What Made the Mustang Squeak?

Several months ago, my 2008 Mustang GT started to develop a squeak during acceleration. The squeak, which came from the right rear quarter of the car, was quite annoying. At first, it only happened once in a while, but it gradually grew worse.

I asked my daughter to sit in the backseat while I drove the car, hoping that she could pinpoint where the sound was coming from. She thought it was coming from behind an interior panel. We lowered the right rear seat, but this didn't help us locate the squeak. I sprayed the control arm, Panhard bar (track bar), and stabilizer (sway) bar bushings with WD-40 and we tested the car again.

The squeak seemed to be a little fainter, but was still audible. I disconnected the right rear shock absorber temporarily, but this had no effect on the squeak. It started to rain as I was test-driving the car. Thinking that the squeak might be caused by the seatbelt retractor, I pulled on the passenger seat belt while driving, and this seemed to stop the squeak. I thought I'd found the problem, so I quit troubleshooting for the day.

The next day, the squeak was back. After driving during several rainstorms, I concluded that the squeak was not so pronounced when the underside of the car was wet. This told me that the squeak was originating on the outside of the car. I looked through Technical Service Bulletins (TSBs) for the year/make/model of this car, but did not find any information about the squeak. I talked to a Ford technician, who said that the frame could be cracked, and would have to be repaired by welding.

I searched the Internet and discovered that some other people had the same problem, and had solved it by replacing the lower control arms. I eventually found a video made by another squeaky (the car, not the person) Mustang owner. In the video, he pointed out what causes the squeaking: the outer diameter of the bushing rubbing against the body flange (mount). When the bushings go bad, they crack and separate from their steel sleeves, and the control arms translate sideways.

The video guy apparently didn't realize that his bushings were bad, and repaired his car by inserting nylon washers and bending the flange. This was a temporary fix at best, and obviously he didn't know that the bolts are supposed to be tightened to 129 lb ft, which would likely develop enough force to destroy the nylon washers very quickly.

When I finally lifted the car and took a close look at the control arm bushings, I saw that the bushings were bad. This condition allowed the outer diameter (steel sleeve) of the bushing to rub against the mount. Replacement bushings are not readily available, but replacement control arms are available, so I replaced them. I purchased performance/upgrade control arms, sold by Ford Racing, because they were far less expensive than the $472.94 MSRP for stock replacements.

The Ford Racing control arms are described as upgrade parts, because they have bushings made of stiffer rubber, but it turned out that the bushings had part numbers that are identical to the part numbers on the original bushings. The only difference between the upgrade control arms and the stock ones is the color (silver instead of black) and a lot of marketing hype.

It is not unusual for control arm bushings to fail, but it is unusual for them to fail after only five years of mostly four-lane driving!

Doug Linkhart has been an RF/Microwave engineer for more than 30 years. He previously worked as a mechanic and among his other credentials, has an associate degree in Automotive Technology.

Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.

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