Clutch Replacement - How-To

Considering the amount of abuse they receive, motorcycle clutches rank right up there with stone axes and anvils in the reliability department. Nonetheless they are an expendable component and as such have to be replaced from time to time. Here's the lowdown.

How do I know I need a new clutch?
Unless you treat your motorcycle in an exceptionally brutal manner, catastrophic clutch failure is rare. Typically a clutch on the way out gives plenty of advance warning, so if yours craps out and leaves you stranded you've got no one to blame but yourself.

One sign the clutch is about to go kaput is a tendency for the engine to flare or rev a little bit, as the clutch slips when you engage the next gear during upshifts, particularly when you're hard on the gas or carrying a passenger. Another is for the engine speed to increase disproportionately compared with road speed whenever you try to accelerate, especially in the higher gears.

If you suspect your clutch is slipping here's a simple test. First make sure the clutch is properly adjusted. While in most cases this means adjusting the clutch-cable free play to factory-recommended specifications, there are some clutches that also incorporate a primary internal adjuster located at the throwout bearing. Your shop manual will provide the 411.

Next, find a quiet stretch of real estate and run the bike through the gears. With the transmission in high gear allow the bike to slow to 35-40 miles per hour and then snap the throttle open. If the engine races and the bike stays put, the clutch is due for replacement.

What kind of tools do I need to replace the clutch?
You won't need a whole lot of iron to replace a worn-out clutch. An OEM shop manual is a must, along with a set of common hand tools, a rubber- or plastic-faced mallet, a gasket scraper and a torque wrench. You'll also need a drain pan and, if you have a bike with Phillips-head screws on its clutch cover, an impact driver.

Toss in the standard expendable stuff like gasket sealer, a can of your favorite aerosol solvent and a handful of clean rags, and you'll be good to go.

As usual I'm going to hedge my bets and tell you that in some circumstances special tools may be required. For example, if your clutch uses a diaphragm-type spring you may need a spring compressor to remove and install it. Your manual will provide the details, and your dealer should be able to order any extra tools you'll need for the job. Last, unless you plan on replacing everything in the clutch stack, which isn't necessarily a bad idea, you should have a caliper or micrometer.

Preliminaries
Before commencing with the wrenching, do yourself a favor and give the shop manual a quick read. If nothing else you'll find out if any other tools are needed or if extraneous parts have to be removed before the clutch cover can come off. The manual should also highlight anything that's peculiar to your clutch. For instance, while many clutches use a given number of friction plates (all identical and all installed in the same way) some bikes have one or more plates that are slightly different from the rest and must be placed in a specific location.

I can't think of a single metric cruiser in current production that doesn't use some variation of the wet, multiplate clutch, so we'll focus the step-by-step procedure on that style of unit.

Removing the clutch cover
Because the new clutch will be somewhat thicker than the old, worn one, start by backing off the clutch cable adjuster. That way when you install the new clutch it won't be preloaded against the throwout mechanism. If your bike uses a hydraulic clutch actuator special procedures may be required, so check your manual.

I can't think of a single metric cruiser in current production that doesn't use some variation of the wet, multiplate clutch, so we'll focus the step-by-step procedure on that style of unit.

Removing the clutch cover
Because the new clutch will be somewhat thicker than the old, worn one, start by backing off the clutch cable adjuster. That way when you install the new clutch it won't be preloaded against the throwout mechanism. If your bike uses a hydraulic clutch actuator special procedures may be required, so check your manual.

Drain the engine oil, then position the drain pan under the clutch cover and remove the cover bolts, noting their length and location in the case. If you're the forgetful type make yourself a cardboard template that mimics the clutch cover to store them (see Tech Tip June '04, "Board Games").

It's highly unlikely the clutch cover will pop right off. Some have pry points cast into them so they can be levered off (your manual will point them out). But unless you know that to be the case, resist the temptation to jab a screwdriver in there and start worrying the thing. All that'll do is gouge the gasket surface and ensure future oil leaks.

One way to remove a sticking cover is to tap firmly around the periphery with your soft mallet-the operative word here being "tap." The idea is to break the bond between the gasket and the cover, not bust a hole in the case. If a few mellow taps won't loosen it, you might have missed a screw or two, so double-check.

Once the cover's loose carefully work it off the engine, watching for any dowel pins that may come off with it, and put it aside for the time being. If the dowel pins did come out with the case, place them back into the crankcase. With the cover out of the way the next order of business is removing the clutch pressure plate.

