Vibration, for serious discussion only

[HarryMann]

Is this sorted now ... ?

(so we can revert to non-serious & highly irreverent comments )

[PC52]

Is this sorted now ... ?

(so we can revert to non-serious & highly irreverent comments )

Wink wink, not sorted. G/box out another in = vibration
g/box mounts checked and replaced = vibration
cvjs checked
back to the engine bay now.
Really don't know and getting well pissed with it aswell in light of certain other circumstances grrrrrrrr

[Aidan]

so the good news is it's not the gearbox

[silverbullet]

Must be a resonance/harmonic problem with the prop and the engine rpm then.
You've done everything else unless it's a buckled wheel or a duff tyre.

[axeman]

pete have you cheaked that one if not more of your drive shafts are not bent, sounds stupid but it would make sence as your only getting the vibration at speed in 3rd and 4th, which would account for you getting the vibes with or with out the prop as the shafts are still connected and rotating?

neil

[HarryMann]

Must be a resonance/harmonic problem with the prop and the engine rpm then.
You've done everything else unless it's a buckled wheel or a duff tyre.

Slight vibe going through 40~45 in top developed on mine in Snowdonia... removed prop before returning, vibes became much stronger under power at same speed, centred on 2100 rpm, definitely crank-speed driven and very torque level driven, vaguely noticeable through 2000 in 3rd, but an order or two less in magnitude.

So prop inertia and front drive had been damping this heavily, not exacerbating it... large peak-to-peak torque impulses from TD probably quite different to Tdi.

as they say somewhere on the planet (sickeningly)... Go Figure!

[silverbullet]

Hmmm...is this a fundamentally diesel-oriented problem then?
If it's a torque-magnitude driven harmonic, then the prop may be deflecting and affecting balance. Time to bin the VW design propshaft and replace with a more robust design maybe? I'm thinking a flanged CV at each end with a damped tube (worked well enough on the Rover SD1) or conventional UJ's and a sliding joint a la Strange Rover?
Has anyone successfully tried an alternative design that works long-term?

[HarryMann]

Yes, I think very much so...

We have:

Completely different torque impulses, crankshaft torsional modes, crankshaft torsional vibration damping, flywheel mass etc
Completely different engine mounting arrangements, engine mass distribution etc

[v-lux]

I dont think a slip joint is the way to go, the prop on mine right now has one and it makes an awful racket at low revs. (think milk bottles jangling) We dont have any need for the slip joint anyway with how our suspension is arranged. Its pretty minimal movement between the Gbox and front diff. I suspect all new box mountings would make a larger difference.

Dave (Futbus) had a brand new prop built up for one of his syncros that's two tubes (one inside the other) bonded to one another with rubber. It uses LR joints on each end so they are cheap to replace and has grease nipples both ends also. Its a very nice bit of kit, but think it was about £350 ish to buy...

[syncrosimon]

Glad I got a WBX

[syncrosimon]

But on a serious note, I wonder if Baxter could look at getting Powerflex to reproduce the (16?) gearbox rubber mounts in varying grades of Powerfex material. I had one n.o.s gearbox mount and it was noticeably more malleable than my 19 year old ones. This has got to help.

[silverbullet]

Syncrospares are now proudly touting props with 2 UJ's and a sliding joint for "ease of installation" but as Al said, is it really needed? Having said that, they probably shouldn't be made dead length to avoid preload or tension issues when installed which could lead to UJ failure.

[HarryMann]

I suspect all new box mountings would make a larger difference.

Mine's got new ones... diff as well. Did help at the time, as did main diesel engine mounts... slack in gbox or diff (and VC on its splies is a biggy I think too), all to reduce thumping on power on/off and 'shuttling' under neutral throttle.

It's been good since then, although you could never flip from overrun to drive or vice-versa too casually, to drive it smoothly still requires a 'certain approach'

Ian, If there is difficulty then the front diff can be shuffled about, the rubber doughnut taking out fractional length differences.
Then nip up the front diff, though never found it necessary myself.
Might be worth a try though...

[silverbullet]

Slight aside but may get the grey matter working:
My old Rover P6 V8 developed a horrible cyclic vibration after I took out the (blown up) BW Auto and replaced it with a 5-speed manual. The prop was unchanged (same length, very handy) and I traced the problem to tired Uj's in both driveshafts (which were fixed length) combined with new wheel bearings in both rear hubs.
Rover had two goes at getting the prophaft "right" on these cars and resorted to deliberately putting the Uj's out of phase to correct the harmonic issues resulting from an engine with a slight "down at the tail" installation in the bodyshell of only 3 degrees odd and an offset centreline for the diff assembly...
Are we looking at a similar alignment problem in diesels, where the donut cannot sufficiently supress the harmonics?
PS the prop was a one-piece design with sliding spline at the gearbox end

[HarryMann]

Search for 'cardan shaft' in the Tech Archives.. should pull up some posts about alignment (i.e. not intended to be..)

The main problem does seem to be engine driven on the diesels, those with bigger clutches & flywheels may find things are different/better