searay340

This is the first time for the Rear End Oil to be changed out. The PO never changed it out, has 70,000 miles on a Daily driven 99 C5. I want to use GM Lubs but checking with the Owners manual and finding now there are several choices all from AC Delco. Here is what I narrowed it down to:
Delco 10-4034LS 75w90
Delco 10-4016 75w90 but may need the LS additive
GM 75w90 Synthetic Not sure if it has LS in it or not.

I'm leaning to the 10-4034LS as it has the LS additive in it already. SO what is the one to use??

Bill Curlee

You MUST use a lube that has the LIMITED SLIP ADDATIVE in it

OR

Put a lube in that doesn't and then ADD it.

If you don't, the differential clutches will be MUCHO UNHAPPY and chatter and moan when doing tight turns.

Any synthetic 75/90 LS oil will work fine.

Bill

craig_vette

Forgive my stupidity but what's the rear end oil? Is it not good for lifetime of vehicle? I have a 2000 FRC with 74K and doubt it's ever been changed (I've owned for 5 months).

searay340

Bill, Thank you for the reply. I would ideally like to use a synthetic which I do not think the 10-4034LS is a Synthetic. I do see Moble1 LS, what others have the LS in them? I think the GM LS additive can be mixed into their Synthetic part number 12378261 75w90.

Bill Curlee

The lubricant inside the differential is a thick 75/90 weight lubricant oil.
Your C5 differential has Limited Slip Clutches inside the unit. The clutches require a limited Slip additive to allow the clutches to slip at a specific coefficient of friction. They allow BOTH wheels to propel the car forward for better traction BUT, when you turn the vehicle the inside rear wheel turns slower than the outside wheel. The clutches allow the wheels to SLIP to prevent the car from hopping around tight corners.

The differential also generates a lot of heat in the process of converting driveshaft rotation to wheel rotation via ring and pinion gears.

The heat and clutch wear particles causes the oil to get dirty and also break down and looses it ability to properly lubricate the gears and clutches.

It is possible to not change it BUT, there are several problems with never checking or changing it.

1. Is it at the proper level? Cant tell without removing the fill plug.
2. Is it causing my gears, bearings and clutches to wear and cause noise and performance issues?
3. Can I afford to purchase and install a new differential if it wears out due to dirty degraded lube?


The oil gets VERY dirty and full of particles around 45-50K miles. That's about as far as I would go before I change mine.

GM doesn't care if the differential wears out after the warranty is over. Selling replacement parts is how they make a lot of money

Black 03 Z06

I used Mobil One gear oil with the limited slip additive already in the jug.

Used a marine lower unit gear oil changer to pump the new fluid in. Make sure you do not drop the hose end in the housing.

Put the gear oil in hot water as you pump it in, it is heavy, sticky stuff and heating it makes the pumping a whole lot easier. Once you down to about 3/4's of the way fill up the existing jug or switch to another, makes it a whole lot easier to pump when the jug is full.

Order two new crush washers from GM BEFORE you start the process. They are expensive, however if the existing ones are deformed you are wasting your time and money, it will leak.

Make sure the car is securely jacked up and sitting level.

Easy job but it is messy and the stuff stinks. Good luck

Borntorun04/17

I just did mine two weeks ago. I have a 04 auto coupe with 17,000 miles on car. I wasn't worried about mileage but that it's been 12 years and no record of differential oil being changed. Lube 88900401 & additive 88900330 . If I am reading receipt correct.

craig_vette

Here's a video on changing rear differential fluid. Any suggestions on which kind of oil pump to buy?

caddman11

I just did mine and used Amsoil, no need to heat anything. I bought a $6 pump from Autozone that worked great. Car has 44,000 miles, don't know when or if it was ever done, the was some metal sparklies in the bottom of the pan but not bad. Job took all of about 10 minutes.

garline14

I used amsoil as well, its some good quality oil. It already had the limited slip additive in it already. Bought a 5 dollar pump in amazon and went to work. A very easy job to do. Make sure u do go to a empty parking lot and do some figure 8's, i also drove the car easy for the first 300 miles just so I didnt damage anything.

BATM4N

Hey Bill. How many years would you suggest it needs to be changed out for those with 12 year old cars but low mileage?

Thanks

Bill Curlee

Its not age that makes it go bad. Its miles... The more wear particles in it, the less protective it is for the gears.



BC

ironranger

I replaced mine recently at 45k with Amsoil Severe Gear Lube (SVG) 75w-90. Limited slip additive was added as I don't believe it is in the Amsoil.

buckeye1872

I changed mine this spring at 17k miles. I went with ACDelco 10-4034 Dexron LS 75W-90 Gear Oil. Used Plews 55001 Lubrimatic Fluid Quart Pump.

bigcypress

bought a 2004 at ''buds'' about three years ago and when it was delivered the diff sounded terrible so we had the fluid changed and additive put in at local dealer [ mileage was around 29,000] . mileage is now 30,020 and diff still sounds bad . local dealer says give it more time and miles . all thoughts appreciated . i don't feel i'm stealing this thread because your info will help everyone . . peace

bigcypress

ttt

Corvette#2

I changed my original differential oil last summer.

I used the "LS" AC Delco fluid that comes premixed with limited slip additive.
It smells good, like grapes. I read the AC Delco 75w90 fluid is full synthetic, it's manufactured by a Canadian company for GM.

Should last at least 100k miles.

Ron C!

And the tip of the day for this job... ALWAYS remove the fill plug before draining the oil out.

Corvette#2

Also on the first drive, do figure 8's in a parking lot to get the new fluid distributed into the clutch packs.

And don't use full throttle for the first 300 miles (to avoid damaging the ring and pinion according to the service manual) after changing the gear oil. The anti-wear additives need a few heat cycles before they are 100% good to go.

Dan H.

I use amsoil severe gear 75-90. My vendor said that I didn't need to add friction modifier as it was already in there. This is copied from amsoil website.

AMSOIL Severe Gear is compatible with most limited-slip differentials. If limited-slip differential chatter occurs, add AMSOIL Slip Lock® friction modifier additive.


If your getting started with servicing your own c5, froggy has a ton of good videos that help out.