Cadillac DeVille Transmission Mount Guide (1978-1984)
Stop the clunking and shaking in your classic DeVille by understanding and choosing the right transmission mount.
- The most common signs of failure are clunking noises when shifting and new vibrations in the cabin.
- New OEM parts are not available; the choice is between affordable aftermarket brands (Anchor, DEA, Westar) or a premium-cost rebuilt original mount.
- Driving with a bad mount is not advised as it can cause damage to other components like transmission cooler lines.
- Replacement is a straightforward job for a DIYer with proper tools or a relatively inexpensive repair at a shop.
Symptoms of a Failing Transmission Mount
When the transmission mount wears out, the rubber cracks or collapses. This allows the transmission to move around too much. You will likely notice one or more of these signs:
🎬 Watch: 5 common symptoms of a failing transmission mount.- Clunking Noises: The most common symptom is a clunk or thud when you shift from Park into Drive or Reverse. You might also hear it during hard acceleration or braking. This is the sound of the transmission moving and hitting the frame.
- Excessive Vibrations: You may feel new or heavy vibrations through the floor, seats, or steering wheel. Since the mount's job is to absorb vibration, feeling more of it is a clear sign the rubber has failed.
- Drivetrain Movement: A mechanic might notice the engine and transmission lurching more than they should during inspection. This excess movement puts stress on other parts like engine mounts, driveshaft joints, and even transmission cooler lines.
Choosing the Right Aftermarket Mount
Original Equipment Manufacturer (OEM) new parts for a 1978-1984 DeVille are generally no longer available. Your options are new aftermarket parts or having your original part rebuilt.
For the Restorer: Rebuilding Your Original Mount
Companies like Steele Rubber Products offer a "revulcanization" service. You send them your old, original metal mount, and they will bond new, high-quality rubber to it, making it like new. This is the highest quality but also the most expensive option, often costing over $180.
Aftermarket Brand Tiers
For most owners, a new aftermarket mount is the most practical choice. The available brands are generally considered economy-level replacements. While they will fit and function, forum users have mixed opinions on their long-term durability compared to the original parts.
- Standard Replacement (Anchor, DEA, Westar): These brands are widely available and very affordable. They are a functional solution to fix symptoms like clunking and excess movement. However, some mechanics and users report that the rubber can be harder or the metal thinner than the original, potentially leading to a shorter lifespan or less effective vibration damping.
- Standard Replacement (Pioneer): While known for cables, Pioneer also makes mounts. Some users have found their quality to be very close to the original factory parts and a solid choice.
The Bottom Line: For a daily driver or a budget-conscious repair, any of these aftermarket brands will solve the immediate problem. If you are doing a full restoration and want the best quality, consider having your original part rebuilt.
Cost to Replace a Cadillac DeVille Transmission Mount
| Part Type | Part Cost | Shop Labor Cost | Total Estimated Cost |
|---|---|---|---|
| New Aftermarket | $13 - $58 | $75 - $225 | $88 - $283 |
| Rebuilt OEM (Revulcanized) | $185+ | $75 - $225 | $260 - $410+ |
Frequently Asked Questions
Can I drive with a bad transmission mount?
You can, but it's not recommended for long. While the transmission is unlikely to fall out, the excessive movement can damage other, more expensive parts. This includes engine mounts, exhaust pipes, and transmission cooler lines, which can lead to a transmission fluid leak.
How do I know it's the transmission mount and not an engine mount?
The symptoms are very similar. A bad transmission mount noise is often most obvious when shifting into gear, while bad engine mounts might be more noticeable when the engine is idling or being revved in Neutral. A mechanic can easily diagnose the issue by safely observing the drivetrain while the vehicle is put into gear.
🎬 See how a mechanic diagnoses bad motor and transmission mounts.Is an aftermarket mount good enough for my Cadillac?
For this specific vehicle, aftermarket is the most common and practical option. While an original part would have been made with higher quality rubber, the aftermarket options will still secure the transmission properly and stop the clunking noises. 🎬 Watch this step-by-step guide on how to install a new mount. They may not last as long as the original part did.
What happens if I don't replace a broken transmission mount?
Ignoring a broken mount will lead to more problems. The constant vibration and movement will cause other parts to fail. A known issue on some GM vehicles is that a bad transmission mount can cause the transmission cooler lines to flex and eventually leak, which can lead to transmission failure if not caught in time. You will also experience a rough and noisy ride.
Helpful Videos
Technical Specifications
OEM Part Numbers: 3633035
This is a single-bolt rear transmission mount that attaches to the transmission tailshaft housing and the frame's crossmember. It consists of a steel frame vulcanized to a solid rubber block to absorb drivetrain vibrations and secure the transmission.
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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.