2 piece driveshaft with [CV - Center Barring | Ujoint - Yoke] Does it need to be balanced? 3

[SP1200]

I'm wondering if a 2 piece driveshaft with [CV - Center Barring | Ujoint - Yoke] Does it need to be balanced since the ujoints are so close??
Please see attached pic.

To me it looks like the CV section between the center support is balanced at manufacturing with a weight, and the other section that has the Ujoint leading to the Yoke has the same weight from center support to the yoke. Do these weights (circled in pic) need to line up? or be opposite form each other? I make a stupid mistake and separated the 2 halves with out making them when replacing the center support barring. yea, I'm getting old.

Here is a link to the drive shaft in question.

https://www.fcpeuro.com/products/bmw-driveshaft-powertrain-26117505214

Vehicle Info: 2004 BMW 330i GM Auto trans.

 

[GregLocock]

Simple thing to do is take it out for a high speed run and see if it vibrates. If so take it apart and reassemble in the other configuration. Yes, it does need balancing.

Cheers

Greg Locock


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[SP1200]

Well I do gave a vibration, but I'm not sure what it is as I replaced all rubber suspension bushings with poly. And there are 10 splines to align with so id have to try 10 different times. maybe I will buy another, or see if I can take it to a shop.

 

[GregLocock]

Yup, any driveline shop should have a dynamic balancer.

Cheers

Greg Locock


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[Tmoose]

I'd download a vibration analysis phone app and determine if the vibration frequency is wheel rotating frequency, or 1X or 2X driveshaft frequency


What's the frequency Kenneth ?

 

[EdStainless]

Small vibrations that you can't feel will damage seals and bearings.
If you can feel it then it is serious.
Pay to get it dynamically balanced.

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P.E. Metallurgy, consulting work welcomed

 

[CWB1]

I'd download a vibration analysis phone app and determine if the vibration frequency is wheel rotating frequency, or 1X or 2X driveshaft frequency.

An old/quick mechanic's test is to jack up the drive wheels then have a helper put the vehicle in gear. With wheels spinning in the air you can visually see whether/not the driveshaft has a significant vibration independent of road/wheel/chassis variables.

 

[GregLocock]

Good point, a screwdriver is a very effective vibration detector.

Cheers

Greg Locock


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[mfgenggear]

I guess it's what the max out of balance is permitted. so there must be a standard some where, if not ask the specialist at the drive shaft balancing. a grossly out of balance is not only annoying it can do damage as stated by ed stainless. and is very simple to balance, and if it is to far out of spec, you will need to manufacture an other drive shaft assy

 

[GregLocock]

I can't remember what we balanced to, it is installation specific, 20 g cm for a truck. Since worst case he just has to reclock the assembly 9 times, less with instrumentation, it's all pretty non dramatic.

Cheers

Greg Locock


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[mfgenggear]

Greg

appears to be very liberal

 

[GregLocock]

I may be misremembering, truck, not Rolls Royce! On aluminium sedan propshafts the small weights were 3mm thick and perhaps 13mm square. Hmm 1.5g so 5g cm. Does that sound better?

Cheers

Greg Locock


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[EdStainless]

I had a custom shaft made years ago. The weights look like a couple penny sized pieces of steel welded to the shaft.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[mfgenggear]

Ya no worries Greg, I should be more descriptive, the tolerance for balancing the drive shaft should be easy and no brainer.. the tolerance is wide open. I had drive shaft repaired as well once, cut the tube off and welded a new tube. never had an issue

 

[TMcRally]

What is the advantage/disadvantage of a 2 piece tailshaft V's a one piece on an IRS car from a manufacturers point of view.

 

[BrianPetersen]

What is the advantage/disadvantage of a 2 piece tailshaft V's a one piece on an IRS car from a manufacturers point of view.

Generally, critical speed. There's a relationship between the length and stiffness of a rotating shaft with free ends (universal joints) and the maximum speed that it can turn before it starts whipping (think of a skipping rope - that's the shape it wants to go into). If it needs to be a certain length that gets into critical-speed issues then the options are to make the shaft stiffer relative to its weight (hollow tube - increase its diameter - but there are practical limits to this) or limit its speed of rotation (depends on final-drive ratio and wheel diameter ... or simply implement a speed-limiter in the vehicle) or ... add a center support, which is more effective by far than any of the other choices, and allows the diameter of the shaft to be shrunk down again.

 

[GregLocock]

Depending on axle ratio etc for a typical large sedan a single piece propshaft becomes impractical (ie OD> 101 mm (I think I had a 5" aluminum for development work but the tunnel would have needed to be bigger)) unless you go to carbon fibre somewhere between 200 and 240 kph. Things are made worse because production car propshafts have internal harmonic dampers and things which lower their bending frequency.

Cheers

Greg Locock


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