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Syncro Propshaft Alignment Problem
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Landsailer
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PostPosted: Mon Nov 05, 2012 11:30 am    Post subject: Reply with quote

The good news about all of this is that if I line up the flanges (equal angles, not pointing at each other) and I still have wobble from the DC shaft, I can bite the bullet and get back to original German design and have the angle thing already sorted out.

Or, something else will be out of balance and everything will explode one day in a chunky, metallic detonation, and I will slump on the curb and cry into a handful of what used to be my transmission and diff, wondering where I went wrong in my life.

Syncro!
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PostPosted: Mon Nov 05, 2012 9:38 pm    Post subject: Reply with quote

I'd take a direct approach at this point. I know it's dangerous, but I'd have the thing up on jack stands (jacks on the suspension members) and see if the shaft is in fact running true. Low rpm/shaft speed and aim the laser at an edge to see if its wobbling at several points along its length. You could also use a wood dowel to reach under and get the tip to rub gently - if it's out of true you'll hear as it touches, then doesn't touch. If no wobble, I'd do the hose clamp trick. A zip tie holding a dime in place tightly enough you can still move it would also work.

I think something's not right either on balance or straightness (obviously) and this is an easy way to check it. It never ceases to amaze me how often people you pay to do things mess things up and won't own up. I base this on your observation that it SHOULDN'T be this hard to get a shaft designed to quell vibrations to run smoothly. I agree. Something's up.

DougM
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Landsailer
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PostPosted: Mon Nov 05, 2012 10:30 pm    Post subject: Reply with quote

I was sitting around thinking about van stuff, because that's what I do a lot, and I came up with a question. So in Z arrangement, which is like Jon Slider's picture, the flanges are at 0 but because the axle side is lower, there is matching U joint angle. So, how does that work in the W or U arrangement, when you have both flanges pointing down. The only way matching flange angles will produce the same angle on the U joint is if the flange of the trans and diff are exactly the same height. If the one is higher than the other, then you get steeper angles on the down side and shallower angles on the upside right? The only time the angles can be the same on the U joints if the flanges are at different elevations are if the flange angles are 0 right (unless you can use geometry to figure out the correct offset angle to orient the flange to)? So, are the flanges the same height? I figure I could measure from the body to the flange. Really, it's like 20F outside and I don't want to crawl under the van right now.

I may have gotten to the point where I am overthinking this.
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PostPosted: Mon Nov 05, 2012 10:48 pm    Post subject: Reply with quote

I've wondered about that same thing, relative flange heights in the "W/U" arrangement. I thought I had it all straight in my mind when I was mucking around with my home made laser alignment tool and comparing results to my electronic angle finder. But now I am not so sure. One thing about these poorly documented things is that it is much harder working alone on the problem. Nice to have another obsessed syncro owner with you to bounce things off (and I don't mean propshaft on head).

good luck

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PostPosted: Tue Nov 06, 2012 5:21 am    Post subject: Reply with quote

Landsailer wrote:
I was sitting around thinking about van stuff, because that's what I do a lot, and I came up with a question. So in Z arrangement, which is like Jon Slider's picture, the flanges are at 0 but because the axle side is lower, there is matching U joint angle. So, how does that work in the W or U arrangement, when you have both flanges pointing down. The only way matching flange angles will produce the same angle on the U joint is if the flange of the trans and diff are exactly the same height. If the one is higher than the other, then you get steeper angles on the down side and shallower angles on the upside right? The only time the angles can be the same on the U joints if the flanges are at different elevations are if the flange angles are 0 right (unless you can use geometry to figure out the correct offset angle to orient the flange to)? So, are the flanges the same height? I figure I could measure from the body to the flange. Really, it's like 20F outside and I don't want to crawl under the van right now.

I may have gotten to the point where I am overthinking this.


Absolutely correct. It is the 'Operating Angle' that has to match at each end of a 'standard' propshaft. It is easiest to think about if both ends are in the same plane, but it does not have to be that way. You can have any configuration so long as the operating angles agree, and the U-joints are clocked properly to compensate the rotational eccentricity. I was calling that 'rotational wobble' but I can see come confusion creeping in to the conversation, because I it looks like wobble is also being used to describe the condition of a shaft outer surface tracing a circle larger than its diameter as it rotates. That axial offset is more correctly called 'whirl'

Anyway, one can design a propshaft for any end configuration, even the one Jon described, so long as the operating angles match and are within spec, and the joints are at the correct rotational angle relative to each other. Having the ends in the same plane, or in orthogonal planes, makes it easy because 90 degrees is used.

