Drive Shaft Refurb and Clean up

[RRoller123]

I have my engine, trans and driveshaft out for an engine upgrade, and am wondering how much effort to put into the driveshaft. The U Joints are fine, the center support bearing is fine, but the shaft itself (both pieces) is covered with a great deal of thick, splattered coating of what looks like solid undercoat or bedliner, that doesn't readily come off with detergent or common solvent. Concern is that it throws off the balance.

Those of you who have been here, have you sent your driveshafts out for rebalancing? If so, were they sent as is, or did you preclean them up by sandblasting, abrasive, whatever? There are no dents, no bends, no damage to mine at all. Just this load of carp on it. Or is this whole process not really necessary?

I do have a driveshaft shop only 10 minutes away from the house. It is tempting to make it look good, but it is the driveshaft, after all. Those who rebalanced one, how far off was it? Significant or negligible?

Will post pic later. Raining like crazy here with high wind right now.

[18Fiatsandcounting]

My thought is that since you have removed the driveshaft and are spending some money on the engine and transmission, go ahead and spend a bit more on the driveshaft. U-joints, center bearing and mount, balancing. At a minimum, clean the goo off through one of the methods you mentioned.

Did you notice any drivetrain problems before, like clicking, rumbling, etc?

I need to take a look at the driveshaft on my '69 as it has a barely noticeable rumble at 39 mph and then (the second harmonic) at 78 mph which is definitely noticeable. Neither of these is a speed that I'm at very often, and it's easiest to just go 1 or 2 mph below or above those speeds, and all is well again. Not sure I want to tempt fate by trying to hit the third harmonic at 117 mph...

-Bryan

[RRoller123]

I tend to agree, although the car ran pretty smoothly beforehand, and it seems hard to identify exactly where any particular vibration is coming from. There is so much gumpcukrus on there that I have to believe it is effecting the balance somehow. Especially since the shaft is hollow, and any d(mass) out at the circumference can make a big difference.

I think I will take it over to the shop; "Cape Cod Axle and Bearing" in Sandwich, and see what they say. Never been there before, know nothing of them, but will find out!

Pete

[18Fiatsandcounting]

There is so much gumpcukrus on there that I have to believe it is effecting the balance somehow. Especially since the shaft is hollow, and any d(mass) out at the circumference can make a big difference.

Unless the gumpcukrus is what's actually keeping the shaft balanced...? It is a Fiat, after all!

If nothing else, I think I learned a new word today: gumpcukrus. One of the very few times that I've entered a search term into Google, and Google just shrugged...

-Bryan

[scrapironchef]

Not sure I want to tempt fate by trying to hit the third harmonic at 117 mph...

-Bryan

Going back to my high school physics ( a long time ago), wouldn't the third harmonic be at 156? That's a challenge worth tackling.

Larry

[18Fiatsandcounting]

Going back to my high school physics ( a long time ago), wouldn't the third harmonic be at 156? That's a challenge worth tackling.

ScrapIron, thanks for keeping me honest. What you say may be true if one considers each doubling of frequency to be the next harmonic in the series. I'm not a musician, but perhaps this is how it is looked at for musical scales. Since my (other) interest is electronics, harmonics in a series are integer multiples of the fundamental frequency. So, for the AC in your house, 60 Hz is the fundamental (first harmonic), 120 Hz is the 2nd harmonic, 180 Hz is the 3rd harmonic and so on.

The problem is that we don't know if 39 mph is the first harmonic of vibration in my car. Perhaps it is 19.5 mph, but too slight to be noticeable, and 39 mph is already the second harmonic. Or 9.75 mph and 39 mph is already the 4th harmonic. The mind boggles...

Well, it's well past 5:00 pm, so cocktail hour, methinks, before my brain explodes. Plus, Pete's gonna kill me if I derail his thread any further.

-Bryan

[RRoller123]

So does the Guibo act as a CV joint? Or does it transmit the fluctuations in angular velocity that a U-Joint does? Not clear from Wiki.

https://en.wikipedia.org/wiki/Giubo

U-Joints cause Angular Velocity fluctuation (sinusoidal?), thus the requirement that the input and output angles be as close as possible to equivalent, and thus the emphasis on engine alignment. Standard min-max range, as far as I can find, is 0.5 deg - 2.0 degrees. Too little flex, and the U-Joint yoke doesn't rotate, and the cross bar gets hardened and fails early. Too much, and the angular velocity variation induces a lot of vibration. (Note that I CHOOSE to misspell Guibo).

https://www.youtube.com/watch?v=LCMZz6YhbOQ

But all this only works if the U-Joints are in proper phase:

https://www.youtube.com/watch?v=dt69zYAcXME

18Fiatsandcounting : Toyota did a long training video on reduction of noise vibration and harshness, "NVH Reduction" as they call it, where they discuss at quite length the natural frequencies of most of the driveline components. They found 15Hz, 60Hz, 120Hz the most likely:

https://www.youtube.com/watch?v=AJ_v9b6nqUI

I think I will probably first just clean all the gumpcukrus off the driveshaft assy and take a look for any damage, like dents, etc. It may take paint remover, the stuff is on there so hard, but I will take care to keep it out of the center support and U-Joints. The original balancing plates are still welded on there properly, the guibo is pretty new, the U-Joints are good. Then measure all the drive angles and see what that shows.

