Drive shaft angles and the front diff.

[Bassyaks]

My question is : if the exact opposite angles on the drive shaft u-joints are what you want to get equal rotation between the transmission and front diff what happens when the angles are different and one spins faster than the other? This I think would be more critical with a straight shaft than a VC.
But how does this effect the VC and would this unequal angler effect top speeds and engine loads and stress on transmission or differential parts with one running at one speed and the other at another.

Ideally would you want a perfectly straight drive shaft and would you shim the transmission or differential to achieve this?

This may be in the VC debate thread but that thing is 30 pages long

[Syncro Jael]

There are numerous threads about the propshaft/driveshaft flange angles.
I dealt with this before and it can drive you crazy trying to get vibrations out of your van.

See if this helps?

http://www.thesamba.com/vw/forum/viewtopic.php?t=580920&highlight=driveshaft+angles
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[Bassyaks]

Not so much vibration but if the angles are wrong the speed of the rotation between the transmission and the differential will be different. The transmission could be pushing the differential faster than it wants to rotate. almost the same scenario as if you had taller tires on the rear and a size smaller on the front differential, would it ruin the VC.
If a straight shaft was used instead of the VC it would be more direct
An exaggerated example would be On a ice lake the rear wheels would be spinning and the front would rotating normally.
https://www.youtube.com/watch?feature=player_embedded&v=gmV4qwLfOMY

[insyncro]

A straight shaft MUST be used with a decoupler.

The straight shaft make sense for only a handful of driving conditions.

Those who know Syncro vans have VCs.

The amount of information involving how the VC works, has an effect on the system and how to set up a VC is staggering.

I suggest that you get reading and ditch the solid shaft immediately.

[MsTaboo]

Oh boy, here we go again.

Vw designed and built the Syncro with a 4 degree tilt on both the trans/engine combo and the front diff. The flanges tilt towards each other, slightly downwards.
I don't know why they did this, but they must have felt it worked better than using a straight alignment.
There are a variety of methods people have used to achieve these angles. I bought the GW laser tool when it was available (not sure whether they still sell?) and have found it a very reliable and easy way to get vibration free driving.
The tool is basically two pucks that mount to the flanges with magnets, one puck holds the laser pointer and the other holds a card with bubble levels attached and a vertical line.
You make sure the van is level and then you stick the puck with the card on one side and level it, the other puck aims the laser at the card. When you rotate the flange the laser will proscribe a circle until you get it centered, you then mark the card with a dot. Next you swap both pucks to the opposite flange and repeat. The marks on the card tell you how far off the alignment is. It takes a couple repeats of this process until you get the proper angles. The idea is to get the dots to land on the vertical center line and about an inch below driveshaft center. (about an inch, it might be more, I don't have the directions in front of me)

I'm traveling right now so can't take a picture of the tool and setup, maybe someone else out there has one?

The other methods involve using digital levels. The drawback on these methods is not being able to see whether the flanges are aligned left to right. (driver's side to passenger side)

On my Zetec conversion I ended up using a couple shims (under the transmission mounts) to get the proper downward tilt on the engine/trans combo, and had to shift the engine/cradle a wee bit for the sideways alignment. After tightening all the bolts for the final time I went back and rechecked the alignment with the tool. A bit of work, but vibration free right out the gate.
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[insyncro]

If you make a few marks before touching the van for conversions, upgrades, what have you...no tools other than a tape measure are needed to have the driveline turn without vibration.

This thread will not be complete without IDoug, Jon Slider, Waldi, Gears....the list goes on and on.

Really, the OP should start searching and reading.
The coverage here, on Vanagon.com, Syncro yahoo list and Euro Syncro lists date back to the early 90s.

One hell of a hot topic at times.

Put on a flack jacket and hard hat as opinions fly like birds heading south for the winter

[MsTaboo]

Insyncro-a couple marks may be fine when just dropping the driveline for some reason, but start throwing in an engine conversion with new carrier bars/cradle, motor mounts, a new driveshaft, a decoupler, or maybe a rebuilt transmission and it's just about guarantied there will be issues. Those marks no longer have any relevance.

