On-off soleniods: failure due to heat
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1. Resistance increases with temperature Solenoid strength drops with temperature.
2. Heat will accelerate the aging of plastics. Plastics will become brittle and lose mechanical properties, O-ring seals get hard and out-of-round Strength of materials goes down with heat.
GM has design flaws in its 4L60-E shift solenoids. The end of the solenoid bobbin where it sticks through the bracket has a wall thickness of around .013.The end of the solenoid breaks right off, launching the armature into the pan. Results are missing shifts. Heat conditions make this problem worse as the bobbin plastic used in the OEM solenoid becomes brittle with heat.
3. Signs of heat
- Smoke!
- Burnt fluid
- Discolored mag wire. AXODE # 2 solenoid Is typical for heat damage. Unwrap the coil, hot spot is a few layers down. It should unwrap easily. If it sticks, delamination has begun.
- Brittle plastic, hardened seals
- Insulation breakdown. Cracks, delamination leads to turn to turn shorts
4. A solenoid is a space heater. Most of the electrical energy is turned into heat. As resistance drops, current increases and heat increases, a solenoid will self destruct.
Components grow and expand with heat. Thermal expansion needs to be considered with initial design. Add some contamination and things just may bind or loose stroke.
Click on an illustration to see an enlargement.
© Scott Kirkendall
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Replace and reuse rules
Failure review chart