The pressure plate will be fastened to the clutch with either several coil springs and bolts or one big diaphragm spring and its retainer. Loosen the coil springs a turn or two at a time in an alternating pattern until all the tension has been removed from the pressure plate. Clean and set the springs aside.

If your clutch uses a diaphragm spring read through the appropriate section of your shop manual before trying to remove it, just in case special tools or procedures are required.

Before you remove the pressure plate take a moment to check its orientation. In most cases the plate isn't keyed to the clutch in any particular way so long as the bolt holes line up. But occasionally you will run into one that's indexed to the clutch drum. In those cases failure to get everything lined up will result in a series of frustrating experiments in which you rotate the pressure plate one bolt hole at a time until everything is finally in place and the plate seats properly. If you're unsure mark the pressure plate and the clutch drum with a Sharpie or dab of paint so everything will go back in the same place.

Ease the pressure plate off the clutch, keeping a sharp eye out for the throw-out bearing that's probably going to drop to the floor. Wipe the pressure plate clean and inspect the face for damage. If the plate is heavily scored replace it, but I wouldn't expect to find anything serious unless the clutch suffered a calamitous failure.

With the pressure plate out of the way you can start removing the clutch plates. All multiplate clutches use two types of plates: fiber or composite friction plates, which engage the clutch's outer drum and rotate with the engine, and steel plates that slot into the inner hub and turn with the transmission input shaft.

While I'm sure there's a bike out there that'll make a liar out of me, the first plate in the stack should be a friction disc. Before yanking it out note the way the disc is installed. In some cases radial grooves are cut into discs at a tangent; this allows oil to escape from between the plates as they engage. If that's the case and the plate is installed backward, centrifugal force will tend to trap the oil between the plates and prevent them from seating, possibly causing the clutch to slip.

The next one in the stack will be made of steel. Normally the steel plates can be put in any which way, but make a note of how they're oriented just in case. Continue to remove the plates, laying them out in order so you know which way they'll go back in when it's time to reassemble everything. If you find the plates a little reluctant to leave their nest, a piece of stiff wire bent into a hook will help pry them loose. Occasionally you'll find some oddball pieces in the clutch; anti-judder springs or plates are always popular. As these may or may not need to be installed in a given direction pay close attention when you remove them. With the plates removed, clean and inspect the hub and drum.

Clutches with lots of miles may have notches worn into the splines, which prevent the plates from engaging smoothly, or cracks between the finger webs of the outer drum. If anything significant is found replacement is the only cure. Finally, check the clutch hub nut just to make sure it hasn't loosened up on you. If it has, follow the tightening procedure detailed in your manual.

Inspection and reassembly
Because the clutch was slipping it's a given that you're going to replace the friction discs, so there's no real need to inspect them. My recommendation is to always replace the clutch springs as well, although if the spring's free length is within factory specifications you can certainly reuse them.

Visually inspect the steel plates for damage. If they're scored, galled or show signs of being overheated (they'll be blued as if put to a torch), toss them. If they look good measure the thickness and compare it to the factory dimension. If the plates are within specification they can be reused provided they're not warped. To check, lay the plate on a flat surface (a heavy piece of glass works fine) and see if it rocks or if a feeler gauge can be slid under any side. Even easier: Place two plates together and pinch them at one point. If they separate they're warped. If they don't, flip one of them over and try again. If they remain flat they're fine and can be reused.

The last step before reassembly is to remove all traces of the old gasket from both sides of the case. This can be tedious, but stay with it-the cleaner the surface the better the new gasket will seat and the less likely it'll be to start leaking down the road.

Installing the new clutch
Clutch plates should never be installed dry; both the frictions and the steels should be given a good dousing in fresh oil beforehand. If you've got time let the friction plates soak for at least half an hour in a pan of clean oil to swell them to their working dimensions.

In most instances a friction disc will be installed first, followed by a steel plate. Before you install the first steel plate rub your finger over the teeth. When the plates are stamped the process leaves one smooth and one sharp edge. Some guys like to face all the sharp edges toward the pressure plate, claiming this gives the clutch a smoother action and prevents premature clutch-hub wear. Some point them toward the inner hub, claiming the exact same thing. I've tried it both ways and never noticed a difference, and as far as I'm concerned, so long as the sharp edges all face the same direction it doesn't matter which way they're pointed.

Once the plates have been put in, oil the throwout bearing and install it, followed by the pressure plate. If your clutch has coil springs install the bolts in a criss-cross pattern and tighten them evenly, using your torque wrench for the final setting.

