DIY: Changing the oil in a base C6 rear axle / differential
If you are experiencing the common differential chatter noise on turns when cold (rubbing, scraping, clunking, grinding or chatter sound), changing the differential lubricant will rid the noise instantly, at least after doing a few figure 8's with the new lubricant in place.
For some, a simple differential lube change has proven to be the cure for many thousands of miles, and for others, it has only helped for just a few thousand miles. If you prefer to avoid the dealership and wish to take immediate action, change your differential fluid and you will get rid of the chatter noise for likely up to a few thousand miles minimum if not much more. It's a good first step in any case.
Overall, changing the oil in a base C6 rear axle / differential is very easy. If it’s your first time, this DIY article will at least give you an idea of what to expect.
This refers to base C6s only. Z06s have differential coolers (base C6's do not) and require a bit more effort. Z06s and export vehicles have different axle oil capacities than the base C6 as well.
First, run the car a while to get the axle oil warm. I ran my car about 40 miles. When I got back, the axle case was quite hot to the touch. 20 minutes after shutting off the engine, the mufflers were finally cool but the axle case was still hot. With this in mind, it is a good idea to wait about a half hour after shutting off the engine until the exhaust system cools down so you do not severely burn yourself… the axle and axle oil will still be very warm for good drainage.
You’ll need to get the car up off the ground a bit as in photos, but keep car LEVEL. First choice would be to use a real lift. Second choice, back the car up on Race Ramps and then jack the front end in order to level the car. Last choice (most laborious), jack the car from both front and rear.
Since you need to access the rear axle from the rear, you cannot block the rear with a jack. I had initially tried to use my 4-point jack system
, but was not able to access the axle plugs with the rear jack and cross member adapter in the way. I had to add stands under the rear puck locations and then remove the rear jack and cross member adapter. I then added two extra screw jacks under the rear “preferred” jacking locations for extra support and safety. This worked out fine. But next time I think I’ll try backing up on ramps… would be easier.
The axle case has two plugs that must be removed… a fill plug and drain plug. The fill plug is on the rear vertical side of the case, the drain plug is on the bottom horizontal side of the case. Both plugs exist on the right half of the case (passenger side). Both plugs are identical in size / type.
Put some cardboard down on the floor and have some rags on hand as you will inevitably spill / splash some oil. Place a drain pan directly under the drain and fill plugs.
Clean the areas around both plugs. Using a 3/8” drive swivel arm socket wrench and 10mm allen socket of about 1 – ¾” total length (as shown), loosen and remove the fill plug. (Always remove the fill plug before removing the drain plug)
There are different ways of accessing this plug but the photos show one method that seems to work well and is easy. Note in the photos that the socket wrench handle extends down through the middle of the aluminum cross member. Some oil may start to drip out. If the plug is very tight, use a piece of pipe over your socket handle for leverage. Both my plugs did not
require much effort to loosen… pipe was not needed.
Next, loosen and remove the drain plug. The oil will come blasting out and may splash in the pan so shield your face. Allow the axle to drain for a while. Mine was still dripping 12 hours later.
Clean the drain plug and area around the drain hole and install drain plug. Torque to 35 Nm or 26 lb/ft. I chose to torque by hand… basically just got it nice and snug. Do not overtighten. You could get a torque wrench on the drain plug easily if you wanted, but not on the fill plug. If you are not sure about the torque “feel”, use a torque wrench on the drain plug in order to get a good “feel” for what it should be, then do your best to apply that same “feel” to the fill plug using your regular socket wrench.
Time to refill the axle:
IMPORTANT: Read the latest GM TSB regarding rear axle chatter to determine which GM gear oil / additive and amounts you should be using. This info has changed over the years and is subject to further periodic change. The latest axle TSB (as well as previous axle TSBs) can be found in post #2 of this thread:
As of January 2008, the oil specified for use in the Corvette differential is Dextron LS Gear Oil 75W-90, part #88862624 (#88862625 in Canada)
. No additive is required or recommended – just add straight Dextron LS 75W-90 only.
Your C6 differential requires roughly 2 quarts (check manual and/or TSB for exact specs for your year / model)
. But be sure to have at least 3 quarts of oil handy since it is almost impossible to squeeze all the oil out of the bottles into the axle, plus you’ll likely spill some anyway.
Since you will not be able to get the oil bottles higher than the fill hole, you must pump or squeeze the oil up into the hole.
The GM oil bottles come with extra pointed nozzle caps and a short piece of clear tubing. I found this set up to be too short and too small a diameter, plus after a while the nozzle gets oily and the hose starts slipping off the nozzle no matter what you do. One solution is to buy an aftermarket fill tube at the local auto store. The product I found (at Pep Boys) is made by Hopkins Manufacturing, called a “FloTool”… it threads right onto the GM oil bottles and has a 12” long section of clear tubing attached… twice as long and larger diameter than what you get with the GM oil bottle. This FloTool fit really nice and made the oil fill a breeze.
Insert the tubing into the fill hole of the axle holding the gear oil bottle up between the mufflers and squeeze the bottle. You will see the oil flow through the tube and into the axle. One headache though is that you can only get about half or two thirds the contents of the bottle into the axle even if you squeeze / crush the bottle as hard as you can… so you need to refill the bottle and repeat. This is the main reason to have at least one extra bottle of gear oil on hand. I guess you’d need a pump of some type to really empty the entire bottle into the axle... but not necessary because whatever oil does not make it into the axle can be saved for the next fluid change.
Note: I am holding the bottle upside down in the photo – was just posing in that shot – bottle nozzle should be as low as you can get it with relation to the rest of the bottle.
Add oil to the differential until oil starts dripping out of the axle oil fill hole. Then allow the oil to drip out for a bit to make sure the axle is not overfull. Again, it's important that the car is level. Reinstall fill plug.
Once everything is buttoned up, it is recommended (per TSB) to run the car in a tight "figure 8" pattern about 8 or 10 times as soon as you possibly can after the oil swap. Many consider this an important step so do not overlook it.
Thanks to the forum and its members for much of the info in this DIY post!
I was just alerted by member Paulct
that the axle drain plug on 2005 models (at least on his 2005) sits above the leaf spring so that you cannot get an allen wrench straight in from below. The spring is in the way. An L-shaped allen wrench tool must be used so that it can be pivoted above the leaf spring. On my 2006 model, the spring is NOT in the way of the plug and you can easily get an allen socket straight into the plug from below. (see photos below) So if you have an `06 or newer C6, you will only need a good allen socket and socket wrench to do the entire job. If you have an `05 model, you will ALSO need an L-shaped allen tool and most likely a short piece of small diameter pipe for extra leverage on the L-shaped wrench. Thanks Paulct
for the below "2005" photos.
We suspect this difference in drain plug position has to do with the differential case change between 2005 and 2006. For more info regarding differential differences between `05 and `06 models, click below link: