When you drive a vehicle with a manual transmission, you need to be aware of the clutch and how it is working. It is possible that what you think is a transmission problem is really only something wrong with the clutch. Of course, if you don't know what you are looking for, you may think you are dealing with a simple clutch issue that can be ignored for a bit when you really have a problem with the transmission. Here are a few clues to let you know when you need to have the clutch repaired.
The pedal can give you a good indication of how the clutch is working. It should not be too hard to press or stick while engaging it. However, it should not be pushed so easily it goes all the way to the floor. It should engage smoothly and spring back to its original position when you remove your foot.
If you get a whiff of something burning as you change gears, it usually means that the clutch plate is wearing thin. However, if it only happens when you are in heavy traffic or on a steep hill, it is probably due to how long you are holding the pedal down.
Once you have shifted into a gear, it should stay there until you change it. If you notice that the gears are slipping from one to another without your doing so, it is due to a clutch problem. It could be that the plate needs to be replaced or there is a leak in the lubrication line. Too much lubrication will cause the gears to slip.
A grinding sound when you change gears is cause for concern unless you are having trouble coordinating shift. It could mean that the place is out of alignment with the gear so it takes a minute for it to slip into place. It could also be that the plate needs to be replaced to mesh properly with the gear.
Any time the clutch is not working properly you should have it checked by an experienced mechanic. Left alone, it could cause damage to other parts of the transmission. It is easier and less expensive to replace the clutch than it is to have work done on the transmission. The money you spend on the clutch will save you a lot in the long run.