Lotus Elan

Simple question - Which oil for the Diff

PostPost by: tdafforn » Wed Jan 25, 2006 10:25 am

Hi all,
The question is as it says in the subject line..
What are people using in the diff as a lubricant.
I have the rear suspension off at the mo and it seems a good time to fill the diff
Cheers
Tim
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PostPost by: pamitchell » Wed Jan 25, 2006 6:37 pm

I use Redline 75/90 synthetic diff oil. I also use their MTL for the gear box.
Both came highly recommended from other users. No issues with either.
Their technical information gave me confidence in their products.
Rgds,
Phil Mitchell San Jose CA.
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PostPost by: ppnelan » Wed Jan 25, 2006 7:11 pm

I use Castrol EP90 Gear Oil - I think this is what the manual says to use too.
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PostPost by: Dag-Henning » Wed Jan 25, 2006 8:27 pm

- Castrol SAFX J.

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PostPost by: type26owner » Thu Jan 26, 2006 3:36 am

Any GL-4 synthetic if the diff is open and you want it to last as long as possible. If you're synthetic hostile then choose a regular GL-4 gearoil. Steer clear of the GL-5 stuff because of corrosion issues of incompatible metals.
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PostPost by: dlbarnes1 » Thu Jan 26, 2006 4:37 am

Many years ago, I had the diff in my Sprint overhauled by a Lotus shop in So. Calif. They advised that I use gear oil as follows:
Sta-Lube, GL-5, Hypoid Limited-Slip, SAE 80W-90
They stated it wouldn't be necessary to change it periodically, just keep it topped up. I add about 4 oz. every 6 months. This has worked for me.

Note that the manual states "any SAE 90 oil can be used which has an addition of 10% 'Anglamol 99' by weight". I'm guessing Anglamol 99 is an EP additive. Another source of maintenance information simply states SAE 90EP.

Dave - 72 Sprint DHC
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PostPost by: rgh0 » Thu Jan 26, 2006 7:03 am

EP gear oils, also called GL5 are normally recommended for hypoid gear style diffs like the Lotus diff. GL5 oils contain higher levels of anti scuff additives to prevent wear in highly loaded sliding gear surfaces as occurs in the hypoid design gear set in the diff. However the suplur in the additives can attack brass components in particular. Though not much is made of brass in a Lotus diff unless you are using bearings with brass cages which are not common these days.

Conventional gear oils (GL4 oils) have less extreme pressue anti scuffing additives ( in particular sulphur) and thus dont perform as well in sliding wear such as in hypoid gears. Normally used in manual gear boxes where the lack of additives does not matter as most boxes only have helical gears. The lower sulphur levels also prevents corrossion of brass synchro rings.

You can actually smell the different suplhur level in the different oils. GL5 synthetics such as Redline contain lower levels of suplhur than most mineral gear oils as they need less to get the required GL-5 properties given there superior basic lubricant.

In an Elan if the diff is well run in you can probably get away with a GL4 synthetic though I would not recommend it. The additives are most needed during running in where the gear teeth lap themselves smooth against each other. A lot of cars used to use special running in diff oils with very high additive levels to help this process, with better basic oils and machining techniques these days they dont bother anymore.

I would recommend a GL-5 rated synthetic gear oil from any of the major manufacturers in the diff of an Elan. I use Redline oils in all my Lotus and Landcrusier tow car, not cheap but it works.

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PostPost by: type26owner » Thu Jan 26, 2006 2:40 pm

Rohan,
Glad to hear you've blazed this trail already. I've been conservative and too cowardly to try it. Since you swear by it I'll take the plunge also. However, the EP additives are quite chemically reactive and would scare me off under most conditions.
http://www.engineersedge.com/lubrication/extreme_pressure_additives.htm
Modern day diffs are built for this stuff with all steel components. Are you sure there isn't any bronze bushings or thrust washers associated with the differentail (spider) gears? Will someone that has a stock open differential unit in pieces please look for any bronze or brass bits. I don't trust my memory and this makes me nervous.
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PostPost by: ianf » Thu Jan 26, 2006 6:42 pm

Keith,

What about the filler & drain plugs? Probably take a couple of centuries to munch its way through though.

Ian
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PostPost by: type26owner » Thu Jan 26, 2006 7:33 pm

Suspect the aluminum housing will form a passivated coating along with those other bits nothing continues to corrode. If you believe what I've been told, what is in jeopardy is the copper, tin or zinc bearing materials that get hot from friction. I don't have any technical papers that supports that though or first-hand experience. Haven't studied this stuff since working on the Keck Telescope either. It could very well be another myth.

My buddy has disappeared into the other side where they don't publish.
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PostPost by: M100 » Thu Jan 26, 2006 11:25 pm

I've been using Castrol TAF-X 75W90 in both the gearbox and the diff for about 10 years now. It's a GL4 and was the oil Lotus recommended for both the 90's Elan and Esprit boxes. Castrol technical saw no reason why it wouldn't be suitable for the Elan box and when I replaced the diff ratio from a 3.77 to a 3.55 a couple of years ago it looked in good condition.
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PostPost by: 1964 S1 » Fri Jan 27, 2006 2:56 am

...did you say simple question? I use what the shop manual suggests.
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PostPost by: rgh0 » Fri Jan 27, 2006 8:36 am

Martin


Lotus actually recommended a GL-5 oil for the Esprit citroen box, I dont know what they did for the later Renault box. Many Esprit owners including myself actually use Gl-4 oils such as the Castrol one you mentioned as the Esprit diff is not a hypoid design and thus does not really need a Gl-5 oil. Because the GB and diff are one unit also desirable to have lower sulphur additives to avoid corrossion of the synchro rings

Tranverse engine transaxles like in the M100 Elan also dont need Gl-5 oils as they also have no hypoid gears. Thus a Gl-4 oil is the normal recommendation for this type of transmission.

Because neither of these transaxles use hypoid gears the Gl-4 recommendation for them is not relevant for an Elan diff which uses a hypoid gear set.

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PostPost by: M100 » Fri Jan 27, 2006 10:52 am

rgh0 wrote:Because neither of these transaxles use hypoid gears the Gl-4 recommendation for them is not relevant for an Elan diff which uses a hypoid gear set.


I dropped the oil about three months back and it looked ok but it's tempting to put a magnetic plug in there and see if anything is coming off the gears. In the years before switching I just used 80 weight gear oil (guess it must have been EP80 Hypoid now!) in box the box and the diff, but having a drum of TAF-X around for the few 90's Elans I look after I thought about using it for the Sprint as well (the early 90's Elans originally used 5W30 Mobil 1 engine oil but synchro operation gets a bit flaky after a while hence Lotus's change to TAF-X)

After specifically taking Castrol's advice on the Sprint box and diff I expected an improvement - it certainly was as far as gear changing is concerned but I hadn't expected nor have I experience so far any downsides - but it sounds like I'm on borrowed time for the diff!
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PostPost by: tdafforn » Fri Jan 27, 2006 12:52 pm

I thought it was a simple question but obviously not..
I have EP80 GL4 at home as well as EP90 GL5,
Which to use is the question!
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Tim
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