How a clutch works and what it does.

[97GSTspyder]

Yeah I'm bored, have a little free time and I figured this may help some people out there in DSM land. I've searched to see if there were any posts like this already and couldn't find any. When I first got my GST Spyder, I loved it. When the motor blew up along with damn near everything else, I was curious as to how these things worked. I had no knowledge about cars really. So I sat here every night on the internet learning the best I can about clutches, turbos, engines, transmissions, etc. In this post I will attempt to explain (to the best of my knowledge) of what a clutch is, and how it works. I figure most all of us push in that pedal every day, multiple times. So i thought maybe there were a few people in here that would like to know a little more about them. This is a long one, so if you're interested in reading, grab a beer and a few slices of pizza lol.

So what exactly does the clutch do, and why do we need it?

Simply, the clutch sits between the engine and transmission. It connects/disconnects the two. We need it to drive, obviously. Not technical enough? Keep reading.

Cars need clutches because the motor is constantly spinning (unless it's off) and the wheels are not always moving. The clutch allows us to engage the motor to the transmission, which in return, spins the wheels.
What happens when your clutch is to the floor, you have the transmission in 1st, and you let up on the clutch slowly? The clutch slowly starts to engage the motor and tranny and puts power to the wheels and you start rolling forward.
What happens when you clutch is to the floor, you have the transmission in 1st, and you quickly let up on the clutch? The car stalls. Why? Because since the clutch sits between the motor and tranny, the engine is spinning, the clutch is not (if it's disengaged). When you quickly engage it, it stalls because there was not an even feed between the speed of the motor and how quickly the clutch was let out.
Now if you revved it to 3,500rpm's, and let the rpm's stay there solidly, and then "popped the clutch", what would happen? You would start to spin tire (if you're FWD), and your rpm's would bog down.
Ok now, let's take the same car (FWD), and let's jack up the front end. Put the clutch in, put the tranny in 1st gear, and let the clutch out faster than you normally would. Didn't stall, huh? Why not you ask? Because there is no load on the motor. When the drive wheels are on the ground, there is a load being put on the motor when you start to accelerate/move. The motor actually has to do much more work.
Ok now that you have the basic idea of how a clutch works and what it does, let's get into the mechanics of it.
A clutch assembly consists of these following items.

Clutch plate
Pressure plate
Throw-out bearing
Pressure plate to Flywheel bolts

When you purchase an actual clutch assembly, you'll usually get the first 3 mentioned, from my knowledge.
Now keep in mind, there are still other parts I haven't yet mentioned.

So what all happens when you push that clutch pedal in?

Since our cars are hydraulic clutches, i'll explain.
Our cars are equipped with a master and a slave cylinder, for our clutches. They use brake fluid. When you push the clutch in the slave cylinder pushes on the release fork, which then pushes the throw-out bearing against the center of the pressure plate's 'fingers'. Doing all of this takes the pressure off of the clutch plate, disengaging it from the motor's spinning flywheel.

What happens when I release the clutch pedal?

Pretty much the opposite. Slave cylinder pulls away, release fork comes back to where it was, throw-out bearing comes back with the fork, pressure plate pushes clutch plate on to the flywheel and holds it there with so many pounds of force so it will not slip.

What is slipping?

When the clutch slips, most everyone will notice it. It's when the clutch plate and flywheel are engaged, but when a heavy load is applied, the clutch begins to slip. Meaning the clutch plate is 'slipping' on the flywheel. So what happens? Engine RPM's increase, with no increase in vehicle speed. What can cause it to slip? Usually grease or some other foreign substance on the clutch components. The clutch plate has a friction material to 'grab' and stick, so it doesn't slip. The operator can purposely slip the clutch, which isn't good for the clutch. This is done by revving the motor to a certain rpm, let's say 2,000rpm's, and the clutch being let out slowly. In either case, it is not good on the clutch.

Ever wonder why you see those springs on a clutch plate? Those are for helping the tranny take the shock of the clutch being engaged.

How does a clutch wear down? Only when the clutch plate and flywheel are spinning at two different speeds. This happens when engagement occurs, or slipping. The clutch will wear out much more quickly when slipping occurs. This is why it's not good to slip it. When the clutch plate and flywheel are engaged, they are locked tightly together and they both spin in sync, transmitting power to the wheels and no wear occurs.

