I would like to change the transmission fluid in my 1987 Carrera that has 77,000 miles. I have been told to either use Swepco or Mobil 1 synthetic. Is there a preference as to which one will improve the shifting of the car? What weight fluid should I use?

Thanks in advance,

 

Mobil 1 works best in the G50 tranny's. Used it both my 87 and 88 Carrera's....work very smoothly.

 

Hi George,
see my user experience with Mobil 1 75w-90 GL5 in this thread;

"911 winter oil"

Regards
Doug

 

Can't go wrong with Red Line 75W-90 NA either.

 

You definitely want a synthetic in the G50. I recently put in Mobil 1 75W90 (as that seems to be the most recommended), and it did not improve my shifting when cold (I don't know what the PO had in there). Now don't get me wrong, my tranny shifts very smooth except for the first few times through the the gears (when cold), it's kind of 'notchy' going into 2nd (which seems to be typical of a lot of G50s). I was hoping this would disappear with the Mobil 1, but it's no better...in fact, I even had a 'catch' on a 3 > 2 downshift ONCE since the change. I'm going to give the Red Line a try...

Keith

 

I know that it's not available everywhere, but I only used Kendall synthetic in '87 and later transmissions. Wonderful stuff, never had a complaint, but I do not know how it would fare in cold climates.

 

I put Swepco in mine and it made a remarkable difference in shifting. Much smoother and easier. Do it today. You'll be glad you did. Some people change in the winter and summer. They say it's the best of both worlds.

 

Swepco! I have been told that synthetics can't handle the pressure of tranny duty.

 

Not the case, but sometimes the synthetics can be too slippery, not allowing proper function of a transmission, in the case of limited slip, etc. I personally have seen mobil one or royal purple's syn hypoid resurrect transmissions that were on their last leg. I've just been careful around GL5 syns in early transmissions, since I have heard that the additives can cause problems for brass components. Amsoil makes a GL4 syn that I use in VW (aircooled) transmissions for this reason.

 

Hi Charles,
what you say is very true. Synthetic gear oils have been around and available for at least 50 years in one form or another

Specific transmissions and differentials may require a special formulation due to their construction and the metallurgy used. Many German and Japanese vehicles are in this situation

Mineral gear oils are loaded up with additives and various chemicals such as those for handling Extreme Pressure (EP) and Viscosity Improvers (VI). Some of these tend to form deposits on seals and etc and become depleted with use. This is but one reason why we need to change mineral gear oils regularly

Synthetic gear oil formualtions usually require very little EP and VI components and this is why they are so durable. In my case lasting without change for over 1m kms in my heavy trucks

GL4 and GL5 are indeed different in application (in mineral form at least) but many modern synthetic gear oils meet both performance standards and this is written on the container. One of the standards is the level of Shock Loading protection built into the product

Regards
Doug

 

Don't put Swepco in a G50 trans. Use a synthetic for those. They use Borg-Warner type synchros.

Do use Swepco in a 901, 911, or 915 trans. These have the Porsche type synchros.

 

I bought my '88 coupe at 74000 miles and although it shifted without any problems, but it appeared the tranny oil was oem so i drained it and ran Synblend Valvoline GL-5 for about 1000 miles. Then changed to Mobil 1 and feel it warms up quicker. Still the first 5 minutes or so i shift casually while the engine oil is also warming up. Then the fun begins. I have also read several times that syn for G-50/borg-warner is preferred, and am happy with the characteristics with the Mobil 1 so far. get it hot before you drain it and let it drain for 30 minutes after pop the drain plug. Shifter bushings and a new master cylinder have gone it since i bought the car three and a half years ago, shifts better than my 993 that has only 9992 miles on it!!

 

just put Mobil 1 in my 91 G50, had swepco prior. while it does take a bit longer to warm up, Mobil 1 shifts a bit better, at least in my case