Volvo 720b

[DMC]

I have a Volvo 720b 2003, something happened to the differential. My guy was grading and he heard a bang and what sounded like a chain unrolling. The grader stopped moving and the only way to get the grader to move is by putting on the diff lock. If the grader comes under to much load the wheels on the left side of the driver will spin.
We removed the top covers on the walking beams and all the chains look fine.
Where should I look next? Did anyone have this problem?
Thanks

 

[Welder Dave]

Are there covers between the wheels you can take off? Maybe a spline stripped or keyway let go on the main shaft that drives the axles or an axle broke. Have read of axles breaking. Lift the wheels off the ground and see if you can turn them easily by hand.

 

[ovrszd]

It's possible the failure is in the differential rather than out in the tandem drives. Hope not.

As Dave said, start at the wheels and work your way in. Let us know what you find.

 

[DMC]

We did some tests today
With diff lock off we lifted one side and the wheels turned, lifted the other side and those wheel turned also.Drove it against a sand stock pile,put down the blade and with the diff lock on only the drivers left side turned.
With the first test without the diff lock the right side seemed like it was stronger?
I'm thinking maybe a spline?

 

[Welder Dave]

Need to look at a parts diagram to see how the tandem drive works and it should give an idea of what could be wrong. It could be a problem in the diff. too. There may be suggestions in a troubleshooting guide in the operators manual. Might find a manual online to look at.

 

[Ben Witter]

When turning the right side wheels does the driveshaft to the differential turn?

 

[Silveroddo]

Whats the fluid look like in the Diff.? I'd check the magnet on the filler plug and drop the bottom plug and drain a little and see what you see. I think theres a cover to access the center drive gear on the tandem. I'd do whatever I had to to get eyes on the drive gear and look for signs of failure. I think the older ones basically used an eaton based differential and an axle to a drive gear. I'd see if there's play in that drive gear to indicate damage/failure. I'm going off of a basic understanding, I've never had to dive that far into one, but I've been into those chain cases. Sounds like the right side would be where I'd start.