Depends on what you have. If you have a Volvo outside of North America, it has a synchromesh transmission. Volvo synchromesh transmissions are extremely rare in North America, and they'll more often have Eaton-Fuller twin countershift unsynchronized transmissions, where you have to manually make up for the lack of a synchronizer gear.
Your truck may not shift gears because the transmission sensor is damaged or broken. It also may not shift gears because the transmission or linkage is damaged.
Need more information. Namely, what the truck and transmission is, and whether it's a transmission fault, or you just not knowing how to shift it.
That depends on what type of transmission you have. The truck having air brakes doesn't affect that.
Depending on power desired in the shift, between 2200-3500
you need a clutch that's all
That's going to depend on what transmission you have. In most cases, they shift in a similar fashion to any other Class 8 truck with an unsynchronised transmission. But some have other transmission types.
12 forward gears and 4 backward gears
First off can you feel it shift through all the gears while off (not running). Second off while running can you shift through the gears or does it grind while trying to shift through them. If it grinds when you try to shift then your clutch is shot. Good luck
If your car/truck is having problems shifting, it may be your transmition. You may want to get that checked out.
Manual transmission is a stick shift. You have to manually change the gears using the shifter and the clutch.
That depends on what your transmission is. If you don't know how to shift an unsynchronised transmission, you need to have someone teach you, hands-on. You're not going to get it simply by reading about it.
my merucry mystique dont shift gears fast