Broken Diff Mount Help - Q45 R200 Shortnose

[qwik240z]

Hey guys,

 

The new owner of my 240Z LS1 car was hearing a clunk in the drivetrain so we go the car on a lift and found that the custom made front diff mount had cracked. None of the new fabricated part was damaged, just the old Datsun thin ass sheet metal that holds the swing arm to the body.

 

This is the custom made mount.

 

 

 

Here is the damage.

 

 

 

Original thread on my diff mount.

 

http://forums.hybridz.org/index.php/topic/43783-project-silver-bullet-update-q45-install-pics-front-mount/

 

So we are not sure what would be the best fix for this. It seems like the sheet metal could be welded up and it would hold just fine. The new owner does not do track days or drive the car hard and wants to fix it the most cost effective way. I was thinking of replacing the mount with a RT style mount or maybe the T3 mount. I just don't want to have to start reinventing the wheel here.

 

Any suggestions would be appreciated.

 

Thanks,

 

David

[NewZed]

I've been pondering a Q45 mount for my car, and I see that yours has one of the design elements that worried me. You've created a fairly long lever arm to work on the body mounting points. The nose of the diff lifts up on the end of your mount at the two diff mounting bolts, putting a much higher twisting load on the body mounting points than the long nose would. The rubber mounting doesn't add any stiffness and just lets the diff nose push up on the lever over and over. The long nose pushes directly up on the body mounts, yours pushes up on the end of the lever arm.

 

It's probably failure by fatigue after a bunch of flexing cycles. You need to get more support over the end of the diff nose, or extend the other end of the mount so that it can't twist.

Edited September 11, 2012 by NewZed

[SUNNY Z]

Weld it back up, and possibly put something to limit travel on top.

 

I'm sure the reason it broke is because you added a lever, which is a force multiplier to the equation by simply making straps that went back to the diff. I would try to triangulate something to the holes where the RT diff mount usually goes. That might keep it from acting like a breaker bar.

Edited September 11, 2012 by SUNNY Z

[wfritts911]

Ya I agree with the guys above, the mounting design is just acting like a lever on that old brittle crossmember. Just like the guys that have had solid mounts and cracked the crossmember in many places. I would definitely look into re-designing the mount, as there is a lot of upward force coming from the nose of the diff when the go fast pedal gets put down.

 

-Will

[qwik240z]

Well we pulled it all apart this week and got it fixed.

 

Yes, the front of the diff was moving up and caused stress cracks. The fabricator had made an upper bump stop that should have stopped the upward movement but he never adjusted it and it was allowing up to 3/8" of movement. We welded up the stress cracks and seam welded the edges and adjusted the bump stop.

 

Here are pics of the upper bump stop that I never posted before.

 

 

 

And the repaired mount

 

 

 

I told the new owner to buy a RT mount and be done with it but this mount worked for 9 years so hopefully, it will go another 9 years.