If you've ever driven a vehicle with a manual transmission, you know how to depress the clutch, select a gear, and release the clutch while applying power to get the car to move. But what really happens when you depress and release the clutch? Let's get to the bottom of that question.

In its simplest form, the clutch allows engine power to be applied gradually when a vehicle is starting out and interrupts power to avoid gear crunching when shifting. Engaging the clutch allows power to transfer from the engine to the transmission and drive wheels. Disengaging the clutch stops the power transfer and allows the engine to continue turning without force to the drive wheels. To understand how a clutch works, we first need to understand who the players are and how the whole shebang works. So let's look at the basic components: the flywheel, clutch disk, pressure plate, throw-out bearing and linkage.

A large steel or aluminum "disc," the flywheel is bolted to the crankshaft of the engine. The flywheel does many things - acts as balancer for the engine, dampens engine vibrations caused by the firing of each cylinder, and provides a smooth-machined "friction" surface that the clutch can contact. But its main function is to transfer engine torque from the engine to the transmission. The flywheel also has teeth along the circumference, allowing the starter motor to contact when turning the engine over.

The clutch disc is basically a steel plate, covered with a frictional material that goes between the flywheel and the pressure plate. In the center of the disc is the hub, which is designed to fit over the spines of the input shaft of the transmission. When the clutch is engaged, the disc is "squeezed" between the flywheel and pressure plate, and power from the engine is transmitted by the disc's hub to the input shaft of the transmission.

In layman's terms, a pressure plate is a spring-loaded "clamp," which is bolted to the flywheel. It includes a sheetmetal cover, heavy release springs, a metal pressure ring that provides a friction surface for the clutch disc, a thrust ring or fingers for the release bearing, and release levers. The release levers lighten the holding force of the springs when the clutch is disengaged. The springs used in most pressure plates are of a diaphragm-type, however a few use multiple coil springs. Some high-performance pressure plates are "semi-centrifugal," meaning they use small weights on the tips of the diaphragm springs to increase the clamping force as engine revolutions increase.

The "throw-out bearing" is the heart of clutch operation. When the clutch pedal is depressed, the throw-out bearing moves toward the flywheel, pushing in the pressure plate's release fingers and moving the pressure plate fingers or levers against pressure plate spring force. This action moves the pressure plate away from the clutch disc, thus interrupting power flow.

Mounted on an iron casting called a hub, the throw-out bearing slides on a hollow shaft at the front of the transmission housing. The clutch fork and connecting linkage convert the movement of the clutch pedal to the back and forth movement of the clutch throw-out bearing. To disengage the clutch, the release bearing is moved toward the flywheel by the clutch fork. As the bearing contacts the pressure plate's release fingers, it begins to rotate with the pressure plate assembly. The release bearing continues to move forward and pressure on the release levers or fingers causes the force of the pressure plate's spring to move away from the clutch disc. To engage the clutch, the clutch pedal is released and the release bearing moves away from the pressure plate. This action allows the pressure plate's springs to force against the clutch disc, engaging the clutch to the flywheel. Once the clutch is fully engaged, the release bearing is normally stationary and does not rotate with the pressure plate.

Now that we have the parts, how do they all work together? Thankfully, it's not rocket science.

A mechanical or hydraulic linkage usually operates the clutch in a manual transmission. If your vehicle has a mechanical linkage, it is usually either a cable or shaft and lever style. The shaft and lever linkage has many parts and various pivot points, including a release lever and rod, an equalizer or cross shaft, a pedal to equalizer rod, an "over-center" spring (to return the clutch pedal to the rest position), and the pedal assembly that transfers the movement of the clutch pedal to the throw-out bearing. In older vehicles, these pivot points need to be lubricated properly on a regular basis to keep the movement buttery smooth and prevent wear.

If you have a newer vehicle, you're lucky, as pivot points are now fitted with low-friction plastic grommets or bushings. As the older "lube-it-yourself" pivot points wear, the extra play in the linkage makes clutch pedal "free-play" adjustments difficult. When the pedal is released, the assist spring returns the linkage to its normal "up" position and removes the pressure on the release rod. This action causes the release bearing to move away from the pressure plate.

