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Conventional wisdom says 1000 easy miles of city/highway driving.

However, BMW's official stance follows:

"BMW AG - TIS
RA: Breaking in SAC clutch
Issue status (03/2002)

Break in the friction linings of the clutch by applying light to medium loads, in the same way as for brake linings. This preconditioning creates a carbon layer between lining and metal friction surface which in the end generates the necessary coefficient of friction. Breaking in can take the form of either normal driving with many gearshifts or a specific breaking-in program on gentle gradients.

"Normal" driving will not damage the clutch. "Normal" driving conditions involve drive-off speeds of up to approx. 2500 rpm on a medium gradient, e.g. when driving onto a transporter. Normal driving off on a level surface at speeds up to approx. 2000 rpm are likewise sufficient.

Sporting driving maneuvers will destroy a new clutch! These include driving maneuvers at high differential speeds, overlaps or very high drive-off speeds, e.g. when driving onto a transporter.

When a vehicle is moved "normally", an empirically established figure of approx. 800-1000 gearshifts is applicable to an optimally broken-in lining.

Please conduct the following breaking-in program in order to avoid later customer complaints:

* specifically for M5 and Z8 vehicles

Breaking-in program for approx. 30 km on road

Vehicle subject to "moderate" shifting processes

Drive off at max. 2000 rpm; upshift 1->2, 2->3, 3->4; upshift at 3500-4000 rpm, downshift 4->3, 3->2, 2->1, downshift at 2000 rpm

Drive off 3 to 5 times on a gentle gradient up to approx. 12%, drive-off speed max. 2000 rpm ."


In suburban driving, with stoplights roughly every mile, one is likely to shift 4 times per mile (1-2, 2-3, 3-4, 4-3, stop).

One would execute 1000 shifts within 250 miles.

1000 miles seems like gross overkill compared to BMW's recommendation.

So who is correct? How long must my balls be blue?
 

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Mileage is almost irrelevant for clutch break-in. You could leave on a trip across country and put 3000 miles on a clutch and not have it broken-in. Follow BMW's testing, and assume that approximately 1000 gearshifts done per their recommendation is accurate. Just don't powershift the 1001 shift. Gradual and measured additional stress makes the most sense.
 

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