Vibration, for serious discussion only

[PC52]

This is an open topic BUT do not post pure crap suggestions regarding this.
Situation:
On one of our syncros we have had a 'prop' tinkle in 3rd and 4th for some time - over the past fortnight we have taken the prop off to attend to it and swap over to a known good one.
We drove it without the prop on (prop hasn't been re-fitted), no tinkles but definate vibration (3rd + 4th)on the floor - not evident on the gear stick or clutch.
On acceleration - vibration, deceleration - no vibration.
The noise is truly horrible, the vibration is now concerning
1st and 2nd gear is fine
Oil change was good - minimal xmas tree



Now the scenario is the gearbox has been sorted, 1.18 3rd + 0.73 4th gear (Albins gears), 4.86 diff. Box was rebuilt 1 month before we went to the Pyrennees so its been running for 4 years, approx 30K + miles on the box, oil changed yearly and the xmas tree is nothing substantial.
Your suggestions...

[syncropaddy]

Im thinking engine/gearbox Mounts, or clutch

[PC52]

Im thinking engine/gearbox Mounts, or clutch

See what you say but have checked g/box & eng mounts over, replaced 1 for 'just incase' , but why only 3rd & 4th on acceleration. The more acceleration/boost more noise

[syncropaddy]

Im thinking engine/gearbox Mounts, or clutch

See what you say but have checked g/box & eng mounts over, replaced 1 for 'just incase' , but why only 3rd & 4th on acceleration. The more acceleration/boost more noise

Id head in the engine direction. 3rd and 4th have a longer time to develop the vibration than 1st and 2nd. Vibrations have a habit of starting at point A but not being noticed until point C if you know what I mean. Unless Aidan knows something about 3rd and 4th in the box

[sandwedge]

Is it possible you have lost a wheel balance weight, I think its unlikley to cause the issue you have as it should still be present during deceleration.
My only other though is your clutch is slipping during acceleration and the reason its only present in higher gears is the higher torque being put through the system.

[PC52]

See what you're saying.

At this point I will say Aidan has not had an insight on this box - due to the time factors when we needed it re-building.
So, as a point of fact this box has not been rebuilt by Aidan.

Now, when it was rebuilt there was an issue with oil leakage and synchro had seized on 4th gear (Russel will remember).
So, during re-build it was apparent that the main shaft bearing had slipped causing wear and our gear box rebuilder re-furbed the casing and corresponding matching casing.
This is what is throwing cause for concern now to us.
Suspisions on that casing refurb failing now

[PC52]

Is it possible you have lost a wheel balance weight, I think its unlikley to cause the issue you have as it should still be present during deceleration.
My only other though is your clutch is slipping during acceleration and the reason its only present in higher gears is the higher torque being put through the system.

Wish it was wheel balance issues - no.

Serious High torque is being delivered and there is no clutch slippage.

[axeman]

Pre the devon weekend i was getting a strainge knocking /vibration coming from the front in 3rd and 4th under load. I swaped the drive shaft for one with new joints on the side that i thought the vibs/noise were coming from. Still there. Drove,to devon took clive, adianul and dave out they will fill you in about the vibs and noise. Swaped the outher drive shaft over (the one i took off before devon) and put it on the outher side. No more noise or vibs.

May be worth looking at good luck with it.


Neil

[PC52]

Neil, Interesting when was you vibration on acceleration and deceleration?

[syncroandy]

Pete, the symptoms you describe sound very like I had recently on my pickup. I was getting a really nasty vibe under load in 3rd and 4th, with prop on or off. It was fixed by swapping in my spare box, after which all noticable vibes went away. The suspect box hasn't been apart yet, one possibility is diff wear, as the n/s output flange has a noticable play which doesn't seem to be just the flange.

[axeman]

Neil, Interesting when was you vibration on acceleration and deceleration?

Only on acceleration in third and fourth

[PC52]

Pete, the symptoms you describe sound very like I had recently on my pickup. I was getting a really nasty vibe under load in 3rd and 4th, with prop on or off. It was fixed by swapping in my spare box, after which all noticable vibes went away. The suspect box hasn't been apart yet, one possibility is diff wear, as the n/s output flange has a noticable play which doesn't seem to be just the flange.

Likewise
play in n/s flange - we have also replaced n/s inner cvj, it was worn (badly) out of interest what is/was your cvj like? Was the driveshaft one of the ones that got wrecked at Whaddon?

[Simon Baxter]

Put it on a ramp and drive it while it's up in the air.
Ever seen a syncro do 90mph while not actually going anywhere?
We do it quite often to trace knocks and bangs, quite useful if you have somewhere to do it, you get to see all manner of strange things, wobbly drive shafts, bent rims etc.

[syncroandy]

Likewise play in n/s flange - we have also replaced n/s inner cvj, it was worn (badly) out of interest what is/was your cvj like? Was the driveshaft one of the ones that got wrecked at Whaddon?

I forgot to mention, when I swapped the box, I found the splines on the inner end of the driveshaft had been slightly rounded off and the joint was loose on the end of the shaft.

[Mudlark]

Gearbox touching bash plate ?