Cable or Hydraulic Clutch

Been looking into a transmission for a custom build. Can someone tell
me if there are any advantages or pitfalls between selecting a cable
vs. hydraulic clutch setup?

 

How strong is your grip? Do you have big strong hands? Maybe you could
squeeze 40 pounds and with a 10:1 clutch lever ratio, you might be able
to throw out a mechanical clutch with 400 pounds of force...

What is the spring rate of your clutch springs, and how many are there,
and how much preload is on them? An engineer would need to know all
that to select a cable system or a hydraulic system...

Hydraulic clutches have better pressure ratios, that's why they are
used on a lot of motorbikes...

Suppose you have a 5/8th inch diameter master cylinder piston and a
2-inch diameter slave cylinder. The 5/8th inch diameter piston has an
area of 0.307 inches. The slave cylinder piston has an area of 3.14
inches...

3.14 divided by 0.307 = 10.2

So, if you can push on the master cylinder with 40 pounds of force, you
can get 400 pounds of force at the clutch throwout bearing...

The slave cylinder piston only moves 1/10th the distance the master
cylinder piston moves, but has ten times as much force as you applied
at the piston...

And, your clutch lever has leverage over the piston too, so the actual
effort it takes for your hand to squeeze the clutch lever is going to
be a lot less than what it would take to squeeze the lever of a cable
system...

 

It's not a motorcycle, but I have a 1990 Nissan Pickup with a hydraulic
clutch.
The ONLY thing that's ever failed on this truck is the clutch slave
cylinder.
mike

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Hydraulic clutches were opriginally supposed to be lighter to operate.
Ho ho ho.

Some people like saying that hydraulic clutches are the only way to deal
with power outputs of 100bhp and over. This is pure crap.

A lot depends on the way the thing is designed. Kawasaki's fuel-injected
Z1300, introduced in about 1984, developed 130bhp and had a cable
clutch, whose actuation (at the lever end) was changed from the earlier
carb model.

If you ever get the chance, look at the handlebar lever, the fulcrum
point, the cable attachment point, and marvel - as I did - at such a
simple and elegant engineering solution.

I don't know any modern hyperbike (say 140bhp-plus) that has a cable
clutch, mind you - but the Z1300 example shows that it may not be
strictly necessary.

My Ducati (see sig) produces about 60bhp, and has a hydraulic clutch
designed for someone who delights in squeezing tennis balls in his fist
for recreation.

 

Looking at your sig, you should know that the Rocket3 is supposedly
140hp-plus, and has a cable clutch - unfortunately.

Actually, I would think the torque output would be a more important
measure than horsepower. Personally, I prefer a hydraulic clutch for
the low maintenance, without regard to the pull.

Gary

 

I have a 20 year old Nissan PU, with nearly 157K miles on it, and I've
been wondering when the slave cylinder is going to give out...

(The first car I ever had with a hydraulic clutch system was a 1957
Jaguar.
It was very difficult to get the transmission to go into first gear
when stopped because it had straight cut gears in first and reverse.
Second, third and fourth were synchromesh. I suspected that I could
help the gear grinding problem by making the clutch release better, so
I rebuilt the slave cylinder and bought a new master cylinder, and
changed the carbon throw out bearing but, it was no use, first gear
continued to grind, it was a feature of that transmission. Wizard
drivers could actually shift into first gear while rolling, but I was
no wizard...)

 

Thanks for that - I honestly didn't know that.

Yes, I think you're probably right.

There is that, but to be honest, the amount of maintenance a cable
clutch needs is minimal - a very occasional twiddle on the adjuster, and
that's it.

 

When you do have to work on the hydraulic system, bleeding all the air
out of the system takes longer than just changing a worn out clutch
cable would take...

The amount of effort required to pull some hydraulic clutch levers in
can sneak up on you...

After riding all day on my GSXR and constantly shifting gears using the
hydraulic clutch, my forearm will become sore, and I start shifting up
without clutching...

The hydraulic clutch on my FZR lacks any feel whatever for when it's
going to engage as I release the lever. Combined with the light
flywheel effect, it's difficult to judge when the machine is going to
start moving from a stop. It's mostly a parking lot and start out
problem that vanishes on the open road...

I complained about this lack of lever feel to a friend who has a cable
release set up from the factory race kit on his FZR. His cable release
system has no more feel than my hydraulic system. The lever has a
totally dead feel to it...

 

That's probably right. But, it's been so long since I had a cable clutch,
I can only remember occasional breakage at the most inopportune
times.

Thanks,

Gary

 

Sure. Here are a few:

A cable won't seep out of a weepy fitting and leave you stranded.

