Here's a breakdown of potential causes and how to troubleshoot:
1. Brake System Issues:
* Frozen caliper piston: This is a common culprit. The piston might be seized due to corrosion or lack of lubrication. This prevents the brake pads from releasing. You'll likely feel significant heat radiating from the affected wheel.
* Stuck caliper slide pins: These pins allow the caliper to move freely. If they're seized, the caliper can't retract properly. Again, heat is a telltale sign.
* Damaged brake hose: A restricted or internally damaged brake hose can prevent proper fluid return, keeping pressure on the caliper. Look for bulges, kinks, or cracks in the hose.
* Low brake fluid: While unlikely to *cause* a completely locked wheel, low fluid could exacerbate a problem with a partially seized caliper. Check your brake fluid reservoir. Low fluid suggests a leak somewhere in the system.
* Master cylinder issue: A failing master cylinder could send uneven pressure to the wheels, though this is less likely to cause a complete lockup on just one wheel.
2. Mechanical Issues (Less Likely but Possible):
* Parking brake cable: Though unlikely to cause a *complete* lockup, a seized or improperly adjusted parking brake cable could contribute. Make sure the parking brake is fully released.
* Wheel bearing: While a seized wheel bearing will usually manifest as noise and binding, it could indirectly affect the brake system by creating binding that interacts with the brake.
Troubleshooting Steps:
1. Safety First: Park on a level surface, engage the emergency brake (if it's not already engaged and causing the problem), and chock the wheels.
2. Check Brake Fluid Level: Inspect the master cylinder's reservoir. Low fluid indicates a leak, a serious problem requiring immediate attention.
3. Feel for Heat: Carefully touch the affected wheel and compare it to the other wheels. Significant heat strongly suggests a caliper issue.
4. Inspect Brake Hose: Carefully examine the brake hose leading to the rear driver's side caliper for damage.
5. Try to Manually Move the Caliper Piston: With the wheel removed, try to gently push the caliper piston back in. If it's seized, it will be very difficult or impossible to move.
6. Inspect the Caliper Slide Pins: These pins are often lubricated with a high-temperature grease. If they're seized, you may need to use penetrating oil and work them free. This often requires removing the caliper completely.
What to Do:
* If you're not comfortable working on brakes, take your truck to a qualified mechanic immediately. Brake failure is dangerous.
* Do not attempt to drive the truck with a locked brake.
* Replacing the brake caliper is likely the solution if the piston or slide pins are seized. You might need to replace the brake pads and hose as well, depending on their condition.
Remember safety is paramount. If you're unsure about any of these steps, seek professional help. A locked-up brake is a serious issue that shouldn't be ignored.
