Someone in the "help me buy an S2000" thread was questioning whether a used S2k will have had its diff fluid changed regularly and mentioned that it was important.

My question:: Why?

I changed my diff fluid in my truck 2 or 3 times - maybe 20 or 30k intervals... but now that there is no more metal glitter (from the gears wearing in) in it I don't ever plan to change it again.

Is the S2k any different? Is there any reason to regularly change the fluid?

It doesn't have slip discs or anything like in other LSDs... my understanding is that the LSD is entirely gear driven.

I figure after one or two changes it is tantamount to changing the air in your tires (same logic regarding changing the tranny fluid).

(BTW - my car only has 20k miles and both things have been changed... so if I'm wrong I haven't done any harm yet )

 

Further thoughts::

They talk about motor oil "breaking down" over time... but the real reason we change our motor oil so frequently is because of all the crap that gets into it from combustion... but oil in a gearbox doesn't have this problem.

Auto tranny fluid does seem to change color and wear out over time... I'm not sure why. Maybe because it really does undergo extreme temperatures and pressures.

 

And you think the fluid in a manual transmission or Torsen diff doesn't?

Gear oil (like the oil in your transmission and differential) is no different than other oil - it breaks down over time. Heat degrades it, and even once your transmission and differential "break in", there is still wear that occurs over time. If you never change the fluid in your diff or tranny, all those fine metal particles suspended in the oil from wear act as abrasive material. This is a vicious cycle - don't change the oil, abrasives build up, which in turn accelerates wear, which adds more abrasives to the oil, which further accelerates wear, etc. In addition, age and heat conspire to decrease the fluid's lubricity over time, which means more metal-to-metal contact, which means more wear, which means more fine abrasives in the oil, etc., etc...

Combustion byproducts are not the only contaminants to worry about in driveline lubricants.

(I'm not a powertrain engineer, I just play one at work )

 

You bring up a good point.

Honda recommends every 30K miles (or 2 years) which is probably adequate. Many that track the car or push it do more fluid changes, but except for the first one that gets rid of initial wear it probably is not really needed.

There have been a good number of diff failures (including mine) but that is because of an inadequate design (improved in later models), not because of lubrication.

 

Okay... so it does need to be changed.. but not too often.

I just wonder sometimes how much of the work enthusiasts like us do is just over-maintenance that doesn't accomplish anything.

Between my two vehicles I feel like I'm ALWAYS changing this fluid or that filter or modding this or that... packing bearings, changing brake pads....

Maybe one of these days I'll find a few minutes to actually work on my "project car"