* Driveshaft imbalance: This is the most likely culprit. As the engine works harder on inclines, the increased torque amplifies any existing imbalance in the driveshaft. This imbalance causes vibrations that transmit through the drivetrain to the steering wheel. This is especially noticeable just before a downshift because the engine is under high load and the driveshaft is spinning at a specific RPM where the imbalance is most pronounced.
* U-joints (universal joints): Worn or damaged U-joints in the driveshaft are another common cause. They allow for the change in angle between the driveshaft and the transmission/differential, but wear can create vibrations, especially under load. A clicking sound might accompany the vibration, but not always.
* Transmission problems: While less likely to manifest primarily as steering wheel vibration, transmission issues (worn bearings, internal problems) *can* cause vibrations that travel through the drivetrain.
* Differential problems: Similar to transmission problems, worn bearings or other internal issues in the differential can also contribute to vibrations. However, this is less likely to be specifically tied to acceleration and inclines.
* Tire imbalance or worn tires: While less likely given the specifics (acceleration-related and on inclines), unbalanced tires or tires with uneven wear can cause vibrations, but those are typically more noticeable at higher speeds and not directly linked to engine load and downshifts. However, rule this out.
* Loose or worn components: Check for any loose bolts or components in the drivetrain. Something loose can cause vibrations under load.
Troubleshooting Steps:
1. Visual inspection: Carefully inspect the driveshaft for any obvious damage, bends, or loose components. Check the U-joints for play or wear. Look for any signs of leaks around the transmission or differential.
2. Tire inspection: Check tire pressure, look for uneven wear, and balance the tires.
3. Driveshaft balancing: If a visual inspection doesn't reveal anything obvious, the driveshaft likely needs balancing. A professional driveshaft shop can do this. This is often the solution for this type of vibration.
4. U-joint replacement: If the U-joints show wear or play, they should be replaced. This is a relatively common maintenance item in motorhomes.
5. Professional diagnosis: If you're not comfortable performing these checks yourself, take your motorhome to a mechanic specializing in larger vehicles or motorhomes. They can diagnose the problem more accurately and perform the necessary repairs.
Since the vibration is linked to acceleration and inclines, the focus should be on the drivetrain components. Start with the visual inspection and then consider the driveshaft balancing and U-joint replacement as the most likely solutions. Ignoring the problem could lead to more serious damage and costly repairs.