And yes, if the flange heights are different relative to your driveway, then the flange angle will be different, relative to your driveway, when the operating angles are the same. As you envisioned, if you start with equal height flanges and equal angles wrt the ground, then if you raise one flange, say the front differential, you could eventually reduce the operating angle to 0. Not what you want.

RonC
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PostPosted: Tue Nov 06, 2012 10:40 pm    Post subject: Reply with quote

I thought that I had my drive shaft vibration sorted out until this summer when the nagging 45MPH vibration started again and this time it was worse than before even though I has used a laser alignment tool to make sure both the front diff. and tranmission flanges were in alignment.

I started checking some things, the front diff. flange angle was 4 degress and the transmission flange angle was 3.5deg. so not a problem there. The two bronze bushings in the rear of the shaft still had a tight fit with the yoke shaft and I knew that u-joints were good since they were replaced about seven months ago.

What I found while taking apart the yokes was that the u-joint cups in the rear yoke no longer had a tight press fit but were sloppy and I could move them easily by hand so there was some lost motion in the rear joint. I found a Spicer u-joint ( 5-129X) that is similar in size to the agg. joints that are considered to be a good replacment for the original so I machined the yokes for the oversize Spicer joint and the shaft runs very smooth and plus I can find the joints at any auto parts store now. Cost was about $60.00

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Landsailer
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PostPosted: Wed Nov 07, 2012 10:11 pm    Post subject: Reply with quote

Update. And the math here is crazy. So I shimmed the engine up, and shimmed the trans down. I got 1 degree down angle in the trans flange. And I already had 3 degrees down on the front flange. Here is where it gets tricky. I measured the distance from the body that my shaft adapters were. It turns out that the trans flange is 3/4" lower than the diff flange. I used some math here and figured that at 4 feet, which was my rough measurement of the distance of the shaft, adapter to adapter, and I know that one side of the triangle is 3/4" and knowing that there is a 90 degree plane at level, I used right angle trig to figure out that the driveshaft has a 1 degree down angle. Now, this is important because it affects the angle of the joints. That down angle backs off the steepness of the 3 degree flange at the front and it steepens the 1 degree flange in the back. It does so by exactly 1 degree. So *technically* I have 2 degrees on each joint. Tomorrow I am going to get around to putting the shaft back in because it's too f'ing cold out now and then I will measure the angle on the joints themselves. But mathwise, this works. I guess anyway. I am definitely all ears to the community.
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PostPosted: Thu Nov 08, 2012 1:01 pm    Post subject: Reply with quote

> the math here is crazy

correct, IF your driveshaft is at 1 degree angle, your trans and diff flanges are both at 2 degrees to the driveshaft

but by my math, 3/4" drop over a 48" run, produces .7 degrees, not 1 degree...

I dont trust your 3/4" dimension to produce as accurate a result as actually measuring the angle of the driveshaft

you could eliminate the crazy math by raising the rear of the van in a way that makes the driveshaft measure 0 degrees (LEVEL).

then you can use your flange angle measurements, without adjusting them for driveshaft angle.

thanks for following up with your results. I look forward to your success!
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PostPosted: Thu Nov 08, 2012 2:14 pm    Post subject: Reply with quote

arctan( .75/48 ) = .895 inch

EDIT: oops...0.895 degrees

Don't mind me...I'm metric.

RonC


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Landsailer
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PostPosted: Thu Nov 08, 2012 2:23 pm    Post subject: Reply with quote

Yeah, I came up with .9 and rounded to 1.

I don't think it matters much anyway, honestly, how close much rounding goes on. When I looked at how much work that I did shimming and how much that equated to on the angle dial, I realized how it wasn't much at all. So, I don't think such a small adjustment will have an effect great enough to defeat the current wobble, and I will be back to the shaft not being balanced correctly. Or the VC. Or an axle shaft. Or one of 8 CV's. Or whatever.