This is an interesting study!

Pete

[Nanonevol]

Pete has coined a useful new term: "Gumpcukrus"
Watch it's use spread wildly through the internet.

[RRoller123]

I also am credited with starting the fad of wearing 2 different color socks, back in Junior High in the '60s. But that fad didn't last. This one will, I am sure of it!

[18Fiatsandcounting]

I also am credited with starting the fad of wearing 2 different color socks, back in Junior High in the '60s. But that fad didn't last. This one will, I am sure of it!

I can see that I am in the presence of a master, so I shall have to treat you with more respect, Pete!

As for the giubo, my assumption was that it is there to provide some "give" in the drivetrain (in addition to the info given in Wikipedia). If it weren't there, the crankshaft all the way to the rear wheels are essentially locked together, with perhaps a bit of "give" due to the gear lash in the transmission and differential. With no give, there would be a lot of stress on the drivetrain if you had a very sharp energy input, such as a backfire/preignition or (from the other end) hitting a pothole with the rear wheel(s). The giubo flexes ever so slightly to absorb some of those transient shocks to prevent damage to u-joints, gear teeth, connecting rods, etc. So, a giubo, or guibo, or Guido, is your friend, although for different reasons.

-Bryan

[RRoller123]

Yes, The BMW people, Land Rover, Lotus, a few others, use them extensively, probably for that exact reason. But it doesn't answer the question of whether the Guibo acts as a CV joint or a U-Joint? That makes quite a difference. U-Joints pass through artificial oscillations based upon their inherent yoke design. Even if the Guibo does act as a CV, it still implies that the pinion angle back at the diff has to match the angle at the first U-Joint in the system. At least within the standard 0.5 - 2.0 degree norm. That demands engine and rear axle alignment to eliminate artificially introduced vibration.

So this drivetrain is actually at least a 3 joint system exiting the transmission, the Guibo, and 2 U-Joints. If the Guibo outputs oscillating angular velocity, like a U-Joint does, then that becomes the input for the dual U-Joint system, and it is then passed all the way through to the Diff. Maybe that's just the way it is? After all, these were just cheap little toy cars back in the day.

This is the key video right now at this point in the discussion:

https://www.youtube.com/watch?v=LCMZz6YhbOQ

Key takeaway is that artificial oscillations are induced when the angle is non zero, and that they are eliminated if the output angle exactly matches the input angle.

Secondarily, if the Guibo DOES act as a CV, i.e. it does NOT pass through artificial oscillations like a U-Joint does, then the dual U-Joint system will be nice and smooth back at the diff, provided that the pinion angle matches the Guibo angle.

(I think that the answer to the Guibo question probably is that the Guibo input/output angle is so slight, that it approximates a CV)

A really interesting study. If we could find out how a Guibo works vis-a-vis a CV, that would help. I haven't found anything on it yet. Then there would be the measurement of the actual angles on the car during normal ride height, which I presume we can either pretty easily measure, or find somewhere in the shop manual.

Come to think of it, all of this also implies that the complete rear axle assy installation needs to be done such that the pinion angle matches the first U-Joint angle (pitch), and is in as close longitudinal alignment as possible (left to right). I wonder if that is being done, or can be done? Hmm, more to ponder. There are plenty of Youtube videos from the strip and street race guys who show them carefully aligning their rear axle assemblies by use of adjustable trailing arms, etc. to accomplish this exact thing. But we have none of that capability on these little cars.

[RRoller123]

Here, this one is really good too, illustrates the issue very clearly:

https://www.youtube.com/watch?v=gmV4qwLfOMY

[F16Waldo]

Pete has coined a useful new term: "Gumpcukrus"
Watch it's use spread wildly through the internet.


An even bigger challenge is try to work the word into your daily conversations!

[RRoller123]

Gump (as in "Forrest") Cuk (like "Cuck"), Rus, (as in "Russ").

Gumpcukrus: Def: "unknown crap on surfaces of Fiat Spider components".

Well it cleaned up really well after a few hours of elbow grease, scraping, brake cleaner, mineral spirits, soap and water, you name it. U-Joints are good, no dents, no rust, nice and straight, Support Bearing good, so I think I will just give it a coat of fresh gloss black paint and be done with it. Move on to measuring alignment angles on the actual car, when we get to that re-installation step.

There are plenty of other parts infected with gumpcukrus that need to be attended to.

[18Fiatsandcounting]

Gump (as in "Forrest") Cuk (like "Cuck"), Rus, (as in "Russ").

Gumpcukrus: Def: "unknown crap on surfaces of Fiat Spider components".

GUMPCUKRUS: Gross Undefined Material Present, Commonly Under Kars Requiring Unusual Service.

And, yes, I know that I misspelled "cars"....

-Bryan