How much damage do these beginner mistakes cause?

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RITmusic2k
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Re: How much damage do these beginner mistakes cause?

Post by RITmusic2k »

Part 2.

Okay, where were we?

Ah, yes. We need our input shafts and output shafts to be turning at the same speed when we're shifting. I glossed over it before, but to be conceptually accurate you should consider the output shaft and the gears of the input shaft to be a single unit They're moving parts, but they're always moving in lockstep. So we're not really coupling and decoupling the input shaft and output shaft to each other, we're coupling and decoupling the input shaft and its own gears. But for the sake of readability, I'll describe it as coupling and decoupling the input shaft and the output shaft.

So, the above accounts for all the 'fixed' parts. By this I mean there is no room for error, connections are all or nothing. if you're a driveline, an output shaft, a gear, or an input shaft, you're either perfectly engaged or perfectly disengaged, no in-betweens. As you can imagine, it's very difficult to transition instantly from an engaged state to a disengaged state, especially when parts are moving relative to each other. ESPECIALLY especially when one of the parts you're trying to connect to is a turning engine in a vehicle sitting still. As such, we have to introduce some slippery, slidey parts into the mix between the fixed parts in order to make it possible to variably and gradually connect two halves of the system.

This is what your clutch and synchros do. Let's first look at the clutch system:

Your engine has a crankshaft. The speed of the engine is the speed at which the crankshaft rotates. Bolted to the end of the crankshaft is a disc called the flywheel. It's large, heavy, and has enough inertia to smooth out the sequential explosions in your engine's cylinders, so that when the engine is running, you get a steady rotation and not a constant series of jerking twists with each firing cylinder. Facing the flywheel, and in fact pressed against it, is your clutch disc. Now The clutch and flywheel are basically made out of the same stuff as your brake pads and rotors. And if you've ever skidded to a stop in an emergency, you understand that those two materials which slide past each other in normal circumstances will completely lock up when pressed together hard enough. But while your brakes' default position is "not pressed together", your clutch and flywheel's default position is "pressed together like a sonofabitch". When your clutch pedal is out and the clutch is fully engaged, it might as well be welded to the flywheel. They are turning together. But just as you can gradually modulate your braking force, you can modulate the degree of connection between the flywheel and the clutch, in a process called 'slipping'. It means that the farther down you press the clutch pedal, the less pressure is applied to the clutch and flywheel interface until they are completely separated from each other. The range of travel between "fully engaged" and "fully disengaged" is occupied by a variable and progressive range of connection. It's like picking a bike tire off the ground and spinning it as fast as you can, then holding your hand against the tire rubber to slow it to a stop. The harder you press, the more you absorb the speed of the tire until you finally bring it to a stop. Your hand also got quite hot in the process. And that, at the end of the day, is what a clutch and flywheel are designed to do: convert a difference in mechanical speeds into heat. If two things are spinning at similar speeds and are brought to the same speed over a long period of time, then there isn't much heat to absorb at any given moment. If things are spinning at very different speeds and are brought together quickly, then a whole hell of a lot of heat is going to be generated. This isn't super important to the main point right now, but it is an important thing to understand when driving a manual transmission vehicle.

So we've seen how the engine connects to the clutch through its interface with the flywheel. And what's on the other side of the clutch? Our old friend the layshaft. So to recap, with the clutch pedal released and the engine fully engaged, if the engine is turning then the layshaft is turning at the exact same speed. It's like one continuous piece. And to recap from the other end - if the car is moving, then the system of the wheels/ driveline/output shaft/transmission gears are also turning in lock step. If the car is not moving, then all those parts are all sitting still, not rotating at all.

