Troubleshooting Help

Transmission Slips

Problem	What to Do
Low oil level	Check and add oil
Wrong oil Grade/Type	Check oil grade ZF Clark Dana Spicer
Weak or broken pressure regulating valve spring	Do Transmission System Pressure Test
Transmission pump suction screen restricted	Remove and clean screen
Low transmission pump flow due to worn pump	Do Transmission Pump Flow Test
Transmission control valve or gasket leakage	Remove valve and inspect gaskets
Clutch cut-off valve sticking	Remove and inspect clutch cut-off valve
Restricted modulation housing	Remove control valve housing and check for restrictions in valve and valve
Excessive transmission element leakage	Do Transmission Element Leakage Test Using System Pressure
Worn clutch disks	Repair transmission

Unit Will Not Move

Problem	What to Do
Low or no transmission pressure	See Transmission Pressure is low (all gears) or Transmission Pressure is low (one or two gears)
Service brakes will not release	Do Brake Pedal Operational Check. Do Service and Park Brake System Drag Checks
Park brake applied or parkswitch misadjusted	Adjust park brake switch
Stuck control valve spool	Check shift linkage operation. Disconnect shift linkage from control valve spool and check linkage movement.
Failed torque converter	Do Torque Converter Stall Test. If engine pulldown is normal, torque converter is good
Broken shafts or gears	Drain transmission to determine if large pieces of metal contamination are present
Broken drive shafts	Inspect drive shafts and universal joints for external damage. Repair
Broken ring or pinion gear	If drive shafts rotate with transmission in gear but unit does not move, a differential failure is indicated. Repair

Transmission Pressure Is Low (All Gears)

Problem	What to Do
Low oil level	Check transmission oil level and refill if necessary
Switch failure	Verify transmission system pressure. Do Transmission System Pressure Test
Suction strainer is plugged	Transmission pump may be noisy if transmission suction screen is clogged. Drain transmission. Remove and clean suction screen. Also, check condition of transmission filter.
Transmission pressure regulating valve is stuck or spring is broken	Remove transmission pressure regulating valve. Inspect for damage
Control valve gasket failure	Inspect transmission control valve for external leakage. Remove control valve. Inspect or replace gasket.
Transmission pump is failed	Do pump flow test

Transmission System Pressure Is Low (One or Two Gears)

Problem	What to Do
Failed transmission control valve gasket	Inspect transmission control valve for external leakage. Remove control valve. Inspect or replace gasket.
Clutch piston or seal ring leakage	Disassemble and repair

Transmission Shifts Slow

Problem	What to Do
Low oil level (aeration of oil)	Check and add oil
Low transmission pressure	Do Transmission System Pressure Test
Transmission pump suction screen restricted	Remove and clean screen
Low transmission pump flow	Do Transmission Pump Flow Test
Excessive transmission element leakage	Do Transmission Element Leakage Test Using System Pressure
Oil passages restricted between control valve and transmission elements	emove control valve and inspect oil passages
Clutch cut-off valve sticking	Remove and inspect cut-off valve

Transmission Shifts Fast

Problem	What to Do
System pressure too high	Do Transmission System Pressure Test
Stuck modulation valve	Remove and inspect modulation valve
Stuck or missing forward/reverse check valve	Inspect transmission control valve
Broken piston return spring	Disassemble and inspect clutch

Unit "Creeps" in Neutral

Problem	What to Do
Warped disks and plates in transmission	Check transmission

Transmission Hydraulic System Overheats

Problem	What to Do
High oil level	Check and adjust
Low oil level	Check and correct
Wrong oil grade	Check oil grade
Park brake on	Release park brake
Lube lines pinched, restricted, or leaking	Check cooler lines
Unit operated in too high gear range	Operate unit in correct gear range
Temperature gauge or sender malfunction Install	temperature sensor to verify temperature. Do Tachometer/Temperature Reader Installation Procedure.
Air flow through oil cooler or radiator restricted	Do Radiator Air Flow Test
Oil cooler thermal relief bypass valve stuck	Bypass thermal bypass valve and check to see if unit still overheats. Do Transmission Oil Cooler Thermal Bypass Valve Test
Oil cooler internally restricted	Do Oil Cooler Restriction Test
Warped disks and plates in transmission	Do Transmission Clutch Drag Check
Leakage in transmission hydraulic system	Do Converter-Out Pressure Test. Do Transmission Element Leakage Test
Low transmission pump output	Do Transmission Pump Flow Test

Transmission Noise

Problem	Solution
Engine slow idle too low	Check engine slow idle speed
Parts worn or damaged in transmission	Remove transmission suction screen. Inspect for metal particles. Repair as necessary
Low or no lube	Do Converter-Out and Lube Pressure Test. Do Transmission Pump Flow Test
Incorrect type of oil	Change oil
High oil level	Drain some oil
Low oil level	Add oil
Air leak on suction side of pump	Check oil pickup tube on side of transmission

Unit Vibrates

Problem	Solution
Aerated oil	Check and add oil
Failed universal joints on transmission drive shaft or differential drive shafts	Check universal joints

Unit Lacks Power And Acceleration

Problem	Solution
Engine fast idle speed set too low	Check fast idle adjustment
Incorrect transmission oil	Check oil
Aerated oil	Check and add oil
Low transmission pressure	Do Transmission System Pressure Test.
Warped transmission clutch	Do Transmission Clutch Drag Checks
Brake drag	Do Brake Drag Check
Clutch cut-off valve sticking	Remove and inspect clutch cut-off valve
Low engine power	Do Engine Power Test

Torque Converter Stall RPM Too High

Problem	Solution
Aerated oil	Put clear hose on thermal bypass outlet port. Run unit to check for bubbles in oil
Converter relief valve stuck open	Do Converter-Out Pressure Test
Torque converter seal leakage	Do Converter-Out Pressure Test
Torque converter not transferring power (bent fins, broken stator)	Remove and inspect torque converter

Torque Converter Stall RPM Too Low

Problem	Solution
Low engine power	Do Engine Power Test
Mechanical malfunction	Remove and inspect torque converter