That old prop vibe thing.....

[toomanytoys]

Well.. bought a prop off Doug last year, he never tried it but had been told it vibed..
I tried it and it did vibe.. at anything over 40

Took prop in last week to local prop refurb/manufacturer (good rep) who ran it up and said there was nowt wrong with it..
Its a solid 1.9 dg prop.

Put it on at CF, drove away from CF Sunday and the vibes at 35 are worse than ever... but clear after 45, didnt go over 55 but still smooth..
went back to CF and dropped the prop.. in 2wd all fine, no vibes..

Now had this prop on with my original diff last year and currently borrowing Aidans spare diff (as mine has some play inside the diff Aidan is going to see about)

Will do an inspection of everything again, might drop all the protection and try the prop on again, but surely it must be the prop........

Or is it? Any suggestions?

[Mudlark]

Si ..my last prop vibrations issue turned out to be a rear wheel bearing failing!

[HarryMann]

Prop?

I would think so, unless something like your VC is loose on its splines, unbalanced or otherwise suspect.

Maybe the balancers aren't aware how spot on they have to be.

I have some prop vibes, having replaced a UJ that had perceptible wear/corrosion in one needle race. Didn't have it re-balanced afterwards. Will first try shifting the diff about a bit, before looking further.

[hotpod]

my prop vibes on the doka were because of knackered UJ's. one of them was really notchy when i moved it. i put new ones on ( from mr baxter, but i had to remove the grease nipples and plug the holes) and it is totally vibe free now. i didnt get it ballanced or anything.

[Ray]

Mine vibed between 40 and 50. UJ's replaced but not rubber or balancing now vibeless.

[HarryMann]

Might switch it round then, with doughnut to the rear, just to see...

and loosen the diff to find its natural centre and length.

Its always possible its become a bit bent or dinged (during Snowdonia lanes, before that was fine)

[silverbullet]

my prop vibes on the doka were because of knackered UJ's. one of them was really notchy when i moved it. i put new ones on ( from mr baxter, but i had to remove the grease nipples and plug the holes) and it is totally vibe free now. i didnt get it ballanced or anything.

I've never had a prop re-balanced after replacing the UJ's on any car and they've always been fine. Shouldn't be necessary as they have so little influence on the rotating mass of the prop tube

[garyd]

I've just had some success in greatly reducing vibes by rotating the prop 90 degrees relative to the front diff flange. Don't ask me why it helps but it has on mine!

This was a prop with new GKN UJs and the right thickness circlips to centre them in the yokes. Vibration was bad initially (but better than with the old joints) and is now almost gone after the rotation.

Garyd

[toomanytoys]

Mmm..

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

Well prop joints are all good, nice and smooth and no play..

Its a silid prop so no donut and floppy bits...

It isnt bent.. apparently...

The original prop was fine, and it was put on and off so many times (tight original VC) I cant have been that lucky every time and was great up to the point I bent it...

No appreciable play in vc or imbalance as its still spiining if prop isnt there...

More investigation required...

[HarryMann]

I've never had a prop re-balanced after replacing the UJ's on any car and they've always been fine. Shouldn't be necessary as they have so little influence on the rotating mass of the prop tube

The UJ's mass maybe isn't the issue,perhaps it's the extent to which any minimal change in coaxial alignment might be affected

Its a longer than normal propshaft

====
Taking everything we know: The whole assembly & transmission system from crankshaft to wheels seems to be important.. maybe often with small differences cancelling and at other times compounding any tendency to vibration

Time someone set up a complete Syncro engine & transmission on a bench jig, to observe the phenomenon in detail...*

* All donations gratefully received, will start laying the concrete slab when the first £1000 is in the bank

[toomanytoys]

Prop?

I would think so, unless something like your VC is loose on its splines, unbalanced or otherwise suspect.

Maybe the balancers aren't aware how spot on they have to be.

I have some prop vibes, having replaced a UJ that had perceptible wear/corrosion in one needle race. Didn't have it re-balanced afterwards. Will first try shifting the diff about a bit, before looking further.

How spot on does it need to be?? got any weight figures? I didnt get chance to phone today....

[HarryMann]

No idea, I imagine there are many different but subtle reasons from prop vibes or general transmission NVH..

else we'd have found all the answers by now ?

basically 'everything' has to be pretty spot on.. or else you have to be lucky (that they cancel out)

The compliance of the engine and diff mounts also comes into the equation

It certainly isn't all down to just the prop

I'd imagine a big blob of mass hung off diff or box in the right place would stand a good chance of stopping the mid speed one (37 ~ 45 on mine)

[toomanytoys]

No idea, I imagine there are many different but subtle reasons from prop vibes or general transmission NVH..

else we'd have found all the answers by now ?

basically 'everything' has to be pretty spot on.. or else you have to be lucky (that they cancel out)

The compliance of the engine and diff mounts also comes into the equation

It certainly isn't all down to just the prop

I'd imagine a big blob of mass hung off diff or box in the right place would stand a good chance of stopping the mid speed one (37 ~ 45 on mine)

Sounds kinda where mine is but it was nasty.....

Have to go back throught he mounts on the diff (as that was out..) and try again...

[KINGPRAWN]

had the same vib/drone at 3k rpm ish but could push through it at 4k ..but where you want to drive most of the time is in the vibe zone! replaced uj's that were shot but not much better so.....got a new prop from syncro spares that dosen't have the rubber damper thing and its perfect!!!!! have read here somewhere though that on a petrol the rubber goes to the rear..diesels to the front..mine was petrol to the rear which could have been my problem all along..........anybody need a prop with new u j's????

[HarryMann]

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

Yes, if it's straight