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Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - Red Line Lubricants

As per my phone call to Red Line here are their latest recommendations For MG T types:
Engine 10W40 HP PN 11404 ( personally I use Harley Davidson 20W50 Synthetic , as it gives about 5 more oil PSI )
Gearbox MT 90-75W90 GL4 PN 50304
Rear axle 75W90 GL5 PN 57904 (Yes GL5 I did question them about it!)
Also I have found that my TD gearbox shifts better, especially when up to operating temperature, ( With Red Line ) when using the whole quart! Yes I know that this is overfilling and some will leak out of the tail shaft housing, but it works.
Len Fanelli
Abingdon Performance Ltd.
Len Fanelli

For TB TC Gearbox use 75W140 NS GL 5 PN 57104
Sorry I could not find how th edit my previous meaasge.
Len
Len Fanelli

And what was their response to why not the same in the rear end as in the trans?

Christopher Couper

I researched GL-4 and GL-5 gear oils last year when I was looking for gear oil for the diff in TF681 after Sta-Lube GL-4 Hypoid Gear Oil was discontinued. I'm no chemist or oil physicist, so I may be totally off base in my interpretation.

GL-5 is for high speed / high load hypoid gears and has more Extreme Pressure additives.

GL-4 is for manual gearboxes for moderate speed and load. The lower amount of EP additives reduces wear and damage to brass synchros.

The amount of damage to "yellow metal" parts caused by GL-5 gear oils is rated by a "Copper Corrosion Test". Gear oils rated as "1a" do not damage yellow metals. Gear oils rated "4c" cause significant damage.

There are no GL-5 gear oils that are rated "1a", but some, including Redline 75w90 that I use in my diff are rated "1b". (I also use Redline MT90 GL-4 in my gearbox.)

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This article from Amsoil discusses GL-4 vs GL-5 additives and uses.

"EP additives

The main difference between GL-4 and GL-5 gear oils is in the level of extreme-pressure (EP) additives. EP additives effectively protect gears by providing a sacrificial layer on gear surfaces; these additives are essential for protecting gears operating under heavy loads and extreme temperatures. A typical GL-5 gear oil provides about twice as much EP additive in its formulation compared to a GL-4 gear oil.

Where are GL-4 and GL-5 gear oils used?

GL-4 gear oils are typically recommended for spur and helical gears found in manual transmissions and transaxles operating under moderate speeds and loads.

GL-5 gear oils are typically recommended for hypoid gears in automotive axles operating under high-speed, high-load conditions."

https://blog.amsoil.com/the-difference-between-gl-4-and-gl-5-gear-oil/

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This article by Penrite shows some of the differences required for gearbox gear oil, vs diff gear oil and a good history of why we can't get the same type of gear oil specified by MG.

https://penriteoil.com.au/knowledge-centre/Gear%20Oil%20Industry%20Specifications/83/what-is-the-difference-between-api-gl-4-and-api-gl-5-gear-oils/1036#:~:text=An%20API%20GL%2D4%20gear,a%20layer%20of%20soft%20metal.

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This 2007 research article by Amsoil compares brands of gear oil and defines the 1a through 4c ratings.

http://www.goodoil4u.com/pdf_forms/g2457.pdf

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Lonnie
TF681
TF7211
LM Cook

OOPS -

You must copy the link to the Penrite article and paste into your browser. Doesn't go to the right place when you click it. 

https://penriteoil.com.au/knowledge-centre/Gear%20Oil%20Industry%20Specifications/83/what-is-the-difference-between-api-gl-4-and-api-gl-5-gear-oils/1036#:~:text=An%20API%20GL%2D4%20gear,a%20layer%20of%20soft%20metal

Lonnie
TF681
TF7211
LM Cook

Maybe this part of the Penrite articles best defines the difference between GL-4 and GL-5:

An API GL-4 gear oil of any given viscosity has about ½ of the level of sulfur/phosphorous additive that would be in the API GL-5 product, so the bond with the metal surface inside the transmission is not as strong, and therefore can be peeled off without peeling a layer of soft metal. This means that the GL-4 product provides a little less extreme pressure protection than a GL-5 oil but less wear on synchromesh components of a transmission. When a GL-5 oil is used in a transmission with synchromesh it can create up to 4 times the amount of copper in a used oil analysis as that of a GL-4 product. Synchronisers will eventually wear to the point where they become ineffective.

When used in a differential, there is a 30% increase in the torque load compared with a transmission, so in this case, the extra EP protection is required, which is where an API GL-5 oil is best suited.

Lonnie
TF681
TF7211
LM Cook

Penrite an Australian owned company still. Founded in 1926. I love their many useful products and informed advice.

Merv
M Hyde

I don’t care what Redline says.

DO NOT USE ANYTHING BUT GL4 SPEC GEAR LUBE IN YOUR TD/F DIFFERENTIALS!!!

You will destroy the soft metal spider gear thrust washers within the carrier unit. They are not available through any sources.


Bill Chasser
TD-4834
TD/c-8151
W A Chasser

Here you are Chris:
TC rear axle / differential Red Line 80-140 GL 5 # 58104
Len Fanelli

I've been using Redline synthetic for many years and many miles in multiple cars and have seen no adverse effects whatsoever. Independent testing has found the same results.
Steve Simmons

This thread was discussed between 18/02/2025 and 20/02/2025

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