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I am probably going to tackle the rear diff fluid swap in the next few days.
I have looked in both the Clymer and the Corvette service books and neither say what type of fluid. But both mention the friction additive to prevent chatter.
I have seen several fluids like Mobil1 and Royal Purple that both say they have friction additive and right beside them on the shelf is friction additive.
The manuals both say read the tag on the diff drain plug but was hoping for a little more information from the brain trust.
Its a 1988 C4 with Auto Trans.
How much fluid will I need (I know to fill till it starts to drip out, but is that 1 quart, 2 or 3???)
Try it WITHOUT the additive. Fill it till it comes out stop it. Take it for a drive and see if it chatters. If it does, suck out a little more than what the contents of the additive is, put additive in and spin the wheels around a bit, top it off.
You will need 2 quarts. I used Royal Purple got 2 quarts and some is left over. RP is pricey but I'm not thinking I'll have to change it for a while. There is no factory installed drain plug. To remove fluid you either separate batwing from housing or get a little suction pump to draw fluid out. There are small suction pumps designed to pull oil out of marine engine dipstick tubes where access to oil pan is limited. I would recommend small pump method. Be care refilling that tube doesn't fall into diff. If it does you will likely have to separate batwing to retrieve it.
FWIW - I personally like Castrol products. on my 85, I used Castrol "limited slip" 80W-90 gear oil when servicing the differential. nowhere on the bottle does it say anything about additive, but since is clearly states "limited slip," i'm assuming it has the additive. however, just to be on the safe side, I first added 4 ounces of GM Fluid 88900330 Limited Slip Axle Lubricant Additive, and topped the fill off with approximately 1.5 quarts of the Castrol 80W-90. it's been about 1000 miles since my differential service, and no issues (155K on the original dana 36)
Your 1988 automatic came with the Dana 36 axle, which holds about 1.5 quarts total. Few people can remove all the oil without tapping a drain plug. So if you are using the hand pump/vacuum pump method, realistically you will probably add 1.2-1.3 quarts. I have the Dana 44 and used Mobil 1 synthetic gear lube LS (limited slip) without any extra friction additive, works fine for normal street use. No chatter during low-speed maneuvers, and confirmed power is going to both wheels
You will need 2 quarts. I used Royal Purple got 2 quarts and some is left over. RP is pricey but I'm not thinking I'll have to change it for a while. There is no factory installed drain plug. To remove fluid you either separate batwing from housing or get a little suction pump to draw fluid out. There are small suction pumps designed to pull oil out of marine engine dipstick tubes where access to oil pan is limited. I would recommend small pump method. Be care refilling that tube doesn't fall into diff. If it does you will likely have to separate batwing to retrieve it.
Separate the batwing to get the fluid out? I just changed the seals on my diff and I can't imagine doing all that work just to remove a little extra fluid that you can't get with the pump.
Separate the batwing to get the fluid out? I just changed the seals on my diff and I can't imagine doing all that work just to remove a little extra fluid that you can't get with the pump.
It isn't the extra fluid I would care about. It is to inspect the system to see if there are sediments or a broken tooth, etc
As aklim stated - my suggestion would be to try the fluid alone with no additive and if you experience problems - go back and put the additive in.
I've done the dana 44 diff fluid change on a couple of C4's. I used Redline 75W-90 gear oil, no additive, and the cars were fine (literally several thousand miles of track use later).
Putting the new fluid into the diff is not the easiest thing in the world - having a small hand operated fluid transfer pump and a few feet of clear tubing available will probably make that part of the job go a bit easier. You'll certainly need 2 quarts to do the job - you just can't get all the fluid out of the containers and into the diff no matter what you try....
Purchase a drill pump. It's a small pump attachment for your electric drill. It will be your best friend for filling trannys and diffs. Drill Pump There are cheaper ones on ebay, and if they don't come with hoses, just pick some up at home depot/lowes
I'd say to drop the rear end today, drill a hole and put a drain plug in so you can drain out all the fluid ESPECIALLY the last few ounces to see if there is any silvery stuff in it.
Just about every good synthetic gear oil already has limited slip additive in it,
2 qts is sufficient, unless you spill a lot of course
I'd get 3. You can keep the 3rd if you don't use it. I really hate running to the parts store or the supplier for a couple more ounces because you knocked over the bottle and you are now short a few ounces or something stupid happened.
I'd get 3. You can keep the 3rd if you don't use it. I really hate running to the parts store or the supplier for a couple more ounces because you knocked over the bottle and you are now short a few ounces or something stupid happened.
I got 2 and used suction gun got 1+1/2 plus out refilled with mobil one ls did right s after running car some 30 miles while it was still hot/warm,will do again after 1000 miles or so to get 90%+ changed.
Last edited by A Peter C4; 07-26-2016 at 11:40 PM.
Two quarts of Mobil I synthetic and two bottles of additive (as recommended on this forum). Fill and forget! Worked for my '87.
Draining's a hassle, but I got most of mine out with a big oil syringe with a long section of pipe attached. I lifted the car a tad on the n/s side to let the oil gather below the filler hole. Fiddly and a bit messy but job done in about an hour all in. No need to remove the diff unless you really want to put in a drain plug, but this is something you only do once in a lifetime.
if you happen to be close to harbor freight, get one of these siphon pumps - http://www.harborfreight.com/multi-u...ump-66418.html - about $5 with the 20% off thing. cheap, and works like a champ. it's the same piece of chinese crap that auto zone and advanced auto sells for $15. for $5, and as much as you'll use it, it's damn near a disposable item -
I keep a couple of these around the shop, "just in case..."
05-05-2016, 03:28 PM
Differential Fluid questions
