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. I have an '89 G50/50. 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 :-)

Miles965uk

hi, yes i used the redline in my old G50 box after having the wining noise reversing and knocking noise round the corners. the oil did the trick and i head some 600hp GT2 guy races with - so just about good enough for me!

GT4T

Miles,

It is good to hear that you have liked the performance of the oil. No notchy shifting then, I take it? Are you using 75W90 or 75W90NS? I would expect the racers could very well be using ShockProof, do you know if this is the case?

Thanks,
Lynn

Please visit us at www.GT40s.com if you get a chance.

911 2

miles what oil are you exactly using i need to change myn where an i get it from in the uk is itok to use in a 3.3 turbo 1991

911 2

miles any advice as to where i could get this oil from

38D

I think you will find that most G50 Porsche owners use Mobil 1 gear oil. The LSD will always have noise regardless of the oil you use, simply because of the fact that it locks under deceleration feature (at least in the 964 turbos it locks 100% under decel).

Doug Hillary

Hi,
Castrol make some of the very best gear oils ever made and their Syntrax 75w-90 is an excellent product in this application. This is a race proven product and since 1996 has had a great track record in Formula 1, WRC and in our V8Supercar series

Mobil 1 SHC 75w-90 (GL5) is also an extremely good product with a great user record

I use both of these products in my fleet of heavy trucks and run out to 1m kms (620k miles) or five years oil drain intervals - using used oil analysis of course. In early testing (in 1997) we recorded a reduction of around 20C in operating temperature with both brands. Gear, bearing and seal deterioration has been virtually zero and they have both maintained "new" gearshift quality

All GL5 gear oils incorporate "shock loading" additives along with EP components and must be used where specified. Many newer formulation synthetic gear oils are both GL4 and GL5 conforming
It is not always a case of "more additives make a better product" either - adding extra additives over the original can be counterproductive

One of the greatest killers in the drive line is heat! Mineral gear oils usually will operate up to 150C intermittently without harm but oxidation rapidly destroys them above this point. Well formulated synthetic oils raise the safety margin (and the average operating temperature) well above this point as well as reducing the average oil temperature by as much as 30C

Regards