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[MD]

Scott,

The mounting of the CV's is in a captive situation. Anotherwords, they are "located" so they spin true. If they are a balanced item in themselves, they should not contribute to an out-of-balance.

Yes there is more spinning mass than with rubber and there is virtually no damping either. Due to a lack of damping, this type of shaft is not suitable for road cars.Too harsh.

Cannot visualise when CV's would cause od bending. Whipping would most likely come from a bent shaft and not from a CV.

[MR2 Zig]

Are the center bearing mounts for the cv / u-joint type drivelines using the stock soft rubber mount? Would going to a stiffer rubber/ solid mount do any good?

[Giuliettaevo2]

Recently i dismantled a bmw propshaft and discovered it had the same diameter centrebearing (the hanging bearing thing in the middle) as the Alfa axle. Maybe that's an option?

prop was from an E38 7 series 740i.

[MD]

confused.

..the same diameter centrebearing (the hanging bearing thing in the middle) as the Alfa axle. . ??

if you mean propshaft, that's interesting. So how much different is the rubber housing holding the bearing to the Alfa one?

[Giuliettaevo2]

The hole where the axle protrudes is the same diameter.

Total outer dimensions where also not to far apart... Would not be a real challenge to make it fit i think.

[MD]

So how much different is the rubber housing holding the bearing to the Alfa one?

Softer, stiffer, more sexy ,what ??

I think this is the heart of what Ziggy is saying.

[Giuliettaevo2]

Very sorry but i got no clear pics of it anymore...

It was a good quality thing and it looked quite stiff but i didn't have it next to a transaxle item so no good comparison.

I'll see if i have any more bmw parts lying around this weekend so i can take measurements.

[slyalfa]

just got a thought. as you can't seem to find any one to balance. you might see if you can get one of the guys that do the prop on small airplanes. they do it in place with a few marks and a vibe sender and a optical mark going in to a laptop, rev it up and down place some weights and done.. I do not see why the same set up would not work on the drive shaft.

[MD]

A good innovative suggestion.

Some key things that are different. A propeller is essentially spinning in one radial plane.

A propshaft may not only be out of balance but also not running true, slightly bent, front half to a different degree to the back one and so on. What is the sum of all these resonaces up and down the shaft instead of just the one radial plane? More complex.

If I had a lathe that I could turn the shaft in and place a dial guage onto it and test it for run out that causes whipping that would be a great start but I dont have one.

Once it can definitely be established that the whole assembly is running true and accurately so, the actual balancing part is relatively straight forward. I think most machinists reading this post would agree.

Nevertheless, I am told that in some workshops in Athens, they are balancing shafts on a similar fashion "in-car". So, the challenge now guys is how to make the Cab amphibious and drive it to Athens, knock on JK's door and ask him for directions..hehhee

[Duk]

You can test for run out with the tailshaft in the car. Just use a magnetic based dial indicator mounted on the body reading from the centre of 1 of the halves and rotate the 'shaft by hand while watching it (we all know you like to watch, MD ).

[Mats]

When I was developing propshafts for a living we made a linear sensor setup that worked like a dial gauge but was logable, two sensors in up/down and side/side direction that was actually touching/sliding on the axle itself. Worked very well. We also made a torsion vibration sensor arrangements which was used to sense unsmooth rotation speed with a toothed wheel and a VR-sensor.

Now, regarding balancing, you have to understand (and you probably do) that if you have run-out and "correct it" with a balancing weight YOU WILL ONLY HAVE A BALANCED SHAFT AT THAT SPECIFIC SHAFT SPEED!
At one time a supplier sent us a shaft that measured perfect but I could actually see that the middle joint had one part at an angle to the tube it was welded to. I saw it the instant I walked into the room from avout 10m away, so it was not a minor mishap. All the measurements looked great but it naturally performed like crap. We mounted it in the rig and ran it just for fun, even made a video and sent back to the supplier and asked them to add a few more rpm intervals to measure at. They were not amused...
Just so everybody understands how sensitive this is: the same supplier had problems getting their props to stay balanced even after they were balanced and done because as a final step in the process they were spray painted, by hand. Very sensitive indeed.

Another thing to keep in mind: the individual shafts needs to have their natural harmonic frequency away from each other, they need to differ at least 15% or you can have problems.

[MD]

Very informative read Mats.

Duk. That idea is good if the shaft is in a "V" block and getting turned by hand. If you think it through, it's almost impossible to turn the propshaft by hand (even with all the spark plugs out) without causing a deviation due to the working of the centre rubber support not being rigid.

On the other hand just doing a bit of lateral thinking, the shaft is less likely to deviate if you turn the ENGINE by hand but having done this countless times for other reasons, due to the flexibility of the mounts collectivley, you are likely to disturb the alignment in the process and cause a non balanace related deviation anyway.

Yeah the more I think about it, I think a check that the tubing is straight in a "V" block with a dial guage and that the couplings are not welded in off centre followed by an "in-car" balance would be hard to beat.

[Duk]

Remove all of the spark plugs (unplug the CAS sensor or coils while your at it so the coils aren't still sending HT voltage where ever they can), stick dial indicator so it points at the side of the rear engine mount, crank engine on the started and view dial indicator to see if the engine moves around on its mounts.
Theoretically it should stay still because the opposing force for the starter motor is the engine itself.
If the engine stays still, reposition the dial indicator to the section of the tailshaft you want to watch.

[Mats]

You will still have unequal turning torque depending on crank position in the revolution and therefore there will be an uneven rotational speed that will be dealt with in the engine mounts. Probably it will jump around a bit.

Turning by hand on the prop in situ sounds difficult to say the least.

[MD]

Hahaa. I can see myself going up another level soon if this keeps going.

I am going to make a torque tube ...

Anyone got a cheap Porsche for sale