SLIPPER CLUTCHES - How they work, & STM UPGRADE

[HardRacing]

SLIPPER CLUTCHES

So, obviously Slipper clutches are something most guys like having. Or the Manufactures
wouldn’t make them standard equipment on nearly all new bikes. It cost them more money,
then a regular clutch so obviously market research shows it’s a good product to have as
standard equipment.
Unfortunately, not all slipper clutches are the same. The ones that come standard in OEM bikes
are the least expensive and just barely do their job. Which is what OEM wants. Cheap, and easy. :-)


After having used STM Clutches on our previous bikes, and seeing them Firsthand how well quality,
fit, finish, and performance is.. we had to add one to our Project BMW S1000RR Bike.

Unlike some of our other mods, this one obviously takes a little time, to install. But, it’s Sooo worth it.
In this write-up, we will explain the procedure and show detail photos on what makes it better.
Even if you just plan on swapping out your clutch pack some day, this post will help you out.

So to make sure we are all on the same page, the concept of a slipper clutch is to prevent wheel hop.
Because, wheel hop means you’re losing control of your rear, and often can cause a crash.
What happens is you dive into a corner, drop the gears down, and let out the clutch too fast.
Your rear tire is spinning faster than your motor, so what happens is rear tire is trying to rev up your motor.
And if you’re doing this really fast, the tire loses traction and starts to hop.
Now, if you have never felt this before, it’s probably because you don’t ride aggressive. (NOT to be insulting).
Just stating the facts.
Because even the best riders in the world, (Rossi, Stoner, Lorenzo, Hayden…etc) ALL use Slipper Clutches.
Most of them use STM Slipper Clutches.
So it’s not a matter of.. “Oh I let my clutch out perfect and rev match 100%... so I don’t need a slipper Clutch” ,
cause even the best riders in the world cannot ALWAYS do that.

If you have never experienced wheel hop, then you probably don’t need a slipper clutch.

But, for those of us, who DO ride our bikes aggressively, and like to dive into the corners,
and NOT worry about wheel hop, then a Slipper clutch is a must have.


HOW IT WORKS:
Well, basically the Slipper clutch has these things called RAMPS. You will see us use that term a lot,
as that is the KEY Element in slipper clutch. These ramps, are what separates your pressure plate
from your drum, allowing your clutch plates to “Slip”. The Ramps are built into the hub,
and work in similar fashion to when you “Feather” the clutch. This way your Rear tire and motor can
match up equal speeds and no wheel hop.

Well on your stock clutch you only have 3 ramps. And they move up and down metal on metal.

That means, lots of friction, and NOT very smooth disengagement.
Where as the STM moves on 6 ramps, and each has Roller bearings on these ramps for nearly ZERO Friction, a
nd ultra smooth disengagement.

It also means, that WEAR is nearly eliminated.. for more durability, and longer lasting.
The Stock clutch uses coil springs, which work great in a normal clutch. But, for a Slipper clutch
they cause it to bind and pinch, as the Ramps do their job, they are fighting with the Coil springs
which don’t like to be rotated..
The STM Clutch uses a Diaphragm pressure spring which does not fight against the rotation and
separation of the ramps. Thus again, smoother, linear clutch slipping when you need it.

Unfortunately, as with most modifications, you really cannot appreciate what we are saying unless you try it.
Kinda like upgrading your suspension, or new brakes, or new tires, or new damper….etc
It just has to be felt.
All we are trying to do here in this write-up, is to EXPLAIN the physics behind a Slipper Clutch, and
how it works, and why some are better than others.

Now that we have that out of the way, let’s get to the install.

First thing WE did was drain the oil (coincided with our 600 mile oil change). This way when we remove
the clutch cover, there is no leaking. Pretty sure the oil level would pretty close to the bottom of the cover.
We always recommend plastic or alum. foil to guid the oil into the pan, and not on your head pipes, or anywhere else.


Once the oil was drained, and the filter swapped, we removed the cover.
Pretty straight forward, just unscrew the bolts, and take it off. The cover is held in perfect alignment
by two Press fit dowels that stay in the motor. So as you pull the cover off, you need to slightly tap the
cover with the handle of a screw driver to help release it. Just be patient as you remove it. Don’t try and
man handle it. It will just pop off if you are gentle with it.
If you’re lucky your OEM Gasket won’t tear, and will just come off.
If so, you should be able to reuse it. BUT, if you do tear it….. Get another one. They are cheap.

So now that you have the cover off, you will see this



Notice the 2 Pressed Dowel pins we referred to earlier.


Next you take an Allen key and remove all the coil springs one at a time, crossing back and forth
like you do with Wheel Lugnuts. Once you are down to your final 2… back them out Equally and
evenly together, so there is no binding of your clutch pushrod.


Once you have removed all your springs, you will need an air gun to remove the Stock Nut.
That’s the easiest way to get it off. Once your nut is removed you can slowly work out the
complete Clutch Hub in one assembly.

