Technical Support
Transmission Installation | Torque Converter Installation
Basic Troubleshooting | Stall Test Instructions | Checking Pressures
Fluid Types | Causes of Clutch Pack Burn-Up
FORKLIFT
AND LIFT TRUCK STALL TEST INSTRUCTIONS
This simple
test will check the performance of the engine, the converter, and
the transmission. The stall test will determine which one of the
three components is producing the "slipping" complaint.
An engine that will not stall is an engine in need of an overhaul
or a tune up. Until the engine is in good working order, you cannot
properly test the converter and the transmission. In other words,
not enough input equals not enough output.
1. A stall test requires putting a tachometer on the engine.
2. You must load the forklift to its load capacity.
3. Put the truck against a larger truck or an immovable object.
4. Run up the engine speed and keep an eye on the tachometer.
The engine should stall within 30 seconds. If not, do not continue
to strain the system with this test.
5. Note the tachometer reading at the time of the stall. Each engine
has a different stall speed. It is important to check with the manufacturer
for the correct stall speed for your engine.
A stall speed 200 to 300 RPM low indicates a poorly performing engine.
This can be caused by something as simple as a faulty fuel system
or as serious as a worn crank.
A stall speed 600 to 800 RPM low indicates a poorly performing torque
converter. The one-way clutch, known as the sprag, may no longer
be holding. If the test indicates the converter is the problem,
replace or rebuild the torque converter, paying close attention
to the stator support or pump stator that the converter hub rides
on.
The test that indicates the converter is not working cannot differentiate
between the sprag and the stator. The slipping can be in either
or both components. When you look at the stator, it should be free
of lines, stripes, or out-of-round wearing. If you can see these
signs, replace both the converter and the stator support.
When the engine stalls at a higher than normal RPM, the
clutch packs are not holding. The cause may be worn clutch facings,
worn seal rings, a problem control valve, etc. Some pressure tests
need to be run on the transmission to pinpoint the transmission
malfunction.
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