This vehicle had been sold new by a local dealership, it ended up having had a vibration problem. The service department tried several things to fix the vibration but could not fix it. The dealership bought the vehicle back and ended up selling it again. The new owner brought the vehicle back to have the vibration repaired. Again, the service department tried several things to fix the vibration but could not fix it. The dealership bought the vehicle back for a second time and then I received a phone call from the service manager asking for help.
While listening to the service manager describe the history of this vehicle I learned that in an attempt to repair the vibration, the dealership service department had replaced the following parts on the vehicle:
- Rear Axle
- Rear driveshaft
- Rear driveshaft again
- Transfer case
- Front axle
- Front driveshaft
They had balanced the tires several times and had the new driveshafts balanced; nothing would fix this vibration. The vehicle must be a Lemon, it can’t be fixed.
Using the same diagnostic procedure outlined in our new NVH smartphone app, a few students and I performed a quick road test of the Chevrolet SUV. The results of the road test indicated that the vehicle had a second order driveshaft speed related vibration. As the NVH app’s own diagnostic help file indicates, second order driveshaft speed related vibrations are only caused by a few select problems on the vehicle.
- Cross Type Universal Joints with excessive radial or axial play
- Driveshaft end yokes being out of phase
- Excessive Cross Type Universal Joint working angles
- Unequal Cross Type Universal Joint working angles
While my students and I were working our way down this list of items to check, we discovered that the working angles of the universal joints of the rear driveshaft were unequal and beyond specifications for that vehicle. We performed some calculations and discovered that if we lift the transmission/transfer case mount a little higher above the crossmember, the universal joint working angles would become closer to equal. We installed a 1/8 inch thick shim under the transmission mount and road tested the vehicle again. The vibration problem was fixed.
There were no bad parts on this vehicle. Two very unhappy customers were the result. Thousands of dollars were wasted on parts and many hours of labor were wasted because nobody really knew how to diagnose a vibration problem; they were just guessing! The NVH app eliminates the guesswork in vibration diagnosis and guides you step-by-step through the entire diagnostic and repair procedure. Get the NVH app today by clicking on the link below.