Transmission fluid for LSD

Time for everyone's favorite discussion: drivetrain fluids! The shifting in my '99 is a bit notchy going into 2nd and it's almost to 90k miles, so it's due for a change anyway. I tried searching but couldn't find the info I was looking for. Does Porsche recommend a different transmission fluid for cars with a limited slip differential? I know a lot of people recommend Mobile Delvac 75-90, but does that have the friction modifiers that an LSD needs? Or, if the fluid is different from the standard Porsche fluid (part number 999.917.546.00), does anyone have the part number for it? Update for people searching in the future: Cars with the factory LSD use the same fluid as the non-LSD cars if you're using Porsche-approved fluid.

Interested too as my 2004 40th AE also has a LSD.

i changed mine on my 40th, with the Porsche fluid from Suncoast, it was expensive and I didnt notice any improvement in the shifting. Hoping there is a better option out there for teh next oild change

Quotes source post: 11059194

I changed the fluid too since it was notchy and even after that, there wasn't really any improvement. You should also try tweaking your settings on your shift cables. It made a noticeable difference for me(especially when cold). Even with the factory alignment tool, your adjustments can be off a couple MM from optimal position. Even factory original shifters might benefit from tweaking the shift cable adjustments.

I'm installing my 997 SSK this weekend, so I'll be playing with the adjustment this weekend. I don't know if/when the tranny fluid has been changed before, so I still want to change it anyway. On a high note with the sloppy 2nd gear, it's just notchy and not popping out of gear, so I have that going for me.

None of the official Porsche sources I have mention anything about any friction modifiers for LSD. For manual transmissions there are just two fluids approved for use. A Mobil fluid and a Shell fluid. If you have an aftermarket LSD in the diff then the LSD maker may have its own recommendations regarding fluid and you should probably follow that recommendation. Also, I have found a fluid change can improve shifting feel most noticeably when the transmission is warmed up at the expense of a bit more reluctance shifting when cold. This is quite acceptable to me, as smooth fast shifting is a must have when the car/tranny is warned up. The cold shifting is not that bad. After a few blocks of driving the shifting improves some and before I know it the tranny is warm enough shifting is just fine. Another thing that can improve shifting is a good brake and clutch fluid flush/bleed. If it has been nearly 2 years or more since you last did this you should consider doing this before fiddling with the shift linkage adjustment, but after you change the transmission fluid.

It's the factory LSD.

Hi Capt, I went through this a couple of months ago. I have the Porsche LSD as well. I could not find any documentation that requires a different fluid for our transmissions. If I knew about Suncoast at the time I would have ordered the Porsche stuff. That being said, after looking at the different posts on Rennlist, I tried Delvac. For me, it was nearly unusable cold. It was fine warm, but, 2nd and 3rd cold was awful. So, more searching. I saw some really positive write ups about Motul 300. I got it locally and it worked great!!! If you can order Porsche fluid from Suncoast or if you have a local Porsche dealer, I would put in the factory stuff. Though my tranni feels great....Motul 300 is not approved by Porsche.

Friction modifiers are NOT for use with a clutch type LSD which is what you have (same with Guard). Designed to help the synchros and gears, it also affects the ability of the clutches in the LSD to work. Friction modifiers may be guilty of some shifting issues because the synchros do in fact need some friction to function properly.... In my race car I use a special fluid from Lubrication Engineers that both Matt @ Guard and Viking on this board have recommended to me. No tranny or diff issue with this fluid which is designed to work in sub- zero temps. Linked below is their 75-90 which is perfect for street applications. They also make a 75-140 which is what I race on... http://products.lelubricants.com/ite..._utmk=64170607

I swung by my local Porsche dealer (Barrier Porsche in Bellevue, WA) and asked about the tranny fluid. They said the same fluid should be used whether or not the car has the factory LSD. Also, they only had fluid in the big container, but were willing to sell it by the quart if you bring your own container.

What'd they charge for a quart?

I tried Mobil Delvac very hard shift when cold. Motul 300 Works perfectly for me. Motul Racing GEAR 300 75W90 - 100% Synthetic Ester

This can get into a heated debated.

I used a product from millersoils.co.uk their products are highly rated.

SWEPCO 201 has "limited slip characteristics" so I have used that for a couple of fills now. It shifts great warm and on the track, but when it gets cold (and by that I mean below 70 degrees) it gets really difficult to shift. I wouldn't recommend it if you live somewhere that is regularly below 50 where you store your car. Unless the Porsche fluid becomes easier to buy, I'm going to stick with the Swepco.

Quotes source post: 11060812

$23 a quart IIRC.

$23/quart is not bad. Just takes a couple of quarts IIRC. Sometimes my service manager even gives me a break on the fluid price. Last time for my Boxster he charged me $5/quart as the shop has some left over from some warranty work. Labor is 0.3 hour. One of the cheapest services available and that's good because I hate to change my car's transmission fluid. (The Turbo takes a bit more fluid and requires a bit more labor, but still not much.) The factory transmission fluid is pretty good. I point out my 02 Boxster has had that almost exclusively -- once I think a dealer or an indy shop put in something else as cold shifting improved at the expense of hot shifting -- and the transmission has almost 276K miles on it. Still shifts just fine. Quiet too.

Motul makes two gear oils in the 75/90 grade, one for regular, and one for LS differentials. On the links below you can see where they differ in their specs. LSD http://motul.speclube.com/products/a...0-ls-75w90-1l/ non LSD http://motul.speclube.com/products/a...-300-75w90-1l/

Alright, one more question on changing the transmission fluid: Is refilling this like on a diff or a lot of other transmissions where you fill it until the fluid starts to drip from the fill hole, or do I need to actually measure out 2.85 quarts and fill it with that much?

