C4in mesa

I just got under my 1992 C4 and changed the gear oil in the differential. It was very dark in color. 74k miles on the odometer. I want to just remind everyone to change your gear oil.

ghlkal

Good idea.

And, it isn't just the fact that you've got 75K miles on it ... it's also the fact that the gear oil has been in there for a quarter century or more.

mickey5

Don't forget the ZF6 if you have one. Used the manual synchro oil from GM. Works well.

C4in mesa

I have Redline brand synchro gear oil. I asked a reputable guy who lives here in the valley what oil to buy? I looked at the drain plug when I was under the car. Wish GM had done the same for the rear hub. I will get it done this week.

bac22

Color is not an indicator of oil viscosity or replacement, but yes it should be changed on a regular basis.

C4in mesa

Here's some Dana 44 Dana 36 trivia, the 44 Limited Slip tag is metal and the Dana 36 is plastic. That's what's on my two C4's.

JrRifleCoach

Like every 50K miles?

radar502

First things first MAKE SURE THE plug were you put the oil back in is out FIRST,sometines the refill plug can be a bitch to get out yes I have seen people darn the oil out and could not the get the return oil plug OUT.. Just an FYI for first timers..

2LZ

Have the Mobil 1 LS goo and need to do it soon. Just hit the 500 mile break-in for the new 3.54's.

Paul Workman

For what it's worth....

The ZF6 on my base 95 car failed and had to be replaced (a new one was available at the time - cheaper than a repair).

According to Bill Boudreau, the failure was partially due to a flaw in the design in conjunction with the original fill.

The remedy was to open up the stock galleries that passed oil to the reverse gear on the lower idler shaft, AND/OR switching to a full synthetic oil.

The prevailing recommendation centered around a particular oil available from BMW dealers which is no longer available.

In its place, full synthetic gear oils including Red Line heavy gear oil, Amsoil Syncromesh gear oil, Mobil 1 synthetic gear oil seem to make the ZF6 work well with no tendency for the lubrication related (seizing) issue experienced by some ZF6 owners.

Corvette differentials require a friction modifier to be added to the factory recommended gear oil change. However, some of the aftermarket oils intended for used in the differentials have a friction modifier in them and may not require additional modifier. Refer to the manufacture of the gear oil and only add additional modifier as needed to quiet "chattering" when turning.

Per recommendations of trusted mechanics and research, I'm using Red Line full synthetic gear oil in both the ZF6 and the Dana 44 and change not more than GM recommended mileage intervals (every other season - 'just because').

DGXR

Thanks for the reminder... also good to mention LS additive for those differentials with clutches. Anyway, this is one of the first services I did on my car. It had 52,000 miles and the previous owner said "all fluids were changed." Well apparently he meant only the fluids that are recommended to be changed, so the manual transmission oil and differential gear oil were not changed.
The differential oil was black like tar with tiny sparkles throughout. Not good. So I changed it, drove it about 2,000 miles and changed it again... essentially this was a "rinse." (The rinse oil was noticeably dark brown after the 2k miles.) Current gear oil has been run for 8,000 miles and still looks perfectly clean.