WORKHORSE CUSTOM CHASSIS
Service Manual
Automatic Transmission – Allison
2007 W Series
© 2006 Workhorse Custom Chassis — All Rights Reserved
SECTION
7.2
PAGE
461
2007 W Series Chassis
WSM082106
If Shudder Occurs After the TCC has Applied
IMPORTANT:
If shudder occurs after the TCC has applied, most likely
If shudder occurs after the TCC has applied, most likely
there is nothing wrong with the transmission.
there is nothing wrong with the transmission.
As mentioned above, the TCC is not likely to slip after
the TCC has been applied. Engine conditions may go
unnoticed under light throttle and load, but they become
noticeable after the TCC apply when going up a hill or
accelerating. This is due to the mechanical coupling
between the engine and the transmission.
Once the TCC is applied, there is no torque converter,
fl uid coupling, assistance. Engine or driveline vibrations
could be unnoticeable before TCC engagement.
Inspect the following components in order to avoid
misdiagnosis of TCC shudder. An inspection also avoids
the unnecessary disassembly of a transmission or the
unnecessary replacement of a torque converter.
• Spark plugs
• Inspect for cracks, high resistance or a broken insulator.
• Plug wires – Look in each end. If there is red ozone
dust or a black carbon substance present, the wires are
bad. Also, inspect for a white discoloration of the wire.
This indicates arcing during hard acceleration.
• Coil – Inspect for black discoloration on the bottom
of the coil. This indicates arcing while the engine is
misfi ring.
• Fuel injector – The fi lter may be plugged.
• Vacuum leak – The engine will not get the correct
amount of fuel. The mixture may run rich or lean
depending on where the leak occurs.
• Exhaust gas recirculation (EGR) valve – The valve may
let in too much or too little unburnable exhaust gas and
could cause the engine to run rich or lean.
• Manifold absolute pressure (MAP) or mass air fl ow
(MAF) sensor for possible vacuum leak – The engine
will not receive the correct amount of fuel for proper
engine operation.
• Carbon on the intake valves – Carbon restricts the
proper fl ow of air/fuel mixture into the cylinders.
• Flat cam – Valves do not open far enough to let the
proper fuel/air mixture into the cylinders.
• Oxygen sensor – This sensor may command the
engine rich or lean for too long.
• Fuel pressure – Fuel pressure may be too low.
• Engine mounts – Vibration of the mounts can be
multiplied by TCC engagement.
•
Axle joints – Inspect for vibration.
•
Throttle position (TP) sensor – The TCC apply and
release depends on the TP sensor in many engines.
If the TP sensor is out of specifi cation, the TCC may
remain applied during initial engine loading.
• Cylinder balance – Malfunctioning piston rings or poorly
sealed valves can cause low power in a cylinder.
• Fuel contamination – Fuel contamination causes poor
engine performance.
Torque Converter Evaluation and Diagnosis
Replace the torque converter if any of the following
conditions exist:
• External leaks appear in the hub weld area
•
The converter hub is scored or damaged