So the only parts left to discuss are your synchronizers, or synchros. These are slippery slidey parts just like the clutch and flywheel, except that they work on a much smaller part of the system - the layshaft and its gears. The other difference is that they work without any direct control on the part of the operator. Stripping everything else away for the moment, remember that the gears on the layshaft are not permanently connected. In fact, they usually spin freely, all at different speeds (since they're connected to different sized gears on the output shaft - this is how we get different gear ratios). But by moving the gear shift into its different positions, any one of the gears may be mechanically linked to the layshaft by a series of teeth that interlock with each other. This is easy to do with both parts sitting still. But what if the layshaft is spinning and the gears aren't, or vice versa? Or what if they're both spinning, but at different speeds? Well, the synchronizers are basically a set of nested cones of friction material - one set connected to the gear, and the other set connected to the layshaft (and can slide along the length of the layshaft because it sits in splines - grooves that run lengthwise along the shaft). When you push the gearshift towards the 1st gear position, for example, you're pushing the 1st gear synchro collar along the layshaft until it starts to touch the 1st gear itself. As the friction surfaces of the synchro cones come together, then the speed difference between 1st gear and the layshaft starts to get absorbed. Eventually, by pushing hard enough or by waiting long enough... the difference in speeds is eliminated, the teeth line up, and the collar fully engages. Now the layshaft is directly connected to 1st gear. All the other gears at this time are spinning freely because their collars are not engaged. If you move the gear shift back into neutral, then the collar pulls away and the layshaft is once again spinning independently from all gears. If you move the shifter to 2nd gear, then the process plays out again on a different gear and a different collar on the layshaft.

The takeaway from this last section is the same as it was for the clutch section. The bigger the difference in rotational speeds between the layshaft and any particular gear, the more work your synchro is tasked with doing to bring those speeds in line with each other by pressing against them really hard and generating a lot of heat.

Stay tuned for part 3 (coming later this afternoon)
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novasorc
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Re: How much damage do these beginner mistakes cause?

Post by novasorc »

Thank you for that great explanation. I've got a much better picture of the situation now. I definitely intend to read more, just haven't found the time.

While researching a weird sound from my gearbox, I suspect I may have worn down my synchros a bit by shifting directly to 1st gear too early when approaching a stop sign. I was under the impression it made no difference as long as my clutch was depressed. I've noticed a slight crunching noise when moving my knob from 1st to 2nd and 2nd to 3rd. I suspect this is related to the synchros, but I have low confidence regarding my diagnosis. It seems unlikely I could wear my synchros this fast after having my car for just a week. The only really bad thing I've done was accidentally shift into 1st at 25-30 mph and stall a few times. Are there any other reasons I could be noticing this noise between these two shifts? The shift from 3rd to 4th is clean and smooth.

Thanks.
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Re: How much damage do these beginner mistakes cause?

Post by theholycow »

It is extremely unlikely that you could have caused any problem like that. Most likely the gearbox is just notchy or crunchy and you didn't have the experience necessary to notice it before.
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Re: How much damage do these beginner mistakes cause?

Post by novasorc »

theholycow wrote:It is extremely unlikely that you could have caused any problem like that. Most likely the gearbox is just notchy or crunchy and you didn't have the experience necessary to notice it before.
Haha thank you. I think I'll just try to worry less and practice for now. This is the first car I've ever owned, so I've been trying to be extra careful. I guess manual cars are more durable than I suspect.
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Re: How much damage do these beginner mistakes cause?

Post by IMBoring25 »

You wouldn't have hurt the second- or third-gear synchro going into first, either.
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Re: How much damage do these beginner mistakes cause?

Post by Squint »

novasorc wrote:
theholycow wrote:It is extremely unlikely that you could have caused any problem like that. Most likely the gearbox is just notchy or crunchy and you didn't have the experience necessary to notice it before.
Haha thank you. I think I'll just try to worry less and practice for now. This is the first car I've ever owned, so I've been trying to be extra careful. I guess manual cars are more durable than I suspect.
That is one of the hardest things for people to learn when they first start driving a stick. The car is designed to take abuse and keep on ticking. Think about it this way: there are tons of people out there driving manuals that DON'T care about the why/how their car works and what might damage it... and their cars still keep on going for a while.

This is not to say you can't damage your car, but it is harder than you might suspect from normal driving occurrences.
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Re: How much damage do these beginner mistakes cause?

Post by RITmusic2k »

So I lied about when part 3 was coming. My bad! Everything I wrote up so far was background information, but none of it addressed your questions about shifting smoother. So I'm going to finish that up today (though not right now).

EDIT: okay, maybe tomorrow - work got pretty busy today.
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Re: How much damage do these beginner mistakes cause?

Post by novasorc »

RITmusic2k wrote:So I lied about when part 3 was coming. My bad! Everything I wrote up so far was background information, but none of it addressed your questions about shifting smoother. So I'm going to finish that up today (though not right now).

