hello i went and picked up a 1990 ford f250 7.3l idi non turbo 2wd with a 4speed with o/d its a pretty solid truck, however i went and got it and it was grinding into second, reverse worked, drove it home, put it in reverse it went in fine but did hop a bit, next day, i put it in reverse and it just grinds, any ideas whats wrong?

 

First check the fluid in clutch master cylinder. Does it feel like the pedal is firm? Like the clutch is disengageing? Where does it engage when letting it out? High or low pedal? It should be lower. If all of these are good. It's probably the syncronisers in the transmission.

 

I think it's normal when these transmissions get old; I've had two of them so far which have been... finickey to get into reverse.
The easy thing to do is practice - when it's going to grind, it's not slipping all the way in, and the stick doesn't go all the way to the reverse position. Try putting it into reverse-neutral-reverse a couple of times, giving it a little wiggling while doing so. Alternately, it it still won't go in, put it in neutral, let the clutch out, put it back in, then try. It's harder to explain than to actually do, and once you get the hang of it, it'll only grind maby one in a hundred times. (think of using a non-synchro transmission)

Yes, it's probably getting worn. You can spend a lot of money fixing it right, or just learn to work around it. I did the latter, as well as putting some Lucas in the fluid; seems to help a little.

Also, checking the clutch isn't a bad idea either, as said above - you can probably help things a bit if it's not quite disengaging all the way, but I doubt that will just "solve" the problem.
Part of the clutch problem is that the firewall tends to flex when they are this old, and the pedal doesn't push as much fluid as it used to. I ended up modifying the shaft which goes between the pedal and the master cyl; made it a tiny bit longer and it seemed to improve things(counteracting the flex of the firewall).

As far as first->second, yeah, the synchro is probably gone. Mine's a bit clunky as well, and mine also feels "gratey" going from second->third.

The other thing to think about is possibly just going to the JY and seeing if you can't find a zf-42 5-speed from a slightly later model truck, but you'll have to do some work. If you can get the entire running gear from the JY truck, it'll be easier.
But then you'll have a higher highway-traveling gear as well.

 

I had a problem with mine going into reverse when cold. I had to shut the truck off to get it to move into reverse gear. But after it was warm it had no problem. Might be the viscosity of the oil is changed from heat and what not. Could be due for a change

 

I had that problem recently on my 87 5spd. Replaced the clutch slave a few days ago and bled the hell out of it. New slave, fresh Valvoline DOT 3/4 synthetic, and now 2nd and reverse shift just fine. Still a little hard and clunky on occasion, but I chalk that up to the time I spent forcing it into gear.