Most likely cause of driveline backlash? Short video for diagnosis included.

[earemike]

Hi all,

hope someone can confirm my suspicions or tell me I'm way off base.

Riding the '77 LeMans at around 3.5-4.5k rpm I could hear a rattle in the driveline that was causing me concern. If I get on the berries up the rev range I don't notice it at all. I'm guessing when everything is under load it's fine but when revs are near constant there's some lash in the uni-joint (or possibly the splined shaft?).

I've ordered some parts expecting the uni joint will need swapping out sooner or later regardless.

If you can spare a moment to look at my video of the bike running in first on the stand & throw in your opinion about the knock I'd appreciate it. If running it in first on the stand in itself is a bad idea you can scold me for that too! I'm posting as I'm guessing but some of you will know!

Thanks

https://vimeo.com/133110362

[oldbike54]

 Get ready for the scolding , I did that once , and almost half the board told me to never do that again , and that was the nice half 
Probably a U joint , push on the boot around it .

 Dusty

[Arizona Wayne]

Probably at least the u-joint.   To monitor the condition of the u-joint before it get's this bad, rotating your wheel back/forth when the bike is off, the more slop doing that the more your u-joint is worn.    After you get a new u-joint in there you will know what doing this feels like as a reference.  I do this same test on my 750 Breva.

[Vasco DG]

Is it making a noise when you are riding it or just on the stand? If it's doing that when you're riding it you have a problem. If it's only doing it on the stand? Well? Just don't.

Pete

[earemike]

Get ready for the scolding , I did that once , and almost half the board told me to never do that again , and that was the nice half 
Probably a U joint , push on the boot around it .

 Dusty

Thanks Dusty, I figured it wasn't designed to run without load. I hope the board considers me thoroughly scolded!

I'll give the u-joint a prod later to see if anything feels odd.

Probably at least the u-joint.   To monitor the condition of the u-joint before it get's this bad, rotating your wheel back/forth when the bike if off, the more slop doing that the more your u-joint is worn.    After you get a new u-joint in there you will know what doing this feels like as a reference.  I do this same test on my 750 Breva.

Thanks Wayne, I did try feeling the 'slop' at different parts of the wheel rotation but couldn't tell the difference. I used my other LeMans as a reference (runs beautifully on the road) but couldn't notice a difference!

Is it making a noise when you are riding it or just on the stand? If it's doing that when you're riding it you have a problem. If it's only doing it on the stand? Well? Just don't.

Pete

Yes Pete, when I'm riding but not all the time. When sitting on 3.5-4.5k rpm I can usually hear it but if I wind on the power I can't notice it. When I say can't notice it I can't hear or feel it & the bike feels great.

Because it was only at a certain RPM & specific load I was thinking the uni-joint or splines must be worn unusually.

I did find  pieces of teeth in the rear drive sump when I changed the Dif oil (850T dif). I can add a pic when my internet is working better

[Vasco DG]

If it sounds like a helicopter is following you down the road when you're riding it the UJ is buggered.

Pete

[mtiberio]

broken cush drive spring can cause driveline slop

run it on the centerstand but drag the rear brake for load...     (donning asbestos suit)