Manual Transmission- Can bad shifting destroy transmission

Question

Been driving a car with a manual transmission for 6 years. I never had to replace the clutch but the transmission recently blew up on me. I was aware that my car was leaking transmission fluid for quite some time so I assumed that was the reason for the car's transmission failure. Upon further thought, I started questioning my shifting habits. Now I know all the basics, like don't hold the clutch down at a red light, don't ride the clutch blah blah blah. My questions are a little more specific to my own habits. For example, When I am in 1st gear (and lets say I am in the drive-through at a fast food place) and I want to inch forward because some space just became available. Is it OK to "half-shift" in order to inch forward in tight spots? (by "half shift" I mean this: So I am in 1st gear, I release the clutch halfway and give a little gas in order to get some acceleration, but then immediately depress the clutch and gently brake before fully engaging 1st gear so I don't crash into the car in front of me) Would a scenario like that damage my transmission?

Another question is if bad rev matching would damage the transmission. I know it could screw up the clutch but my main concern is about the transmission?

Is it just a myth that with manual transmissions the clutch will eventually need to be replaced, and the transmission should go for 100s of thousands of miles no problem?

I have a friend who insists that bad shifting will only damage the clutch...but I don't know if I believe him.

If anyone can tell me any other ways that bad shifting could damage the transmission I would love to know! Thanks!

Answer 1

Is it OK to "half-shift" in order to inch forward in tight spots?

This is usually called slipping the clutch and as long as you don't do it for prolonged periods of time will not damage the clutch. Doing it for prolong periods will cause heat buildup to occur, which is very bad for the clutch and for the flywheel (can form heat cracks). As far as the transmission, this is typical driving and will not damage the transmission.

Another question is if bad rev matching would damage the transmission. I know it could screw up the clutch but my main concern is about the transmission?

Absolutely can and will damage the transmission, but not the clutch ... at all. This affects the transmission by damaging the synchros and other soft parts.

I have a friend who insists that bad shifting will only damage the clutch...

While you don't want to beat him up for it, he is absolutely wrong in this case. Think of it this way: the clutch (to include flywheel, pressure plate, and friction disk) is a sub-system as part of the drive train. The transmission is another sub-system in the drive train. The two are unique sub-systems. While they work together to complete the drive train, just like the engine and differential do, they will not affect each other in a mechanical sense.

(Note: There are some weird situations where they could intermix, but that is a rare occasion. This also doesn't include dual clutch systems either ... another story.)

The clutch is used to couple the torque/power from the engine to the transmission. The transmission takes torque and multiplies it through gear reduction to make it more usable for the vehicle. It then further transmits that torque/power further along the drive train so it can be used to motivate the vehicle down the road.

If the clutch were to go out, it doesn't affect the transmission's operation. The transmission can still be functioning exactly as it's supposed to. The thing is, it wouldn't be getting any power to do its thing. Looking at the transmission, the clutch can still be working fine. It is capable of coupling/decoupling the power/torque from the engine to the transmission, but the transmission may not be able to use it because it's dead (for whatever reason).

Answer 2

car was leaking transmission fluid

On the urgency of things-to-worry-about scale, this is a 10/10.

questioning my shifting habits

By comparison, this is a 2/10.

Transmissions can go a very long time with bad shifting, but not without lubrication.

Answer 3

OK, riding the clutch is OK from time to time, but will shorten the life of the clutch plate, and also the fingertips of the diaghragm spring. No biggie.

Bad shifting will hurt your gearbox. Grinding gears is a risk. The gear teeth are hard, and unless you have an exotic vehicle, are always in mesh. You should be concerned about the synchromesh cones. Changing down is always hard on them as they have to accelerate mass. Double de-clutching (revving in neutral between the change with the clutch engaged) can help because as far as the gearbox is concerned you may as well be changing up and it is easier to slow down the spinning load as friction is working with you. When the synchromesh is "gone" you'll be doing this to shift up (without the revs) too.

I should stress that the intent of double de-clutching is "good" rev matching. It should be good for your passengers too, and pretty much mandatory for heavy vehicles taking a hill. I've never heard it called transmission fluid in a "traditional" manual it is gearbox oil. These split shaft boxes with two clutches (ala VW/Bentley) should cope with anything automatically but can be fooled into selecting a less optimal gear prior to a shift.

If you have a shifter for a transfer box (Mitsubishi forklift, Austin Champ) for separate forward/reverse you can break a tooth if you shift on the move.

Likewise, only go outside of recommendations on High/Low transfer boxes in life threatening situations. Read the manual.