Gearbox and LSD Oil

[chris_seven]

I am just about to fit a 915 transmission complete with a new plate type LSD and have been considering the beat oil to use for this set up.

I would imagine that a synchro box would work best with a GL-4 oil but the LSD would be better with a GL-5

I am sure that there is a good compromise but would appreciate any comments/experience.

Thanks.

[mhinch]

Chris, Berlyn Services stock the Swepco GL-5 201 oil in the UK

http://www.partsforporsche.co.uk/osc/

Seems a popular choice on this forum, just got some to change the oil in my standard 915 box.

Mark

[chris_seven]

Mark,

We have used Swepco 201 in a few 901 Transmissions, it just concerns me that GL-5 is great for the diff but not so good for the synchro.

I seem to remember a couple of posts where there were comments about shift quality being a problem with 915s using Swepco but I can't find the reference any longer.

The new box we have just built has Wevo Race Cases, a Wevo internal gear shift a modified mainshaft with a 5 new close ratio gears, synchros, sliders etc, (the gears have all been REM treated), an 8:35 Ring & Pinion and a new design of plate type LSD and I wanted to think long and hard about the best lubricant as this box has cost at least an arm and half a leg and is worth a bit of effort.

[sig_a]

Here's one you might consider.

Works great in my 911 1987 Carrera with G50 and no LSD

Mobilube 75W 90 SHC

www.lufteknic.com ad

"Hard to find in the states, but we stock it. Original fill in 996 GT3/Cup cars, and GT3Rs. Works well in all 901, 915, G50, G96 gearboxes. Used extensively in Porsche Motorsport products in every grueling test there can be LeMans, Sebring, Daytona, etc. We also use it in our service department in all street and race cars.

Great lube, surpasses all others in research and development.

Mobilube SHC 75W-90 is a fully synthetic drivetrain lubricant engineered to meet the most demanding extended drain and OEM warranty requirements. These products are designed for use in heavy duty drivetrains that require gear lubricants with excellent load-carrying capability and where extreme pressures and shock loading are expected The state-of-the-art technology in Mobilube SHC 75W-90 and delivers unequalled performance for low and high temperature applications, including outstanding oxidation stability, wear protection, corrosion resistance, improved shear stability, extended service capability, and excellent fuel economy.

This is not the same formula that is available in mass market auto parts stores in quart bottles. 1 gallon containers."

[Early_S_Man]

All air-cooled Porsches require GL-5 gear oil in their transaxles!!!

[Steve@Rennsport]

Warren is spot-on.

These transmissions NEED a GL-5 to protect the ring & pinion and synthetic lubricants are too slippery for the Porsche baulk-ring type syncromesh to work properly.

I do not think there is anything better than Swepco for the 901-915-930 transmissions based on long term experience with racing these cars (RSR-934-935) since 1976.

Synthetics are just the ticket for G-50's with their Borg-Warner syncromesh,..

[chris_seven]

I guess that my confusion is driven, to some extent, by the Workshop Manual.

The early 915 data specifies an SAE90 to either MIL-L-2105 or MIL-L-2105 B.

In the document that I have the first mention of GL-5 is on a page printed in 1981 but refers to gearboxes from 1976.

MIL-L-2105 seems to be a GL-4 rather than GL-5.

I thought that most GL5 oils had additives which adsorbed onto the surfaces of gear teeth and reduced friction quite significantly compared to GL4s and that this wouldn't help with gear shifting hence my interest.

There seems to be a great deal of debate going on about GL4 versus GL5 and I was interested to see if anyone had made comparisons with the various types of fluid.

I have used Amsoil Synthetic in a Renault Transaxle in the past (A110) with good results but have only used Swepco in my 901 and I have never made any comparisons.

[Mahler9th]

Interesting thread. I have a friend that worked on the World Championship winning local team when they ran 935's and such... and he also raced in IMSA himself. He built my car and does all of the engine work on it. I do the transmission work myself with his help and guidance... also some excellent help from Wevo. Anyway, my friend has all of his customers run Redline synthetic. In all of my past street/track Porsches I have run the Swepco, and I liked it. I stick with the recommendation of my friend-- that; what he uses in his 915, and he ran that tranny in a 700 bhp ++ track/street car with a 3.8 tt engine for several seasons of racing and commuting.

[Steve@Rennsport]

Mike:

One can use Redline, but with friction modifiers to help the Porsche syncromesh.

The only drawback to these excellent lubricants is higher rates of wear on the operatings sleeves and brake bands (syncro rings).