Differential oil change

My car manual says I need to change the differential oil at 70k miles. I went to a tune and lube and they want $100 for a “flush”. I say draining and filling the rear end with new oil will do the job and a “flush” is just a gimmick to get more $$. Am I right or wrong?

Drain and refill. There is little to be gained from “flushing” . . One of the easiest jobs and one that’s tough to mess up, unless you are a quick lube. Heck, a dealer isn’t that expensive. But, I definitely would have it serviced.
They are really trying to flush your pockets of cash.

I’ve heard of flushing a differential.

Remove the cover or plug and refill.


On the off chance that your car is a Honda, do NOT take it to a quick lube place for differential fluid. Hondas require special differential fluid, and the quick lube place may not have it or put the wrong fluid in.

This is a perfect example of why the OP should avoid chain oil change places.
Aside from the lack of expertise on the part of their employees, they tend to push services that are absolutely not needed and–in many cases–are no cheaper than what a dealership would charge.

The OP should go to an independent mechanic and simply have the diff drained & refilled.

that reminds me, time to dip my finger in my rear

Well, you see, on the Hupmobile, …
C’mon, man, tell us what we’re talking about here!

Ya know you really have to know your car! I am doing mine this spring, 2 quarts at 32 bucks from the dealer, but it has the limited slip, many people have done straight but auto parts store recommended an additional add on. Go for oem!


Lots of advise for not knowing what kind of vehicle the OP is driving…

Well, my truck has a limited slip rear axle that calls for special synthetic gear lube with an LSD additive. 3 quarts and the additive cost me $75. Drain and fill was at least easy part. At least it has an extended change interval. But the OP is right. A ‘flush’ just flushes your wallet. Drain and fill is all that is required.

Some differentials have drain plugs…Some don’t…Some have a back cover that must be removed and then replaced. Some don’t. Others have a removable “pumpkin” but they usually have a drain plug…Some take GL-5 gear oil, some take other, special lubricants plus even more special additives…“Flush?” I’d like to see how they do that…

GM’s Posttraction recommended fluid changes were 20,000 miles for normal service and 12,000 miles while trailer towing. However, this info was not in the normal owners manual of my 1988 Caprice; it was a supplementary document.

@BustedKnuckles rightly found that synthetic fluid was better because of the high heat buildup. My mechanic added twice the required additive and we could extend the drain interval that way. If not enough additive was put in the differential would shudder in low speed sharp turns. I paid $95 for the fluid change and additive.

I learned that not servicing it properly meant an early death for many owner’s machines.

Not sure whether John Lennon used the LSD addditive in his psychodelic Rolls Royce!

When I changed diff fluid at the shop I just used a hand pump through the fill plug, didn’t remover the cover. Probably got out about 90% of the fluid, which was plenty enough IMO.

Texases, a better way is to remove the cover. That way you can get everything including any sediment or metallic wear products at the bottom of the case similar to inspecting the contents of a transmission cover. What you did, however, is probably good enough.

I agree. We’d do it this way for a ‘normal’ swap, if there was an issue we’d remove the cover. At the time ('73 or so) we didn’t worry much about rear diffs, except for the few limited slip ones we saw.

I hear you. Would like to find out what kind of vehicle we are talking about.

The word “flush” seems to find it’s way into a lot maintenance plans regardless what the component is in quick lubes. I just wonder why these businesses that promote it’s a use seem to feel that the reading programs in all schools have really deteriorated over the years. I have yet to see the word “flush” used in the maintenance of any component in my owner’s manuals. Guess education in general has not kept up with modern vocabulary and those responsible for car manuals are a bad influence on the youth of our nation. Neither is doing their job .