Quotes source post: 11073394

Captain, just fill till oil drips from the fill hole with the car being level. You should feel a big improvement if your fluid is original. I change mine every 30k and can feel significant difference already.

Quotes source post: 11064854

I'm hoping I won't get flamed for bringing in info from non-Porsches. :-) There is periodically a discussion of this issue on ferrarichat. Ferraris, Panteras, Porsches, even rear-engine Fiats use transaxles, where the transmission and rear axle are combined into one housing. If you use an oil designed for an LSD axle it is too slippery for proper synchromesh engagement and you will wear them out prematurely. The answer is Red Line 75W-90NS, which does NOT have the friction modifiers. If you feel the LSD clutches binding when making a sharp turn you can add a tiny bit of the modifier until that stops, but most people do not find that necessary. The advantage of synthetic oils like the Red Line is that it is less viscous at low temps-- hence easier shifting until it warms up. I would not recommend using non-synthetic oil-- the Red Line is not THAT expensive. I get it on Amazon with free shipping.

I don�t know how long it�s been since the trans/diff oil has been changed in my 99 c2 with factory LSD. Its not exactly cheap fluid to replace either, but I will probably stick with the Porsche brand, as I�ve done that in the past and never had any issues with my transmissions. The shifting on my car is quite difficult when it comes to putting it in first gear unless I�m stopped. And when the trans is cold, all the gears are difficult to grab. I just wish there There was a way for me to know when the oil was last replaced, since I�m not sure if replacing it will result in easier shifting. Like I said, not exactly cheap oil.

I used the Fuchs stuff . I'm running a factory lsd that's had the full guard upgrade , clutches , plates , 40/60 ramps etc. https://www.pelicanparts.com/catalog..._pg1.htm#item0

I use Motul and have been pretty happy with it. Sounds like your synchronizers could use a refresh. Also, the chances are that your LSD is completely worn out. A good was to test is to jack up one rear tire. Release the emergency brake but put it into first gear. Make sure you are on a flat surface obviously. Now take your torque wrench, set it to 10 or 20, put it on a lug, and see if you can spin the wheel with it. If you can, your LSD is shot. If it requires 50 or higher, it still probably has some life in it. Over 80 and it’s probably had a rebuild recently.

Quotes source post: 14761981

I don�t think the issue is synchronizers being worn out. It�s just a high effort thing when cold. A lot of folks complain about first gear being difficult to grab on these cars. I don�t get any gear feel - where the shift results in being able to feel the teeth before grabbing the next gear, resulting in a crunch.

Quotes source post: 11080483

I just picked up my 99C2 MT with LSD, and had asked the local indy shop to change the transaxle fluid. I hadn't done any research, but they used the redline 75W 90NS as mentioned above. I need to ask them more about the background.

Quotes source post: 14761981

Regarding the LSD torque wrench test, I found this

Quotes source post: 14762499

And how does it shift? I�ve read up on folks using different branded oils in leu of the Porsche factory fill, and I don�t think the factory fill is the only fluid that will work as intended. I�m guessing not all of these oils have the exact same viscosity as each other, so some oils might result in easier shifting than others at different temperatures with different tradeoffs. I tend to be gentle when shifting, so I could probably get by with an oil that�s more forgiving and easier to shift, whereas other folks that track their car�s light choose an oil that�s offers slightly better protection when hot.

Interesting. Must be the difference between clutch and TB. My Gikken started at 90lbs and the M3 I had was at 86lbs.

Quotes source post: 14762544

I will report back once the snow clears. The car was warm and shifted great/fine when I picked it up, I need to try it again when cold to give a full comparison.

For the 996 manual trans, I seem to sell a lot of the Fuchs and Liqui Moly, I'm a big fan of Motul myself for my cars. But you can't go wrong with any of those brands. https://www.warehouse33auto.com/cata...al.Trans.Fluid -Jason

I just bought this Porsche OEM fluid and will replace it soon: 000-043-305-49-OEM.

In my 99 non lsd I used Motul Gear 300, and it shifted smooth as silk. Plan to put it in my 02 this winter.

As a data point my car has a motorsport LSD the previous owner installed. It currently has 75/90 mobil devlac. I'll be renewing it next service with the same. ​​​​​ ​​

More important than the brand of transmission oil ( anything that meets Porsche spec will be fine ) with a plated clutch limited slip diff is that you should change it more often than with an open diff transmission . Little tiny pieces of the wear plates and clutchs will be present . Cheaper oil changed often ( especially with a track day car) is better than expensive oil left in there for years

Quotes source post: 14778002

I am currently changing the fluid once per year ('99 with OEM LSD). Putting on about 5000 road miles + ~10 track days per year. Does this sound OK, or should I do it more often?

Quotes source post: 14780305

For the street, That�s too frequently and wasting oil and money, but since you track the car, I think it depends on how you treat the lsd.

Given 5000 miles and ten track days , annual changes is about right .

Quotes source post: 14762544

Finally got the 996 out for about an hour today. From cold (31F), the shifts were significantly better/smoother (especially first and second gear).

Quotes source post: 14812887

Thanks, good to know. My oil has shipped and arrived, but I haven�t had time to do it yet.

Quotes source post: 14762781

Bump. How's it shifting with Redline? I'm trying to decide whether to use Porsche, Motul or Redline in my '99 w/ LSD.

Sorry for the delayed response. I would call it marginally improved across the board. No concerns here!

Quotes source post: 15156927

Thanks. I went ahead and used Redline and had a significant improvement.

Good to know. I replaced my fluid with Porsche OEM and it made little difference. So I�m guessing I need to adjust the shift linkages.

Previous owner confirmed my cars Porsche "motorsport" LSD is filled with Mobil 1 devalac 75w90 gear oil. Which I think OPC usually keep in stock. Renewing it next service.