Let’s compare another shop’s 4 spider center diff against a TRE.

Their cross shaft.

  • When they cut through the hard nickel chrome plating it ruins the tribology, causing spider gears to tear up the cross shaft.


typical galling

  • Their cross shaft posts now has a 20 point of hardness difference between it and the spider gear.  This will certainly gall up and seize.


Their center diff.

not a TRE

  • This is the typical machine work from a competitor. Notice the uneven surface and how they milled too deep and cut through the housing and ran into the gear. You’d think they’d know better than to do this.



Here’s what TRE is doing:

  1. We start with a new 4 post cross shaft not some cut down stock part. This keeps the diff housing from getting all pounded out and the cross shaft running out of square.
  1. The new cross shaft is forged, heat treated and has large corner radius for strength. It’s 60HRC and it’s also shot peened.
  1. Prior to milling the housing we magnaflux it to make sure we aren’t starting with some junk that has cracked gear teeth.
  1. The center diff is first squared up the housing so it’ll get machined properly. I have yet to see anyone do this correctly and it shows in their work.
  1. We CNC mill the housing with accuracy of better than 0.0005″ and checked via Renishaw part probing for accuracy.
  1. We leave more meat in the housing at the bottom corners. This keeps the housing strong so it doesn’t spit.
  1. The end-mills have a large corner radius, reducing stress risers in the housing.
  1. We mill the housing in such a manner that squares up the walls and cross shaft slots. This is beneficial as it repairs worn out pounded housings.  Most center diff housings can be salvaged.
  1. We also mill openings so the oil can get in and the metal fragments can’t build up.
  1. The housing is shot peened to increase the strength of the outer gear while improving oil retention which reduces wear to the housing.
  1. We’ve seen just about every attempt to machine a center diff and feel that we do it best. You may find cheaper work but it’s not being done correctly and they are simply using your old cross shaft.