Transmission vibration fault finding

[oldbury863]

After a nut and bolt rebuild of my 13/60, I finally got it back on the road only to discover that it suffered from dreadful vibration at anything over 30mph. I ran the car up with axle stands under the vertical links to eliminate anything tyre related. The vibration remained so I removed the (strap drive) propshaft and had it rebuilt by Chards of Bristol. They completely dismantled it and machined a new bush for the worn centre spigot. They then fitted new u/js and balanced it. Things are considerably better now but still not as I would expect at anything over 45-50mph but I dont know if the vibration that remains is (still) propshaft related or is it from the halfshafts and their u/j's? I dont want to have to remove the propshaft again and go back to Chards if the problem isn't with the propshaft! Is it possible to unbolt the halfshaft flanges from the diff and run the car up (either with the suspension supported or with it unsupported) without removing the rear spring first?

[glang]

So even now if run with the wheels off the ground theres vibration? If so and engine, gearbox and diff mountings are good it doesnt leave much. You could try without the wheels in place to discount they being unbalanced....

Cant see the problem caused by the halfshafts but I think you could run it with them disconnected except when undone they tend to push back in against the diff. You could, as you did before, put axle stands under the vertical links to keep them away but be very careful how youre supporting the car (use chassis) while it runs especially if theres vibration!

[Clive]

I remember reading that the strap drive props are problematic, and sometimes they may balance on a machine but not on the car. Think that was in the canleys catalogue? 

You may be able to undo the spring eye bolts, and then the halfshafts, and keep the flanges off the diff. My gut feeling is that the prop is the likely culprit (as the work has improved matters a little) 

Another option that is pretty simple. Mark the straps and where they fit. Take the straps out and rotate the prop 90 degrees, then bolt it up solid. All done in situ, takes 10 mins. That may solve the issue. It did on a car I helped with. And is quick/easy to do and reverse.

[Nick Jones]

Driveline vibration in small chassis Triumphs does come back to the propshaft most of the time. Strap drive props are the worst offenders.

First thing to check is that both UJs move freely on both axes, but without any free play. One tight axis will cause vibration.

I bought a bespoke prop from HJ Chard many years ago. It vibrated. I took it back and had it rebalanced. It still vibrated. I balanced it on the car with jubilee clips and since then (about 50k miles now) it’s been good to 100mph, and not just on axle stands. I’ve done several other cars since, with success.

My technique is to raise the rear of the car and support firmly on sturdy axle stands. Remove the rear wheels and brake drums. Check that the driveshafts aren’t rubbing on the chassis and add jacks/stands under the damper mount to raise them a little if necessary. 

With the engine at fast idle and 4th gear engaged, inspect the driveshafts/hubs etc to ensure they are running true. Bent driveshafts and hubs are not rare! Watch out for whirling wheel studs......

Note that with the driveline unloaded, vibration, shunt and backlash are accentuated. If all seems true, increase revs and note the point (speed) at which vibration becomes noticeable.  If all seems well now, it’s your wheels and tyres....... If not, you need to add a couple of jubilee clips (other worm-drive clips may be used) to the rear of the prop. Finding the positions that give least vibration is a matter of trial and error. A paint pen is useful to keep track of what you’ve tried. I prefer to do this on my own so I’m not tempted to cut safety corners and remain under the car while the tests are done!

If you wanted to disconnect the driveshafts at the diff flanges and prop/tie them away, then it should be possible without further dismantling but I’ve never found it necessary.

Nick

[oldbury863]

Thanks for the replies, its got to be worth having a go with a couple of jubilee clips rather than taking it back to Chard's time and time again.  I know it would be foolish to expect a Herald to drive like a modern car but I really dont remember my previous Herald suffering such harshness in the drivetrain that made me reluctant to exceed 55mph!  I'll keep you posted as to my findings.

[oldbury863]

Unfortunately fitting the jubilee clip only made matters worse in all 4 quadrants. In fact it was as bad as it was even at 30mph before it was balanced so clearly it doesnt take much to upset things. Theres nothing else for it but to disconnect the half shafts.  If it is still unsatisfactory I think the culprit will be the diff. This would be SO much easier if it had a live axle! I'm hoping that if I attatch a ratchet strap from both ends of the spring and take it over the roof, that I can then disconnect the half shafts without it all being under tension🤞

[Bradison]

On 11/06/2021 at 18:22, oldbury863 said:

Unfortunately fitting the jubilee clip only made matters worse in all 4 quadrants. In fact it was as bad as it was even at 30mph before it was balanced so clearly it doesnt take much to upset things. Theres nothing else for it but to disconnect the half shafts.  If it is still unsatisfactory I think the culprit will be the diff. This would be SO much easier if it had a live axle! I'm hoping that if I attatch a ratchet strap from both ends of the spring and take it over the roof, that I can then disconnect the half shafts without it all being under tension🤞

I had horrible vibrations on my saloon, from 60mph and up it felt as though the car had magically transformed into one of those massage chairs found at the odd motorway service station. I noticed at night the vibrations were cylindrical as headlights from following cars were spinning in a small oval shape.

After swapping the prop shaft, checking all UJ's and still having the same problems I bit the bullet and had a spare diff rebuilt. Vibrations gone, now I can hear the layshaft bearings instead... I would try the diff rebuild route and you should hopefully notice a difference.

[oldbury863]

A friend of mine asked why I hadnt used 2 jubille clips........If the clips are set almost opposite one another you can get much finer adjustment than using just one clip.

Never even occurred to me 🤭

 

[glang]

oh dear Nick did suggest that in his original post but unfortunately we should have explained it better. Still its something you'll never forget now😁

[oldbury863]

Thanks for the replies, I measured the diameter of the prop to calculate the circumference and from that, printed off a paper strip of exactly the correct length marked into 12 points of the clock and glued it around the prop (just ahead of the strap drive at the rear). I unbolted the spring in order to relieve some of it's tension, unbolted the driveshafts and tied them up out the way to remove any potential contributions from them, before I started. By trial and error I used 2 clips (almost opposite one another) at various 'points of the clock'. I wont deny it, this was a very tedious job! First I set the clips at 12 O'clock and 5 O'clock  then rotated them both together 1 'hour' at a time to establish the optimum position, then I altered the angle between them in order to add or subtract the total weight. Eventually I ended up with negligible vibration right up to 60mph that I was happy with. (With the transmission tunnel cover removed, the amount of engine noise was considerable though!) The clips ended up at '12 O'clock' and '7 O'clock' so almost directly opposite one another, meaning the effective weight required wasnt very much at all. It just goes to show how critical the balancing is.   Dont forget this was on a prop that had already been 'professionally balanced'! At least the engine behaved during this process after I had changed the carb float valve for the second time. (see my other post) but I'm still concerned that it may play up again in the future......🤞