Tail shaft vibration

I know this has been covered before but here we go.

Last summer my Syncro did a uni (gearbox end). After removing the tail shaft the journey was completed without problem. Knowing the shortcomings of the original setup, and the price of the unis, I decided to go for an aftermarket solid shaft. After fitting it there was a bad vibration from about 40 - 60 kph then again around 100. Thinking it must have been the shaft the supplier very generously had another made, same problem. Tailshaft out, smooth again. In desperation I went to a tailshaft guru recommended by Spicers, he made a magnificent tailshaft using a CV joint and readily available uni’s. Again the same problem. There didn’t appear to be any movement at either end or unusual noise however the decoupler did leak a little oil when engaged so, as a precaution, we rebuilt it. That did seem to improve it and after refitting the tailshaft it appeared that the vibration had mostly gone, however the testing was mostly at highway speeds. Now that it is back in the city I notice that there is still a vibration at 50 - 60kph.

Since then I have borrowed a good, original shaft from a friend and also put new tyres on it. Same problem. Everywhere I take it they say “it must be the shaft” but after 5 shafts (the second fellow also made
another in case) I find that very hard to believe.

The way I see it’s got to be from the decoupler forward seeing it is fine without a shaft. It doesn’t seem to make a noticeable difference whether the decoupler is engaged or not and the front diff has no movement in the shaft or noticeable noise.

Currently I have a very good 2wd Syncro!

Any ideas?

Andy

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Hi Andy. Did you change anything with how the front diff is mounted? New mounts? Greg

Same as what Greg said. I’d be checking all mounts front and rear for wear.
Also check alignment of both.
If the shaft is out, it’s also worth checking the flanges (each end of shaft and on GB and front diff) are all nice, clean, flat. No dings or nicks in the flange faces from putting shafts in/out.
Richard

I had similar issues with that shaft, yet it was much better de-coupled than locked in.

Then finally fitted the Uwe shaft and that was a big improvement but I still had minor vibration which was more noticeable around 90km/hr.

After replacing my 18 year old tyres - the vibration is gone - completely at all speeds (up to legal speed anyway).

How old are your tyres?

Not really, the gearbox had been rebuilt recently but when fitted it was fine. We did try loosening the front diff to see if it would find its own alignment but no different.

Tyres are brand new, it did it with the old tyres and same with the new, bigger 15’s, just at a slightly higher speed.

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Have done but will do again when I pull the shaft out.

The first two shafts I tried were Uwe shafts. Both vibrated so definitely wasn’t his shafts.

Hi Andy, sad to hear its still causing a problem.

When we were at Luke’s workshop one of my thoughts was using a dial gauge to measure the trueness of the gearbox and front diff flanges. Seeing things where better once the decoupler was rebuilt it sort of suggests that area which Richard is also thinking.

Not sure how violent the moment of the uni breaking was, perhaps it altered a flange slightly or a bearing.

Hi Uwe, thanks again for your help and patience at Luke’s. I think Luke did put a dial gauge on at least one of the flanges but I agree that’s an area that needs to be revisited. I have it booked in to a driveline specialist in early October and I’ll make sure it’s something they check as well as all the alignments. I was just hoping someone here might have the magical definitive answer, I know it’s a bit of a “how long is a piece of string” type question and I appreciate everyone’s input.

Andy are you running the genuine or aftermarket mounts on the gearbox and more importantly on the front diff? The front diff needs to “float” in its mounts. If it is mounted too rigidly you will chase your tail with vibrations that change slightly when you make adjustments but never go away. You have my number, give me a call and I will guide you through it.Greg

Thanks for the suggestion, as far as I know mounts are original. Not sure I’ve got your number?

Andy

Sorry wrong Andy! So you should be able to grab the front diff in your hands and move it. At the two rear mounts of the front diff its ideal to have a gap between the upper washer and the mount. Sometimes with the original mounts you just swap the top and the bottom. At worst you might add a small washer. What you don’t want is the big washer resting on the outer part of the bush or worse still bolted up hard against it.
The same princible goes for the other three mounts, the front most mount rests rather than hangs so you are looking for a gap at the bottom.
Greg

Thanks for the info, I’ll have a look as soon as the rain stops. Oh, to have a shed to fit the Syncro!

Gold star for Greg! Just loosened rear mounts of front diff and vibration gone👍 I think, initially, the decoupler was the issue as rebuilding it did improve things but I must’ve done up the front diff mounts too tight when I was fiddling with alignment. Thanks everyone for all your input, I haven’t had my Syncro for over three years (long story) but now I can hit the road, happy days😁

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Fantastic.

Heading into the warm season for off-road camping fun.

Hi Andy, those bolts need to be tight. Add small washers to gain clearance and torque bolts. Greg

Thanks Greg, will do. Don’t suppose you know the torque setting?

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