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1972 Corvette: Service News: Positraction Chatter - 1972 Passenger Cars and 10 Series Trucks

Subject: Positraction Chatter - 1972 Passenger Cars and 10 Series Trucks
Model and Year: 1972 Corvette
Source: Chevrolet Service News
Page Number: Page 1
Date: November 1972, Volume 44, Number 11

Field Reports indicate that some 1972 vehicles equipped with positraction rear axles are being overhauled to correct a chatter complaint (snapping or clunking on slow turns).  Two major cause of positraction chatter are:

  1. Depletion of lubricant anti-chatter additives during the break-in period of a new axle.
  2. Rear tires that do not rotate the same number of revolutions per mile.  This could be caused by:  a)  unequal tire inflation  b)  uneven tire wear  c)  tire mold variations  d)  different tire brands or sizes on each side.

The circumference of each rear tire should be measured around the center tread with a tape measure after ensuring that tire pressure readings are equal.  If the diameter difference is more than 1/2", constant slipping of the positraction plates will result.  Two tires must be selected for the rear which measure within the 1/2" tolerance.

If the axle noise is diagnosed as being caused by a lubricant breakdown, the axle should be drained (while hot) by removing the axle housing cover.  On Corvette Models, the lubricant may be drained by using an oil suction pump, thus eliminating the need to remove the rear cover.

NOTE:  A new cover gasket must be used if the axle cover has been removed.  Refill axle with G.M. Positraction Lubricant; 1 qt. can - 1051022, 15 gal. drum - 1051023.  This lubricant contains additional anti-chatter additives over previously used lubricants and is preferred for all Chevrolet positraction axles.

When the axle assembly is filled and driven approximately 50-100 miles, sufficient new lubricant should have worked between the plates to eliminate chatter condition.

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