Now you will it will look like this.


...To be continued.


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[HardRacing]

....


There are a few parts you retain when you install the STM, and one of them Is the
Big Washer on the back side of the Stock Hub.
So you now you take your STM Clutch and as they say “Assemble it”
In other words, you take your 6 ball bearings, on put each one into the capture on the ramps.



Drop on the Clutch Drum, making sure the ramps are aligned up, and take this STM Clutch hub
assembly and slide it onto your Splined Shaft.
Then you take your STOCK Clutch Pack (Fibers and Steels) and put them on EXACTLY as you took
them off. The ONLY change is, you remove the 2 judder springs located in the pack. They will not
be used.
Make sure you install these plates EXACTLY as you took them off. Same order, and Same Sides out.
As long as you kept the pack intact, when you removed it, you simply slide them back on.
Then install the Drum Stopper Plate. (Use a little assembly grease to keep it in place).


Now it should look like this.


Next you take the Secondary spring and put that into the Hub. (Use a little assembly grease to
keep it in place). Then the, Pressure plate, Evoluzione Primary Spring, Spring stopper plate w/
Bearing Ring, and stopper hub, notched washer, and Finally the Nut.

Now it should look like this.


The 30mm STM Nut has to be torque to OEM Spec. of 150 N/mm
Now, you can just Air Wrench that sucker on there, and be done with it.
OR
You can properly torque it on there with a torque wrench. If you choose the later (What we
recommend) then you will probably want this STM Tool, that keeps the hub from Spinning while
you torque it down.
Or as some customers have done, you can be creative and make your own.



Next, you pop out the Stock Bearing from your OEM Clutch and push it into the STM Bearing
Rest, and bolt that down with supplied bolts.
And finally install the OEM Push Rod, and adjust it accordingly.


This is what it looks like Complete Install





Overall it took about 45-50 min. Not to bad. And as with most installs, learning, understanding
and seeing first hand how your bike works is really rewarding.

Then the test drive. The Whole point of a Slipper clutch is to go UN-NOTICED. And that is exactly
what the STM Slipper Clutch Does.
As with ALL our STM Clutches, the Slipper action is butter smooth.
No Chatter, no wheel hop, just perfectly smooth clutch disengagement.

We could write a book about this stuff, but we just wanted to hit on the highlights.

If you guys have any further questions, please feel free to post up.
We are always here to help.


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[Ducky]

Ahh that's interesting, I have an STM slipper on my Ducati (v.nice clutch indeed) and assumed the BMW's also employed balls on the ramps, I didn't realise it was metal on metal!

[Mick46]

Nice detailed post and explanation as to why the aftermarket unit is so much better than the stocker BUT the stock slipper clutch works perfectly for me at least (as a street rider)
Anyone had any wheel hop or unexpected backing in problems?

[H-2 CHARLIE]

I like to on all my bikes to rev the motor then slip the clutch a bit on the way down from the RPMS . it does sound mean when you do it right and gets looks . Well this bike gives a huge grab-kick so i dont do it cause it feels like it wants to grab and kick instead of just the light hooking up like all other bikes do

[dagor6]

Ah yes, but do you guys finally have them in stock yet??

[viperclaw]

Nice right up.

The oil level is lower than the cover so there is no need to drain the oil--at least not for that reason.

[HardRacing]

Originally Posted by viperclaw

Nice right up.

The oil level is lower than the cover so there is no need to drain the oil--at least not for that reason.

.

We weren't sure, and didn't want to find out the hard way.
But, Good info to know, specially for anyone else who may do some Clutch Mods, or swap out in the future.

One less step you have to do.
Great Info.


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Originally Posted by dagor6

Ah yes, but do you guys finally have them in stock yet??

.

We had a couple arrive at our shop, unfortunately, they were already pre-sold before they showed up.

Should be getting more soon.


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[HardRacing]

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Huh..??

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Originally Posted by H-2 CHARLIE

.... it does sound mean when you do it right and gets looks . Well this bike gives a huge grab-kick so i dont do it cause it feels like it wants to grab and kick instead of just the light hooking up like all other bikes do

.

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[kismetcapitan]

extremely informative - these instructions are so good that pretty much anyone could do it. Beats having to buy a part, then taking it to someone to get installed. Much more satisfying and fun to do it yourself

fwiw, I haven't noticed my stock clutch doing anything odd; I suppose it could be smoother, but I have gotten into the habit of simply popping the clutch on everything except moving off from a standstill, and I've never felt the rear do anything other than stay in place and behave. Stock might not cut it however on the track, although IIRC World Superstock rules require the use of the stock clutch, and Badovini is completely unbeatable on his S1000RR this year.

Would smoother mean less engine braking? One thing is clear - we now know why the clutch feels like the cable "catches" on something - it's those stock springs popping back into place - the ones you toss out in the STM clutch install.