Rear Differential

The VTM-4 is the type of rear differential used in the MDX. The terms for the mDX are therefore interchangeable.

There is a TSB for the MDX that emphasizes the initial interval for the rear diff (VTM) must be 7500 miles. http://www.hondacuraworld.com/bulletins/MDX/SB00-035.pdf They use a special fluid and you'll get proper break-in. I'm not surprised a dealership is going AGAINST a factory recommendation- despite Acura's assurance that "ask your dealer- they are factory trained and know what is best for your new vehicle" (right)

I've done three changes, and eack time the fluid I drained out was perfect. Still, follow the factory schedule, and don't buy the dealers' garbage.

Use ONLY VTM4 fluid. this is the only stuff you should put in the Honda Variable Torque Management Rear differential... ($19 a gallon)

On another front, watch the dealer on the transmission service. 30k (severe) or 45k (normal service)- heard of one guy that had a dealer suggest it every 15k...

Ard

Easier than the engine oil...

Yep. Two bolts- actually you take a 3/8" socket drive extension and insert that directly into the bolt head (has a square hole)

The fill is super easy: use a $4 hand pump from the auto parts store, and just pump into the fill until it runs out. Remove the nozzle, When it stops, the level is *just* at the edge of the hole. Replace the bolt and tighten.

Most differentials are 'on all the time', that is they are simply changing the drive shaft rotation to 2 90 degree outputs. A simple gear mechanism. Perhaps with a viscous coupling for Limited slip.

The VTM4 is active, and is controlled by electromagnetic clutches, and gets a lot of on-off-on-off. This is why the fluid is critical, and the change intervals are frequent. My RWD Q45 has a service to check the rear diff at 90k. Prior to that, you only look inside if you see a leak. For conventional diffs, I'd recommend Synthetic and change it at 60k.

Ard

Both



That is, new washers AND properly tightening...

The part numbers for the two washers are (94109-20000 and 90471-PX4-000). If I recall, one is 18 and the other is 20mm. (Some dealers are only selling the first number for both locations...I don't know why.)

35 ft-lbs for each

Ard

Bruce-


Where ya going with this?

Just because there is "nothing to indicate any particular break-in element to the fluid" are you claiming this to be proof there is, in fact, nothing special about the fluid?

(In fact Acura has indicated otherwise, but not in writing.)

Likewise, there MAY be competing issues with changing the fluid: Acura engineers may have wanted a 7500 mile interval on breakin, but also realized that fluid age was an issue, and therefore limited it to a 6 month limit. Again, being able to construct a scenario in which the 6 month limit occurs at 3000 miles does not mean it should be changed at 3000 miles, or even that it is equal to change it at 3000 versus 7500.

We really have no idea what is optimal, so I just follow the MANUFACTURERS recommendations (not the dealer).

JR-

I really don't know the specific technical answer to that question.

Of course, we should all follow the maintenance schedule, just to protect the warranty.

Oil doesn't have a 'shelf life', so why would it need to be replaced if it sat in your crankcase for 6 months with zero miles versus in the box?!

I think the answer is elsewhere:

In some motor applications, they do not track mileage: my tractor, jet engines, trucks, etc all use hour meters that measure running time. Running time is THE measure for wear and oil performance. Look over at theCastrol/Valvoline/Mobil sites and many technical reports list hours not miles. In fact, 50 hours is a typical interval for industrial diesel oil change. Just so happens that 50 hours at 60 MPH is... 3000 miles.

But, if you only drive 8 miles a day to work, at 8 miles an hour, you will rack up 60 hours in three months- but only 480 miles.

Since the MDX (and any other passenger vehicle in the US) has no engine runtime meter, the time/distance metric is likely the best compromise.

It is also the reason the "severe Service schedule" includes short trips, idling, etc.

My 2 cents

Ard