"gear oil" Vs "hypoid/EP gear oil"

Jan 13, 2023
I have a 1961 Land Rover where EP90 oil is recommended for gearboxes, axle differentials, steering box, steering swivels etc.
What I have noticed is that most manufacturers sell a "gear oil" and an "EP gear oil" of similar viscosity, and both stated to be suitable for transmission and differentials?
I know that hypoid gears differ in their meshing from say bevel gears, and so a hypoid oil is recommended. But why an EP oil in a steering box etc?
So a couple of questions please:
# Is "EP oil" just the same as"hypoid oil"?
# Is EP/hypoid required just for hypoid gears, and other differentials, gearboxes can use simple gear oil?

I hope for enlightenment!

Ian F
It all depends on what was available or commonly known in 1961. Times change. Substitutes exists. Knowledge and technology also changed.

My recommendation will be a GL-5 gear oil, in a viscosity similar to, or weather permitting, to whatever was recommended back then.

I don't recommend LS additives or gear oils with LS additives, unless equipped with an LS diff that requires it.
A hypoid gear (spiral bevel) is a particular design that puts a lot of load on the pressure faces of the meshing gears. For this reason there are extreme pressure gear lubes that are designated for hypoid gear sets.

A gear box with straight cut gears or helical cut gears will have a different lubrication requirement than a hypoid gear set. You can use extreme pressure lubricants in a standard gearbox provided there are no issues with material compatibility but I wouldn't use non-extreme pressure gear lubes in a hypoid gear box

I believe that all GL-5 rated gear lubes are designed for hypoid applications.
Hi, nice truck. Few thoughts;

-I would guess that LR recommended what they did given the availability of options then as well as the intended use of the vehicles; one bottle for 5 applications.
-Do not use a GL5 as the additives may harm the yellow metals in the drivetrain. There is some dispute on this, but with many Gl4 options as well as non corrosive, higher end choices (Redline), little reason to take the chance. Lot's of reading out there on this subject.
-I use LR swivel ball grease in my S3 steering box, no more leaks and a good feel

I use Redline in my old Rover drivetrains; MT90 and 75w-90, both confirmed by Redline's tech folks to be non-corrosive to yellow metals including in my Roverdrive/Roamerdrive.

Pic please!
I haven't seen a GL5 gear oil cause problems. Most are buffered and yellow metal safe. The issue is with LS additives and synchro slippage. LS additives, preblended and too common for consumer simplicity, is THE problem. My Nissans/Toyotas/Mazdas even recommended GL4 or GL5 for their manual transmissions. Back then, LS additives were simply added as needed and not preblended into the common gear oils. Now its difficult to find a non-LS gear oil at local stores... catered to foolish US owners that cried about LS chatter, since they or their shops didn't add any!

The threadstarter needs to be specific as a general consensus recommendation is usually foolishness.

What component? what required spec? pictures of owners/service manual spec/requirements/substitutes? any known failure points to address? weather conditions or intervals to adapt to? What location since Europe still had a high volume of manual transmissions and fluids catered to them?

Select a proper fluid for each device individually. Skip the whole EP non EP synchro hearsay, and ancient requirement hogwash.
Also, list aftermarket add-ons or replacement brands/parts, that might have their own requirements.
The threadstarter needs to be specific as a general consensus recommendation is usually foolishness.
"What component? what required spec? pictures of owners/service manual spec/requirements/substitutes? any known failure points to address? weather conditions or intervals to adapt to? What location since Europe still had a high volume of manual transmissions and fluids catered to them?"

"gearboxes, axle differentials, steering box, steering swivels etc."

The info. needed is all there, at least to other vintage Series addicts owners :)

Seriously, aside from different wheelbases and body choices, the core parts of the Series trucks were all very similar from ~'58 thru '71, and there weren't that many drivetrain options, never an automatic...and what was the spec for a Fairey overdrive???.
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No, the info isn't there for all. Just a single blabber teach me all the tech/science in a few sentences post from a new member.

Why does every new thread require teeth pulling?

Let me share my Mazda from the owners manual. If I asked for help picking a fluid, some info that I would provide for each specific component if I was fluid confused.
Manual transmission: Any GL4 or GL5 80w90 or 75w90 gear oil.
Rear differential GL5-only: SAE90 or 80w below some arbitrary temps(don't remember) but prior to SAE 85's and 110's in updated often SAE J306 grade listing. There were no locally available single grade SAE90 or SAE80w oils.... The stock diff, with LS, gets the typical locally available 75w90LS for many years. When the power was increased, I used a 75w140 for the rear diff.
90 grades are plenty thick for the MT and thicker would cause more shift effort. So, the MT continues either 75w90NS or MT90, and have some Ford GL4 75w90 for the next change. In a colder climate, I would consider a 75w85 thumbing my nose at the owners manual's obsolete recommendations. Times change.

