* Low Power Steering Fluid: Low fluid level can cause the pump to cavitate (draw air instead of fluid), leading to loss of assist and potentially a stiff or locked steering feel. This is exacerbated under braking because the engine's RPM might momentarily drop, reducing the pump's output. Check your power steering fluid level immediately.
* Power Steering Pump Issues: A failing power steering pump might be struggling to provide sufficient pressure, particularly under load (like when braking). The added stress of braking could push it over the edge into complete failure. Listen for unusual whining or groaning noises from the pump.
* Power Steering Pressure Switch/Sensor: A faulty pressure switch or sensor could be sending incorrect signals to the power steering system, causing it to malfunction when the braking system is engaged. This is less likely, but possible.
* Vacuum Leak (in some configurations): While less common in power steering, some older vehicles have vacuum assist for power steering. A leak in the vacuum system could lead to loss of assist, especially under the added load of braking. This is less likely on a 2000 F350 diesel, but worth considering if the other causes are ruled out.
* Brake Booster Interaction (Very Unlikely but Possible): A highly unlikely but theoretically possible scenario is a mechanical interference or a faulty component causing an interaction between the brake booster and power steering system. This would require a detailed mechanical inspection.
* Hydraulic Leak Causing Intermixing (Unlikely but Catastrophic): A serious but less likely possibility is a leak somewhere allowing brake fluid to enter the power steering system or vice versa. This would severely compromise both systems and is dangerous. Check for fluid leaks near the steering and brake components.
What to Do:
1. Check Power Steering Fluid: This is the first and easiest thing to check. Low fluid is a very common cause of power steering problems. Top it off if necessary and check for leaks.
2. Inspect for Leaks: Look carefully around the power steering pump, hoses, and rack and pinion for any leaks of power steering fluid or brake fluid.
3. Listen for Noises: Pay attention to any unusual noises coming from the power steering pump or system while the engine is running.
4. Professional Diagnosis: If the problem persists after checking the fluid and looking for leaks, you need a professional mechanic to diagnose the issue. This requires specialized tools and expertise to pinpoint the exact cause, as the possibilities involve complex interactions within the vehicle's systems. Ignoring this problem could lead to a steering failure while driving, which is extremely dangerous.
Do not drive the truck until the problem is diagnosed and fixed. Driving with a potentially failing power steering system is extremely risky.