Hydraulics won't fray on the end and break, launching you into traffic at a
stoplight.

You can usually find replacement bits for cable operated clutches at most
independent bike shops and often at HD dealers. That's less often true of
hydraulics, but hydraulics are more resistant to wear so it's less of an
issue.

With hydraulics you can easily figure out your master/slave ratio to change
the force necessary to operate the clutch.

Cable operated clutches have more feel than hydraulics. Or perhaps it's that
they have a different feel. With a cable clutch you can feel the engagement
point of the clutch in your hand (or foot, in my case). You can't with a
hydraulic clutch. At least I can't. With a hydraulic clutch I have to feel
the engagement point by sensing when the bike is just starting to move.

If you want to worst of both worlds, you could set up a hydraulic clutch with
a remote, cable operated master cylinder.

Regarding the slave cylinder, since you're posting this to a harley group, I
assume you're building some sort of harley clone. All of the hydraulic
clutches I'm aware of for these trannys incorporate the slave cylinder
directly into the end cover of the transmission.

While shopping these, make certain that there is a reasonable way to check
and add tranny fluid. I picked up one cheap from eBay ( a Ness thing) that
works fine, but there's no dip stick to check the tranny oil, no sight window
to check the oil level,and the only way to add oil is through a tiny little
fucking 3/8" bolt hole on top of the cover. Ever try to replace you tranny
oil through a 3/8" hole? Sooner or later I'm gonna meet Arlen Ness and I"m
going to bitch slap the son of a bitch for being so goddamned
form-over-function.

 

Cables stretch, pieces wear... it's insidious.

Hydraulic always maintains the same feel. The fluid reservoir
compensates for any slack that would otherwise be felt at the clutch lever.

The other replies about pressure ratios, torque, etc. are nonsense.

 

Go find a master cylinder and slave cylinder with the same piston
diameters and report back here when you do...

 

Go find a master cylinder and slave cylinder with the same piston

Your answer to the question of cable vs. hydraulic was
"Hydraulic clutches have better pressure ratios, that's why they are
used on a lot of motorbikes..."

You clearly seem to think that cable systems have simple 1:1 ratios,
with no force multiplication. So go find one, and report back.

 

Consider yourself lucky that it wasn't the brake m/cylinder that decided
to have an off day =:0

 

No, I never said that I thought any such thing. Obviously a clutch
lever is a clutch *lever*, and there is force multiplication at the
cable end of the lever...

But a hydraulic system has two kinds of force multiplication, pure
lever and the pressure ratios of the two systems...

You might see master cylinders and slave cylinders with approximately
the same diameters in foot-operated systems, like a car's hydraulic
clutch throwout system, but motorbikes are going to have to have a
small master cylinder diameter and a large slave cylinder diameter to
multiply force, or the rider needs forearms like a gorilla to squeeze
the lever and the similar piston diameter hydraulic system becomes
nothing but a fluid cable that never needs adjusting...

 

Nicely put. Succinct, clear, and accurate.

I can tell you don't do technical writing for a living. Your description is
much too clear.

 

But you ignore that there may be additional mechanical advantage applied at either end of the cable.

For Harleys, various ball-and-ramp assemblies and modifications are available to adjust clutch pull
to the rider's preference.

If the clutch throw-out is operated by an external lever, a sliding extension would allow you to
tailor the clutch pull to get the lightest pull while still getting enough travel for full
disengagement. With hydraulic, you're stuck with one MA unless you choose to replace one of the
cylinders. Aside from the expense, fine tuning of bore diameters would be limited by the
availability of seals of the desired diameter.

I still prefer hydraulic as they are self-adjusting and eliminate the need to make compromises in
cable routing. If the original cable of my FLHRCi fails in the *next* 110,000 miles, I'll probably
switch to hydraulic.

 

Think that was clear? What does "the pressure ratios of the two systems"
mean?

First, krusty wants us to believe that two *kinds* of force
multiplication are somehow stronger than two multiplications of the same
kind. Nonsense!

And then, as James Clark noted, krusty just ignores leverage at the
other end of the cable anyway! That leverage is analogous to the slave
cylinder. Why did krusty forget it?

 

<snip>

I'll take his advice over yours. Sorry, old chap.

 

How kind of you, sir...

The original poster cross posted his enquiry to rec.motorcycles.harley
and rec.motorcycles.tech and never responded to any message of advice.
Somebody else crossposted the message to rec.motorcycles...

Now the thread will live forever, it may grow to hundreds of messages
in length as the trolls and flamers and users who are weeks behind in
their important task of monitoring all their Usenet NG's...