Ever have your car shake/rattle badly when the clutch is engaged? To the point where it feels like the motor is going to grow legs and hop out and run away? Haha, I've had this problem more than once. The cause of this could be warped clutch plate/flywheel/pressureplate, or bad throw-out bearing. Usually if there is a problem with the throw-out bearing, engagement will be rough and usually the clutch will not completely disengage from the flywheel. This causes more wear and tear on the clutch components. Also, not good.

Ok, I'm going to try and break everything down.

You have the tranny, clutch and motor. Clutch sits between the tranny and motor. It is a device that engages/disengages the two. Since the motor constantly spins, and the wheels don't, there must be a way to 'disconnect the wheels'. So when you come to a stop, the motor doesn't stall. Any of you newbie's ever come to a stop and forget to push the clutch in and the car stalls? It's because the clutch is engaging the motor and tranny together. The wheels want to keep turning, but when you stop, the wheels stop spinning and causes the flywheel to stop spinning, resulting in a stall. That's why you disengage the clutch by pushing it in. Simply, it disconnects the wheels from a spinning motor so the motor can continue to spin when you stop. The clutch allows us to engage an engine that is spinning to a dormant transmission. Which in turn, like mentioned before, causes the wheels to spin. Simply, you have the clutch plate against the flywheel, then the pressure plate against the other side of the clutch plate with the fingers toward the tranny. The bolts go through the pressure plate to the flywheel. The clutch plate has splines in the center hole. This is where the transmission input shaft goes. The release fork is on the transmission. The throw-out bearing connects to the release fork with a clip. The operation on how this all works is explained above. When the clutch is engaged, the transmission input shaft turns at the same speed as the engine.

Normally when driving a manual transmission car, you want an even feed between the throttle pedal and clutch pedal. This is so the clutch can engage smoothly and the car starts rolling. The more throttle you give it, the faster the flywheel spins.
'Dumping' the clutch is a common term used. Otherwise known as launching. It's when you rev the car to a certain rpm (say 3,000) with the clutch being disengaged. You dump the clutch while in 1st gear, and give more throttle and you launch. Normally with FWD you spin tire. AWD just takes off like a hungry beast. Keep in mind, any time you launch you're putting much more stress on everything so things are more likely to break. I have pics posted in one of my threads of my Centerforce Dual Friction clutch that was fried. Here is the link. http://www.automotiveforums.com/vbul...d.php?t=348734

It has pics of my shattered throw-out bearing and my warped clutch plate and pressure plate. Notice how the clutch plate is purple/blue. That would be from heating it up lol.

Well everyone, I'm sick as hell and can't think all that straight so if I left something out, feel free to add something/correct me. I just figured this might help some of you understand how a clutch works.

[PearlGT]

pretty good read. Most know the rules of driving a manual transmissions (aka use your clutch if you don't want to stall out) but not exactly how everything works.

[JoeWagon]

Good stuff, enjoy being at the top for a while.

[99JLEclipse]

Thanks this gives me a great understanding of it all. I got how it worked but not exactly this make me picture it in my head.

[xavier3jr]

good write up kevin

[Gsx_hooptie]

Originally Posted by xavier3jr

good write up kevin

Consider it a compliment?

[97GSTspyder]

is that a compliment or do you think i'm trying to be like kevin? if it is a compliment, thanks. being that kevin is one of the most knowlegable people in here. if you thought i was trying to be like him, that's not the case. i just figured this post would help and educate some people.

[kjewer1]

I think that was a compliment. Hard to tell with no smileys or anything though

Looks good, not sure why I didnt see this sooner. Gave it quick once over, the only mistake that stuck out is saying the springs that absorb the shock from engaging the clutc are on the clutch plate, which is another term for the pressure plate, and I'm sure you meant to say clutch disc. Otherwise it seems to be quite accurate.

I'll add what had me confused for the longest time, if this was in there and I missed it I apologize for the repeat. I always wondered how pushing the clutch fingers toward the flywheel disengaged the clutch. I found out years later that they are on a flucrum, so pushing the fingers toward the flywheel pulls the friction surface away from the disc. A wave spring typically provides the clamping force when those fingers are released. Seems so simple know, but I couldnt get my head around that until one random day when I was loking at a plate, and I knew a little more abou the whole system. Good times...

