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Old 04-15-2021, 12:53 PM
Dick Boneske's Avatar
Dick Boneske Dick Boneske is offline
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Default Driveshaft Issues

Amazing how little is posted on this G8 section!

My 2009 G8 has a bad center bearing carrier, clunking at acceleration. I've read about replacement--requiring exhaust system removal, etc. Sounds like a big job.

Some have said the answer is to go to a one-piece driveshaft. This makes me wonder why Holden didn't design that way if one-piece is the best way to go. It certainly would have been cheaper.

What have you all discovered with this issue?
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Old 04-15-2021, 04:36 PM
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Default

One piece vs two piece has to do with the driveshaft "critical speed", the point at which it begins to swing like a jump rope.

It is affected by length, outside diameter, wall thickness, material, mass and rpm. Highest shaft rpm is affected by vehicle top speed, rear axle ratio and tire diameter. Length is affected by wheelbase and driveline configuration (trans length, t case, etc).

The driveline is also affected by any unusual or unpredicted system resonances, which can crack a Tcase or some other failure mode even at a speed lower than the critical rpm.

From an OE perspective the driveshaft choice (one piece vs two piece) can be manipulated by controlling any one or more of those variables. Vehicle top speed is limited by several different components, including tire speed rating or driveshaft critical speed. Sometimes the driveline is the designated "fuse" (as directed by the program team) and speed is controlled through the use of fuel or ignition cutoff or some other ECM parameter, in order to maintain a one piece system as a cost save or warranty avoidance.

You can also move to a one piece if you are willing to get extreme on the shaft itself: larger diameter, special lightweight materials (aluminum, carbon fiber, "metal matrix"). That's where the piece cost discussion enters in.

You or I (as individuals) might decide to do a one piece shaft figuring we are not going to be driving all that fast.

So, in this particular case, someone (or a group of someones) decided to play it safe and just go with a two piece design, probably because it had always been that way, not realizing they were going to get into some other problems.

K
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