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Propshaft noises and vibrations
12-02-2012, 12:20 PM
Post: #1
Propshaft noises and vibrations
A question please as I'm terribly pedantic about noises and resonances and hums and vibrations...as Stuart knows :lol: . How many of you out there have a totally different experience when driving your Syncro with the propshaft on as opposed to having it off?

I ask as I am just not happy with my propshaft, this after a rebuild including center bushes and balanced a few times, alignment with lasers for the diffs and experimenting with the rear and front diffs at different shimmed heights and angles. I have also read up on all the tech data out there re propshafts in general and specifically the Syncro one and i am at a dead end on this issue.

At 45-50km/h I definitley have a slight vibration regardless of what i've done and again at 120km/h I experience a distinct difference in noise levels and resonance. Not sure if actually vibrating at that speed, but take the prop off and at any speed she is dead quite, smooth and comfortable, a completely different ride :!:

Syncro, Sailing, Subaru, Scuba Diving, Surf, Sun, South Africa...
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12-02-2012, 07:49 PM
Post: #2
Re: Propshaft noises and vibrations
the 5 cylinder inline engine has balanced harmonics and an unbalanced couple when it comes to crank shaft balancing, this means that there will be a constant vibration at all rpm due to the unbalanced couple and not a vibration at a specific rpm which unbalanced harmonics causes (just something I learnt in engineering)

I wonder if the vibration is not coming off you front diff mountings ? and being transferred to the front diff through the prop

try fit another prop shaft in and see if it does the same thing

2.6i Syncro Doka 1984
2.5i SSA PlayBus Syncro 1989
2.5i Factory 5 Cylinder Syncro 1991
2.0i Cox Camper Syncro 1989
2.0i Big Window Syncro 1992
2.6i 2WD Doka 1986
1.9TDI Golf Syncro 1991

"If you dont think syncro's are cool, then you better check your pulse"
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12-02-2012, 11:29 PM
Post: #3
Re: Propshaft noises and vibrations
I agree with Dean. Those are inherent issues with that engine. I'm not saying it is impossible to get it all smooth but you are not just having to work with the prop. The motor is working against you. What is the inclination of the motor and gearbox and the front diff? In other words, are they perfectly level or are they inclined downwards towards the prop? How many degrees? I know you said you have played around with shimming these. Did it not make any difference? Did the vibration stay in the same range? Usually these angles should make a big difference. Also as Dean says try another known good prop and see if it changes anything. If everything is right you should hardly be able to tell whether the prop is in or not except on full lock turns on tar.

Ian

PS. Dean, out of interest, how smooth is your 5 cylinder Syncro. I've only driven two and neither were perfectly smooth.
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12-03-2012, 07:07 AM
Post: #4
Re: Propshaft noises and vibrations
mine is perfectly smooth, don't have a single vibration it took me long to get it right but it's there

2.6i Syncro Doka 1984
2.5i SSA PlayBus Syncro 1989
2.5i Factory 5 Cylinder Syncro 1991
2.0i Cox Camper Syncro 1989
2.0i Big Window Syncro 1992
2.6i 2WD Doka 1986
1.9TDI Golf Syncro 1991

"If you dont think syncro's are cool, then you better check your pulse"
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12-03-2012, 07:55 PM
Post: #5
Re: Propshaft noises and vibrations
> experimenting with the rear and front diffs at different shimmed heights and angles

I recommend measuring the flange angles. I use an iPhone app called Clinometer. You want the flange angles to be equal, greater than zero, and less than 4 degrees. My trans and front diff flanges are both pointing down by 2 degrees, relative to the drive/prop shaft, not relative to the horizon, unless you set the van up with the prop shaft level with the horizon.

I have a 5 cyl AEL TDi in a T3 Syncro, that has been eating trannies. Ive tried 3 different prop shafts. None of them made a difference. And unlike you, removing or installing the propshaft on my van, does not change its vibrations. I use a vibration measurement tool available for iPhone, and android, called iseismometer.

What solved my 3200rpm vibration was to set the injection timing to spec. Originally my motor was mistakenly timed to a 4 cyl spec, which is retarded for a 5 cyl. After getting the Injection Timing right, my 3200rpm vibration was almost completely eliminated.

with the help of this group, I have now found a source for a transmission brace. I think that is a MUST have with a 5 cyl motor.
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12-04-2012, 07:51 AM
Post: #6
Re: Propshaft noises and vibrations
jon_slider Wrote:> "that has been eating trannies."

Isn't that illegal.
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12-04-2012, 11:54 AM
Post: #7
Re: Propshaft noises and vibrations
Hi all and thanks for all the feedback and suggestions.