And yes, it can be a hot topic. I only know what worked for me.
(that damn laser tool was expensive, but worth it!)
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Currently:
'90 Syncro Westy 3 knob w/Zetec

The information age has morphed into the age of disinformation and willful ignorance. Agnotology!
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[insyncro]

[insyncro]

I definitely stand by my statement in Ron's linked thread...I have not ever needed to shim the front diff or transmission mounts on ANY Syncro that I have owned or worked on.

The Bostig kit comes with shims for the engine cradle system.

[MsTaboo]

Like I said, here we go again.
But I'm not gonna play.
_________________
Currently:
'90 Syncro Westy 3 knob w/Zetec

The information age has morphed into the age of disinformation and willful ignorance. Agnotology!
Help the fight against Truth Decay.
Defend democracy, support Ukraine.

[insyncro]

OK, cool.
There is plenty of info waiting to be read and digested anyway.

[Wildthings]

It has always been my understanding that you want a few degrees of offset in a yoke style driveline so that the rollers will move around a bit and don't just sit in one place causing dimples to form. A lot of rigs where set up with way more than 4* of offset, think of the Ford 4WD pickups circa 1970, they must have run an angle of at least twice that.

To say that having the driveshaft angles mismatched is the same as running different sized tires front and rear is just wrong. The average output speed of the driveshaft is always going to be the same as the average input speed no matter how the alignment is done, whereas with different sized tires the front and rear wheel are going to be want to turn at different speeds. With a yoke style driveline the center section of the driveline will speed up and slow back down slightly twice in every revolution of the drive shaft, if everything is aligned properly these pulsations will be cancelled out by the second joint and the output will be smooth.

[SyncroGhia]

[insyncro]

The OP owns a "magical" Syncro

[MarkWard]

Somewhere buried in the threads is a link to a video describing how flange speeds are affected by angle. Unfortunately I did not bookmark it. I will try to find it.

Based on my experience, the stock syncro flange angles are not common to the automotive industry. My guess is VW may have been limited using the 2WD tub and adapting it for AWD. Their engineers figured out something that would be suitable.

Edit: Found it.
Link


Here is the thread. http://www.thesamba.com/vw/forum/viewtopic.php?t=627887
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[Bassyaks]

Using string is about as good as doing it by eye, and your forgetting the horizontal angles. I have a flange with a shaft( squared) in the center which a electronic level indicator can be mounted, or a laser (like a bore scope) can also be mounted to it to pinpoint matching angles.
This gets bolted to the flanges on the transmission or diff. and the level can tells me how and where the angles have to be moved or shimmed.
This weekend I'm heading down to the shop and we're making a straight shaft drive shaft, two flanges with a centered tube up the same length as the original drive shaft. This will be bolted in place and the driveline mounts will be loosened and shimmed to get a zero angle to start.
we'll see what happens, this will zero the angles 360 degrees, some thing like static balancing.

The 4 degrees both facing down seems wrong, per video, unless they are counting for deflection from the torque.

[MarkWard]

When you say straight driveshaft, are you describing a driveshaft with no U joints?
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[MsTaboo]

[Bassyaks]

That's what my static shaft does, it gets it close to equal angles.
When guys are putting new conversions in they are not installing them square, with slotted motor mounts and drilling new holes the chances of being off center horizontally is great. The 4 degrees is only on one plane, vibration can come from horizontal misalignment also, if fact anywhere in the 360 degrees
Straight zero angle is what I want to play with, I'll see how close the static shaft can get.
With the stubby flange checker I have I can always go back to 4 degrees vertical with shims.

When changing drive line mounts of different thicknesses the drive angles are also changing.

I'm just playing

[crazyvwvanman]

This kind of error is what the laser pointer method of scribed circles is meant to detect. It is a 3 dimensional problem as you say.

Mark