* Worn-out shock absorbers (rear): This is the most common culprit. Worn shocks allow excessive rebound, causing the bouncing. They're relatively inexpensive to replace.
* Worn-out or damaged leaf springs (if equipped): Leaf springs can break, become excessively fatigued, or develop cracks, leading to instability and bouncing. This is more common in trucks with leaf spring rear suspensions.
* Faulty or worn-out rear brake components: While less likely to *directly* cause bouncing, severely worn or seized brake calipers or drums/rotors can lead to uneven braking and contribute to instability. This should be checked as well.
* Problem with the rear axle: While less frequent, problems with the rear axle components, such as worn bearings or a bent axle, could affect the suspension's stability and cause bouncing under braking.
* Improperly adjusted or damaged brake lines: In rare cases, a leak or kink in the brake line can affect braking pressure and contribute to instability.
What to do:
1. Safety First: If the bouncing is severe, it's unsafe to drive the vehicle. Have it towed to a mechanic.
2. Visual Inspection: Carefully inspect the rear suspension for any obvious damage, such as broken or cracked springs, leaking shocks, or loose components.
3. Professional Diagnosis: Take your Sierra to a qualified mechanic or auto repair shop. They can properly diagnose the problem and recommend the necessary repairs. Mention the bouncing specifically when describing the issue.
Don't attempt to diagnose or repair this yourself unless you have significant mechanical experience. Ignoring the problem can lead to more severe damage and potentially dangerous driving conditions.