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insyncro
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PostPosted: Thu Nov 08, 2012 2:29 pm    Post subject: Reply with quote

Its all in the details.....having a vibration free Syncro that is.
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lloydy
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PostPosted: Sun Jun 23, 2013 4:51 am    Post subject: Reply with quote

sorry to dig up an old thread, but how loose do you undo the front diff mounts when you try this van cafe method?
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PostPosted: Tue Oct 08, 2013 10:30 pm    Post subject: Reply with quote

So many of these really hard vibration threads never have an ending...bummer...so I'll put here what I learned from this thread that helped me get to a solution...or at least on my way.

Since my engine conversion I've not been able to get vibration free. Rebuilt the DS, tried van-cafe method, shimmed up/down, etc. no luck. So finally decided to replace the DS with a new one from van-cafe. Slapped it in over the weekend, still have vibrations. Loosened the diff, drove around, still no luck.

So read this thread and decided I was going to have to get more scientific and measure angles and make sure the DS as the Bentley describes is "longitudinally" aligned. So I got me laser level, the kind the projects a line on a wall for hanging stuff level and "shot it" from the front diff "middle seam" to the tranny "middle seam". Everything was aligned there.

Ok so next started measuring angles at the diff and tranny. I have long suspected that my engine conversion (svx) points the tranny a bit more down than stock, i.e. the engine/tranny mount point is higher than stock. so with my iphone inclinometer I was able to measure the tranny angle and it was indeed greater than the diff. So I decided that the easiest thing to try first was to increase the front diff angle. I did that be removing the two large washers from the mounts on the rear diff mounts. Some success!

With my decoupler uncoupled, the vibrations are almost entirely gone (my problem was at 30 mph), with the DS coupled, I still have some vibrations.

My next change is to raise the front of the tranny by removing the two large washers at the front tranny mounts to reduce that angle. Hopefully that will get the angles close enough to eliminate the vibrations fully when the DS is coupled. I'll crawl back under there Thursday perhaps.

Any input on these steps/changes I've made here are welcome.
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PostPosted: Mon Oct 19, 2020 10:21 pm    Post subject: Re: Syncro Propshaft Alignment Problem Reply with quote

I found a great article on driveshaft geometry when I was looking for info on the double Cardan (CV) joint. Look at the drawings of the proper geometries for the single and double Cardan joints. The double cardan joint driveshaft should have 0 degrees of angle on the single joint end whereas the single joint shafts use the same angle on each end.

I was surprised to see from posts on the syncro that both the tranny and differential point downwards. I had assumed that they would be like most cars and trucks with one down and one up.
If the vanagon front flange is tilted down and the rear flange is tilted up it seems that the inherent design is prone to vibration. If both flanges are not in parallel planes then it seems the u-joints natural wobble will not cancel one another out.

Here is the article for your perusal;
https://4xshaft.com/blogs/general-tech-info-articles/tail-shaft-conversion-kits
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PostPosted: Tue Oct 20, 2020 8:54 am    Post subject: Re: Syncro Propshaft Alignment Problem Reply with quote

jalan wrote:

I was surprised to see from posts on the syncro that both the tranny and differential point downwards. I had assumed that they would be like most cars and trucks with one down and one up.
If the vanagon front flange is tilted down and the rear flange is tilted up it seems that the inherent design is prone to vibration. If both flanges are not in parallel planes then it seems the u-joints natural wobble will not cancel one another out.


I was surprised too.
The difference is “the phase”.
Theres Z shape and U shape configurations.
This is difficult to explain without arm waving. (Like at a campfire)
But if you compared a propshaft for Z and U you can see the difference.
The yokes are clocked 90 degrees different on the shaft.
If you went to a 4x4 shop with no example Syncro propshaft and they put in a Jeep shaft you would have incurable vibration.
However if this shaft had a slip joint allowing you to clock the yokes 90* (for The U) you could “cure” it.
Its all about U isn’t it? Wink


Z shape allows for suspension movement.
If the two shafts remain parallel, the U-joints cancel perfectly.
So the jeeper, adding a lift kit, needs to set the shafts paralell at neutral criusing/highway suspension position.
But understand that the shaft’s rotational speed is varying anytime the U-joint is bent.
Not in whole RPMs but within one rotation, there is a pulsation of rotational speed.
One U-joint causes it, the other cancels it. Perfectly.
Within each full rotation.
There is no pulsation when the two shafts are aligned, but when each u-joint bends a little there is an angular pulsation.
And the other u-joint (at equal angle ! ) cancels it, resulting in perfectly smooth output.
Got it?