Or my Toyota:
rear diff 75w85 GL5
transfer case 75w90 GL5
I used 75w140 in the Toyota since the xfer tends to develop leaks and the diff(older design) took more grades a few years earlier and before the SAE grade reassignment. I went for southern climate thick oil tow protection, especially since it occasionally towed 1.5-2.5 tons as needed, and wasn't looking for the best MPG gear oil. Thumbing nose at Toyota's recommendations!

I don't need to know why/what Mazda/Toyota were thinking, or what is going on concerning ISO/AGMA/SAE ratings, the automaker considerations, or what the additive suppliers have been doing with their formulas and science, and don't even care. Pick an appropriate gear oil, specific to the gearbox, its strengths/weaknesses, and expected usages. That answer is NOT available with the information provided by post #1.

Rarely do I see the same gear oil recommended everywhere. I also thought some 'swivels' had special grease, and maybe aftermarket ones took gear oils.

I also don't see the massive selection of EP vs non EP gear oils at Walmart or any major local autopart store chain. But, we don't know where the OP is located, or what he plans on substituting in place of whatever the OE requirement exists.

Pick the sump, just one..... transfer case, manual transmission, swivel, rear differential, or front differential, steering gearbox, whatever....
Post the specific requirements for that specific component directly from the service manual or owners manual, or both since it sometimes varies, and any mods that might stress that component in order to adapt to what is available now, along with any known issues that some experience with that product range.
Pick a brand that you're familiar with or has some reputation.
Pick an equivalent, substitute, or upgrade available to you in your area.
Repeat for each component sump.

Today, we don't care for EP or non-EP, hypoid or non-hypoid... pretty much down to 'grade', GL rating, and LS or synchro compatibility(only if one cares).

I do care for my manual transmission by picking a suitable MT spec gear oil. I care for my open diffs with a non-LS "GL-5" gear oil. I either LS dose the non-LS gear oil, or use a LS specific gear oil, for my limited slips(common spring/clutch chattering nightmares). I avoid LS additives when not needed. I do NOT fear GL-5 gear oils with my manual transmissions. So, MT GL-4 is just a preference. If I had steering gear boxes, cv joints, swivels, slide yokes, spline gears, slip joints, u-joints, bearings, or other sumps, I'd give them equivalent to what is needed, and maybe adapt/upgrade to weather/climate, usage, failures, or current availability.
Mobil Delvac 1 is a versatile gear lube that has always served me well in my G80’s and now my Jeep‘s Dana stuff …
It is used by the Porsche track crowd to HD on/off road equipment …
Not that expensive either … especially since it’s ESI lube …
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# Is "EP oil" just the same as"hypoid oil"?

No, there are EP oils not suitable for hypoids gears.
EP is an oil propertie necessary for specific systems.
Hypoid is a gear contact that usually requires high EP properties (but there are hypoid gears to work with medium or low EP like GL4+, GL4 or GL3).

# Is EP/hypoid required just for hypoid gears, and other differentials, gearboxes can use simple gear oil?

Answered above. Usually if there are not hypoid gears then don't need hypoid oil properties like manual transaxles with spiral gears + bevel differential not hypoid. Anyway sometimes manufacturer ask for high EP/hypoid oil when not hypoid gears.
Spent my early mechanic years working on all manner of Landrovers.I wish I knew then what I know now.The differentails are all open and any 75W90 or 80W90 that is GL5 rated will be fine.
The gearbox is another matter.Back in the day everyone used differential lube,usually called EP or HD gear oil.This was long before synchromesh fluids were available.So today I would recommend a 75W90 synchro oil,of which there are many available.For anyone who has had the pleasure of removing a Landrover gearbox you would do anything to not have to.So keeping the box in good order is important.The synchro oil will prolong the life of the synchromesh assy which is only on 3rd and 4th gear and the brass bush which supports the 3rd and 2nd speed mainshaft gears.The transfer case is fine with any 90 weight gear oil,however my recommendation would be a 90 weight Synchro oil.This will mean if there is leakage between the transfer and main gearboxes the oils will be compatible.Just my 2cents worth.