| Free A.S.E. Study Guide An ASE Study Guide for the Automotive Technician |
| Automatic Transaxle: Final Drive |
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Helical final drive transaxles are similar to the rear wheel drive type differentials and
should also be checked for worn or chipped teeth, backlash, and excessive differential
side gear play. These gears and bearings should be turned and checked for
smoothness.
Use an inch pound torque wrench to check for proper preload. The ring gear should be
checked for backlash using a dial indicator. Always compare readings with
manufacturer specifications. The collapsible pinion shaft spacer should always be
replaced once removed.
Many transaxles use a chain and sprockets to drive the transfer gear. These chains are
checked for play or slack by deflecting the chain up using a screwdriver and marking
the case. Then moving the chain down and marking the case again. The sum of the two
is the total amount of chain slack. There is little deflection in a good chain.
Some transaxles use transfer gears instead of drive chains to achieve the same
transfer of power from the output shaft to the transfer shaft and in turn to the differential
case.
Planetary final drive assemblies are checked similar to the helical type transmissions.
These gears should be checked for chipping and wear. Use a feeler gauge to check
the pinion gears and roll them against an even surface to check for smoothness.
If these gears are loose on the shaft there will be a whining noise when the gear is
placed under a load. These gears are often colored blue from the manufacturer but will
turn black from excessive heat. The pinions can get loose on their shafts. When this
happens the entire carrier must be replaced as they are not sold separately.
The differentials in transaxles are constructed like and perform the same function as
those found on rear wheel drive vehicles. The idea is that while cornering the outside
tire rotates faster than the inside tire. The differential compensates for this by allowing
the pinion gears to “walk” around the slower ring gear. This allows the outside tire to
spin more times than the inside providing smooth cornering.
Hypoid gears are used only on longitudinal transmissions.
should also be checked for worn or chipped teeth, backlash, and excessive differential
side gear play. These gears and bearings should be turned and checked for
smoothness.
Use an inch pound torque wrench to check for proper preload. The ring gear should be
checked for backlash using a dial indicator. Always compare readings with
manufacturer specifications. The collapsible pinion shaft spacer should always be
replaced once removed.
Many transaxles use a chain and sprockets to drive the transfer gear. These chains are
checked for play or slack by deflecting the chain up using a screwdriver and marking
the case. Then moving the chain down and marking the case again. The sum of the two
is the total amount of chain slack. There is little deflection in a good chain.
Some transaxles use transfer gears instead of drive chains to achieve the same
transfer of power from the output shaft to the transfer shaft and in turn to the differential
case.
Planetary final drive assemblies are checked similar to the helical type transmissions.
These gears should be checked for chipping and wear. Use a feeler gauge to check
the pinion gears and roll them against an even surface to check for smoothness.
If these gears are loose on the shaft there will be a whining noise when the gear is
placed under a load. These gears are often colored blue from the manufacturer but will
turn black from excessive heat. The pinions can get loose on their shafts. When this
happens the entire carrier must be replaced as they are not sold separately.
The differentials in transaxles are constructed like and perform the same function as
those found on rear wheel drive vehicles. The idea is that while cornering the outside
tire rotates faster than the inside tire. The differential compensates for this by allowing
the pinion gears to “walk” around the slower ring gear. This allows the outside tire to
spin more times than the inside providing smooth cornering.
Hypoid gears are used only on longitudinal transmissions.