Wipe down the gasket surfaces of both cases with a solvent-soaked rag to remove all traces of oil. Then apply the gasket sealer according to the manufacturer's instructions and let it air-dry. Hang the gasket on the crankcase side, then slide the cover into place and screw it down. Many a good clutch has been ruined by a sticking clutch cable, so inspect yours and if need be replace it before you consider the job finished. Likewise if your bike uses a hydraulic clutch, now's the time to change the fluid. A new clutch will wear in over the first 500 or so miles, so don't be too concerned if the adjustment goes off slightly during that time. By that same token the bedding-in process will contaminate the oil and filter to some degree, though by how much is debatable, so my advice is to halve the recommended interval to the next oil and filter change.

Aftermarket Kits
What's that, bub? You say ever since you built that killer engine your bike's stock clutch slips like the Dynaflow tranny in your Aunt Ethel's '56 Buick, and you'd like to know what kind of upgrades are available? Well, just about everything. There are kits that add an extra plate or two to your clutch, as well as heavier springs and pressure plates. There are even kits for converting your diaphragm spring clutch to coil springs. To see what's available try barnettclutches.com.

Tech Tips
JUMP THIS
Homemade jumper wires the easy way

Deep in the bowels of my toolbox lies what might look like a motley tangle of old wire but in reality is a bunch of highly evolved diagnostic tools that can be used for anything from isolating and repairing complex (and not so complex) electrical problems to effecting a quick, albeit temporary, roadside repair.

What we have here are known as jumper wires. And yes, I do mean wires, not cables. Jumper cables are intended to transport a substantial number of electrons during periods of high current draw-for example, when you're jumpstarting a car or motorcycle-while a jumper wire is used to complete or temporarily bypass a low-current circuit so a component can be tested.

For example, suppose your horn has suddenly given up the ghost, you have no test light or voltmeter handy and you'd like to test the circuit before shelling out for a new hooter. The question is whether the horn failed on its own, has a bad ground or is not receiving current. Because a bad ground is always a prime suspect, you can use your jumper to connect the horn's ground terminal directly to a known good ground. If the horn blows, great; if it doesn't, take a second jumper and connect the horn's 12-volt terminal directly to a known good power source (the battery's positive terminal is the preferred choice). Still no horn? Well, that bites, but at least you know the circuit is working and you won't be wasting your dough on a horn you don't need.

A jumper wire is normally made with about 14- to 18-gauge wire, with either alligator clips secured to both ends or, less often, a terminal of some sort crimped on so the wire can be plugged into the appropriate receptacle on the bike. The raw materials can be found at any hardware, automotive or DIY store, or my favorite spot-the local Radio Shack.

Make your jumpers a convenient length; anywhere from 12 to 24 inches should suffice for most motorcycle-related applications, although there's no harm in making them longer. Most of the time simple primary wire will do, but if you really want to make a nice jumper head on over to an electronics store and ask them for a couple of feet of what's called instrument wire, which is a very flexible, high-quality wire used to make test leads for the electronics industry. If you go with primary wire and want to make a neat job of it, tightly wrap the wire around a pencil or long rod. When the wire is slid off it should retain its coiled form.

I'd recommend making at least two jumpers, preferably using different-colored wire (red and black are always popular) so you don't inadvertently confuse them and connect a power source directly to a ground or vice versa. Of course if you're the overachiever type you'll install an inline fuse holder in your jumper just in case you accidentally ground a powered circuit.

In short (that's an inside electrical joke), the jumper's uses are limited only by your imagination and of course the wire's current-carrying capability.

The clutch adjuster may be located at the lever or built into the cable.
This is one job that can get a little messy.
The dowel pin fits into the shouldered hole; the one from this Sportster cover has already gone south.
Loosen the coil springs like the ones on this Ducati clutch a turn or two at a time to prevent warping the pressure plate.
This tool is used to compress certain types of diaphragm clutch springs so the snap ring can be safely removed.
The throwout bearing usually has a fairly loose fit in the pressure plate, so be careful not to drop it. Note that this one also has a primary clutch adjuster built into it (the threaded rod sticking up). If your bike uses a similar setup make sure it's backed off before you dismantle the clutch.
The friction plate is on the left, the steel on the right.
The typical wet multiplate clutch. That odd-looking riveted plate in the middle of the stack is an anti-judder plate.
The photo's not great but you can clearly see the wear marks in the hub and drum. This one's actually in pretty good shape.
If the steel plates aren't scored or blue from overheating they can be reused provided they're still within specification.
All-new plates and springs are the way to go.
Top: A homemade jumper with an inline fuse. Left: A commercially available jumper. Right: Another homemade set.