Balancing GTV6 driveshaft with hose clamps - Alfa Romeo Bulletin Board & Forums
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post #1 of 25 (permalink) Old 02-23-2019, 09:49 PM Thread Starter
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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!
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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!
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post #2 of 25 (permalink) Old 02-23-2019, 10:21 PM
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Well, that's cool.

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1989 Milano, Shankle Sport
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previously owned since 1964:

62 Morris MiniMinor 850, 67 Austin 1275 Cooper S (Downton 3/4 race), 64 Giulia Sprint GT (1st red one made), 72 Fiat 128 Sedan, 75 Alfetta Sedan, 78 Alfetta Sedan, 78 GTV, 81 GTV6, 86 GTV6
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post #3 of 25 (permalink) Old 02-24-2019, 05:40 AM
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Nice work. Surprised nobody in LA could handle that...

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post #4 of 25 (permalink) Old 02-24-2019, 05:57 AM
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Did you find the distance along the shaft to locate the clamps by trial and error and what is the relative distance from the two suspension points for that shaft? Is there less runout now that it is balanced?
Thanks.

Ed Prytherch
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post #5 of 25 (permalink) Old 02-24-2019, 08:22 AM Thread Starter
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Nice work. Surprised nobody in LA could handle that...

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There might be someone who could. . . . . I talked to a place in Ventura that is part of a small SoCal chain of driveline shops, and the guy there said the Garden Grove location could handle it. I called the Garden Grove place and some particular machine was broken, or something like that. I probably called a half-dozen driveline shops in total. I also never asked a prominent Alfa shop like Santos.

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!
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post #6 of 25 (permalink) Old 02-24-2019, 08:29 AM Thread Starter
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Did you find the distance along the shaft to locate the clamps by trial and error and what is the relative distance from the two suspension points for that shaft? Is there less runout now that it is balanced?
Thanks.
Hi Ed,

To be honest, it ended up being trial and error by the end of the process. I did start by measuring the runout a 4 different points along the suspected area pictured in my post; I removed the spark plugs and turned the engine by hand via the crank pulley nut and watched a dial indicator. I marked the high and low spots of each. In the end, these marks were useful as basic reference points---the worm gears of the hose clamps ended up being opposite the general area of the "low" spots. I simply kept moving the clamps up the shaft by one hose clamp-width at a time until the vibration was minimized as verified by the iPhone app.

My last movement of the clamps towards the front of the car resulted in a slight vibration at 3500 and 4000 RPM, so I moved them back to the previous spot and all was good.

To answer your question, the actual runout of the shaft is unchanged, but now there are some weights to counterbalance this. By the same principle it is often possible to dynamically balance a slightly bent wheel.

I might revisit this and study the subject more and write a proper article about it (I write tech articles for Porsche publications).

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!
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post #7 of 25 (permalink) Old 02-24-2019, 08:59 AM
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Nicely done!

I have always believed that if you balance each half individually that ideally they should be balanced as a whole. But I don't have any data to back that up, and my vibrations class is 30 years behind me.



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post #8 of 25 (permalink) Old 02-24-2019, 11:09 AM
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I had the driveshaft rebuilt and balanced. Drives like a new car. I suspect the proper procedure for these cars when servicing the driveshaft is to have it balanced. Much like when replacing tires, when replacing giubos.
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post #9 of 25 (permalink) Old 02-24-2019, 01:09 PM
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"Where?" I can hear a few people saying, Alfistaa...
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post #10 of 25 (permalink) Old 02-24-2019, 04:07 PM
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I once got a GTV6 that had a hoseclamp clamping a small square wheel weight to the driveshaft. It didn't vibrate,,,.
I have had cars that had driveshaft vibration because the trans crossmember spacers were missing.
They are different thicknesses for a reason!

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post #11 of 25 (permalink) Old 02-24-2019, 04:34 PM
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If the driveshaft is not bent, there does not HAVE to be any correlation between the "static" runout and the balance.

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75 Alfetta GT (Original owner), 92 164S, 86 GTV6
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post #12 of 25 (permalink) Old 02-24-2019, 04:59 PM Thread Starter
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If the driveshaft is not bent, there does not HAVE to be any correlation between the "static" runout and the balance.
True. As mentioned in my first post of this thread, from watching the driveshaft movement while holding the engine RPM at the point of max vibration, it appeared that the rear portion of my front driveshaft half could be bent due to the amount of visual "wobble." I measured static runout at a few spots it it seemed significant enough. I did put a straightedge all around the suspected bent portion and it seemed straight, however (of course static runout can be caused by a bent/misaligned yoke, etc instead of the shaft itself).

I will do some more studying of the saved traces from my vibration analysis app and post the results here. From my research, I do know that there are differences in the causes of first, second and third order vibrations (balance vs alignment vs bent components, etc). Anyone here who is more knowledgeable about this subject than I should feel free to chime in!

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!
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post #13 of 25 (permalink) Old 02-24-2019, 05:23 PM
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"Where?" I can hear a few people saying, Alfistaa...
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post #14 of 25 (permalink) Old 02-24-2019, 06:57 PM
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post #15 of 25 (permalink) Old 02-24-2019, 07:20 PM
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Yeah, I never thought it was likely to work for me...
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