I have a 1995 Chevy K1500 pickup, V8 5.0L engine. The 5-speed manual transmission was rebuilt about 10 years ago. Recently, I’ve noticed that when the vehicle is cold, I get a grinding noise from the transmission when shifting into second gear, and also that it’s generally difficult to shift the lever into 1st or 2nd gear. Once in gear, everything is fine, and the problem also goes away after a few minutes when the vehicle is warmed up. Any ideas what the problem might be?
You don't really give us much info about this except to say it was rebuilt 10 years ago. How many miles since then? What kind of service?
There are two most likely causes: clutch and synchros. The clutch is obvious. It can get a loose driven plate which will keep it from completely disengaging all the time. However, you did not mention any other symptoms which would support this theory.
So I will suggest that your synchros may be worn. These are mini-clutches or mini-brakes (depending on your view) which are used to match gear speeds when shifting. The ones for second tend to fail sooner in some applications and with some drivers, because when they are used the engine is at high RPMS and there is a desire to get into the next gear (2nd) rather quickly.
Assuming it is the synchros, you can try one generalized approach: change the transmission fluid. Use a good fluid, and be careful that you get the fluid that your rebuilder recommended. Sometimes the rebuild shops recommend a different fluid than the manufacturer. This can be regionally influenced (temperature) and also influenced by service (dirt, road conditions). Change the fluid when it is warm from driving, and refill. A general word of caution is to make certain that you can get the fill plug out, before you pull the drain plug.
If new fluid fails to improve your problem, you are likely looking at another transmission rebuild.
BTW, what was the reason for the prior rebuild, and how many miles were on the vehicle at that time?
I would suggest that you do not delay in changing your fluid...as getting improved lubrication in there now may extend your transmission a bit longer. And your existing transmission could have a bit more contaminants which tend to precipitate out at cold temperatures. Or you could even be low on fluid. At this point, it is worth the $20 it will cost to drain out and refill the transmission fluid. Good luck.