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njg02
Samba Member
Joined: October 11, 2007
Posts: 97
Location: Australia
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 Posted: Wed May 31, 2023 2:59 pm Post subject: drive train vibration harmonics and shakes |
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Guys,
I have had my front diff input shaft seal changed and also the gearbox end uni joint.
I now have vibration from about 60 to 80km/hr.
I have read that I can loosen the front diff and go for a drive and the diff will settle into position.
Now I have searched but cannot find info in regards to how fast and for how long I have to drive for it to settle.
Also my driveway and yard is a bit bumpy so would this then put it out before it is tightened down?
_________________
1971 Super Beetle. Almost ready to roll.
1991 Syncro Camper |
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Sodo
Samba Member
Joined: July 06, 2007
Posts: 10627
Location: Western WA
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| Posted: Wed May 31, 2023 3:41 pm Post subject: Re: drive train vibration harmonics and shakes |
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What is your R&P ratio?
There are specific propshaft vibration speeds for 4.86 and slower for 5.43.
For 4.86 it’s 45-50 mph.
For 5.43 it would bu 89% of that (40-44mph).
Did you “center” the new u-joint cups between the retaining rings?
What’s the condition of the Guibo bushings?
Driving a long time on a bad u-joint can ruin the Guibo bushings.
When Guibo bushings are worn, it cannot hold the driveshaft straight and is guaranteed to vibrate.
You probably know that you cannot drive with driveshaft vibration or you will ruin stuff.
I’m a little curious why your front diff seal.
I’m agreeing that a tough driveway could disturb the “found smooth location”.
Don’t wait until you get home.
Tighten the bolts while you’re on smooth road.
_________________
'90 Westy EJ25, NEW oil rings (!) 2Peloquins, 3knobs, SyncroShop pressure-oiled pinion-bearing & GT mainshaft, filtered, cooled gearbox.
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered original gearbox
....KTMs, GasGas, SPOT mtb |
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njg02
Samba Member
Joined: October 11, 2007
Posts: 97
Location: Australia
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| Posted: Wed May 31, 2023 5:54 pm Post subject: Re: drive train vibration harmonics and shakes |
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Thanks Sodo.
I believe our aussie spec syncros are 5.43.
I had my mechanic change the uni joint and he knows what he is doing.
I had a leak from the diff seal for some time and I also had a slight vibration at low speed which was the stiff uni joint.
Mech also changed the diff seal.
The guibo bush 'looks' ok.
I marked up both ends of the tail shaft and it is back in the original position.
Because I don't have anyone close to do a balance I want to try all other possible fixes.
I have only driven it once to see if there was vibration after the couple of changes and my fears are realised.
Again, I appreciate your reply.
Neil
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1971 Super Beetle. Almost ready to roll.
1991 Syncro Camper |
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Sodo
Samba Member
Joined: July 06, 2007
Posts: 10627
Location: Western WA
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| Posted: Thu Jun 01, 2023 1:12 pm Post subject: Re: drive train vibration harmonics and shakes |
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| njg02 wrote: |
I believe our aussie spec syncros are 5.43.
I had my mechanic change the uni joint and he knows what he is doing.
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OK so 40-44mph = 64-71kph.
You are within the realm of propshaft resonance so it’s likely propshaft balance. You can drive slowly like 40kph etc for example grinding around in 4wd off-road etc.But every time you speed up and pass through the "resonance zone" you’re fooking stuff up.
I’m inclined to reiterate the seriousness of this problem, and that you will ruin No Longer Available stuff if you drive it with that vibration.
The aluminum nose cone bearing gets loose in its bore then that housing is no good. (they are NLA)
Eventually it breaks off the entire front of the nosecone (at the bolt ears, one ear after another) until the propshaft drops off the gearbox.
The gear oil dumps out.
Lots of mechanics change Syncro u-joints and some percentage of them end up with prop shaft vibrations, regardless of their experience.
Is this mechanic a Syncro specialist? By that, I mean does he have a healthy fear of the Syncro Propshaft?
I’ve never heard of "centering the Syncro u-joint cups" but it’s feasible.
I am amazed every few years by Syncro details that haven’t been worked out yet (over 36 years etc) because very few investigate it - or of they do, they don’t publish it.
Not surprising that only a few “publish” such things but its sure appreciated when they do.
Did the mechanic notice any shims upon disassembly?
VW assembled _some_ uni joints with shims.
See a pic of a shimmed uni joint here: https://www.thesamba.com/vw/forum/viewtopic.php?p=9967618#9967618
| njg02 wrote: |
| The guibo bush 'looks' ok. |
Not referring to the outside appearance of the Giubo rubber - but the brass bushings & shaft etc inside.
Pics here of a beatup Giubo shaft and bushings: Giubo (Syncro talk)
_________________
'90 Westy EJ25, NEW oil rings (!) 2Peloquins, 3knobs, SyncroShop pressure-oiled pinion-bearing & GT mainshaft, filtered, cooled gearbox.
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered original gearbox
....KTMs, GasGas, SPOT mtb |
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