wmuller150

Just changed the oil in my 95 differential after 23 years. Put in synthetic plus GM additive. Can't tell any difference on the outside but I suppose the gears and bearings like it. There is no drain plug. You might say changing the oil in your rear end is a real pain in the ***.

drcook

A cheap Harbor Freight fluid transfer pump works wonders for this.

ChumpVette

Joe C

- catch them on sale for about $5, or 20% off and a free flashlight -

95LT1ZF

I need to do this as well. Might have to make a trip back to HF later today.

drcook

The pump is the one I used.

https://www.harborfreight.com/multi-...ump-63144.html

Great for pumping it out, and then back in. My driveway has a slope to it. Just perfect for putting one end of the car on ramps and keeping it level. That is how I do my own oil changes comfortably on all our vehicles and work on other tasks.

Pete919

Sadly mine leaks enough that I only have to add fluid.

drcook

Don't forget that if you are adding straight diff oil, you are diluting the positraction additive. If it was me, I would mix up a batch at the required mix rate and use that to pump into the diff.

wmuller150

are the seals leaking?

c4cruiser

Some of the Corvette accessory catalogs used to offer a drain plug kit for the C4 diff. You had to drill a hole in the diff housing and install the self-tapping plug. It was important to locate the plug offset from the center to the passenger side of the housing so that you wouldn't drill into the ring gear or otherwise damage it. While the idea sounded good, the diff fluid didn't really require replacement if a stock C4 was driven "normally".

The HF pump does work for evacuating and refilling the gear oil and you can't beat the price of it! It's a good idea to suck out the old fluid and then add the GM Posi fluid first then the gear oil. The Posi fluid will mix quickly once you start driving the car.

DGXR

Yes it is a pain in the *** but thank God it is not done frequently. I have one of the drain plug kits but have not installed it yet... I have become hesitant to drill the case, for several reasons.

I don't care what your owner's manual says, all fluids *eventually* need to be changed. Anyone who says otherwise... either they are not aware of the effects of time, oxygen, and shear (wear), or they do not keep their vehicles very long.

My 1995 C4 had 52,000 miles when I bought it 4 years ago. That's not a lot of miles. But the differential oil was BLACK like tar, with a sparkly metallic sheen. Made me cringe, had to change it out. Glad I did.

TorchTarga94

I changed the fluid about 4 years ago at 115k miles. I don't plan to again for the life of the car.

Polizei45

The Harbor Freight pump worked great on the differential and if you have a manual transmission. I did both while it was up in the air.

Local2Ed

Do those Harbor Freight pumps pump a full stream?
I've had two of those pumps, not from Harbor Freight, and they just spit 80w90 gear oil on vehicles other than a Corvette.
The fluid was hot and it took a long time to pump out the small amount of fluid.

drcook

The HF pump I had worked exactly as intended, no spraying etc. Pumped the old out, pumped the new back in. (diff oil)

Joe C

same here. I remember the first time I used the HF pump - said to myself, this is too phuckin' easy! best part, they're cheap enough and not worth the clean-up effort. when finished, just a toss into the recycle bin.

vettespecial

when I had zip Corvette change out my 3:33 to a 4:11 I purchased the drain plug kit, and did the mod it come with a drill template that goes under a case bolt so it's no worries about drilling into the gear.

maddogwyatt

My '93 developed a "moaning" noise when manoeuvring after driving a few miles. Being in the UK where Corvettes are rare, I feared a diff or trans rebuild might be necessary. I actually had it booked into a transmission shop for a diagnosis, when I mentioned it to an American car specialist where it was having some work done. They knew exactly what it was, and prescribed the additive for posi-traction that the previous owner had omitted!! Needless to say. I now go to them for anything that isn't basic maintenance.

81c3

Yes,,, BMW likes to play that game too....(transmissions/Diffs..) meanwhile GM built many Transmissions for BMW through the 90's.... I think everything with fluid in it needs maintenance...

BigBilll

I'm thinking od getting a Zip diff for my '96 LT4 ... getting some strange noises now, 73,000 mixed miles on it... and I feel the 4.1 ratio will be a lot more fun than the 3.45 that I have. Happy with your Zip Diff?? All went well?? I can't find anyone here or near me on Liberal Long Island that has a clue...
Thanks in advance for any info!

BTW... Clearly NOT Liberal!