Lotus Elan

Differential Oil Level

PostPost by: Stevie-Heathie » Sat Feb 25, 2017 1:36 pm

Hi folks, would appreciate your thoughts on Diff oil levels

My S3 has had a weeping diff since I acquired her 15 months / 1,000 miles ago.

I topped up the diff today and it took about 200ml of oil to reach the level of the plug. I believe the capacity of the diff is about 1litre. So I lost 20% over the course of 1,000 miles and 15 months.

The leak seems to have stopped now - presumably because the level is "too low".

Any thoughts on whether running a diff with 80% oil level could do any harm? Sprited road use.

Going forward, I plan to sort out the leak "when I get around to it" and meanwhile top up the oil every six months or so. Does that sound reasonable or should I prioritise addressing the leak?

Thanks all.

Steve
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PostPost by: nmauduit » Sat Feb 25, 2017 2:56 pm

I don't think only missing a bit of oil for 1000 miles of road use is going to make a difference to the diff: these are real strong units, and unless they are wildly abused (overheat on the track, poor oil quality possibly with chips or nuts etc) they can withstand quite a bit. We were on the track with a friend's Westfield eleven one day and it started making a lot of noise after a dozen laps, we could not understand each other even screaming, we thought a transmission shaft was dead inside of something major : diff was just empty - once refilled, it has been just fine since. But if it was making noise while there was still 80% of the oil I'd be cautious.

An other anecdote, I gave our city car to a pro mechanics a couple years ago for changing the transmission shafts, and he forgot to put back the gearbox oil plug. I noticed 2 years later when I eventually decided to change the oil... and there was about 2 glass of black oil left in it rather than 2 liters. The gear change had become a tad less smooth maybe, but it's still working (I use it as a workhorse - and do not do the maintenance myself on current cars if I can avoid it). The thick oil is very efficient, as long as there is a bit of it where it's needed.
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PostPost by: ericbushby » Sat Feb 25, 2017 3:16 pm

Steve,
Be watchful with that. My diff was just dripping for a long time from the shaft seals, but mainly from the pinion shaft. It went on like that for ages but then deteriorated rapidly such that it would leave a pool in two hours.
I had it rebuilt and it has been dry since.
I now have a 4" diameter access hatch in the boot front face. It takes longer to remove the spare wheel etc. than to check the oil level. After removing the plug I can see the oil with a torch.
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PostPost by: Stevie-Heathie » Sat Feb 25, 2017 5:00 pm

Access hatch through the wheel well is such a good idea Eric - got any photos you could share by any chance?

I presume it's 4" dia bung (if you can find one that large?) in a 4" dia drilled hole?

TIA
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PostPost by: ericbushby » Sun Feb 26, 2017 10:02 am

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Hi Steve, some pictures of what I did.
The access hatch is a 4" unit used for boats. The fibreglass is quite flimsy when you cut a large hole in it, so I fitted an aluminium ring at the back of the panel which holds the whole thing straight.
It would have been better if fitted more to the right, but it works just fine.
You will notice the special spanner I made for it from a sawn off open end spanner, drilled and filed to take a 3/8" extension.
Hope this is useful
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Edit, I don`t know why there are two photos the same but I am that pleased to get it to work at all, that I dare not alter it. The hatch came from ebay
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PostPost by: nmauduit » Sun Feb 26, 2017 10:21 am

ericbushby wrote:You will notice the special spanner I made for it from a sawn off open end spanner, drilled and filed to take a 3/8" extension.


one can purchase similar tools as "crowfoot wrench" - can be useful on the last exhaust header nut for instance...
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PostPost by: Paul Chapman » Sun Feb 26, 2017 10:41 am

Great job Eric, you have made a 'mission impossible' check an easy to do routine task.

Well done !
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PostPost by: billwill » Sun Feb 26, 2017 12:38 pm

To get the big hole centered over the drain/fill plug you can drill a row of small holes in the likely area then poke a nail through each and get underneath to see which is nearest to the drain plug.
Then use that as the centre for cutting the big hole.
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PostPost by: The Veg » Wed Mar 01, 2017 8:03 pm

I like the boat-hatch idea! Been meaning to make some sort of access in that location but hadn't thought of that. Will deff look into it!
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PostPost by: promotor » Thu Mar 02, 2017 8:20 am

Stevie-Heathie wrote:
Any thoughts on whether running a diff with 80% oil level could do any harm? Sprited road use.

Going forward, I plan to sort out the leak "when I get around to it" and meanwhile top up the oil every six months or so. Does that sound reasonable or should I prioritise addressing the leak?

Thanks all.

Steve


Hi Steve,

I've seen Hot Rod / Oval racers (a lot of them use English axle and diffs) give these diffs hammer and they manage to survive OK for a season or so considering that the oil is always at the outside wheel bearing and not in the gears due to centrifugal forces associated with going around a clockwise or anti-clockwise direction only.
Eventually they do cook the diffs though to the point where the crownwheel and pinion are usually scrap.

However I think that in the Lotus casing where the oil can't go anywhere except out of a small leak hole - providing the level is topped up and there's a diligent owner present - and there's just "spirited road use" keeping a check on it for now should see you through.

HTH
Last edited by promotor on Thu Mar 02, 2017 10:04 am, edited 1 time in total.
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PostPost by: elanman999 » Thu Mar 02, 2017 8:28 am

That's a very good idea with the boat hatch.
The spanner is also good, but oldies like me still have our Whitworth sockets. :lol:
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PostPost by: ericbushby » Thu Mar 02, 2017 9:49 am

Yes John, I know what you mean. As a fellow oldie, I have stuff that I have had since I had a nearly new TR2, but the alignment is not quite good enough for a socket and universal joints are awkward through a hole.
Also it cost nothing and works well.
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PostPost by: KevJ+2 » Fri Mar 03, 2017 10:34 am

Same sort of idea...
I made mine (for Plus 2) as a box as my handbrake tree was fouling on the body and this gave a bit more room.
It also had the added advantage of giving the diff filler access :D

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PostPost by: 2cams70 » Sat Mar 04, 2017 10:27 am

The usual thing that happens on an English axle run low on oil is that the crownwheel carrier bearings become pitted and worn. May not necessarily cause the axle to whine but it does result in a constant "gravelly" noise similar to worn rear wheel bearings on a live rear axle car.

It takes a severe oil loss to damage the crownwheel/pinion or the pinion bearings since these operate much lower in the carrier housing and usually still remain immersed in oil.
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PostPost by: William2 » Tue Mar 21, 2017 6:55 pm

Such a good idea that I went for Eric's boat access hatch option. Easy job apart from drilling the lower pair of holes. Another plus point is that it gives good access to grease and check the handbrake tree. I believe that the diff oil filler nut is 3/8" whitworth so I have ordered a 1/2" drive socket off Ebay.
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