GT4T

I am representing that portion of the GT40 replica community that uses a G50 family transaxle. This subject would also be of interest to Ultima builders and, indeed, anyone using a G500x or G50/5x transaxle. We have been having a discussion on the use of the various synthetic gear oils in the transaxle. The issue arrises from trying to find the right oil (or combination of oils) that will, all at the same time, take into consideration the needs of the Borg-Warner style synchros, the LSD and the care of the ring and pinion gear. This discussion has mainly revolved around the Red Line family of products and we have narrowed the choices down to 75W90, 75W90NS with just enough FM (Red Line or GM) to quiet the LSD or ShockProof (light for street, heavy for race/street which is what PHII recommends). In searching the forums here, it seems that the Mobile 1 products are very popular as well.

We see great advantage in using ShockProof gear oils to take care of the R&P, especially, but all of the gears and in keeping the LSD quiet. But this leaves the question of the synchros performance with this very slippery oil. There doesn't seem to be any clear cut consensus in the industry, so we'd really appreciate any real world experience with these gear oils.

Regards,
Lynn

PS: if you consider this an invasion of hallowed ground, please pardon the sacrilege; we love the Porsche too :-)

Timothy Stewart

You might want to speak with David Granquist at Red Line.
He has a 993 and he recommended 3 75W90NS and 1 Light
weight gear oil.

tim

por9146gt

Hi there, not sure what everyone else has found but we put 3000 miles on our RSA's G50 with mobil one and no problems, the synchros were factory and not the steel ones.
hope this helps.

por9146gt

oops did not clarify that the 3000 miles were all racing miles.

GT4T

Thanks guys! I will get ahold of David, for sure! I have used Mobil 1 oil in all of my engines, but had not really considered it for the transaxle until reading through the threads here. I did not see an "extreme pressure" version of their gear lubes though. With high torque V8s, we give the ring & pinion gear a hard way to go and like the extra protection that EP oils provide. Amsoil also has an EP gear oil like Red Line's ShockProof, but I haven't seen where anyone has used it in a Porsche transaxle and I have been looking all over the web.

Thanks again,
Lynn

Alon

I replaced my 1997 993 C2S (with worn LSD) factory fill gearbox oil with Motul 75w90 and it developed an occasional (more occasional than I would prefer) crunch into 2nd gear when shifting (or downshifting) quickly. I have been told by a local Redline dealer to use 3 parts Redline 75w90 and 1 part shockproof. I'd like to here more about that combo if anyone has tried it.

GT4T

Alon,

I would call Red Line directly, Orinn at Eurosports Ltd in Denver, Bobby Hart at California Motorsports in Lake Havasu City, AZ or Roger Brown at PowerHaus II in Boulder (or all of the above.) The mixture I have seen recommended by Red Line is 3 parts 75W90 and 1 part Lightweight Gear Oil (this is different from Lightweight ShockProof Gear Oil.) If the Motul is indeed the cause of your notchy 2nd gear, IMHO the suggested mix will make it worse. Here is why I say that: the Motul is very slippery oil and, if your synchros are starting to wear, the increased slipperiness is inhibiting the synchros from spinning the gears up adequately to allow them mesh smoothly. The Red Line mixture suggested is AT LEAST as slippery as the Motul you are already using. My recommendation would be Red Line 75W90NS, specifically for synchromesh transaxles, and add just enough GM Friction Modifier to stop any LSD chatter if that is a problem.

There is also the chance that your crunchy shifting may be from something other than worn sychros and slippery gear oil. If this is the case, then there is also a chance that the 75W90 with the Lightweight ShockProof is the exact way to go. If you don't mind the cost, you might try the suggested mix and see what happens (if you didn't mind the cost of Motul then Red Line shouldn't be an issue.) As long as you don't slam the tranny into gear, you are not likely to hurt anything; just use a little finese. If the shifting gets better, you're good to go; if the shifting gets worse, then it is likely the synchros and you might want to try a less slippery oil as I have suggest. That said, I am not claiming to be an expert (and I didn't even stay in a Holiday Inn Express last night :-), but I have been researching this stuff lately. Please do verify my suggestion though before acting on it as my research has been specifically for high torque applications.

Regards,
Lynn