Gear Oil

I enjoy doing mechanical things working with my hands.  Ten years ago, taking my new duramax in for service and finding the dealer had elected to forgo lubricating the chassis, a decision they say was made by a rogue mechanic, I decided to take the maintenance of my vehicles on myself.  This way, I would become more familiar with my vehicles and right or wrong I became responsible.  Not to mention saving money.

I simply do not drive that much, most of my maintenance comes down to annual vs by mile.   Everything gets an annual service from my two vehicles, motorhome and generators.  I have stayed ontop of all schedules maintenance including transmission service,  radiator flushes, replacing radiator hoses, thermostats, idler/tensioner pulley and serpentine belts at five years.  It is cheap insurance to avoid both costly repairs and breakdowns.  I can do this work for 25%, with AC/Delco and Mopar parts, verses taking it to the dealer.  Moreover, I have the pride in doing it myself.

The subject of this post is differentials.  It is easy to ignore the differential in your vehicle.  Front wheel drive with a transaxle is handled by scheduled transmission fluid changes, but on a rear wheel drive or 4x you have one and two traditional differentials.  For me, I have a 3/4 GM Sierra, a TJ Rubicon and a Workhorse w-20.  GM built the differential, but the Jeep and W-20 have Dana, specifically Dana 44 and Dana Spicer S110.

There are three types of differentials, open, limited slip, and gear based posi-traction.  A differentials job is to compensate of the delta in wheel speed when you go around a corner.  Without this, the inside tire would have to break traction.  From "My Cousin Vinnie" an open differential is when you get the stuck in the mud and one tire spins and spins and the other tire does 'nothen.  Limited slip attempts to provide traction to both wheels when one side loses traction.  Performance cars do this, it helps distribute power output to both wheels.  Off-road vehicles do this to provide better traction.  Locking differentials, unlike limited slip, use a collar that make the axle solid, this makes going around a corner nearly impossible with out something giving like snow, rain or dirt or the tread of your tire.  This is why it hard on your 4x to drive in four wheel drive on dry pavement.  Mechanical devices suffer from non-use as much as abuse.  It is important to make it habit to shift your 4x in and out of four wheel drive and high and low range.  Rainy days are a good time to run in four wheel drive.

Fluid.  Unlike motoroil the type of fluid is not backward compatible.  Manufacturers will recommend a weight, 75w90 synthetic GL/5.  Oil comes in thickness, the lower the number the thinner the oil.    GL/5 is not an improvement of GL/4.  In fact using GL/5 in a GL/4 application can destroy the "soft or yellow" metals like brass found in older vw differentials and manual transmissions.  Manual transmissions contain soft metal "synchros" these floating gears help to align the gear to shift without grinding, it makes shifting smooth and requires less "double-clutching" techniques.  

Clutch based differentials require a limited slip agent.  Regardless of what Jeep says, I finally called Dana and gave them the build numbers from the diffs on my Jeep.  Because of the air-lockers these differentials are open and have no limited slip, therefore, the additive is a waste.  On a light duty vehicle, the additive on an open differential will not make any difference.  Keep in mind this is not the only error Chrysler has in the owners manual.  They list GL/5 for a manual transmission, the sulfer in GL/5 which helps the oil stick to the gear will eat the syncrhos.  Two strikes...

The Dana Spicer 110 is a different animal, this is heavy duty axle rated at 15,500#.  This is an open differential and used in a variety of over the road (OTR) applications.  What Dana recommends is GL/5 75W-90 synthetic, no additive.  In a heavy duty environment the LS additive can oxidize and has a shorter life with diminished efficacy cushioning the gears.  Only problem is trying to find it without buying a 50 gallon drum.  I called Mobile1, Lucas, Royal Purple, they all arbitrarily add some ls additive.  Finally, I stumbled onto Mobile Delvac in one gallon at Zoro (my fav anti-amazon site).  This is rated to 500k miles between drains.  For an RV this interval would never happen, but oil breaks down over time.  My rig has 40k miles on it, but its 10 years old.  I was shocked at the sludge and gunk that I vacuumed out of my s110.  Part of this may have been related to the sloppy stove pipe vent that was updated, that I never knew about.

Be kind to your differential.