So if the angles are “not proper” for your propshaft angles, there will be pulsation on the output shaft.
Which is zero problem at low speeds, can be a big problem at highway speeds.

The U configuration of the Syncro causes/cancels angular pulsation too, at the fixed 4* angle.
There is no suspension movement on a Syncro propshaft of course.
I suppose this 4* U-configuration was in lieu of adding a driveshaft hump to the Vanagon floor. And engine height concerns, adapting the 4wd to the 2wd.

If you were ever wondering what was constant about a “CV”, this is it.
Constant angular shaft velocity, even when “bent”.
And, no Z or U or clocking or specific angles required.
CVs are elegant, more expensive, bulky, add frictionall drivetrain losses.
Can have more maintenance issues (Vanagons only).
CVs are essential for some applications.

I’ve seen recommendations to “clock” CV joints on the axle.
I don’t know what principle this is based upon, if any.
Perhaps its for a condition of shaft angle-over-extension.
But this over-angle condition would exist only occasionally, on very “uneven ground” for a few turns at very low speed, and the effect so subtle to be absolutely inconsequential. Exponentially inconsequential - if high-angle is the condition of focus.
If anyone knows the principle behind clocking a CV I’m interested, but until then it sounds like a husband’s tale.
Not a physics denier. Wink but always interested in something new.

U-joint is the proper unit for the 4* Syncro propshaft.

Image may have been reduced in size. Click image to view fullscreen.


Here’s an info sheet I made for some reason I can’t recall a few months back.
Just being a Syncro nut I suppose.
Its unfinished but shows the 4* U-configuration.
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Last edited by Sodo on Wed Oct 21, 2020 6:42 pm; edited 1 time in total
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PostPosted: Tue Oct 20, 2020 10:36 am    Post subject: Re: Syncro Propshaft Alignment Problem Reply with quote

I think the Audi 4000 quattro had CV joints on the drive shaft.
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PostPosted: Tue Oct 20, 2020 11:40 pm    Post subject: Re: Syncro Propshaft Alignment Problem Reply with quote

Hi Sodo!

I`m confused, what does U and Z refer to?
Also, I don`t see a 90 degree clocking on the syncro shaft on pictures online?
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PostPosted: Wed Oct 21, 2020 8:07 am    Post subject: Re: Syncro Propshaft Alignment Problem Reply with quote

MarkWard U-joints are used in pairs so the 2nd cancels the velocity pulsationn.
Whereas a CV joint can change shaft angle as a single unit (‘cuz its Constant Velocity).
I’m no driveline expert though (just interested Wink)

I’ve read the names U and Z but I don’t know if that’s the proper names.
“Very Lazy U” and “Even Lazier Z” might be better names. Wink

Notice the “phasing” of the yokes on the propshaft.
The U and Z configuration propshaft yokes are clocked 90* different.

(Oops this is wrong)

https://m.youtube.com/watch?v=Idk3BVDVHq4

Best that I link a YouTube..... It does have the proper name.
I’m out in the woods 👍🏽👍🏽 with poor internet so I’m trusting this is a good Vid to link. I can’t watch it but if you search “driveshaft phasing” there are several. Theres one by Spicer that’s probably good. I don’t know if any will address the “U” configuration as most vehicles are probably “Z”.
I can see the fellers driveshaft & U-Joint contraption in the preview, and have high confidence it will answer good Qs👍🏽👍🏽
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PostPosted: Wed Oct 21, 2020 8:23 am    Post subject: Re: Syncro Propshaft Alignment Problem Reply with quote

Guy in Albuquerque has one for sale $200: https://albuquerque.craigslist.org/pts/d/albuquerque-volkswagen-vanagon-syncro/7203706071.html
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PostPosted: Wed Oct 21, 2020 8:50 am    Post subject: Re: Syncro Propshaft Alignment Problem Reply with quote

That thing has spent some time rubbing on the dirt.
Wonder if it could be bent....
I suppose it could be checked / straightened / balanced by a driveline shop.
I wonder if theres springback sometime later (after straightening).

Notice the two yokes are “aligned” on a Syncro propshaft.
Thats for the U configuration. oops - sorry
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