That old prop vibe thing.....

[Bwana John]

For years I suffered this problem, even with a different propshaft (complete with rubber doughnut) on. I have virtually cured it by putting a large diameter jubilee clip mid way down the prop and by randomly rotating it, have effectively "tuned "out the vibrations.It`s a bit trial and error but it worked for me.It may be better one end or the other,but I`m sure not messing about while it`s this good!

[KINGPRAWN]

anybody need a prop with new u j's????

Yes, if it's straight

can't swear it is straight but i have no reason to think its not!...uj's have done 5k max. have collected a few odds n sods prior to welding and full body job so was going to ebay a load of stuff..just not got round to it yet !!

[Mudlark]

Mmm..

Both rear bearing changed and free of play.. (why would it only do it with the prop on?)

..

No idea; although I have come to accept that the whole drive train is finely tuned to any variations and introducing an otherwise imperceptible vibration in one connected component can result in it being amplified on the prop as it spins through the harmonic range of the wave it is opposing. (i think thats what I mean )

What i do know is that i drove 2000 miles suffering a bad prop vibe at 60-80kph which disappeared completely when the rear wheel bearing was replaced. There was none of that traditional failed bearing rumble or whine until it literally collapsed which is what I found most surprising. I then ruined the hub by driving the 5 miles to a mechanic at 20kph

Anyhow if you have good bearings it aint that.

[HarryMann]

But Mark, could you have confused the rear wheel vibration (due to bearing play) with a prop vibe. Because the harmonic speeds are roughly the same, do we assume one is the other

[rollercoaster]

I was convinced my prop was vibrating and needed UJ's or something, it was unbearable at the usual prop vibration speeds, I have experience of driving with knackered UJ's and replacing them on other vehicles.
However despite removing the prop and the vibration dissapearing, the problem seemed to have been that the bottom end of the motor was worn out. (2.1 DJ WBX) It did finally let go completely, and since the new motor (2.2 EJ Subaru) has been in the old (and I thought knackered) prop has been back on with no vibes.
My suggestion therefore is that although UJ's or balancing may be needed sometimes, the propshaft seems to be an indicator of other problems too sometimes. It must have a good harmonic resonance with other parts of the van.
No reason not to sort out a prop though, as this works both ways..

[HarryMann]

Yes, good post

It must have a good harmonic resonance with other parts of the van

Or an unhappy harmonic complicity... might be another way of putting it

[Mudlark]

But Mark, could you have confused the rear wheel vibration (due to bearing play) with a prop vibe. Because the harmonic speeds are roughly the same, do we assume one is the other

Quite possibly.

But the perception of this driver was that due to the resonances in my van the vibe was under the middle of the floor; the prop was exhibiting all the signs of a failing UJ/out of balance problem with the self same physical sensations as those I had experienced when the UJ did start to fail on my old Tristar when in the Isle of Wight all those years ago.

Now; had i taken the prop out in Venice as intended instead of drinking that cold beer and then driven round to Rijeka i may well have found that there was some god awful vibration on the wheel and realised i was on the wrong track; but as it was the symptoms pointed to the prop; and as the rear wheel bearings were 'new' I did not think too much about them.

I only offer the information in terms of adding to the collective wisdom of 'that old prop vibe thing.....' as we all seem to be reaching the same conclusion that quite often it has nothing to do with the prop itself; and can be many other things.

[syncropaddy]

Vibrations and the like can be a pain in the ass to pin point, never mind fix ..... two people in the same van, listening to the same noise will suggest two different things!

I had a vibration in my 300 SE which I thought was wheels .... or propshaft .... or flat spotted tyres. Turned out to be a steering damper!

[HarryMann]

.' as we all seem to be reaching the same conclusion that quite often it has nothing to do with the prop itself; and can be many other things.

Ohhh Yeees (in a Churchillian tone)

==== Adding more observations: ======

Subject to slight to moderate noticeable vibes (37 ~ 47 mph) on return from Coney

Today I quickly loosened all 3 front diff mounts( slacked off, but nylocs safely on bolt threads).

Drove 5 miles, Drove 5 miles back

Could not identify any vibration (though may reserve judgement as not as heavily loaded as upon return from Coney)

Tightened bolts up upon return

===Tomorrow ===

Retest to see if can identify any vibes (with diff tightened in its 'settled' position

[ Just experimenting ]

[toomanytoys]

just what I plan to do Clive...

When I get time.....

[silverbullet]

It does make me wonder why SDP/VW didn't spec a damped tube for the prop, like some manufacturers in the mid-80's were. It rings like a bell because it's a plain tube, surely a rubber-bonded tube-in-tube would have been loads better (admittedly with an increase in inertia, perhaps it would be to the detriment of the gearchange?)
Drawing from other sources, the manual transmission Jag XJ-S (6-pot) had just such an item, with a "plug-in" splined connection to the rear of the Getrag gearbox and U/J's each end.
Even a lined/internally insulated tube would be better.

[v-lux]

surely a rubber-bonded tube-in-tube would have been loads better

This is exactly what Dave (futbus) is running on his van. Custom made bonded tube with Landrover UJ's each end. Very nice bit of kit.

Still vibrates a little though...

[jed the spread]

surely a rubber-bonded tube-in-tube would have been loads better

This is exactly what Dave (futbus) is running on his van. Custom made bonded tube with Landrover UJ's each end. Very nice bit of kit.

Still vibrates a little though...

Be careful...

Jed

[HarryMann]

Update:

Tightened up bolts and still can't detect any vibes through that speed range.

However, I know not to assume they aren't there, as often a longer run when one gets more in tune with the vehicle, soon brings to light noises, vibes and behaviour we can easily miss in a short test drive... which is why I always suggest people don't set things like ignition timing by experiment and doing short test runs... very misleading.

So will see what happens on smoother roads if I load the van up a bit and do a longer run that requires more power to accelerate through that range.

[v-lux]

v-lux wrote:

surely a rubber-bonded tube-in-tube would have been loads better



This is exactly what Dave (futbus) is running on his van. Custom made bonded tube with Landrover UJ's each end. Very nice bit of kit.

Still vibrates a little though...




Be careful...

I'm only meaning that i think there is more to the prop vibe thing than just the prop itself. in fact lots of it probably not the prop at all, but slight intolerances in the multitude of other things that all play a part.

I had a knackered prop a while back that never vibrated at all, only started vibrating once it was rebuilt one end.

Same for the one ive got on the van right now, (borrowed from Dave) was right as rain when it went on the van, quiet as a mouse. a couple of years on and one of the UJ's needs replacing and its developed a loud ringing at certain low rpm. But despite all this it still doesn't vibrate?

Theyre odd things that's for certain.....