Gear Lube testing Lab Results
 

I came across this very detailed lab study of Gear Lubes and found this an interesting read:
http://www.synthetic-oil-tech.com/Gear%20Lube%20White%20Paper.pdf

Most interesting was how top end gear lubes FAILED corrosion testing. These failed:
Mopar Synthetic 75W-90 with Mopar LS additive
Royal Purple Max-Gear 75W-90
Lucas 75/90 Synthetic

But in the end the best overall results and winner was:
AMSOIL Severe Gear 75W-90

Here are the top 5 in order:
1 - AMSOIL Severe Gear 75W-90
2 - Mobil 1 Synthetic 75W-90
3 - GM Synthetic Axle 75W-90
4 - Castrol SYNTEC 75W-90
5 - Red Line Synthetic 75W-90

I started this because I'm getting ready to change the gear lube in my 915 box and was wondering what to put in. I'm leaning toward one of the top 2 above.

What do others run and recommend.

Swepco for 915 transmissions

Mobil 1 for G50 Transmissions

1. I would not recommend synthetic in your 915. I doubt the synchro's will feel right swimming in that. But if you are set on doing it please post your results.

2,. I suggest Castrol or Swepco. Non-synthetic. (Wear and corrosion ratings are way down the list or important properties when selecting a 915 oil.)

3. Do you consider that report an independent source of information? Shockingly, the Amsoil Drivetrain Division ranked Amsoil as the best oil.

It looks like that report deals with oil as used in a differential gear. Although the 915 does have a ring and pinion in it, it also has synchros, brake bands, etc. There is a lot more to consider than just the R&P wear. This is why people recommend against the synthetic... they say synthetic is "too slippery" for the brake bands to work right in the synchros.

Well, I've used Amsoil in my 915 since I rebuilt it; almost a year now, with no balky shifting or other problems.

I intend to change it out this winter with Swepco, The Miracle Oil (TM), and see if I notice any comparative difference.

I guarantee that an independant test would yield far different results.

To the webs defense, on Bobistheoilguy.com I have read great things about Amsoil.

But it is an election year, and I agree... I find it fishy, that Amsoil found that Amsoil is the best.

But we are talking about 915 transmissions, so none of that matters.

I think if you put synthetic is a 20+ year old 915 you're going to be lining your garage floor with cardboard pretty soon.

When I rebuilt my 1972 915 I dumped Castrol in there because I knew I'd have to change it after a break-in period (500 miles or so) and swepco is not only expensive, it's hard to get around here. I had swepco in there before and didn't notice a lick of difference in shifting with the Castrol. When I changed it after the break-in period, I just bought another jug of Castrol and it shifts fine. Well, as good as a 35-year-old 915 ever shifts...

Castrol LSX90 is an excellent oil for the 915.

Dose haveing a Limited Slip Diff come into play?

Is there an additive needed for and LSD or somthing?

That's a source I would trust before Amsoil...