Oh Boy, seems like everytime I go around the back end I find more issues. Changing the diff oil, I saw the track bar was way off to the front of the diff. The attachment point on the top of the diff had broken off.

Some of you may remember my issue with the frame cracking and the work I did to repair the crack and to stiffen the frame rail. Well that stiffening worked well an transfered all the stress and the weakest link broke, the weld of the bracket to the diff. It was not welded well to start with. With such a short track bar there is a lot of stress as the bar pivots up and down with the axle movement.

Time to re-engineer the entire rear system. A "Z" link would be the correct approach but will be a lot of work and a challenge to get 5 pivot points under and around the diff. Earlier Breakaways with the Dana 80 diff had a longer bar that went from one side chassis rail to nearly the spring mount on the opposite side. Not as good as a "Z" link but a lot better than what I had.

The Eaton 15040S is MUCH larger than the Dana 80 and probably the track bar used with the Dana 80 would not fit on or with the Eaton.

I will be pulling the trailer this time so it will not wonder very badly but will require more attention. It was broken for awhile and I have made the trip to Texas in March with no issues.



Very clear the placement and welding was very BAD and poorly done!

Looks like another fun filled summer!

Dana to answer your question about the track bar mount failure.

The root cause of the failure this time was because I had beefed up the frame and put in diagonal bracing. It really helped rear end wander but with such a short bar, verticle movement of the diff will put a tremendous load on the bar mounting points and springs.

This time it was the track bar mount that broke off the top of the diff. It is very clear that the bar mount was not welded well to the top of the diff. Half of the mount flange was not welded so as the forces were exerted to the mount flange it was flexing the half that was not welded and the mount broke in half.

Check the previous pictures and one can see half of the mounting plate is still attached to the diff and the other half is is attached to the bar. The bar was NOT centered on the top of the diff so the part that broke could not have been welded correctly to distribute the load across the bracket.

Probably the reason it didn't break earlier is there was so much frame flex that the forces on the mount were not high. When I re-enforced the frame it just increased the forces applied to the mount on the diff and of course the weakest part broke off.

I have been studying the reared layout and will try to come up with an improved track bar and mount. It drives OK now but requires a lot more attention and more steering wheel movement to counteract the wander. Pulling the trailer helps a lot.

Ed,
I will check the mount on mine. My frame was beefed up also when they found the frame cracked. This was before I got DBarth. I don't know if I told you. That fix amount was over $8000.

I'll give mine a serious once over looking at the mount and welds. When time permits.

As always your posts are insightful and helpful. Your and my coach drivetrain are so similar.

Find anything?

Your Panhard is far too short, thus the extreme forces on the differential and frame. All design texts say the bar has to be as long as possible to make the travel arc as straight as possible. The bar needs to be mounted to the frame as close to the horizontal plane on one side and the bottom of the axle housing closest to the wheel hub (near the lower shock mount) on the opposite side. Use Google Scholar and put in Panhard and search in articles. If you reweld to the top of the differential one or the other end will still break, whichever is weaker. That will probably be the differential casting now that the frame is doubled.

I agree Tom, I knew it was too short when I first started to repair the frame after it was broken.

I have no plans to re-weld the broken mount on the top of the diff. I have been studying ways to make a longer bar from side to side. Not easy. Not only should the bar be as long as possible, truly horizontal in the normal ride position, should be as straight as possible, bends reduce a bar's effectiveness.

I haven't heard anything back from Spartan engineering yet.

I am in discussions with a fabricator that does race and exhibition big trucks (tractors). They have some interesting suspension tricks that might be applicable to the Spartan chassis with the BIG diffs.

Probably will not get to this until race season is over in November

When Spartan gets back you might discuss a Watts Linkage fix. It also requires new rods but completely eliminates the arc travel that moves the rear end a bit. From the articles it suggests a Watts allows smaller diameter rods and shorter links. Adding this is just a matter of welding and bolts.

quote:

Adding this is just a matter of welding and bolts.

Hi Tom, I wish it were this simple to do a Watts linkage or "Z" bar! There is no room above the diff and no real mounting areas ahead of the diff. The Watts ("Z") center pivot needs to be centered but would be hard to find a suitable place on or around the front of the diff and clearance for 5 bushing pivots points.