Chasing up vibrations in the drive train - Syncro

[Arne@kleinersyncro]

Hey Guys,

I'm just a couple of feet away to give up on my Syncro I'm chasing some vibrations and I have tried pretty much every option and I still can't locate/eliminate them. Need some new brain input what else it could be!

Background story:
I had a clicking noise coming from a uni-joint in the tail-shaft. I changed the tail-shaft with another second hand one whit one bad joint, however the purpose was to get rid of the clicking noise - and it did work. In the long term, the second hand tail-shaft gave me some rumble at low speeds which was odd (like a joint seized up) and then all my problems started...

Just as a side note, in the same time i did lift the van by approx. 30mm


The vibrations are there at a speed form roughly 60km/h +.
- without the tail shaft, you can feel them but I'm able to drive event at higher speeds
- with the tail shaft (tried numerous ones, used and new), 60-80km/h slight vibrations, 90km/h not drive able (roaring nice and vibrations)
- disconnecting the front drive shafts and tail shaft, vibrations are there, but not as noticeable


What I did so far with no success to fix the problem
- tried numerous tail-shafts (new and used ones)
- changed wheels (different rims and tires)
- took out all drive shafts, checked CV joints (and replaced with good second hand one if marks were shown), re-greased and put back in in different order
- Changed all gearbox rubber mounts (front and back, now Powerflex)
- swapped the front diff (Note: vibrations without tail-shaft were less, but with tail-shaft same a mentioned above)
- swapped rear gearbox with a reconditioned one
- did gearbox alignment numerous times

And it still vibrates and drives me nuts

Anybody an idea what else it could be? I'm thick of throwing in more and more money and time to solve the problem... I want to use it, frustration is up high!

Wheel bearing might be something, but I have got my doubts as the roaring sound/vibrations do not change when swing left/right.

Cheers Arne

As a side note, I'm in Australia and mechanics are (sorry to say) hopeless with Syncros... so I'm doing it all myself
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1991 Syncro self made camper van, cruising around the Black Forrest area (Germany)
1990 Syncro converted by Camperize NSW, cruising around Australia

[stormforge]

Frustrating! I fought with similar problems but eventually sorted it out with new transmission mounts and a careful driveshaft alignment.

(Is your "tail shaft" what we yanks call a drive shaft?)

How's your drive shaft alignment? Take a look at your engine mounts as well?
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Bill '89 Syncro in the Adirondacks, NY

[Arne@kleinersyncro]

[Sodo]

A Syncro should be smooth & quiet as you have heard. You’ll ruin the nose cone driving with vibration so don’t do it. Them are big bucks.

Sorry you’re having trouble. There are so many details to check, and its all on you, we can only throw ideas across the pond.

I’m curious how you disconnected the front drive shafts to drive. Did you put axle stubs in or large bolts to hold the bearing races together?

Are these tailshafts that you tested all OEM?

It sounds like the tailshaft is not the main problem maybe theres a couple problems. Syncro shaft bends like the letter “U” not “parallel” like a lazy “Z”. Consequently the Syncro tail shaft u-joints are not “timed” like a normal 4wd truck, they are 90deg off that.

Theres some other feller from Oz on theSamba rebuilding his transaxle, are you in contact with him? Doesn’t sound lik theres a lot of Syncro knowledge to draw from down there.
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'90 Westy EJ25, 2Peloquins, 3knobs, pressure-oiled GT mainshaft, filtered, cooled gearbox
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered gearbox
....KTMs, GasGas, SPOT mtb

[mackaymanx]

The alignment is called Broken Back and the phasing is the same as a normal driveshaft
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[url=http://www.vw-mplate.com/mplate2-18600.png]Click to view image[/URL]

[Sodo]

[newerwesty1987]

I'm confused on how that angle would ever vary. I'm only used to conventional shaft set-ups and have had them professionally balanced before. Is there a good article on how to align the syncro specific system?

[mackaymanx]

Changing the "phasing" is done when the angles can not be made the same and is done to reduce pulsations, only done for specific applications.If you hunt around there is a Hardie Spicer PDF on it.
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[url=http://www.vw-mplate.com/mplate2-18600.png]Click to view image[/URL]

[Sodo]

MManx that sounds dicey, either the pulsation cancels or it does NOT. In any case, I’m sorry I brought it up. But anyone who builds their own drive-line should know about phasing the U-joints.

[Sodo]

Arne mentions lifting the Syncro 30mm. If thats 30mm from OEM it might be OK. If its from some other fellers pre-lift maybe not OK.

