The XR1200 Clutch

XR Clutch

The XR1200 uses the same clutch assembly as a Buell XB. While the large friction and steel clutch plates are common to other Sportster models, the clutch hub (37898-02A) and clutch shell (37899-02A); and, the stackup of the plates, spacers, spring, and misc parts is the same as the later XB Buells. Of course, now that the Buell XB is no longer made, I guess one could just refer to this as the "XR clutch."


Clutch Pack

The XR clutch has 7 full fiber plates (37911-90), 7 full metal plates (37913-90), one narrow fiber plate (37897-02), and a diaphragm spring (37934-06).    The center of the narrow fiber plate has a concave "judder" spring that helps reduce clutch chatter by moving the clutch pack away from the bottom edge of the clutch hub, when the diaphragm spring is compressed by pulling the clutch lever.  The judder spring then spins freely on on its seat (another metal ring).  This helps ease the engagement of the clutch pack as it initially engages/releases.
Standard Sportsters use a mix of 8 full fiber plates (37911-90), 6 full metal plates (37913-90), and then an intermediary spring plate to reduce chatter.
One of the major benefits of the XR1200/XB clutch shell is its built in compensating mechanism.  The compensator is comprised of a two-part base in the clutch shell actually, which is buffered by 6 springs.  The 6 springs are located inside protective shields in the base, and allow the base to rotate slightly during sudden accel/decel of the primary drivetrain, taking some of the shock out of the "hit" of acceleration.  This compensator should make the XR drivetrain slightly smoother and take some of the wear off of drivetrain components due to the shock of hard accel and quick downshifts.

For a more detailed look at the XR1200 clutch assembly, click here.

The stock clutch seems to hold fine for stock XR1200 motors on the street.  Although I thought I noticed a little clutch slippage on the drag strip with the stock motor, it was not bad and the stock clutch was ok if properly adjusted, (Racers and people with special needs, e.g. sidecars and/or heavy loaded riding,  may however, find they need to upgrade it.) 
But, cam and head work in the engine it was clear that the clutch needed a bit more clamping force to launch like I wanted.  Personally, I have found the stock fiber and metal clutch plates to work fine (although I did later upgrade to SE plates because I had some on hand), but the stock 320 lb diaphragm spring was not quite holding the extra power of my engine build. 
Initially the fix that worked for me was to replace the stock XR1200 clutch diaphragm spring (320 lbs)  with a stronger Barnett MT-77 spring (400 lbs).  Then, to counter the extra spring force and be able to more easily modulate the clutch lever off the starting line, I installed the Mueller Powerclutch ball and ramp assembly.  This is a surefire fix, but would be overkill for most XR's,  I have since moved to a more moderate SE diaphragm spring.

XR Clutch Upgrade Possibilities
The rest of this page includes some options for upgrading the clutch in the XR1200.
Or, for a different look at upgrade possibilities for the XR1200's "XB" clutch, click here - BadweatherBikers

SE Clutch Pack Kit

The SE Performance Clutch Kit (38002-04) offers one option for upgrading the XR clutch.  It includes large friction plates and a 350 lb diaphragm spring. While it is intended for the XL clutch and does not include the narrow plates used at the bottom of the XR stack, it will upgrade the clamping force of the XR clutch.  For riders who are aggressive in their shifting, use of this kit alone could be a good solution.
Barnett MT-77 Clutch Plate

Barnett MT-77 Diaphragm Spring

Initially I kept the stock fiber and metal plates and changed to a Barnett MT-77 spring plate.  The Barnett plate (400 lbs)  is significantly stronger than the stock (320 lbs) and the SE (350 lb) diaphragm spring plates and provides excellent clamping force for the XR1200's clutch - even when pushing 100 HP and 90 ft-lbs of TQ. 
This is a monster diaphragm plate for the XR though, and, it is probably overkill for an XR.  To maintain a reasonable clutch lever pull, a set of light/easy pull ball and ramps need to be installed in the clutch.
For those who are interested, the Barnett part number is 502-00-01077.
Barnett MT-81 Clutch Plate
According to Barnett, the Vance and Hines race bikes use the Barnett MT-81 spring plate.  The Barnett MT-81 diaphragm spring is also stronger than the stock and SE diaphragm springs, and Barnett says that it provides 360 lbs of clamping force.  Nominally though, it is the same as the SE diaphragm spring.
The Barnett part number is 502-00-01081.


The AIM Variable Pressure Clutch (VPC) provides variable pressure clutch engagement that increases in clamping force as the engine's RPM increases.  At idle and around town the feel can be significantly lighter than stock, while providing increased clamping force when the torque builds at above 4,000 rpm.  It consists of a set of weighted throwout arms, and is installed on top of the clutch diaphragm spring.  It is not a "slipper" clutch which would help with high RPM downshifts - it is more like a "lockup."  The minimum clamping force at low RPM is the strength of the diaphragm spring, and under high-speed high-RPM shifts it has additional clamping force to help keep the clutch from slipping. 
The picture to the right shows how In installed the VPC on the XR1200 clutch basket, but alas, after many hours of machining parts to gain clearance to install the VPC in the primary, I have determined that it is not possible to use the VPC in the XR1200.  When everything is installed, the centrifugal weights for the VPC end up in the path of the clutch cable.  While the VPC can be made to physically fit in the XR1200 case, once installed the clutch cable can not be attached.  Sorry, but this will not work!

Mueller vs Stock Ramps

The Mueller "PowerClutch" (1130-0004) ball and ramps are an excellent modification to the XR1200's clutch when using a stiffer diaphragm spring.  It will also work of course with the stock clutch spring.  But with a stiffer spring like the Barnett MT-77 the Mueller ramps bring the clutch feel back down to the stock, or below, feel and allow the rider to modulate clutch force.  Without something like the Mueller ramps, it is tough to consistently modulate the clutch lever and clutch release is pretty much on/off - which can mean dumping the clutch when one really does not want to, or a great deal of difficulty feathering the clutch while riding in city traffic.
The stock XR1200 clutch plates seem fine for normal and heavy duty use.  But, YES, it is possible to burn up the fiber plates even in a stock bike.  Heck, I burned up a couple sets of kevlar plates in a Bandit Machine Works 6 spring clutch pack in my Fatboy by excessively slipping the clutch during burnouts at the track.  Slipping the clutch will burn plates up, not the XR1200's power level.
So, except in unique circumstances, I believe the XR1200's clutch plates are fine.  I have also installed the SE fiber plates, and they are excellent.

When power levels approach 100 HP though, aggressive riders will want to upgrade the clutch.  For me the initial  "fix" that worked wellwas to switch to a Barnett MT-77 heavier spring plate, with a Mueller PowerClutch ball and ramp set to reduce clutch pull to a level that is easily modulated.   It is overkill though, and whether due to the heavier spring, or just riding style, the seat for the diaphragm spring retaining ring in my clutch did break with this spring.  Alternately,  the SE diaphragm spring (
or Barnett MT-81 diaphragm spring) should be more than adequate for most XR riders,  Since I had them on hand, I have also installed SE fiber clutch plates in the XR.  A combination similar to this should hold XR's at 100 HP and approaching 100 ft-lbs. 
But for the Cadillac of XR1200 clutch upgrades, a guy could always try this option from ErikBuellRacing

Follow @PhaedrusStuff