Hi,

Can somebody please describe me how I should check differential oil level and how does the oil changing procedure go? I remember my Jeep had a rubber cap which I could pull out and stick my finger in to feel the level. I'm not sure if the Corvette has it.

What tools do I need?

Thanks.

 

recently did my diff. Need to get car off ground. remove square threaded plug on pass side of diff.
Then used a hand pump to remove the fluids. Put in correct posi additive and diff fluid, do some figures 8's for about 5 mins. and all good. Took about an hour of my day. Easier if u have a lift.

 

There is a fill plug on the passenger side of the diff that you remove. You can stick a small finger in there or use a mirror+light and make sure the diff fluid is near the bottom of the drain hole. If you wan to replace it, most people go to the auto parts store and buy a little bulb shaped hand pump or take the diff out and remove the cover.

I think for my 79 I used 1 little thing of LSD additive, plus it took another 1.25-1.5 bottles of gear oil to fill it back up to the plug again.

 

I used a turkey baster and a length of tube to suck out old fluid. It won't get it all, but the only other way is to remove the diff or open the back cover and let it drain. Some guys install a drain plug. To fill, use a squeeze bottle and a length of tubing and fill until it starts to drain out of the fill hole. Don't forget GM posi additive.

Temvette72

 

Thanks for the quick answers. I believe I don't really need to get the 'wheels' off the ground, I just need to get under the car? We have a channel in our garage from old times and today I tried to use it first time in my life. I guess I could do it from under there?

What's the type of oil needed? Is it manual transmission fluid where I need to add the GM posi additive?

Is it some special bolt on the diff which means I need to buy some new tool?

 

The fill plug could be either one of two types- a 3/8 drive female square or a square male plug you can use a wrench on. Plug out, you should be able to touch the grease with your finger. To drain, it's a PITA- a suction gun or remove the differential from the car. No "drain" plug unless someone installed one. The only thing you'll need is the new grease (2 quarts of 85W-90 gear oil, and 2 bottles of limited slip lube)

Congrats on having a pit (channel) in your garage- not may guys have that available to them.

 

The proper fill level for the diffy is to fill with differential gear fluid (thick stuff) and a bottle of posi-traction additive until the fluid just starts to run out the fill hole. If you want to drain it, go drive it a while so the fluid heats and loses viscosity (thins out). Wear gloves and use turkey baster and piece of rubber hose. Suck out as much as you can. Fill half-way with gear lube...add posi-trac additive...fill rest of the way with gear lube. Drive figure-8's in a parking lot for a while.

 

I did the same thing except I taped some bailing wire to the hose so I could force it down to the bottom of the case.

 

I appreciate the tips here on changing the Diff fluid, too. I used most of them. And took some pics in case someone else needs them.

I took the spare tire out and removed the right rear spare cover bolt to access the Diff clearly. Also, I removed the right rear tire. You may not have to do all this, I wanted the room to work and take some pictures.

Here is the '79 L82's Diff Filler plug on the passenger side of the Diff. The red flag is covered with junk. I used a 12-point 3/4" socket to remove it. It worked perfectly on the square head.



Next, I had a $3 siphon from Walmart that I wrapped a length of stiff wire around. (The bailing wire was a great suggestion to keep the tube stiff!) I was able to get the tube forward and down in the bottom as far as I could tell, then got the siphon going. The fluid was still pretty thick--I should have warmed it up more. But it slowly came out. Took over an hour to siphon out, but no worries, I had other things to check over.



Then, to fill the fluid back, I used this green flexible 50 cent oil can extender (Walmart) that screwed on the end of the GM Axle Lube bottle. I cut the threads off the other end to fit it into the Axle filler hole with a little tuck into the top. The 4 oz. GM additive bottle just squirted into the hole without the extender.



I filled, as suggested above, Axle Lube (23 oz.)--Additive (4 oz.)--Axle Lube until full (23+ oz.). The green extender was nice because you could see fluid through it and tell when the fluid was at the top of the filler hole. I confirmed it full by touching the tip of my finger into fluid right at the level of the fill hole.

The torque for the Axle Filler plug was 20 Ft-lb on the '79. (Shop Manual Spec)

 

I did the same, but I put the wire inside the hose with no tape.