[Solved] Grinding Noise in Front Wheels - 2007 Ford F-150

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Customer Complaint:

This 2007 Ford F-150 came to the shop with a complaint of a grinding noise in the front wheels. The grinding would be random, but it was concerning.

General Information:

After listening to the sound from the truck, it sounded like the four wheel drive was engaging even when the switch was on 2WD.

The crazy part in this grinding noise was the fact that it was random and it seemed like only one side had the noise at a time.

Diagnostics:

My first instinct with this F-150 was to dive into the four wheel drive to see if it was operational.

On these Ford four wheel drive systems, they require vacuum to operate correctly.

Vacuum is supplied from the engine to disengage the four wheel drive hubs.

When vacuum is lost, the four wheel drive engages.

Since I suspected a four wheel drive issue, I needed to check vacuum at both hubs.

Each hub has a vacuum supply hose.

I disconnected the hose while the truck was running and got a vacuum reading.

On both sides, the vacuum to the four wheel drive hubs were -5 inHg.

This is not enough vacuum.

I suspected a partially broken vacuum line or hose.

Smoke machine connected to the driver side vacuum hose

Normal smoke coming from four wheel drive vacuum switch

Smoke machine

I connected the smoke machine to the vacuum hose on the driver side and pumped smoke throughout the four wheel drive system.

As you can see from the picture above, there was a ton of smoke coming from the four wheel drive vacuum switch, which I found is normal.

What is not normal is the small bit of smoke that was coming out right after the vacuum switch.

Small cut on vacuum line right after the vacuum switch

Vacuum line broke easily

I looked a little closer at the plastic lines that came off the vacuum switch.

I saw a small puff of smoke coming out the plastic line running beside the battery.

I found my leak!

After I repaired the line with some hose, the vacuum was in the correct level and the four wheel drive stopped making a grinding noise. Fixed!

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