1966-1976 Chevrolet Impala Transmission Kickdown Solenoid Guide
If your Impala has lost its passing power, a faulty transmission kickdown solenoid could be the culprit.
- This electric solenoid is for the TH400 transmission; the TH350 uses a mechanical cable.
- The primary symptom of failure is the loss of the automatic 'kickdown' or passing gear.
- Replacement is a simple DIY task that requires draining the fluid and removing the transmission pan.
- Aftermarket brands like ATP and Pioneer offer affordable, stock-level replacements.
Is This The Right Part for Your Impala?
Before you buy, it's critical to know which automatic transmission your 1966-1976 Impala has. This electric solenoid is used on the Turbo-Hydramatic 400 (TH400) transmission. Many Impalas of this era used the Turbo-Hydramatic 350 (TH350), which typically uses a mechanical cable for the kickdown function, not an electric solenoid. Check your transmission pan shape to be sure: a TH400 pan has an irregular shape, often compared to the outline of the state of Texas.
Symptoms of a Failing Kickdown Solenoid
A bad kickdown solenoid has one very obvious symptom and a few less common ones. Since these vehicles do not have computer diagnostics, you have to rely on how the car drives.
- No Passing Gear: The most common sign of failure is that the transmission will not downshift when you press the accelerator pedal to the floor. The car will feel sluggish and won't accelerate as quickly as it should.
- Stuck in a Low Gear: In rare cases, the solenoid can fail in the 'on' position. This can cause the transmission to hold a low gear for too long or refuse to upshift at all.
- Electrical Failure: The solenoid itself can burn out, or the wire leading to it can break. You can often test the solenoid by listening for a 'click' from under the car when a helper presses the gas pedal to the floor (with the engine off but the key in the 'on' position).
A Note on Aftermarket Part Quality
For a vintage vehicle like the '66-'76 Impala, new OEM parts are no longer available. You will be choosing from aftermarket brands. Forum discussions among classic car owners suggest that the quality of modern replacement solenoids can sometimes be inconsistent compared to the original factory parts. Some owners recommend trying to clean a clogged original solenoid before replacing it. However, if the solenoid has failed electrically, replacement is the only option.
Choosing the Right Aftermarket Solenoid
Brands like ATP and Pioneer Cable offer direct-fit replacements for the original TH400 solenoid. These are considered standard, stock-level replacement parts suitable for a daily driver or stock restoration. Forum users have had generally acceptable experiences with both brands for various stock parts. ATP has been noted for making good quality transmission kits, while Pioneer is known for a wide range of parts that often mimic original factory designs. For a standard Impala, either brand should restore the kickdown function effectively.
Cost of Replacing Your Kickdown Solenoid
| Part Type | Estimated Cost |
|---|---|
| New Aftermarket (ATP, Pioneer) | $62.84 - $120.19 |
| New OEM | Not Available |
| Shop Labor | $100 - $225 |
Pro Tip: Easy DIY Job
Replacing this solenoid is a straightforward job for a DIY mechanic. It is located inside the oil pan and held on by two small bolts. The process involves draining the transmission fluid, dropping the pan, unplugging and unbolting the old solenoid, and installing the new one. The biggest challenge is the mess from the transmission fluid.
Frequently Asked Questions (FAQ)
Can I just remove the kickdown solenoid?
You can operate the vehicle without a functioning kickdown solenoid, but you will not have an automatic passing gear and will have to downshift manually. On a TH400, the solenoid also boosts line pressure to protect the clutches during full-throttle acceleration, so running without it may reduce the transmission's lifespan under hard use.
Is this the same as a modern shift solenoid?
No. This is a simple on/off electric switch for the kickdown function only. Modern vehicles use multiple, computer-controlled solenoids to manage all gear shifts, pressure regulation, and torque converter lockup.
Will a bad solenoid cause a transmission fluid leak?
A bad solenoid itself will not cause a leak. However, the process of replacing it requires removing the transmission pan. It is essential to use a new pan gasket and tighten the pan bolts correctly to prevent leaks after the job is done.
Are there any recalls for this part?
There are no known recalls or Technical Service Bulletins (TSBs) from the NHTSA for the transmission kickdown solenoid on the 1966-1976 Chevrolet Impala.
Technical Specifications
12-volt electric detent/kickdown solenoid for GM Turbo-Hydramatic 400 (TH400) automatic transmissions.
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The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.