Measure axle center to bottom of fender lip, with the van loaded normally on flat ground. Also applies to the front Syncro CVs.

Legend has it the Lengyel brothers lifted their Syncros until CV boots were disappearing in a puff of smoke.
They arrived at the 20” max number some years ago, maybe 15 years ago?
Knowing how these guys push the envelope I decided to use 19.5”.

Anyway, might verify the van’s not lifted too high.
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'90 Westy EJ25, 2Peloquins, 3knobs, pressure-oiled GT mainshaft, filtered, cooled gearbox
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered gearbox
....KTMs, GasGas, SPOT mtb

[Jeroen_M625]

From experience I am 90% sure the VC joints in the back (and maybe the inner in front) are the problem. When lifting the CV joints have to compensate for a greater angle, so the balls have to travel more inside the joint. Also the higher angle of the shaft makes it "shorter" so the balls also have to run on a different "track" (if you know what I mean).
And since there is always wear in used CV joints, the path they travel back and forth is not even, resulting in an oscilating amount of friction, tension, vibration.

Adding the tail shaft gives more tension on the drive train, so also on the CV joints. Thus even more vibration.

A friend of mine drives with 21+" height, when lowering the pressure in the shocks, it drops to 20", the amount of vibration between the two is huge. next step is bringing the car down to 19" and using porsche CV-joints.

The power flex mounts are rubbish, they do not absorb vibration. Original rubber mounts are ok as long as the big steel ring does not touch the outer part of the rubber. Overtightening those rubber mounts result also in more vibration.

If you want to check:
remove tail shaft and the front drive shafts (only outer part of cv joint is needed), so you have a real 2wd, ad/change 1 item at the time. Don't use cheap quality CV joints (bought them for testing, but they were worse and lasted only 200km).
[/list]

[newerwesty1987]

Is the CV vibration and sound similar in sound to when a tire is "cupping" and worn out unevenly? I have read other threads on this but haven't seen this mentioned exactly.

I am having some of the same issues as the OP. Mine is a lifted Syncro, at 21" unloaded after measuring today. It has heavy racing shocks up front.

I took the driveshaft out which reduced overall vibration (car headlights in mirror dont dance as much) but I have a roaring sound that I can almost tell is coming from right under the seats. It's like a WHAaaaaa WHAaaaa WHAaaaaa sound just like the cupping tires noise except that I don't feel the vibration in the steering wheel much at all. It is not a perfectly consistent vibration but pulsing. Its almost more noise than vibration.

Other problem is that the shocks up front have an adjustable spring but the rear is just a spring I think so not sure how to lower the rear without lots of trial and error spring work. ?

[Sodo]

So your sound is roadspeed related, with no relation to engine RPM?

If you borrow a set of quiet tires from someone that could help to eliminate possibilities.
If you have big brakes ya gotta find someone with 15s or 16s and street tires.
This sounds easy to everyone except the two guys who have to jack up their vans. But its "conclusive".

A bluetooth microphone that you could place in different locations and record sounds (or just listen) to localized sounds could be useful. Can this be done?
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'90 Westy EJ25, 2Peloquins, 3knobs, pressure-oiled GT mainshaft, filtered, cooled gearbox
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered gearbox
....KTMs, GasGas, SPOT mtb

[newerwesty1987]

My issue has nothing to do with engine or transmission. The front end starts rumbling above about 30mph. I drove it this way over 400 miles and it hasn't changed. I wish it were my tires but they aren't that old and have great tread on them. Plus I have no insulation inside, for now, so the noise really comes through. I can look down at the walkway between the seats and its obvious its coming from the front end.

[joeyTWOwheels]

@newerwesty1987 did you ever figure it out?

[Steve M.]

Have you tried loosening the front differential mounts, but not remove them. The idea is to allow the front end find it's own sweet spot after driving it around a smooth street changing gears so that the front diff settles in where it is happy. Then tighten down on the mounts to keep it secure.

Here is a good link to a lot of questions
https://www.thesamba.com/vw/forum/viewtopic.php?t=...p;start=20

The tailshafts/driveshafts you've replaced to find this problem, have they all been the original OEM with the rubber donut?
Have you tried an aftermarket one that does not have the donut?

https://www.vancafe.com/251521101D-p/251521101d.htm

https://www.gowesty.com/product/made-in-usa/23382/syncro-drive-shaft-new-?v=
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[MarkWard]

A rumbling sounds more like a wheel bearing. Try moving the steering left and right while you are hearing the noise. Often a wheel bearing noise will change with the load shifted.
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