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MG MGB Technical - Steering oil

I am planning on replacing the Bellows on my front steering rack. What GL oil should I use? I see articles that says 80-90wt GL4 should be used not GL 5 then an article that says the exact opposite.
TRH Hammond

The factory specified the same oil as used in the rear axle. Going by Castrol bottles I have that is GL5 labelled for differentials and showing a picture of an axle, GL4 is labelled for gearboxes and shows a picture of a gear lever, that is used in the V8 gearbox.
paulh4

On another MGB forum there are discussions on GL4 vs GL5. There seems to be a problem with GL5, in that it attacks brass / bronze bits.

Herb
H J Adler

Try to locate GL4 to use in your steering rack and differential. It's much friendlier to softer metals such as brass and bronze. GL5 contains a high amount of sulfur which attacks these metals. RAY
rjm RAY

Get GL 4, you can then use is in your axle as well. The trouble with GL5 oils is they are too good and form a strong, sacrificial attachment to the metal gears etc. When they are stripped off under high pressure operating conditions, they take some of the softer metals metal with them.
Not so much a problem in a steering rack, but why use it when you need GL4 for the axle!
Allan Reeling

GL5 oil composition has been changed since 1900 but plenty people here seem not to have heard about it re attacking yellow metals and excess sulphur.

GL5 includes additives for hypoid axles, GL4 does not, therefore use GL5 in the back end.

As others have said use GL4 in the gearbox but some manufacturers were advising engine oil in the gearbox in the 60's and 70's and there are stories that towards the end of MGB production BL were suggesting GL4some oil.

On the other hand those that have not heard of the properties of modern GL5 oils will probably have from the 50's old tubs of oil that there dad used on his tractor and it never damaged that.

Eddie Cairns

The problem with GL5 oils is in gearboxes, where it can damage the synchromesh components due to stripping as described above. It's not a problem in axles, or the rack.
paulh4

GL5 is not good news for the bronze "shims" behind the planet gears.
Allan Reeling

GL4 is a hypoid oil, which simply put means a high pressure oil designed to protect areas where two or more gear teeth are in contact, under high pressure, at one time. It's too thick for use in a transmission. BL advised using it, in the transmission, towards the end of the B's production. They later rescinded this advisory due to poor operation when the transmission was cold. Shifting the transmission, with Hypoid inside, is like trying to move a large stick in a bucket of mud. RAY
rjm RAY

Gear oil viscosity is measured on a different scale to engine oil. EP 90 is not thick oil, it is roughly the equivalent viscosity to 40- 50 engine oil. It's just not multigrade, hence it's poor cold performance. Gear oil was specified for the V8 gearbox, rather than the 20W 50 used in the largely similar 1800 box because it was deemed to offer the high torque performance needed to cope with the output of the V8. Similarly a higher specification Hypoy B was recommended for the final drive.
Allan Reeling

Try some 600 weight gear oil like in my Model T. Very highly viscous. All the Ford oldie places sell it, trick is not to get repackaged STP oil treatment. That's right, about the same viscosity. Not grease, it is oil.
S Nott

I've never had any problem with GL4 gear oil in the V8 gearbox, even when it was a daily driver, parked outside, and in winter at temps well below freezing. It is to cope with the higher torque of the V8 as Allen says. I've seen this comment from America about gearboxes with gear oil being unusable regularly over the years, maybe their gear oil is different to ours.

But comparing my V8 and 4-cylinder manuals the specifications for the rear axles and the steering gear oil are exactly the same for both, which is basically a higher spec (GX instead of GP, or HD instead of EP) than for the V8 gearbox. Castrol containers are quite clear in that GL4 is for gears, and GL5 for axles. Whether GL4 in an axle would cause a problem - eventually - or not is another matter. GL5 hasn't yet in my 100k/22 year experience.
paulh4

Paul, Below taken from Castrol's product specification pages.
CASTROL EP90

Extreme pressure multi-purpose gear oil for hypoid and non hypoid applications where specified by the manufacturer.
API GL-4 It seems the "B" has been dropped and the "less extreme pressure sea 90, i.e., Hypoy 90 is classed as STD (standard).
Allan Reeling

"where specified by the manufacturer."

Was it specified by MG? The WSM for Castrol in the axle says Hypoy B 90, but the terminology will have changed several times since then. Castrol for the V8 gearbox is 'Hypoy', i.e. not even Hypoy 90, which is a less extreme oil than Hypoy B 90.

It may well have been decided that the 4-cylinder axle didn't need the more extreme version, but it's not doing any harm, and I certainly wouldn't derate the V8.
paulh4

This thread was discussed between 20/05/2016 and 24/05/2016

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