grn356

While shopping for some Mobile 1 75/90 Synthetic fluid I saw that there is a Mobile 1 75/140 (SuperSyn) Synthetic advertised for SUVs & Light Trucks. Noting that my '87 911 has a slight snarl in the lower gears my common sense tells me our G50s are basically heavy duty trannys. It would seem to me that this Mobile 1 75/140 would be ideal for our use. It's a little pricy at $16+ a quart but I think I can afford that. My question is: Has anyone had experience or knowledge of its use in the G50?? Does any one know what the 90 and 140 numbers mean?? Thanks for any input.

Peter Zimmermann

Porsche specifies 3 liters (approx.) of SAE 90, API classification GL5. I wouldn't stray as far from the beaten path as 75/140 requires you to do. For instance, there probably isn't anything wrong with a high quality, 85/90 synthetic gear lube as long as the product meets all the requirements listed in your owners manual.
Pete

pshahn

My G50 likes Redline 75/140 - quiets the chatter. After a year of combo street/track, it still looks and smells good

imcarthur

I had distinct chatter - esp on mild acceleration at lower revs. When I drained it, it was filled with Royal Purple. I too went with Redline - 75w90 NS (for non-LSD). The chatter is now gone. I am sold.

Ian

TMH

I've used straight RedLine 75w90NS in one G50 which was getting a little notchy going into 2nd or 3rd. Don't know what was in there before, but after going with the RedLine all issues were gone. Second G50 was getting fluid changed just for service (no issues), and respected Porsche mechanic suggested going 50:50 RedLine synthetic with standard SAE 90 mineral gear oil. That is what we did for that unit, and all continues to go well with it. He mentioned that the mix of synthetic and mineral oils gave overall better performance than full synthetic, and he knows much more about P-cars than I ever will.

Tom

grn356

Pete - Thanks for your advice. The recent purchase of my '87 911 was due to reading your "The Used 911 Story". Great Book! As for the fluid I'll use, I'm still doing my "due dilligence" on this. As one possibility I'm considering a mix of three: a 75/ 90, a 75/140 in synthetics, and a 90 mineral. (1 liter each) From comments on this subject from this site Mobile 1 seems to be slightly preferred over Red Line. I live in Colorado, so the weather here runs both hot and cold.... I suppose this also should be a factor in choice.
Charlie
P.S.: I was wondering after reading your book is there any significant difference between the '87 Carrera and the '88 & the early '89. (it seems like you almost had them in different catagories)

Peter Zimmermann

Charlie: I'm not so sure about this "mixing" oils. I would not do it! Regarding viscosity of the synthetic gear lube used in your area, wander into your local dealer and see what they're pumping into gearboxes '87 and later. I would be surprised to see anything other than 75/90 or 85/90.

Regarding the '87, 88 & 89 cars, I separated them in the book (thanks for your nice words!) because of the discussion about special edition cars. The three years are very much alike (the '87 will require a throwout bearing fork update at clutch time), they all drive extremely well and nothing separates them regarding build quality. Wonderful cars!

Cheers, Pete

pgrunwald

Peter,

I have an '87 and I believe it has the original clutch though I'm not 100% sure. Is there an easy way to tell if the upgrade has been done?

What is involved in the upgrade as opposed to a straight replacement?

Best regards,
Paul

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'87 Targa

Peter Zimmermann

Paul: The original design used a fixed shaft secured into the bell housing. The fork was mounted onto the shaft with needle bearings, but dirt was able to penetrate the bearings, dry out the grease, and a very "heavy" clutch action resulted. The update involves using a special reamer to machine the shaft bore to a larger size in order to facilitate the installation of needle bearings with seals. The new shaft floats (rides) on those bearings, and the new release fork mounts on the new shaft with bushings. Visually, if you know what to look for, with the car on a lift you can see the early shaft's mounting tab, which is gray in color, bolted to the bell housing. If the release fork has been updated you will see a silver tab that is holding a plastic plug in place, which will keep dirt out of the left shaft bearing. The tabs, one or the other, will be found on the left (driver's) side of the bell housing near the top.
Best, Pete

der Mond

I replaced the fluid in my G50/LSD with Redline 75W-90NS at Redline's suggestion and the LSD chattered. I added some GM non-slip additive and it seems fine. I drive the car in winter and so would not want to try the 75-140, although I used it once in a '84 Suburu and it made the shifting perfect in that car. I get a rattle at low rpm's but I thought it was the infamous G50 rattle. Some folks have had it disappear by changing the clutch. I sure appreciate the '87 mod info from Pete, now I have more to look for the next time I'm under the car. I used his book also and I'm sure glad he's being an elder of the tribe for us.

pgrunwald

Pete,

Thanks for the info, I appreciate it!


Just as an FYI, When I got my car last year, I replaced the transmission oil with Mobile 1 Synthetic 75w-90 GL5 and I have not had any chatter or shifting problems.

Paul

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'87 Targa

grn356

How would a new owner know whether or not his/her transmission has the LSD feature assuming he was not informed of such upon purchase??

pgrunwald

If you don't have the warrenty/feature card with the codes, you can call Porsche with the VIN number and they can give you the original configuration of the car.
http://www22.porsche.com/usa/accesso...ervice/n8/n51/
1-800-PORSCHE, Option 3


If you know the codes, you can look them up here:

http://www.kindel.com/porsche/options.asp
You might check to see if there is a sticker under the hood as mentioned.

or here:

http://www.performance2and4.co.uk/3.2optioncodes.htm

HTH,
Paul
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'87 Targa

Peter Zimmermann

LSD; lift the back of the car so both wheels clear the floor. Turn one wheel, if the other wheel turns the same direction you have LSD. If the other wheel lazily turns the opposite direction you do not have LSD. Enjoy your cars, guys, they're the best!
Pete

grn356

About a week ago I changed my G50 fluid to Mobil 1 75/90 synthetic and put in the 3.17 quarts per owners manual. I just received the Bentley Porsche Carrera service manual and it states 3.6 quarts is to be used. Which is correct??.... or does about .4 quart make any difference?? What's the Rennlist recommendation?