A cable-type clutch linkage is simple, lightweight and is the most common linkage on newer cars today. Normally, a cable connects the pivot of the clutch pedal directly to the release fork. This simple design is flexible, compact, and eliminates nearly all of the wearing pivot points found in a shaft and lever linkage. There is one downside to this type of setup: cables will gradually stretch and can break due to excessive wear and electrolysis.

On a typical installation, one end of the cable is connected to the clutch pedal and a spring is attached to the pedal assembly to keep the pedal in the "up" position. The other end of the cable is connected to the clutch release fork with a fitting that allows for free-play adjustments. When the clutch pedal is depressed, the cable pulls the clutch fork, causing the release bearing to move forward against the pressure plate.

Commonly found in mid- and rear-engine vehicles, a hydraulic clutch linkage is basically a mini hydraulic brake system. A master cylinder is attached to the clutch pedal by an actuator rod, and the slave cylinder is connected to the master cylinder by high-pressure tubing. The slave cylinder is normally attached to a bracket next to the bell housing, so that it can move the clutch release fork directly.

Just like depressing the brake pedal on your car, depressing the clutch pedal pushes a plunger into the bore of the master cylinder. A valve at the end of the master cylinder bore closes the port to the fluid reservoir, and the movement of the plunger forces fluid from the master cylinder through the tubing to the slave cylinder. Since the fluid is under pressure, it causes the piston of the slave cylinder to move its pushrod against the release fork and bearing, thus disengaging the clutch. When the clutch pedal is released, the springs of the pressure plate push the slave cylinder's pushrod back, which forces the hydraulic fluid back into the master cylinder. The biggest plus to a hydraulic linkage is the physics: a small amount of pedal force can be used to manipulate what would normally be a heavy clutch with a shaft and lever linkage.

 

Great stuff. Thanks a lot. Now I can visualize how the clutch disc works when pressing in the clutch. ha ha.

 

I hope that helps... lol.

I'm thinking, from looking at your pics(the first one, actually, tells the most)... that the side with the spline shaft sticking out further from the disc is the side that goes AWAY from the flywheel and toward the pressure plate. But, to be safe, if you're not certain, I would just ask a mechanic in the morning. Just drive it in to any transmission shop and be honest, let them laugh, and then they'll tell you, NO DOUBT, which is the proper side. 99% OF THE TIME, the springs will protrude further out on one side. That is the 'transmission side', because there's plenty of room for it there and it has to slide into the tranny side's bearing(release bearing, right guys???? lol). It doesn't have to slide in far, because it's sharing the same line of teeth on the shaft.(just like on your adjusting tool)... But if you put the side that protrudes inward, it never lets the disc fully PRESS against the flywheel.... which means, in essence, NO GO GO! lol. I doubt it would damage anything to test it out as was mentioned and try to get it in gear, etc., and see if it holds firmly in gear......if you can get it in gear, lol. Getting it in and out of gear is the most telling means to verify.. only problem is, you'd have to install the trans again just to find out?

As i've said, I'm not a pro at this by any means... quite the newb... that's why I mentioned getting help, IN PERSON, from someone who can hold it in their CLEAN HANDS(don't get grease on this... i'm sure you know that,...nor the flywheel!) Pretty sure you could call Aisin in the morning and probably get an answer in 5 minutes. Try either one, if you can't get a FOR SURE answer that you're comfortable with. I mean, why keep taking it apart, it's RISKY of damaging something like the forks, etc., ya know?

Dang, sorry man,.... OOPS! lol.

 

Isn't that the opposite that your clutch says tho? You are talking about the half that points toward the top of the photo in photo 1 of the 3 on the first page.

Here, in this photo.

The first photo is of it straight down, obviously. The second photo is shot of the part that is pointing toward the top of the photo in the fist image. The last photo is of the side in the first photo that points toward the bottom of the image.

edit: shoot, it didn't let me put the photos here again.

