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for all year MGBs, MGB-GTs and Midgets
Established in 1975


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TECH TIPS

Gear Oils
this is an excerpt from the articles appearing in the OCTAGON

also see upkeep and performance hints on our message board at board.mgclub.org

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Gear Oils

Q:     Hello Art, its me again. Thanks for your help in the past. My 1973 MGB/GT is making a whirring sound when I shift from 2nd to 3rd and 3rd to 4th. It sounds like its coming from the rear axle assembly, although Im not totally sure. As a starter, I decided to drain the gear oil from the axle and replace it since its been a long time since I did that last. The Official Manual says use 90EP gear oil only.

I went to the auto parts store today and although there was a huge selection of gear oils, there was nothing like 90EP. All were multiple viscosities, some with 90 as the high such as 75W90 and some with 90 as the low e.g. 90W140. What would you put in your GT? I live in western Colorado where it can be 100 degrees plus in July and August and five below zero in January. Also, how scared should I be about the whirring sound?

Thanks again.

Don Colby

 

A:     Hi Dan, the correct designation is actually EP90 HP (high pressure) hypoid gear oil. This is a fairly common gearbox oil and is the designated type for Land Rover and Leyland products. It's what I use in my B's differential. Transmissions use engine oil (straight SAE 50, which is getting harder to find, or 20W50 multigrade). I live in northern New Jersey and, while the weather may not be as extreme as Colorado, it gets pretty cold and hot here as well.

Below are some descriptions of the oils you were talking about and their properties. The 80W90 is closer the original EP90 and has lower pour point, so would well in colder conditions. It would be a good alternative if EP90 is not available. The 75W90 is describe as synthetic and has a higher viscosity index, so I would not advise it. G90/140 or 90W140 (not listed below, but questioned in your letter) is a "climbing" oil designed to cling to gears in extreme applications. I have used it in industrial reducers and, while very good, can be very dense (viscous), especially in cold weather. It can do more damage than help in most daily-use automotive applications.

In changing your differential oil, just make sure your 'whirr' is not just low oil related. A consistent whirr noise to me is the beginning of a bearing failure. Catch the oil and sift it through a paper or fine screen filter to see if there's any metal entrained. Also, there are these small fiber washer spacers that tend to wear, break and drop out. Their failure is usually characterized by a slight "clunk" when accelerating or slowing, but in the extreme can cause gear wear that will make more of a thrumming noise, but might actually be what you are hearing.

I hope this helps you. Let me know what you find. Good luck.

Art Isaacs

Information below courtesy of Hindustan Oil, Ltd.:

HP GEAR DRIVE EP 90

- HP gear drive is multipurpose gear oil containing extreme pressure additives for moderate service condition

- Meets API GL-4 , MIL l 2105 & EP type GL-4

Level of IS 1118

- Application areas are manual transmissions of automobiles requiring this type of extreme pressure oils

- Excellent thermal & chemical stability

- Protection against rust & corrosion

Ensuring longer trouble free protection

Kinematic viscosity, cst. @ 100c 16.5 -17.3

Viscosity index, min 90

Flash point, (coc), c, min 180

Pour point, c, max - 9

Corrosion copper strip at 121 c,

For 3 hours , max 2

Channel Point - 18

HP GEAR OIL EP 80W 90

- Hp gear oil ep 80w 90 is multigrade gear oil

Containing extreme pressure additives for moderate condition service

- Meets API GI-4 , mil l 2105 and EP type GL-4 level of IS 1118

- Application areas are synchromesh transmissions and manual transmissions of automobiles

- Excellent thermal & chemical stability

- Protection against rust & corrosion

Ensuring longer trouble free protection

Kinematic viscosity, cst. @ 100c 13.5 -24.0

Viscosity index, min 90

Flash point, (coc), c, min 165

Pour point, c, max - 21

HP GEAR OIL EP 75W - 90

- HP gear oil EP 75w 90 is fully synthetic gear oil containing extreme pressure additives for sever condition service

- Meets API GL-5

- Application areas are all gear boxes

Where a viscometrix of 75w 90 is recommended for extended drain intervals

- Excellent fuel economy

- Enhanced low temperature properties

- Good performance even under extreme

Pressure & varying load conditions

- Long drain intervals

Kinematic viscosity, cst. @ 100c 13.5 -24.0

Viscosity index, min 170

Flash point, (coc), c, min 180

Pour point, c, max - 42


 


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