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Discussion Starter · #1 · (Edited)
Ciao GTV6 Alfisti,

As per ‘pangolin’s’ pervious thread we’re also undergoing the process of aligning the crank shaft and rear gearbox input shaft to try and eliminate the current tail shaft vibration.

In the meantime, I’d like to clarify whether the position of the central spline has any contribution to the vibration! As per the photo below my rebuilt driveshaft has been assembled differently to an unmolested/original tail shaft and asking the question if any other unmolested, or properly working tail shafts have the same alignment or it’s just random?

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Note that the end spine has a fixed position, so that I’m comparing apples-with-apples
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Look forward to the feedback. Thanks
 

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It is my opinion that separable driveshaft pieces should be balanced individually, so we don't need to make special assembly requirements. The individual balancing means you can randomly assemble.
Did Alfa do individual balancing or balanced assemblies? I don't know.

I haven't taken note of how the center fork is clocked relative to the front, so I will get pictures of mine.
 

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A Milano driveshaft I have as a spare.
The center yoke is about 10-15 deg from being in line with the front. I also note, that the rear driveshaft yokes are clocked together. I have no reason to believe the center bearing was ever replaced...it wasn't damaged either...so ...who knows...because.....>30 years old.
I agree with Alfar7, in that 60 deg away is best. But, I would assemble the way I found it, especially if it's a non removable crossmember car. Much too difficult to experiment with those.
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If you're referring to this, I guess the answer is yes. This seems to be for the 4 cylinder cars though. My hardcopy of Section 15 for the V6 2.5 is only 3 pages (tile pg, lubricants, tightening torque pg and special tools. Basically worthless.
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More info. '81 GTV6. Maybe it's about 20 deg apart from front. Based on what I've seen of this car, if previous owner took apart, he would have slapped it together randomly, but actually I think the driveshaft wasn't molested.
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My 86 GTV6 driveshaft has a "key" in the splines, so that the pinch bolt assy can only slide onto the splines in one orientation. Do earlier cars not have the "key" in the splines?
My '81 has the same.
 

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Yes, the front giubo coupler with pinch bolt can only installed one way, due to keyway. However to get to the center bearing, the rear flange of the front driveshaft needs to be removed. That 3 fingered yolk fits on a spline on the rear of the front driveshaft. Because the orientation differs on many assemblies, apparently this is not keyed. I actually don't know because, I have never actually performed a proper center bearing repair. My repairs have always been squeezing RTV into torn center mounts. Always worked so far, one of these days, I'll actually replace a center bearing.
 

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Discussion Starter · #11 ·
Ciao pangolin, thanks for clarifying and appreciated all your feedback :)

For the sake of the of the exercise we’ll firstly horizontally allign the crank and gearbox input shaft and reinstall the tail shaft as is and assess the vibration! If there’s still a vibration issue we’ll install the unmolested tail shaft and assess the difference.

Can you please confirm that your GTV6 has no tail shaft vibration issues?

Thanks in advance
Saluti
 

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Joe Elwell
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Wouldn't it be best to start with an assessment of whether the driveshaft was balanced or not before taking it apart? My driveshaft is very smooth, so when I pull it apart, it's going back together exactly as it is - regardless of these orientations - doesn't this make sense?
With unknown driveshaft parts, I'd start with Richard's advice of even spacing.
Joe
 

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Yes, that is my intention also, to install as is, and then asses vibration, if any. It will be awhile before I get my GTV6 up and running. I bought it disassembled.

I have a Milano that will be getting new transmission mounts, it is starting to have vibration issues. I will put my laser guide to the transmission input. My Milano has been hit from behind, but chassis seems straight. The right front door is also a different shade, so something happened there before I acquired it.
Maybe I will make a front giubo out of steel sheet as suggested by Doss410 (in my thread) although for the front, that bellhousing gets in the way of measuring things.

I do believe that making things as straight as possible will increase the longevity of the giubos.
 

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Discussion Starter · #15 ·
Wouldn't it be best to start with an assessment of whether the driveshaft was balanced or not before taking it apart? My driveshaft is very smooth, so when I pull it apart, it's going back together exactly as it is - regardless of these orientations - doesn't this make sense?
With unknown driveshaft parts, I'd start with Richard's advice of even spacing.
Joe
Ciao Joe,
The drive shaft has been already been balance in it's current orientation by previous owner.
 

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How did you hold the laser pointer on the front?
I thought of getting a 26mm OD, 10mm ID bearing to fit into flywheel, like using it as a clutch pilot bearing. Then use scotch tape to bring the OD of a .38 spl laser pointer to 10mm. You would need to spin the laser in the bearing to see the circle that is drawn.
Did you spin the bearing, to see that circle?
I think engine torque would make the engine tension the left side mount, and compress the right side mount. Not sure of which way the center will move, under torque. Basically the engine will have a roll center based on its 3 point suspension. Come to think of it, same with transmission.
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Discussion Starter · #19 ·
I don’t have a pic of my mechanics alignment tool but believe it’s a specially lathed adaptor….I’m leaving this issue with a Pro ✅

As per my original post I’m interested to see if when it’s aligned, whether the configuration of the driveshaft assembly will still have a vibration!
 

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Here's my result. The bearing I bought was too cheap. The inner race allows too much movement. I might bump the rear engine mount, but not now. I also will put together and hope for no vibration. Images show left right range while wiggling laser.
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