Bad VibrationI have been involved in the Mustang hobby for about 20 years and worked with my dad restoring several cars, including a '65 fastback, a '67 fastback, and a '68 convertible. My question involves a nagging problem about a '67 Cougar that I have owned for about 15 years. The car has a vertical shake that occurs when I drive more than 50 mph and increases in severity when I increase the speed to about 60 mph. After passing 60 mph, the shake is less apparent-below 50 mph, the car is smooth as silk. The shake seems to vibrate through the body of the car and is not very noticeable in the steering wheel itself. If I shift the car into Neutral and rev the engine between 50-60 mph, it doesn't seem to affect the shake. Also, if I accelerate hard beyond 60 mph, the shake is barely noticeable. The car has a 289 V-8 and an automatic transmission.
In the course of restoring the car, virtually all suspension components were replaced: new lower control arms, ball joints, control arm bushings, strut rod bushings, front springs, spring perches, an idler arm, tie rod ends, a rebuilt steering box, new rear springs, and new rear spring bushings.
In addition to the above, I have replaced and tested numerous items to correct the problem, with little success. At first, I thought the tires were out of round-but after buying new tires, the problem continued. In addition, I installed Mustang-style strut rods (Cougar strut rods are different and have additional bushings), replaced the driveshaft (which helped some), installed an export brace, and replaced the rear transmission bushings. I have inspected the suspension, the motor and the transmission mounts, and the drivetrain numerous times and can find no problems. A friend of mine suggested that I consider replacing the harmonic balancer on the engine. I have also considered replacing the brake drums. Both of these are high-dollar parts, but I am running out of alternatives and getting desperate. It's frustrating to not be able to enjoy driving my restored car! Any assistance you can provide me with in solving this problem would be greatly appreciated.David Dubevia the Internet
Vibration problems are among the most difficult to diagnose and usually require considerable time and patience to correct. You have approached your situation correctly and have systematically replaced any item that may contribute to a vibration; however, I believe your problem might still be in the driveshaft.
Driveshaft-related vibrations are common in Mustangs and Cougars. The symptoms are similar to those you describe, such as the shake feels as if it is occurring throughout the entire car. The fact that you can accelerate through the shake is typical driveline unbalance-the driveshaft will not vibrate as severely when under a load. Stock driveshafts are actually two tubes bent together in rubber to help eliminate driveline noise and vibration. Throughout the years, the shafts develop an out-of-balance condition that can be difficult to trace.
I suggest you get a new, one-piece driveshaft made and properly balanced. As you mentioned, changing the driveshaft was the only repair that affected your vibration at all, therefore, hinting toward a bad driveshaft. A local heavy-truck repair shop should be able to make a new shaft by utilizing the cast U-joint ends off your old shaft and simply replacing the tube.
Sending MessagesA couple of years ago, you ran a tech article about gauge malfunctions in which you specified what the sender resistance should be for the oil pressure, temp, and fuel gauges. I think it was in Beyond the Basics. I've looked through my back issues and cannot find this info. As the proud owner of a '66 Mustang, a '73 Mustang (I converted this one from lights to gauges), and a '69 Cougar XR-7 with many electrical problems, this will be very useful to me.Doug OsbornRoyal Oak, MI