Drive shaft mod save fuel.

[dwtaylorpdx]

This is the reason BMW uses the "Guibo" for the center joint. Its lighter than a U joint and helps dampen the drive line harmonics. Center bearings don't really impact the amount of torque to turn the driveline, at least the ones I've worked on spin like nothing. The weight is a good point...

I agree a seven piece drive line would be total overkill, but your not necessarily saving energy with a one piece drive line. It goes in and out of harmonics at varying speeds, its pure luck and your driving style that determines the effect

Now using Guibo's instead of U-joints might work on some cars,, Just a thought there...

Oh well it was a thought, if it makes 50MPH at the end of the salt flats there should be a gain somewhere... its also the reason so many cars used to crash, drive-line would whip and tear the car up... Of course that was at silly speeds, not what were are talking about.

Dave

[Christ]

I'd think that balancing the driveshaft to higher RPMs would make decent work of harmonics... but even then, you could always just play with different gear ratio sets to keep the driveshaft RPM down while maintain the same engine/vehicle speed.

[Frank Lee]

Drive Shaft Harmonics

These guys explain where and when a multi-piece shaft is a good idea:

Two-Piece Driveshaft Technology - Rod and Custom Magazine

Then this guy did pretty much what I did with my old Chevy PU:

Two-piece to One-piece Driveshaft Swap

[dwtaylorpdx]

Originally Posted by Christ

I'd think that balancing the driveshaft to higher RPMs would make decent work of harmonics... but even then, you could always just play with different gear ratio sets to keep the driveshaft RPM down while maintain the same engine/vehicle speed.

The harmonics are more complex than just balancing the shaft, they result from the engine power pulses, chassis rigidity, axle setup etc... The longer the element the more susceptible to harmonic whip it becomes its why the GM AL drive shafts have a weight ring about 10 inches from the end of the shaft, its to dampen the harmonics. Slower is surely better, especially for a street car!

Long as you can stay in the sweet spot for your engines design.

Dave

[Frank Lee]

Different shafts for different strokes... or folks... or something.

[Christ]

Originally Posted by dwtaylorpdx

The harmonics are more complex than just balancing the shaft, they result from the engine power pulses, chassis rigidity, axle setup etc... The longer the element the more susceptible to harmonic whip it becomes its why the GM AL drive shafts have a weight ring about 10 inches from the end of the shaft, its to dampen the harmonics. Slower is surely better, especially for a street car!

Long as you can stay in the sweet spot for your engines design.

Dave

I thought about the harmonics vs. balance thing after I posted, just didn't bother to edit it.

Slower is definitely better, but obviously, you can only get so many gear ratios reasonably.

I think for EM members, the one piece driveshaft is more attractive because there are less maintenance items to think about, and they do tend to run smoother IMO.

[Frank Lee]

I paid a lot for that center carrier bearing that has now sat in my garage for 20 years.

[dwtaylorpdx]

Originally Posted by Frank Lee

Drive Shaft Harmonics

These guys explain where and when a multi-piece shaft is a good idea:

Two-Piece Driveshaft Technology - Rod and Custom Magazine

Then this guy did pretty much what I did with my old Chevy PU:

Two-piece to One-piece Driveshaft Swap

Good article, they are talking about the end effect after the harmonic resonance has peaked.

I think its probably a mission decision, and it hinges on the design of the vehicle. Your truck likely does not see speeds over 80 (often) and has a lot of travel so the longer drive line works fine, and is likely almost needed to get eh suspension travel. My BMW sees speeds well over 100 on track days and the diff and transmission stay in constant relationship cause I have IRS. I'm also rolling on short tires with 3.78 rear gears so I get some RPM in the drive-line.

I still wonder if the guibo might help as a different way to get around the natural wobble of a Ujoint or a CV joint in rotation. There are several small race cars that use them instead of CV's and they are all lower HP spec cars.

What do ya think?

Dave