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Adjusting Drive Belts


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Rear Belt Drive Adjustment

Performance and Technical information on the rear belt drive for Harley-Davidson motorcycles.
Belt Drive Adjustment for Big Twins

Set belt tension a the tightest rotational point on the sprockets.
The adjustments should be done when the bike is cold.
The adjustments should be made with the weight of a rider on the bike.

1. At the lower strand, position "A", mid-way between transmission sprocket and rear wheel sprocket, apply 10 Ibs. of upward force on lower span of rear belt. Harley-Davidson has a BELT TENSION GAUGE (Part No. HD-35381) to help.

2. Measure belt deflection "B" several times, each time with belt moved (by rotating rear wheel) to a different position on sprockets. With sprockets rotated to tightest belt position, belt deflection "B" (measured at position "A") should be 5/16-3/8 in. Check your manual to be sure of the measurements, the newer models have changed.


1. Loosen rear axle nuts.

2. Measure each side from the flat to the end of the swingarm, to be sure rear axle is correctly located.

3. Turn axle adjuster nuts (metric) on each side of swing-arm to adjust belt deflection.

a. Turn clockwise to decrease deflection (increase tension).
b. Turn counterclockwise to increase belt deflection (decrease tension).

Turn each adjuster nut exactly the same number of turns to maintain rear wheel alignment.

5. Tighten axle nut to 60-65 ft-lbs.


Keep dirt, grease, oil, and debris off the belt and sprockets. Clean the belt with a rag which is slightly damp with light cleaning agent.

All belts must be handled carefully to prevent bending stress. The belt must never be formed into a loop smaller than 5 inches in diameter and never be bent back wards. Sharp bending can weaken the belt and lead to premature failure. Old belts that are taken off a bike during repairs must be reinstalled so they rotate the same direction.

Tricks of the trade
With a high horsepower engine, it is better to have the belt a little tight rather than loose. A loose belt will break much more readily than a tight one. Most people do not tighten the belt to its proper tension. If you plan on "racing" or hot rodding your bike, invest in a Harley-Davidson BELT TENSION GAUGER (Part No. HUD-35381).