GMC P15 Transmission Filter Kit Guide for 1975-1978 Models
Keep your P-series van's automatic transmission shifting smoothly with the right filter kit.
- You must identify your transmission (likely a TH350 or TH400) by its pan shape before ordering a kit; fitment depends on the transmission, not the van's model year.
- Symptoms like slipping, harsh shifting, or whining are serious warnings that your transmission needs service immediately.
- For this vintage vehicle, high-quality aftermarket brands like Wix and ATP are reliable and readily available choices.
- Changing the filter and fluid every 30,000 miles is inexpensive insurance against catastrophic transmission failure.
Is Your P15 Van Telling You It Needs a New Transmission Filter?
A transmission filter doesn't fail suddenly; it clogs gradually over thousands of miles. Paying attention to the early warning signs can save you from a major transmission failure. If your GMC P15 starts showing these symptoms, a clogged filter is a likely culprit.
Common Symptoms of a Clogged Filter:
- Delayed or Harsh Shifting: You might notice a long pause or a clunk when shifting from Park into Drive or Reverse. Shifts between gears while driving may also feel rough or jerky.
- Transmission Slipping: The engine RPMs might increase, but the van doesn't accelerate accordingly. This suggests the transmission isn't getting enough fluid pressure to engage the gears properly.
- Whining or Buzzing Noises: A whining sound that changes with engine RPM can indicate the transmission pump is straining to pull fluid through a restricted filter.
- Burnt Smelling Fluid: If the fluid on the dipstick is dark brown or black and smells burnt, it's a sign of overheating, which can be caused by a clogged filter restricting fluid flow.
Choosing the Right Aftermarket Filter Kit
For a vehicle from the 1970s, original OEM parts are virtually nonexistent. Thankfully, the aftermarket offers high-quality options that often meet or exceed the original specifications. The key is to choose a reputable brand. Your P15 most likely has a TH350 or TH400 transmission, so you must identify which one you have before ordering, as the filters are different. You can do this by checking the shape of the transmission pan.
Pro Tip: The TH350 pan is square with one corner cut off, while the TH400 pan has a more irregular shape, often described as looking like the state of Texas. Count the pan bolts to be sure.
Aftermarket Brand Tiers
- Premium Aftermarket (Wix, ATP): Brands like Wix and ATP are well-regarded among mechanics for their quality and reliability. Wix is known for excellent filtration media. ATP specializes in transmission parts and their kits often include innovative gaskets that help with installation. These are excellent choices for owners who want maximum protection and longevity.
- Standard Aftermarket (Premium Guard, Pioneer Cable): These brands offer a solid balance of quality and value. They provide reliable, OE-style replacement filters that are a significant step up from no-name parts and are perfectly suitable for regular maintenance.
Transmission Filter Kit Cost for 1975-1978 GMC P15
| Part Type | Price Range |
|---|---|
| New Aftermarket Filter Kit | $11.74 - $56.59 |
| Shop Labor for Installation | $100 - $225 |
| New OEM Filter Kit | Not Generally Available |
Frequently Asked Questions (FAQ)
How often should I change my transmission filter?
For a classic vehicle like the P15, a good service interval is every 30,000 miles or every two to three years, whichever comes first. If you use your van for heavy hauling or towing, consider changing the filter and fluid more frequently.
What type of transmission fluid should I use?
Most GM transmissions from this era use a DEXRON-type Automatic Transmission Fluid (ATF). DEXRON-III would be a common modern equivalent. Always check your owner's manual or dipstick if possible, and confirm the requirements for your specific transmission (TH350 or TH400).
Does the kit come with a new gasket?
Yes, all reputable transmission filter kits include a new pan gasket. It is critical that you use the new gasket and never reuse the old one, as this will almost certainly cause leaks.
Is a rubber or cork gasket better?
Both can work if installed correctly. Cork gaskets were common originally but can be brittle and are prone to cracking if the pan bolts are over-tightened. Modern rubber or fiber-composite gaskets are more forgiving, seal better, and are generally preferred by mechanics.
Technical Specifications
Fitment is dependent on the specific automatic transmission installed (e.g., TH350, TH400), not the vehicle model itself. Kits typically include the filter and a pan gasket. Some kits may also include a new O-ring for the filter pickup tube.
We Have This Part in Stock
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.