between the others. There's an upgrade kit available.

Not saying this is what it is, but the googling pulled this up, as a main result, for that issue, every time.

awesome thanks, I'll pass that on to my buddy as something to check.

J-

4th gear is direct drive.  All of the other gears go through the counter shaft.  Likely lost the gears driving that shaft.

https://www.freeasestudyguides.com/manual-transmission-countershafts.html

gotcha makes sense. I'll pass this on to him, thanks.

J-

They ALL go through the countershaft, just one at a time via the gear you’re in being locked to the mainshaft. The gears you’re not in are all still meshed with their countershaft gears, but they’re able to freely rotate at different rpms on their bushings on the mainshaft.

My suggestion is to remove the shifter and top cover, and inspect the shift rail notches, the end of the shifter that engages the notches, and the shift forks. That’s generic manual trans troubleshooting, without more details no more suggestions can really be given. With the transfer case in neutral and clutch disengaged you can engage each of the gears using a large screwdriver or prybar, and by prying the input gear around see if your chosen gear turns the output shaft.

Awesome thanks, I'll pass this info on to him.

J-

Pull the drain plug and look for chunks.