UPDATE: NV5600 Breaking gears

[zzman]

I had my trans rebuilt 2 times with broken 6th and/or 5th gear. The first time was within a couple weeks after I had added 2-1/2" spacers to the overload spring bumpers. The second time was about 4 months later, same problem.



After the second time, I removed the spacers and installed air bags. I believe I found the solution to my broken gear problem.



Some folks may not agree to this but I believe with the stiffness of the spacers on the overload springs, this caused the rear wheels to loose traction when traversing at highway speeds and bouncing from rough road conditions.



Just wanted to follow up on my findings.

Curse the spacers and the air bags are well worth the money.

 

[jelag]

I've had 3 trucks with this transmission... All of them have been used towing the 04, towing a 20K lb trailer for the first 250K miles of ownership... We've only had trouble with the 04 and towing this heavy trailer and we believe that the 6th gear wasn't designed for this weight... we had our one and only failure at around 230K miles... All the other trucks tow, up to 15K lbs but we've changed our standards... . we now only tow heavy in 5th gear... anytime we have a trailer over 15,000 we restrict the speed and the gear the truck is in... .

All our trucks have an air bag system to level the load... I agree that 2 things might be going on... the increased angle of the u-joints might be part of the cause as the increased angle caused the joint to work harder and will stress the transmission with the extra side load as the joint goes around... in addition I also agree that the truck might be loosing traction as it bounces with that stiff suspension...

For us, the air bags have been the key... lower pressure for no load and higher pressure for the higher loads to level the truck so you can see at night with the head lights.