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What's
the slipper clutch for and how do I adjust it?
All competition buggies and trucks have transmissions
equipped with a slipper clutch. On a transmission
without a slipper, the spur gear is keyed directly
to the top shaft of the transmission, which drives
the rear axles through a gear train and ball differential.
On a slipper-equipped transmission, the connection
of the spur gear to the top shaft is made through
an adjustable friction coupling that allows some
slippage.
The slipper, used correctly, both improves performance
and reduces wear and tear on the transmission:
• The slipper reduces wheelspin as the car
accelerates from low speeds, so the car accelerates
faster and is less prone to spin out exiting turns
on slick tracks. The slipper also gives more sure-footed
landings after jumps, so the car handles rough sections
and jumps better.
• The slipper reduces sudden forces on the
inside of the transmission, especially on the ball
differential.
The slipper is a fussy topic. It takes awhile to
learn when to loosen the slipper and when to tighten
it. Most beginners set the slipper too loose, which
makes the car easier to drive but slower overall.
Before you start adjusting the slipper, you must
double-check the diff adjustment. Remove the gear
cover. Tighten the slipper all the way so it won't
slip. Hold both the spur gear and the right rear
tire with your right hand, and try to turn the left
rear tire with your left hand. It should be quite
hard to turn. If the left rear tire turns with moderate
effort, with the transmission top shaft stationary
as the left rear tire turns, tighten the diff and
repeat.
Now loosen the slipper adjustment a few turns, hold
both the spur gear and the right rear tire with
your right hand, and turn the left rear tire with
your left hand. It should not be extremely easy
to turn the tire, but not be extremely hard to turn
it, either. Fiddle the slipper adjustment to get
it into the right ballpark.
Now put the car on the track pointing toward you.
Press down on the car and punch the throttle on-off.
Listen to that sound -- that's the slipper slipping.
Feel how much forward drive the car has. If the
forward drive is weak you need to tighten the slipper.
Keep the car on the track pointing toward you. Back
away a couple of feet and punch the throttle on
until you catch the car. The slipper sound should
last only for about a foot -- it should stop before
the car reaches you. (It takes practice to hear
the slipper sound among all the other sounds, especially
the sound of slipping tires.) If it slips more than
this, tighten the slipper; if there is no slip at
all, loosen it.
Go out and drive the car. If it is working well,
bring it in and feel the adjustment again by turning
the left tire. Learn how hard the tire is to turn.
This will help you get closer to the right adjustment
next time you have to adjust it from scratch.
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