Not shifting into 1st gear

Hi, I just bought a 1984 Toyota Pickup 2.4L Diesel and it does not seem to want to go into first or second gear at a complete stop. If I rev the engine it will go in or if I down shift into first while still moving it will go in. It was leaking clutch fluid from the rubber boot around the slave and master cylinder so I replaced both of them but it still does not want to go into first. I adjusted the clutch pedal so that there was no play in it. I have read online that it could be a slightly warped flywheel or clutch plate. Does that sound like the problem or does it sound like it it inside the transmission? OK thanks, Alex

it could be the clutch or the tranny gears.

Are there any tests that I could do that would point to the exact problem? OK thanks for the advice, Alex

You really need to put a little free play back into the clutch pedal. If you do not, the clutch will probably not last long; assuming it’s still in good shape.

I’d add a bit of free play, put it in 1st gear, and slowly let the clutch pedal out.
Note how far the pedal moves out before the truck starts to move. If it has to move quite a bit the clutch is probably worn. If it engages pretty quickly then the problem could be in the 1/2 synchronizer hub assembly.

If you have a warped flywheel or clutch disc you should notice some clutch chatter or shudder when taking off from a dead stop.
To test the clutch for slippage, put it in 3rd gear, set the park brake, hold the foot brake, rev the engine to about 3000 RPMs, and let the clutch pedal out. The engine should die quickly. If not, the disc is worn and slipping.

Hope some of that helps.
(If everything works out ok on the clutch tests and the problem appears to be in the transmission this means the trans would probably need a complete overhaul as one would not want to go in on a 25 year old transmission and do piece work.)