 

Well, I think it's only sticking out on yours and not mine because it's a different manufacturer. Mine is a Daikin Heavy Duty Clutch kit from Japan... Maybe that inner ring I'm speaking of(NOT THE PART STICKING OUT ON YOURS.... I mean the ENTIRE ring outside the springs, just before the disc material, got me?) is just more evident on mine, and the shaft cyl just isn't sticking out in mine because my spring set up is a lil bigger, etc. I think I remember that the other side of my disc was almost completely flat, compared to the other side. Let me try to show you in paint shop... I might have to do it tomorrow. But I'll get it up there asap.

 

Ok, now see the 'inner ring' I'm speaking of, outlined in orange??? Ok, see how mine, that section, is literally risen like 1/4" or more from the rest of the assembly, where the disc material is, etc.? If I could turn it over, I could show you that, on the other side, that inner ring is pretty much completely flush with the rest of the disc material surface. Get what I'm saying now?

 

Sure do..... the orange is toward the transmission? If so, that is how it was installed

I didn't do the rear main seal or the pilot bearing, but I think since i'm in there AGAIN I will do it this time around. I'm gonna see if I can call up the dealer and get the rear main seal (I would assume that would be the best place to get a part like that instead of something cheaper from like NAPA, input?) and then head to harbor freight and get a pilot bearing puller.

What's the trick for puttin it in. I've done a lot of bearings, but this is a pretty small one. Use a special tool or what?

 

I would get the seal at the dealer.... WHY SCREW with anything else when it's 7-10$? lol.

Far as the bearing, there are many threads on this, but I did mine with wadded wet paper and an 8mm socket on a ratchet screwdriver. You basically force wadded wet paper in there, over and over, until it forces it out due to pressure. You're pulling the bearing? I'm so tired I'm brain farting,....but I thought you just had to use a seal puller and yoink it out, then press the other one in with a kit I got from kragen for installing bearings... it fit right over the bearing but perfectly onto the edge of the rear main seal... tap tap tap,,, installed! lol.

OHHHHHHHHH, you didn't do the pilot... Ok, well, then just do what I said, or rent a bearing puller kit from autoMoan! lol. Might try the paper thing, it CAN NOT hurt anything, and it usually works for even really frozen ones. You can find it on youtube under "remove pilot bearing" and then look for that one with the paper. One of them is really clear on how to do it and he shows you how it worked.

Night man, I'm up at 5:30... hope it helped some and wish you the best, brudda.... just gotta give you kudos for naming your thread with humility, something you KNEW might get you some smart arse responses, lol. Good idea, NO, BEST IDEA to do it right, once! Turst me, I did a few things many times, on mine, because of OTHER PEOPLES ERROR! Grrrr! lol. Just read my build or even better, troubleshooting threads in my signature, colored below... MAJOR GREMLINS! lol. However, couple things? ...I DID THEM WRONG, straight out, or didn't take extra care to verify, or just had FREAK THINGS HAPPEN! HAHAHA. SORRY, it's emotional for me, lol, jk.

Night man

 

PS> The pilot might be fine, depending on the miles. There are pretty simple tests for that, too. Mainly Noise, BUT ALSO FREE ROLL WITHOUT SNAGGING.... Not 'rolling like a skate wheel, IT SHOULD NOT do that, either. But you should be able to turn it freely and hear no noise. ALL my bearings had 160K on them, and they were STILL PRETTY DECENT, believe it or not. Just sayin... might wanna make sure you need to do it. Of course.... it's not expensive either and probably worth it in the long run while you're in there.. yeah.

 

PSS> Not sure if you know this, but you CAN get 20% off at the dealer counter like I do. Just ask them for an account, for one. Be really nice and explain that you're building these classics, trying to restore one, etc. Also, if that doesn't work or not, even with my 20% off, I've taken print outs of authorized Toyota parts online dealers and they dealership almost always gave me more off. For instance... with 20% I think they wanted 78$ for the TPS... when I showed him the print out, he said, "well, I can do 68$ but nothing less, ok?) WORTH A TRY, RIGHT? Napa DOES carry good seals, too, and good bearings, too, ...you just have to ask if they have 'premium' in some of this stuff. They even carry Altrom, which someone has pretty much proven to me , are Aisin parts.

