Proper Diff Fluid?

[DABARTH]

Hello all -

After 15 years I'm back into +2 ownership. This car suffers from being taken care of, but unused for 10+ years and thus I'm in the process of replacing bushes, Roto-Flex for CV's, Sump pan gaskets, Shocks and Springs and Diff seals.

What is the recommended Gear Oil to put in our Diffs? I'm over in the U.S.A., and Redline has been suggested to me, but I'm hoping to not have to deal with this again for a long while and want to do what's best. Any advice would be greatly appreciated!

Cheers,

Aaron
St. Paul, Minnesota, U.S.A.
'69 +2 #501904

[1owner69Elan]

Upon recommendation of my engine builder/vintage race mechanic and racer (Dave Vegher) I am using Swepco 203 in my diff (also equipped with a Quaife ATB):

Dave uses this in a variety of precious vintage race cars including 26r's that he maintains for his clients.

I bought the oil on Amazon.

[rgh0]

Redline 75w90 gear oil is specifically designed for differential applications like the Elan. I have used it in my competition elan, all my other Lotus and other road cars for many years without issue.

https://www.redlineoil.com/75w90-gl-5-gear-oil
Lot of good technical data on the Redline website around their product specifications and testing performance.

Just looking at the website now it looks like Redline has been purchased by Phillips66, hope they keep the same quality approach to the oils and don't get buried in marketing hype like most lubrication oil companies do.

cheers
Rohan

[SENC]

Just looking at the website now it looks like Redline has been purchased by Phillips66, hope they keep the same quality approach to the oils and don't get buried in marketing hype like most lubrication oil companies do.

Phillips66 bought them in 2014, so so far so good. I noted an immediate improvement with your Red Line recommendation for my gearbox, so followed your recommendation for my diff, too.

[The Veg]

Welcome Aaron!

Great looking car, show us more pics!

[661]

Redline 75 90 in the road car and Redline 75 140 in the LSD containing GTS
Redline is a great product.

[Gordon Sauer]

OK, isn't there something about only going to GL4 because it's better on the metals in the older applications, bronze?
Or maybe this only applies to 60's stuff, Thanks Gordon Sauer

[Esprit2]

Gordon,
GL4 is for transmissions, especially those with synchros... and yes, many/ most synchros make use of copper alloys, mostly brass or bronze.

GL5 is for the extreme sliding friction demands of hypoid gears. "IF" there are any copper alloy bushings & bits in the Elan's diff assembly (I doubt it, but I don't know), then the the chemical erosion of the copper alloy in a GL5 oil will occur slowly and be cheaper to repair, compared to the rapid wear of the hypoid ring & pinion if you run them in GL4. The priority in a rear end has to be protecting the "high frictional wear by design" hypoid gears. It's the GL5 that keeps them in the game.

Old-school GL5 gear oils made liberal use of sulfur-based anti-wear/ anti-friction additives, and that's a major part of why those oils had such a 'stink'. Sulfur in the oil could combine with any water that might be present due to atmospheric condensation, and form sulfuric acid. In the concentrations that might occur in a rear end, the acid did little to the gears, but it could be particularly corrosive to copper alloys. Any damage occurred at a glacial pace, and the copper bits weren't destroyed quickly. The damage to copper alloys in GL5 was significantly less than the damage to hypoid gears in GL4... and the gears are far more expensive. It is unwise to put protecting a few brass/ bronze parts ahead of protecting the gears.

Many modern GL5 gear oils have replaced the old sulfur compounds with modern copper-friendly compounds. Read the labels and you'll find that many full synthetics carry a dual GL4/ GL5 rating. They can give the hypoid gears the protection they require, and still be compatible with copper alloys.

Regards,
Tim Engel

[Gopherit]

Another vote for Redline 75W/90 in the diff - and MTL 75w/80 in the 4 speed gearbox. Not sure why we don't have a Redline equivalent in the UK but possibly because of this forum I have used their transmission oils and been very satisfied. Total Quartz 20w/50 in the twincam at the moment - fully syn and seems to be doing the job - no more leakage than "usual" but I've yet to attack the sump with modern sealants!

Waiting to see that 26R Graeme!

Paul

[661]

Another vote for Redline 75W/90 in the diff - and MTL 75w/80 in the 4 speed gearbox. Not sure why we don't have a Redline equivalent in the UK but possibly because of this forum I have used their transmission oils and been very satisfied. Total Quartz 20w/50 in the twincam at the moment - fully syn and seems to be doing the job - no more leakage than "usual" but I've yet to attack the sump with modern sealants!

Waiting to see that 26R Graeme!

Paul

Thanks Paul.
Looks like I can get it MOT'd now. ( although my declaration may not be entirely truthfull!)

[Gordon Sauer]

Great clarification always Tim and thanks to everybody so I won't trash my gears and yes Aaron that's great you're running your +2 and putting all those refinements into it. Gordon Sauer

[2cams70]

I reckon most oils from reputable manufacturers of the correct specification and grade perform pretty much the same regard of the brand, after all that's why performance standards exist for oils. It's mostly just marketing spin that some are better than others - the reason being to extract more from your wallet! The only things that are a bit sensitive are modern automatic and automated manual transmissions with wet clutches that require oils with very precise frictional characteristics.

Put it this way - has anyone had a mechanical failure that can be directly attributed to using a poor quality oil as opposed to one that was an incorrect specification and/or grade for the application?

[rgh0]

Modern lubrication oils are all much much better than those of 40 or 50 years ago when our cars were first made. This is largely due to two factors . Better additives packages and better base stocks

However there is still a large degree of variation in oil performance and oil performance over its life and oil life that depends on variation in these factors between manufacturers.

Most reputable manufacturers use similar additives packages for the various applications but they don't use similar base stocks and using better base stocks enables less compromises in the additives package. In general using a better ( more expensive ) base stock oil results in better long term performance as the additives package can be focused on the application better rather than compensating for short coming in the base stock so much. The Redline manual transmission lubes are an example of this where the oil characteristics and additives are focused on superior gear change performance or their GL5 gear oils where they are focused on sliding contact differential performance

For a better understanding of oil base stocks see:
https://www.machinerylubrication.com/Re ... oil-groups

Moving from group 1 to group 5 base stocks provides for big improvements in high temperature stability, Viscosity Index, oxidation resistance, film strength and scuffing prevention. The most expensive "synthetic oil" oils used in our cars such as Redline use Group 5 polyolester base stocks. Slightly lower priced oils use a blend of polyolester and group 4 poly alpha olefin base stocks, cheaper again use all group 4 PAO base stocks. The cheapest oils that can be labelled "fully synthetic" use group 3 severely hydrocracked base stocks

All these oils are better than those of 40 years ago which were all group 1 and 2 mineral oils. Even current group 1 and 2 mineral oil lubes these days are better than they were 40 years ago due to better additives so provided they are changed frequently enough they are "good enough" for road use during the typical 10 year life of most cars.

However in high stressed race use you want better than "good enough". In road use for your car it really depends on your philosophy and if you want to keep your car for 40 plus years then investing in the best oils is cheap IMHO.

In my competition Elan I use group 5 base stock oils for both engine and gear box and diff from Redline
In my road cars I use group 3 ( group 4 base stock if on special) engine oils from various manufacturers depending on price and Redline group 5 base stock gear and diff oils. Maybe overkill but worth it for my "babies"

cheers
Rohan