Differential oil

[RonJ]

Hi, newbie type question here about my 85.

The differential oil is a bit low, so I thought I would drain what was there and refill it with fresh oil and additive.

Can't find a drain plug. How do I get the old oil out?? With a suction gun or vacuum pump?? And the filler is in such a nice spot .... HELP!!!

 

[Ken]

There is no drain plug, unless you install one as I did:

...you have to suck it out.

To fill it you either need patience and some ingenuity, or you need a transfer pump, such as the Mityvac.

 

[Bluesbrother]

Went to a class on the C4 by Gordon Killebrew this summer. He says to use suction gun to remove old fluid then refill with two (yes he emphasized 2) bottles of GM Posi fluid and then fill the remainder with Mobil 1 synthetic diff oil. He da man!

 

[brimis]

Hi, newbie type question here about my 85.

The differential oil is a bit low, so I thought I would drain what was there and refill it with fresh oil and additive.

Can't find a drain plug. How do I get the old oil out?? With a suction gun or vacuum pump?? And the filler is in such a nice spot .... HELP!!!

I have a 84 and the plug is on the right side of the differential looking at the car from the rear. My plug has an allen key head.
You can buy a suction kit at your local auto store. Remove the plug and suck out all or as much of the oil as you can. My unit called for just about 4 pints. You will know the differential is full when you see the oil start to run out of the hole. Be sure to add a 4 oz. bottle of GM limited slip additive. Also confirm proper weight oil. I believe I used 80/90 when I replaced my oil.
Brimis

 

[Ken]

... used 80/90 when I replaced my oil.

The book states:

• Lubricant type recommended: GL-5 gear lubricant
• Lubricant SAE viscosity: 80W or 80W-90 summer, winter or extreme cold.

_ken

 

[B17Crew]

This is a great thread -- great question... anybody have suggestions as to which would be a better route to go?

A. Use the Mityvac, or
B. Install a drain plug kit in the differential

Do you have to raise a C4 on jackstands to use the Mityvac or can you shimmy underneath with the car resting on its tires and perform the fluid change while on your back?

Thank you for any input!

B17Crew

 

[RonJ]

Thanks for the quick answers fellows!!!!

I have both a vacuum pump and a suction gun, I'll see which might be easiest to use.

Thanks again!!!!!!

 

[Ken]

... can you shimmy underneath with the car resting on its tires and perform the fluid change while on your back?

Well, it helps if you're a pinhead. :L

Seriously, there is little room between the ground and the differential (I forget and don't feel like looking up the exact clearance ) which makes it difficult to see what you're doing. It's better to have the car in the air, on jackstands, and level.

_ken

 

[B17Crew]

Well, it helps if you're a pinhead. :L

Seriously, there is little room between the ground and the differential (I forget and don't feel like looking up the exact clearance ) which makes it difficult to see what you're doing. It's better to have the car in the air, on jackstands, and level.

_ken

Ken,
thanks for the response, I've never changed the rear diff. fluid myself, I've always had the dealer do it.

Changing the diff. fluid is one more thing that I want to bring “in-house”.
I hate going to the dealer for anything except to drool over the new Corvettes on the showroom floor.

B17Crew