i know better than GM, I've never gone bankrupt or asked for a bailout

the T56 6-speed uses Dexron III automatic transmission fluid. Dexron 3 licensed atf has expired so you will not find it. Dexron VI is the current ATF and runs around $7 or more per quart. The T56 takes 4 quarts. The drain plug is at the tail end of the housing where the driveshaft is, very easy to drain. The fill plug is a 3/8" pipe plug halfway up in the middle of the case, i think on the opposite side of the drain plug. You can either fill the case here with a gear oil pump, or you can pull the center console out and remove the shifter and pour in 4 quarts that way.
I've been using pennzoil synchromesh (alternative to GM syncromesh) for the past 5+ years in my 2002 ss, I think it shifts better than atf but that's just my opinion.

for a 1999 SS, which I've had, you most likely have the torsen differential. But the auburn differential was an option, so you should check the door sticker for the auburn RPO code, which will be from SLP I think. You can also tell which you have once you remove the rear cover off the differential.. if you know what the two look like (google). If you have the auburn, you will want to get regular 80w90 mineral gear oil from the parts store for around $5/quart. This is what's recommended by auburn, along with using about 3-4 ounces of friction modifier (limited-slip) additive. The rear diff. will take just under 2 quarts of fluid, so buy 3 especially if you're squeezing oil out the bottle. If you were the original owner of the car and know how it's been used/abused then I would say only check the diff and make sure it's full of oil. I recently picked up a 2006 GMC truck with 70k miles and popped the rear diff cover and the factory purple smelling stink drained like mud and was frothy, so you are smart in wanting to service the rear.
If you have the torsen rear axle, you can use the same fluid along with the friction modifier additive, but the additive is not required. You can use any GL-5 gear oil at any price if you have the torsen, most people go with mobil-1 75w-90 synthetic which is around $10/qt. You can also get a felpro rear differential cover gasket, I think it's easier than sealing the cover back on with rtv, up to you. If it wasn't mentioned, when draining the rear you will be pulling the cover. Undo all 10 bolts on the cover except for 2 in the middle on each side and one on one side on the bottom. have these 3 bolts about half way out, then use a flat blade screwdriver to pry the lower right or lower left side of the cover gently until oil drains in a controlled, clean manner. Don't just rip the cover off and drop 2 quarts of stink in less than a second. Get some nitrile gloves too, unless you like that smell on your hands.

 

Recommend not taking the cover off the differential It will make an absolute mess and stink up everything it touches. I use an oil extractor and suck out the fluid. I've never had any issue and change about every 60k. Just pick up ST 75/90 full synthetic diff fluid. I've never put in gm additive
While you are picking up diff fluid get some ST dexron VI and use that in your tranny. Pickup few qts of dot 4 brake fluid and use an oil extractor to suck out most of fluid from brake resevour and clutch as well if you have 6 speed.

 

For me it was easier to unbolt the shifter from the top of the trans to refill it. I left the upper plug off with a pan under it. When I heard the fluid coming out and hitting the pan I was done filling.

 

I hope you guys know that Dexron VI is NOT recommended for manual transmissions! GM even has a bulliten out about this.

I just changed ALL the fluids in my AWD Escalade. I used Mobil1 75w90 in the front and rear differentials, and Dexron VI in the transfer case. (As long as you don't have the blue ****. That's $16 a qt)

I didn't remove the cover on the rear diff. There was a great write up on CadillacForums that showed a guy just loosen the lower 9 bolts, stick a flat tip screwdriver inside about an 1/8", and let it drain. Re-torque to spec, and refill.

a month later the rear diff has no leaks, so I see no need to pull the entire cover and gasket.

Again though, do NOT put Dexron VI in a manual trans.

http://www.bobistheoilguy.com/forums...Number=1413049

Anyone else need more proof?

 

My dexron vi has been in 2 years this month. When the tranny fails I'll replace the fluid.

 

i'd like to see the gm bulletin you say exists.

a bunch of posts on bob is the oil guy is not proof.

 

When GM came out with the new lower viscosity Dexron VI, they superceded the Dexron III spec and phased it out. When they found the Dexron VI did not work well in manual transmissions, they rereleased the Dexron III with a new part number, 88861800, but they don't call it Dexron III anymore.

Here is a quote I found online:
"Per GM service news

This information applies to 2007 and prior GM passenger cars and trucks.

Dexron III is being phased out as a product name. It is being renamed Manual Transmission Fluid and carries p/n 88861800 U.S. (88861801 Canada).

If fluid p/n 88861800 U.S. (88861801 Canada) is not yet available when servicing a manual transmission or transfer case, Dexron III can be used in its place.

DO NOT use Dexron VI in place of manual transmission fluid in any manual transmissions or transfer cases that specify Dexron III, as a failure may result."

 

Precaution: DEXRON-VI in Manual Transmissions

When DEXRON-III is indicated as the fluid fill for manual transmissions and transfer cases, DO NOT use DEXRON-VI. Instead, use GM Manual Transmission Fluid p/n 88861800 in these components.
TIP: Refer to PIP3836B (Feb. 2007).

 

Hell, why do't I just post the document

 

thanks.

so it seems dexron vi is not fully backward compatible for everything that used dexron-iii like gm said,
they're like subway with that any footlong $5 bullshit.

 

That's pretty much what I got out of it, too. I'm simply trying to pass the word on, that's all. I hate to see people break **** when it's needless and could be avoided.

 

Been running royal purple ATF in my t56 for years... no issues... Im not even sure what it is technically... dex III or dex IV? I remember when I first used it I just saw that it was compatible with dex III. Tranny has probably 180k miles on it. I had some issues with this tranny sticking or something back in 2005 time frame and used redline atf and worked perfect. Luck? Who knows.. changed the fluid and problem went away. Dont know where to get the redline now so... RP ended up being my default.

Im curious about the royal purple 75w90 fluid for the rearend. Folks here saying you dont need the friction additive? I recently bought and installed a craigslist rear with 4.10s and put her in... fluid looked brand new so I didnt change it out. Got a bit of whine around 30-60mph now and figured, what the hell, I'd try a fluid change out... will the additive do anything bad with the RP gear oil? Or is it just not required... i mean, ill try it without and then maybe add it in a few days if the whining is still there just to rule out the possibilities before doing more.

I think the rearend sat for a while (maybe a year) and the gears barely have much milage.. it was a loud whine the first day but has quieted down some on its own already from a few days driving... all the bearings and seals looked new and so did the fluid like I said so, I figure since I was a cheapskate and left the fluid I'd change it now just to see if it helps.... again, just curious about the limited slip additive stuff with the RP... any further details or info?

 

The Dex 6 really IS too thin (as is the current version of Valvoline Max Life ATF, which is the same viscosity as a Dex 6) for our T56es/TR6060s/etc.

IF I lived inside the Arctic Circle, and drove the car in the winter up there, I would consider the Dex 6.

As far as I know, the RP gear oils all contain at least some limited slip friction modifier, but IF you have a clutch pack/cone clutch type diff (Eaton Posi/Auburn, etc.) it may not be enough to keep the diff from chattering/groaning/squawking around slow speed, parking lot turns.

IF you have a Torsen/gear type diff (Torsen T-2/T-2R, Eaton/Detroit Truetrac, etc.) you should not even need any Limited slip additive, although I think that there was a TSB about 4 ounces of the l.s. additive quieting down the "rocks in a box" coast down noise of the factory Torsen T-2s (non-SLP, '99-'02s).