When i put my car in reverse in the morning it go in reverse fine and when it warm up it won't go backward what can it be?
It is most likely a internal problem. If the seals in the reverse clutch drum are dammaged it will slip hot cause the fluid is thinner when it gets hotter.
Get a chilled pack and put it on your forehead. Then take a warm shower and dry yourself before putting your clothes on. Put a nice warm top on and long trousers. If you are going out and it is slightly cold, wear a sweater and a jacket. If you aren't, lie down and rest. You should be fine by the next morning. (Even by the afternoon)
When your 1985 Chevy van gets warm you lose reverse and drive but when its cold it drives fine. any Ideas?
Well if you have checked the transmission fluid levels when its cold and warm, and they are good, then you might want to get the fluid changed and have the transmission ajusted... assuming its an automatic, if its a manual, then it might be the throwout bearing, but i dont know why the temp would affect that.