Changing Differential Oil

[CAJUN C4]

What's the best way to suck / siphon the 90W oil from the differential?

 

[Black Bart]

What's the best way to suck / siphon the 90W oil from the differential?

The way that I did mine was looked at a cutaway drawing to get a better idea just were to drill and I drilled a hole just off to the side of the pinion shaft and tapped it for 1/4" pipe thread and after draining and flushing several times with some cheap motor oil to make sure their were no shavings left I installed a 1/4" pipe plug.
Now when I want to change it I just remove the drain plug.
I have it made like GM should have done in the first place

 

[CAJUN C4]

That's what I did on my 84' But don't you have to remove the exhaust to get to it?

 

[Black Bart]

I have a 89 but it has custom exhaust but I think you can drill under the pinion shaft right in the center and get a socket in to change it.
Probably will need to remove pipes to drill through.
It is a dam shame that GM cant afford to put a drain in the radiator and gear boxes but what can you expect for a $50.000 car.
They could build these car much better but if they did then it would be 80 K

 

[Edmond]

They could build these car much better but if they did then it would be 80 K

We're just asking for too much, aren't we.

 

[jrzvette]

What's the best way to suck / siphon the 90W oil from the differential?

Right here: http://www.c4guru.com/articles/ChangingDifferentialFluid.pdf

 

[CAJUN C4]

How much oil does it hold?

 

[jrzvette]

How much oil does it hold?

According to the owners manual:

4 oz of additive
23 oz of gear oil.

I'm not sure of the size of the additive bottle (the write-up says two bottles). In any event I add the additive first then fill the rear with gear lube until the level is even with the botom of the fill hole.

 

[Vettefan87]

I think some of the diff oil you can get has the additive in it already.

 

[CAJUN C4]

I think some of the diff oil you can get has the additive in it already.

I think Amsoil says you might not need any additive.

 

[Edmond]

I think Amsoil says you might not need any additive.

Amsoil discourages the use of additives to their products because their products already have additives and additional additives might mess with the formula and shorten the life of the lube. One thing I have seen them sell an additive for are cars with Limited Slip, Positraction and Locking Differentials.

Check their stuff out: http://www.amsoil.com/products/gearlubes/index.aspx

 

[CAJUN C4]

Amsoil discourages the use of additives to their products because their products already have additives and additional additives might mess with the formula and shorten the life of the lube. One thing I have seen them sell an additive for are cars with Limited Slip, Positraction and Locking Differentials.

Check their stuff out: http://www.amsoil.com/products/gearlubes/index.aspx

All Vettes have Posi ? I guess I'll need it then.

 

[Louis Bartay]

rear end

I use Redline Synthetic 75W90 GL-5 Gear oil. Did not use the GM additive with it. My 96 LT4 Coupe has had Red Line in it for 6 years and 60,000 miles. Chage it every 30K. No problems so far.

 

[CAJUN C4]

According to the owners manual:

4 oz of additive
23 oz of gear oil.

I'm not sure of the size of the additive bottle (the write-up says two bottles). In any event I add the additive first then fill the rear with gear lube until the level is even with the botom of the fill hole.

My 96' owners manual says 1.5 Qt's plus additive.

 

[Louis Bartay]

RE

My 96' owners manual says 1.5 Qt's plus additive.

I just paid to have mine done while it was in the shop having a new ZF installed. They charged me $27.92 for two of GM# 89021671 80w-90 and $16.52 for 2 of GM# 1052358 Posi add. and $85.00 labor. Next time I will do it.:bash