01 Volvo /ISX vibration when going slightly downhill

Sounds like it is drive line related...Any play in the rear gear housing or the yoke at the tail of the trans?

 

Check the ride on the drives(assuming air ride suspension). Always the first place to look any time there is vibration, especially if it is coming from the drive line.

Probably needs a leveling valve.

 

This has happened to me and it was the yoke that was frozen or seized on the shaft next the transmission and had no free play in it. When the suspension gose up-and-down, it put a lot of pressure on the power divider, Specially heading down a hill or coasting on level ground,

The air Leveling valve pretty weak I give those things one year,. I keep all my receipts from the Volvo dealer, when 9 months come around I just go get a new one all parts warranty for one year from date of purchase, Never had to pay for a new valve again.

 

I have the same vibration when decelerating and a worn yoke between the rears... I think that's where it's coming from.

 

A bad leveling valve, or the air ride height being off can give you goofy driveline symptoms. I thought I was losing a bearing in the tranny in mine, but only heard it while going over the hump on overpasses, it was the ride height.

 

Yes, the Levering Valve was the main problem, the second problem was that yoking seized on the shaft so when the levering valve start to go bad, it puts a lot of stress on the power divider.