Firstly I do have a brace on the gearbox. I also do think the back or 3rd engine mounting should be put on somehow. I am making a plan with this. I say this as its clear that the weight and positioning of the 5 cyl leans the entire engine and gearbox assembly to the left rear of the vehicle and is worse under load. You can see this by measureing the gearbox mountings and will see that the right hand side is further up and compressed more than the left. I have also shimmed the rhs of the engine mounting down slighlty which releaved some of this pressure. I think is why VW placed a 3rd mounting as the torque, weight distribution of a slanted engine and heavy block made it twist badly, hence the need for the gearbox braces too.

With regard to angles on front and back diff i have tried it at what I assume to be about 2.5 degrees down and also 3.5degrees down. This using a laser with measured centimeter drop scale.

I find the 2.6 is mounted at a much flatter angle than the original 2.1. My original settings from factory on both were about 3.5% down. I find it now works best at front shimmed up to about 2.5% which is what the tranny is attached to the 2.6. (Using VW mountings and 2.6 bellhousing.)

Obviously longitudinal alignment accurately done and taken as a must.

I still get vibrations now at 120km/h but seem to be almost nil or very minimal at 45km/h and at 80km/h which were there originally. I will keep experimenting with heights etc.

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12-04-2012, 12:05 PM
Post: #8
Re: Propshaft noises and vibrations
Quote:mine is perfectly smooth, don't have a single vibration it took me long to get it right but it's there
. Dean, which vehicle are you referring too, the playbus? Was it a case of experimenting with incremental height shifts to get it right?

Quote:the 5 cylinder inline engine has balanced harmonics and an unbalanced couple when it comes to crank shaft balancing, this means that there will be a constant vibration at all rpm due to the unbalanced couple and not a vibration at a specific rpm which unbalanced harmonics causes (just something I learnt in engineering)
I understand, although some sources feel a 5 cylinder to be incredibly smooth. My bus without prop can run through all rev ranges way up to 5500 revs without hardly any vibration its beautifully smooth and quiet ... how is your factory fitted 2.5 by VW by the way in terms of drive quality? I think they used a shorter prop on that one which may help...

Also i dont mind some noise, etc as its an older vehicle now but i am worried as I have had a gearbox crack before due to unbalanced prop and vibrations. Vibrations can break anything. Paul showed me one l about two weeks ago that they got in, also front nose cone cracked right open!

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12-04-2012, 10:16 PM
Post: #9
Re: Propshaft noises and vibrations
The 5 cylinder engine itself can feel smooth but that is just because the engine mounts are doing a good job absorbing the vibrations. If you don't have an iPhone there is an Android app called XClinometer which is very useful for measuring angles on the front diff and gearbox.
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12-04-2012, 10:46 PM
Post: #10
Re: Propshaft noises and vibrations
> I find the 2.6 is mounted at a much flatter angle than the original 2.1. My original settings from factory on both were about 3.5% down. I find it now works best at front shimmed up to about 2.5% which is what the tranny is attached to the 2.6. (Using VW mountings and 2.6 bellhousing.)

excellent details, you are confirming that matching angles is most effective
you also reveal that your 2.6 motor sits lower than your 2.1, you lost ground clearance, when you lost that 1 degree of transaxle down angle with the new motor. Glad you got the front shimmed to match.

at this point, the problem seems to be narrowing down to the driveshaft itself.. get it rebalanced maybe?

you also comment on lateral alignment.. there is not much that can be done at the transaxle, but there is some you can get at the front diff.. a popular trick this side of the pond is to loosen the front diff mounts and drive the vehicle, so the mount moves to where it finds its own sweet spot of least resistance, then retighten the front mounts..

another factor relating to lateral alignment, is the motor positioning during installation.. not sure that applies in your case
from [link]http://vanagonsyncroproject-herman.blogspot.com/2007/03/drive-shaft.html[link] (you have to copy and paste the link)
"On the Syncro, it is important that the drive shaft is well aligned, both the tranny and the front diff flanges have an angle of about 4 degrees. If you do an engine conversion, and the engine hangs too low, you could end up with some vibration. Another thing to watch out for when doing a conversion is that the original VW engine is slightly offset towards the driverside, about 17 mm, if the new engine is installed in the center of the engine compartment, it will put another angle on the drive shaft that is not compensated for by the front diff and it may cause a vibration also. It is too bad that VW didn't put a CV joint in, one would have been enough.
On a two wheel drive Vanagon it is not that critical if the engine is centered, the axle CV joints will compensate for that."
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