Edit> This is also why on a 2600 and heavier ACT clutch the fingers are much thicker than stock or 2100 pound plates. Apparently stock fingers will just flex when trying to overcome that 2600 pound wave spring. Note that the fulcrum is very close to the plate end, so the throw out bearing has a lot of leverage against the wave spring. The thicker fingers allow transfer of that motion with none lost to flexing.

Edit again> Waiting on sme bullshit at work, and I'm ina generous mood, so I might as well explain a little further about hte hydraulics and the flywheel.

Hydraulics. All hydraulic systems, wether the brakes, the cluthc, etc, share some basic princicples. You are using an incompressible fluid to transmit work. You can increase power, but not work. When you step on the clutch pedal, a piston in the master cylinder displaces fluid, pushing it towards the slave. The corresponding piston in the slave will move as the fluid pushes on it. This is what moves the throw out fork, throw out bearing, clutch fingers, and ultimately the friction surface. The spring in the pressure plate will resist this motion, so pressure will build in the hydraulic system. A basic formula worth remembering is pressure times area equals force. Lets say the pressure in the system is 1000 psi, and the slave cylinder piston is a 1 sqaure inch area. You will have 1000 pounds of force. Lets say you double the piston size to 2 square inches, now its 2000 pounds of force. Pretty slick, but there no free lunch with physics. The amount of fluid you have to displace doubles as well, so that means an increased stroke, or a larger master piston required. Thats why the work doesnt change. If you cut the force required at hte pedal in half, but double the stroke, work hasnt changed. Etc.

WTF is a flywheel? Its a battery for mechanical energy, to put it simply. Mechanical (kinetic) energy is stored in the spinning flywheel. The heavier the mass, the more energy it stores. Jsut like a capacitor wil release stored electricity when needed, so will the flywheel. When you engage the clutch and it tries to pull down engine rpm, the stored energy in the flywheel will try to keep it running. Its essentially a mass in motion that wants to remain in motion. When going to lighter flywheels you are moire likely to stall when letting the clutch up, because less stored energy is available to try to keep the motor turning. In response to that poeple rev a little higher before letting the clutch out, which of course puts more energy into the flywheel to compensate.

Hope that makes some sense, I had some actual work come up and got distracted in the middle of it

[spyderturbo007]

Originally Posted by 95 GSXracer

When you step on the clutch pedal, a piston in the master cylinder displaces fluid, pushing it towards the slave. The corresponding piston in the slave will move as the fluid pushes on it. This is what moves the throw out fork, throw out bearing, clutch fingers, and ultimately the friction surface.

Why use both a master and slave cylinder. If all the master cylinder is doing is pushing the piston in the slave, why not eliminate the slave cylinder (one less thing to break )???

[97GSTspyder]

Originally Posted by spyderturbo007

Why use both a master and slave cylinder. If all the master cylinder is doing is pushing the piston in the slave, why not eliminate the slave cylinder (one less thing to break )???

you need the slave because the piston in the slave is what pushes the fork, which in turn throws the bearing towards the pressure plate, relieving the pressure, disengaging the clutch.


as for the mixup, you all probably knew what i meant. the springs on the clutch DISC. sorry, i have always called the actual clutch disc both terms. clutch plate and clutch disc. i just called the pressure plate, well, pressure plate. sorry if this caused any confusion.

[kjewer1]

You need something to MOVE the fluid, and something to BE MOVED BY the fluid. Most often, a pump moves the fluid, and a piston/cylinder or a motor is moved by it. In our case, we are basically just using another piston/cylinder in reverse to move the fluid, its simpler and cheaper and more reliable.

Don't worry about the terminology mixup, after a while it all just runs together I thought I'd point it out before some one jumps in with an asshole comment.

[xavier3jr]

uhhh my bad lol i was hafe asleep and drunk when i read this and seemed like somethin kevin would do so i just figured it was him for some ungodly reason lmao so yea i guess consider it a complement

[JoeWagon]

Added to the FAQ. Hope to see this brought up again if someone has a related question.

[Trueeclipse]

You know where I can get a shop manual to guide me on installing my clutch?? Like a free one?

[JoeWagon]

you can buy the manual or look for a FAQ on www.vfaq.com