I didn't expect this when I change the fluid in my rear diff.

I was shocked when I changed my rear diff fluid last night. I AM using synthetic (Mobile 1 75-90) so I figured I could go a good bit longer. I put this stuff in 50k miles ago so I thought it would be due for a change. I remeber when I drained the stock fluid it looked really dark and dirty with no clearness whatsoever.

I suppose next time I will let it go longer because even after 50k it looked extremely clear still as you can see below. What kind of intervals are you guys getting from synthetic rear diff fluids?

 

Get it analyzed before you start extending intervals. Looks is just one part of the equation...

 

Not sure, but isn't it in the manual to have it changed at 100,000 miles?

 

Looks pretty normal to me for 50K. Drain it through a coffee filter and see if you have any magnetic particles larger than what you already picked up.

 

My diff oil looked bad at 900 miles. When you build differentials you run them through a break in cycle and change the oil before running them as normal (similar to engine break in). Once that initial break in takes place the ongoing wear should be minimal.

 

I'm pretty sure it's normal for oil to go dark/black. Doesn't mean there is a problem!

 

I am just pointing out the fact the Mobile 1 stuff looks much cleaner than the regular ol' oil that I saw come out of there at 45k miles.

I suppose for $30 worth of oil and the 30 minutes it takes to do this service it is a deal. There's just something about seeing drained fluids look so nice when they come out. Makes me feel like my diff is nice and clean inside as well.

I may try the coffee filter trick. I DID run a strong magnet through the used stuff and you can kinda see from the pic what it picked up.

 

Heh, I went 15 years and 145k miles on the original diff, trans, trans case oil in my 1st gen. Recently lifted and regeared and its all shiny new again. I changed after 1k miles following the regear.