1979-1985 GMC P3500 Automatic Transmission Mount Replacement Guide
Stop the clunking and shaking in your P3500 by understanding and replacing your worn transmission mount.
- A clunking noise when shifting is the most common sign of a bad mount on a P3500.
- Replacement is a straightforward DIY job for most owners, requiring basic tools and a jack.
- Aftermarket brands like Anchor and Pioneer are budget-friendly options, but OEM quality is not expected.
- No specific recalls or TSBs exist for this part on your vehicle, making inspection based on symptoms key.
Is Your Transmission Mount Failing?
A worn-out transmission mount on a GMC P3500 can cause a range of noticeable problems. Because these are heavy-duty trucks often used as work vehicles or RVs, the symptoms can be more pronounced. If the rubber in the mount cracks, collapses, or separates from the metal plates, the transmission can move excessively.
Common Failure Symptoms:
- Clunking or Banging Noises: The most common sign is a loud clunk or bang when you shift from park into drive or reverse. You might also hear this noise when you accelerate or decelerate suddenly. This is the sound of the transmission shifting and hitting other parts because the mount isn't holding it securely.
- Excessive Vibrations: You may feel a new or intense vibration throughout the truck, especially when accelerating. A bad mount can no longer absorb the normal vibrations of the drivetrain, so they travel through the truck's frame and into the cabin.
- Drivetrain Movement: A mechanic can often spot a bad mount by having someone hold the brake, put the truck in gear, and lightly press the gas. If the engine and transmission assembly rocks or lifts excessively, the mount is likely worn out.
Don't Mistake It for a Bad Transmission
The symptoms of a bad transmission mount, like clunking and hard shifting sensations, can sometimes be mistaken for serious internal transmission problems. Before assuming the worst, a quick inspection of the mount can save you a lot of worry and money.
Choosing the Right Aftermarket Mount
For a vehicle from this era, Original Equipment (OEM) parts are often unavailable. The market for the 1979-1985 P3500 consists mainly of aftermarket brands. Quality can vary, so it's important to know what you're buying.
Aftermarket Brand Tiers:
- Standard Aftermarket (Anchor, Pioneer Cable): These brands provide functional, budget-friendly replacements. User reviews are often mixed; some find them perfectly adequate for the job, while others report issues with the hardness of the rubber or slight fitment problems. For a simple, non-hydraulic mount like the one on the P3500, brands like Anchor are often considered an acceptable repair solution. Given the low cost, they offer a practical way to fix the problem.
- OEM-Quality Aftermarket: These are not typically available for a vehicle of this age and for this specific part.
Pro Tip: When replacing the mount, check the condition of your engine mounts as well. Worn engine mounts can put extra stress on the new transmission mount, causing it to fail prematurely.
Estimated Costs for Replacement
| Part Type | Estimated Part Cost | Estimated Labor Cost | Total Estimated Cost |
|---|---|---|---|
| New Aftermarket (Anchor, Pioneer) | $11.55 - $14.90 | $75 - $150 | $87 - $165 |
| New OEM | Not Generally Available | $75 - $150 | N/A |
Frequently Asked Questions
Can I replace the transmission mount myself?
Yes, for a 2WD P3500, this is a relatively simple job for a DIY mechanic. It involves supporting the transmission with a floor jack, removing three bolts, raising the transmission slightly, and swapping the old mount for the new one. Always use jack stands for safety.
How do I check if my transmission mount is bad?
You can perform a visual inspection by looking for cracks or separated rubber in the mount. A more definitive test is to have a helper put the truck in drive with the parking brake set and their foot on the brake, then briefly rev the engine. If you see the transmission lift or move significantly, the mount needs replacement. Be sure to stand safely to the side of the vehicle, not in front or behind it.
Are there any recalls for the P3500 transmission mount?
No, searches of the National Highway Traffic Safety Administration (NHTSA) database did not find any recalls or technical service bulletins (TSBs) specifically related to the automatic transmission mount for the 1979-1985 GMC P3500.
How long does a new aftermarket transmission mount last?
The lifespan of an aftermarket mount can vary. While factory mounts can last up to 100,000 miles, an economy aftermarket part may have a shorter life depending on driving conditions and the quality of the part. Given the heavy-duty nature of the P3500, regular inspection is a good idea.
Technical Specifications
Standard two-bolt top mount with single bottom stud, common to GM rear-wheel-drive platforms of the era.
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.