I'm trying to replace gear oil for my Viscous LSD rear diff. My mechanic drained the fluid from the bottom bolt and refilled it from a bolt located around middle of the cover.

From my understanding of Viscous LSD, the Viscous discs MUST be entirely submerged in viscous fluid. This is an exerpt from www.howstuffworks.com,

"The viscous fluid, stuck between the plates, tries to catch up with the faster disks, dragging the slower disks along. This transfers more torque to the slower moving wheels -- the wheels that are not slipping. "

Here's my question:

If mechanic filled the rear diff from the middle bolt, the gear oil will start overflowing before the LSD is entirely submerged in the viscous fluid. Wouldn't this cause the LSD to not operate correctly? and possibly make noise?

Jay Kim

P.S. Would this be a cause for the whinning noise from my LSD when I decelerate?

 

All I know is that when I changed mine, I drained with the bottom bolt, and filled it with the top bolt........ I put Redline ShockProof in the rear. Make sure to add GM Syncromesh addative to it. That solved my LSD making noise problem.

 

You're only supposed to fill it to the top bolt. Mazda says so. The gears are probably completely submerged when it's AT the top bolt hole. The people who made this car AREN'T stupid .