Do you have a fill/drain plug?

Well I guess that settles that. How often are you supposed to change the fluid in a differential? I'm putting in a limited slip unit while I have it apart, I guess that means you should change the oil prior to break downs. Should I put in a drain plug or take it apart every time?

I use a vacuum/filler pump.  One side sucks the old oil out of the diff and the other pumps the new into it.  At different times!  They are cheap and are designed just for diffs w/o drain plugs and trannys.  I've had mine for a long time because I don't have to change that oil very often.  They can be had at any parts store.  You are ging to need one anyway to refill it.

Last edited by lowercasesteve (2/22/2017 11:49 AM)

Chaplin wrote:

I was thinking about this the other day...my new axle from Strange came with the exact same instructions, drain the oil at 500 miles. I don't think any new car manufacturer tells you to drain the diff after 500 miles, the service interval is usually measured in the 10s of thousands of miles. Wonder why the aftermarket requires it when the OEMs don't?

That's because OEM gears are "run in" prior to installation on a fixture at the factory, so they are broken in before the car leaves the assembly line. 

I'd like to tag on to this topic.  Any recommendations for what brand/type of fluid to use in my differential?  My recently rebuilt and dry differential is essential a stock 1969 Mustang rear end.  Any suggestions (and why)?  Thanks.

Last edited by hydrantwrench (4/30/2017 10:45 AM)

Have the gears been broken in yet?  If not DO NOT use synthetic oil.  Just like in an engine it will prevent proper break in.  Now, once the gears are broken in and its fluid change time go ahead and run synthetic fluid.  I too prefer Amsoil.  A bit pricey, but really, really good stuff. 

Last edited by TKOPerformance (5/01/2017 4:38 AM)

Thanks all.

I got a push-pull pump at my local parts store.  Small and cheap.  Just tell them what you want to do and they will take care of it.  You can also use it to refill the diff when ready.

Having a vacuum pump to pull the old gear oil out of the housing (if no drain plug) is good for reducing the mess prior to pulling the 3rd member loose from the housing.

Simply suctioning the old gear oil out and then immediately refilling it will not get all the debris out of the housing sump/inside the housing tubes. The inside of the housing will have to be wiped out to remove it all (this is best done with acetone and lint-free rags. If you don't have any lint-free rags, Tampons will suffice --they're good for other things besides female problems). The only way to do that is to remove the 3rd member from the housing.

While the 3rd member is out, this will also give you the opportunity to run an eyeball over the ring/pinion gears and to look at the splines on the axles to check their condition and the condition of the axle bearings. If you don't pull'em, you're not going to see'em to know what is or isn't going on in there.  ...what's the saying? An ounce of prevention is worth a pound of cure?