Join Date: Jun 2016
Location: Santa Barbara, CA
Balancing GTV6 driveshaft with hose clamps
As some of you may have read in a couple of other threads, I have had a persistent vibration from the driveshaft of my GTV6 since I bought it almost 2.5 years ago. The vibration was quite severe at ~2500 RPM when cold, but was greatly diminished when warm. I replaced the giubos and center support bearing, replaced the front "olive" for the pilot bearing, replaced all engine and trans mounts, tried adjusting the engine and trans every which way, with no significant change. Despite living an hour north of the LA area, I could not find a local place that could balance a GTV6 driveshaft.
I have long been aware of the notion of using hose clamps to balance a driveshaft, but I had never tried it myself. I finally decided to do so this weekend, serendipitously right after the latest Grand Tour episode aired.
I downloaded an iPhone vibration analysis app (simply called "Vibration") and did some online research about driveshaft vibration in addition to consulting some textbooks.
The nice thing about the hand throttle of the early GTV6 is that I could use it to hold the RPM at the point of worst vibration while observing the driveshaft from underneath. I had always felt the vibration to be the most severe in the center support area, and a visual confirmation showed that the rear portion of the front half of the driveshaft appeared to be either bent or severely out of balance.
I attempted to be somewhat scientific at first by checking the runout of the suspected portion of the driveshaft at several different points using a dial indicator, and marked the high and low spots of each (though I soon realized that surface rust and peeling paint probably affected these readings). A couple of sections had over 0.010" runout, which seemed significant.
I then took a baseline reading of the vibration traces using the iPhone app, though I found that it was tricky to get consistent readings. I started with a single hose clamp (the forward half of the driveshaft is 70MM in diameter), and positioned the weight of the worm drive opposite the highest of the high spots measured. This actually worsened the vibration, so I tried several different positions until I reached the baseline again. I eventually added a second clamp, and after enough trial and error I finally go the vibration to diminish. I would like to say that I closely analyzed the vibration app readings after each test, but in the end I kept making small movements of the clamps until I found the exact position where the vibration was felt to be the least.
I am happy to report that the vibration is 95% gone; even when cold it is not very noticeable. I will likely revisit this soon and see if it can be further diminished, but I am quite happy with the results of a half day's worth of work! The downside was a couple of light burns due to the proximity of the catalytic converter, but worth it in my book considering the results!
Chris A: '81 GTV6 rescued from junkyard, "GT" car/'86 Porsche 944 Turbo track/street car/'73 BMW 2002tii fun street car/'74 Jensen Healey Lemons Rally car!