EDIT: okay, maybe tomorrow - work got pretty busy today.
Sure. Take your time. I'll read it for sure.

If this might help anyone, I read that Mazda shifters can have a notchy feeling in cold weather, when the car isn't warmed up enough. So, I think that explains it. The daily temperatures have dropped from about mid-high 60's from when I first got my car to low 50s, high 40s.
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Re: How much damage do these beginner mistakes cause?

Post by potownrob »

novasorc wrote:I've never driven manual before and I've been making some mistakes that are surely causing wear on my car. I'd like to know how bad each one is and if I should really worry about it.

Today, I accidentally let go of my clutch when I downshifted from fifth gear to first gear while preparing for a stop light. I heard a noise similar to one using a sander on a floor. I'm guessing this is from the clutch not being able to grab on fast enough so it made that noise.
sorry i'm late. you need to stop driving immediately and send your car to me so i can "fix" it for you. :) 8) :lol: :twisted:
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Re: How much damage do these beginner mistakes cause?

Post by Squint »

potownrob wrote:
novasorc wrote:I've never driven manual before and I've been making some mistakes that are surely causing wear on my car. I'd like to know how bad each one is and if I should really worry about it.

Today, I accidentally let go of my clutch when I downshifted from fifth gear to first gear while preparing for a stop light. I heard a noise similar to one using a sander on a floor. I'm guessing this is from the clutch not being able to grab on fast enough so it made that noise.
sorry i'm late. you need to stop driving immediately and send your car to me so i can "fix" it for you. :) 8) :lol: :twisted:
No, you'd just trade it in for an automatic again. :twisted: :twisted: :lol:
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Re: How much damage do these beginner mistakes cause?

Post by potownrob »

Squint wrote: No, you'd just trade it in for an automatic again. :twisted: :twisted: :lol:
not if it's a Miata. Please tell me he's got a Miata (tl;dr) :o
ClutchFork wrote:...So I started carrying a stick of firewood with me and that became my parking brake.
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Re: How much damage do these beginner mistakes cause?

Post by Squint »

potownrob wrote:
Squint wrote: No, you'd just trade it in for an automatic again. :twisted: :twisted: :lol:
not if it's a Miata. Please tell me he's got a Miata (tl;dr) :o
According to his profile, it's a 3 sGT.
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Re: How much damage do these beginner mistakes cause?

Post by novasorc »

Hey guys. I've been practicing more and getting better at driving. I have some new questions now.

Do you recommend adding gas while releasing clutch on an upshift, or just push-in, shift, and let out really fast?

Also, today, I brought it up to like 6000 RPM in first gear and quickly shifted to second gear and let go of the clutch pretty fast and it immediately dropped to 4000 RPM. Is this bad for the car, or was it designed for this to happen? I thought I might've smelled something funny, but I'm not sure if that would even be possible in this scenario.

Thanks.
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Re: How much damage do these beginner mistakes cause?

Post by theholycow »

novasorc wrote:Do you recommend adding gas while releasing clutch on an upshift, or just push-in, shift, and let out really fast?
If you can do the second one smoothly enough for your comfort, that's my preference. Both techniques are acceptable.
Also, today, I brought it up to like 6000 RPM in first gear and quickly shifted to second gear and let go of the clutch pretty fast and it immediately dropped to 4000 RPM. Is this bad for the car, or was it designed for this to happen?
It's not great for the car but neither is doing the same thing in an automatic. When you're in a hurry, that's just what you do. I did it a bunch of times yesterday...
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Re: How much damage do these beginner mistakes cause?

Post by novasorc »

theholycow wrote:
novasorc wrote:Do you recommend adding gas while releasing clutch on an upshift, or just push-in, shift, and let out really fast?
If you can do the second one smoothly enough for your comfort, that's my preference. Both techniques are acceptable.
Also, today, I brought it up to like 6000 RPM in first gear and quickly shifted to second gear and let go of the clutch pretty fast and it immediately dropped to 4000 RPM. Is this bad for the car, or was it designed for this to happen?
It's not great for the car but neither is doing the same thing in an automatic. When you're in a hurry, that's just what you do. I did it a bunch of times yesterday...
Thanks. Is there any systematic way to tell what RPM I could dump the clutch at? I actually prefer to dump the clutch when upshifting, since it seems easier, but I don't really know what RPM I should look for during each shift.
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