Transmission Problems on 49 jeep

[cdp20]

I am 17 yrs old and me and my dad own a 49 Willy's jeep. We are having trouble out of the transmission. It will jump out of 1st gear while driving. Also it will grind gears when downshifting from 2nd to 1st. You have to come close to a complete stop before it will downshift without grinding. I have read some posts about similar problems and people have mentioned the synchro or forks. Any advice or solutions are appreciated. Thanks!

[1948 Cal Willys Pickup]

Sounds like the clutch is gone to me.

[Beacher425]

I have not heard of jumping out of 1st gear before. Jumping out of 2nd gear does appear to be a fairly common problem with the T90, Mine did it and had a broken brass synchronizer ring. I have read that worn out sifter forks can also cause it. Since there is no synchronizer rings on 1st gear, you will have to get very slow or stop to get in without grinding. I have heard that double clutching will also work but haven't seen it or tried it. Overhauling the T90 is relatively easy and lots of internet indtructions, youtube videos to help. Maitainance manuals are a must have,

[JeepCJ5]

Be advised that first gear in that transmission is NOT synchronized...which means absolutely NO downshifting back into first gear while the Jeep is in motion...ever !...come to a complete stop and then pull it into first gear...this is not a modern transmission...back when this Jeep was built, most vehicles had non synchronized first gears...Jeep is no exception here...do your Jeep a huge favor and drain the transmission's nasty gear oil and refill it with fresh SAE 85/90W hypoid gear lubricant...check the old gear oil for metal chips and any silvery streaks (metal shavings)...this would be caused by shifting the transmission like a caveman, trying to get into first gear while still rolling forward...if you keep doing this, you will destroy the entire gearbox and have to spend big $$$ !!!...don't forget to purchase and use a magnetic oil drain plug too.