 

Thanks for the input. I usually just shout out the questions I have on here if I have mulled them over myself, regardless of how dumb they may be. Sometimes I get an answer and can't believe I asked, but it's easy to overlook things sometimes. I'll replace it since I'm there. I already have the replacement. Just have to get it out and I'll be good. The rear main seal should be easy, especially since the housing it goes in unbolts. Can't get much better than that. It think the worst part there is that I have to drain some of the new oil i just put in the engine. ha ha. If I can get the seal and the bearing installed tomorrow I'm going to really grind in the hours and see if I can't get back to where I started this morning, working on the starter, by tomorrow night.

 

Looks like you got this licked.

Ain't working on stuff grand!

:wabbit2:

 

Which way are you referring to because I have heard that it goes either way and obviously that is not correct. Is the way chefyota and I were talking about the correct way? Thanks.

 

You guys are gonna make me go pull the whole body off my jeep just to check if I put in the clutch right -.-

 

That isn't too helpful, but nice to see a local. I'm from Medical Lake, WA.

 

You didn't stop in a trans shop today, brudda? lol... could have answered this FO SHO, ya know? I'm CERTAIN the way I showed you, orange ring, goes toward the transmission side(pressure plate side)...not the flywheel....ON MY TRUCK or YOURS. But your disc is so similar on both sides, other than the shaft housing protruding a lil like that, I just would be guessing, to be honest, Soccer... I still say if you had the side with the spline shaft sticking out further pointing toward the trans... you were right.. .But again, without seeing both sides of it , flat, up close, it's even harder to tell with that disc.

Hope you get it quick....gotta move on to your starting issue, or it wont matter if the clutch is in or not, right? hahah. Have a good one, Soccer, ...I'll check in later.... .Just got back from Chef'n a huge party at a snazy hotel... it's taxing, hahaha. Gotta catch up on some chores here at my private/daily gig and I'll check back.

Mark

 

Nah, I didn't stop in a shop today. woke up, worked, ran in town to get the rear main seal from the yota dealer ($45 with tax, but it's oem so should be good). Then to hardware store for some thread locker to put on the flywheel bolts when I put it back on. Now I'm back at it. I actually have a guy that I'm going to call about it, he's installed a bunch and should be able to help out.

edit:

I've gotten flywheel and everything off. Just reading on the rear main seal replacement (manual instructions). Then I'll get that done and all that bolted back on and ready for the tranny engine mate, which is gonna be a B***h. Sucked when dropping the engine in and I don't really have the right tranny lift, something i fabbed up in about 45 mins and a couple other jacks I've got working with is, including the original yota jack that comes with the truck on a rolling piece of wood. You should see this thing, very sketch. ha ha. It's working though. I'll post up progress as I make it. Should be able to call the clutch guy here real quick.

 

Cool, anxious to hear if I'm wrong or right, lol. More anxious, trust me, FOR YOU TO GET ON THE ROAD! lol.

Far as the seal......45???????? You must mean the rear main seal AND PILOT BEARING.....right? lol

Hope the guys helpful.... that's great!

Mark

 

Nah man. That was just for the rear main. That's what I said, but I'd rather have a good one in there. I don't pay that kinda $$ for parts like that usually, but it's an essential one. Yeah, I got screwed over on it, but it's not that much $$ considering the time it takes to take everything apart. I already had a pilot bearing, so I used that. Just got that in and the rear main seal cover off and cleaned up. Replacing the seal now, but I don't have the gasket that goes behind it. Napa is ordering the gasket in for me, will be here tomorrow. I will have that thing ready to pop on there by that time and then the tranny up by tomorrow evening (gasket really set me back).

 

Just got off the phone with the guy and it is the side you said Mark. The one with the orange on it goes toward the tranny and away from the flywheel. There isn't much difference between which side is "flatter". That term sucks. ha ha