1991 Ford F-150 Vibrates at High-Speed

Reader Question: Hi!

I have a 1991 Ford F-150 with 83,000 km. I have experienced a vibration at exactly 80km/hour, which continues as I increase speed. It does not get better the faster I drive.

We have changed the tires, Universal joint, and the front end is excellent. Could it be the Torque converter or the Transmission?

We are stumped.

Any help would be appreciated.

Al

Hey there Al,

These types of complaints can be tough to figure out. I always like to start with the basics and the easiest items first.

If you were in my shop, I would raise the vehicle up in the air with the tires off the ground, run the truck at the 80 km speed, and look for anything visually out of balance.

Pay special attention to the drive shaft, rear end, and tires. If you have a two-piece drive shaft, there will be a center support bearing holding the shaft together, check the support for wear or slack.

If the vibration is not felt, this could mean that the problem is in the front of the vehicle or there needs to be weight placed on the truck for this problem to surface.

So, have the front end shaken down again for wear and have the two front wheels rebalanced paying close attention to the wheel as it spins on the balancer. I have seen bent wheels wobble on the balancer BUT the machine said the wheel was in proper balance.

I also have a portable spin balancer that will allow me to spin the wheels ON the vehicle so I can watch what is going on with each independent wheel.

If you did not experience the vibration with the truck lifted off the ground like I suggested earlier, try moving the two front wheels to the rear just to rule out a bent wheel or out of round tire. If the vibration is in the front, usually the steering wheel will shake side to side.

You can also put the transmission in neutral and turn off the engine next time you get this vibration to occur. It might help rule out a transmission or an engine vibration. You could have a torque converter issue, but changes are the problem is tire, wheel, front-end, or driveline related.

The biggest problem I see with these types of complaints is complacency with the mechanic. They assume the wheels are balanced properly, and they are sure the front end is tight. They spend more time chasing possible big problems like a torque converter and overlook the simple more obvious things because they quickly ruled them out.

Blessings,
Austin Davis

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