Gearbox oil; Redline MT-90; Synthetic or not? | MG TD TF 1500

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MG TD TF 1500 - Gearbox oil; Redline MT-90; Synthetic or not?

I just had my gearbox rebuilt and its been over 500 miles so I want to change the gearbox oil. Numerous threads on this BBS recommend Redline gear oil MT90 so I bought some. I noticed it was synthetic oil. I do not know what oil was in my gear box; synthetic or regular. Is there any problem with draining the oil out of my gearbox and replacing it with Redline MT90 even though it is synthetic? The specs for MT90 say it is compatible with petroleum oils.
Thanks for your comments.
Milton

Milton Babirak

Yes Milton absolutely!
Len Fanelli
Abingdon Performance Ltd.

Len Fanelli

It seems to make shifting easier, and there is no down side. Use it happily!

Tom Lange
MGT Repair

t lange

Are these comments appropriate for the rear end too?

Christopher Couper

I use Redline MT90 in the transmission, and 75/90 in the diff. I have heard of people using MT90 in both, but have no experience.

Tom Lange
MGT Repair

t lange

Like Tom, I use MT90 in the transmission and 75/90 in the differential. My gearbox has very low miles on it and it is still a little stiff, but loosened up a bit after I converted over to MT90. PJ

PJ Jennings

The specs for Redline MT90 say that it is not suitable for the rear end.
From what I have read so far, it is important to not use a GL 5 type oil in the rear end; use a GL4 type oil. Someone recommended to me to use a GL1 type oil in the rear end. If anyone has any comments about GL1 for this application, I'd sure like to hear them.
Milt

Milton Babirak

Milton: Do you have this backwards?
"From what I have read so far, it is important to not use a GL 5 type oil in the rear end; use a GL4 type oil."

https://www.redlineoil.com/gear-oil-for-differentials

That webpage has the differential oils as GL5 and most of the gearbox oils as GL4

https://www.redlineoil.com/gear-oil-for-manual-transmissions

Christopher Couper

John Twist says to use GL-4 hypoid gear oil, not GL-5, because of bronze/"yellow" parts in diff.

He buys Sta-Lube API/GL-4 Multi-Purpose Gear Oil SAE 85W90 for hypoid gears from NAPA.

I'll probably use it in my diff -- if I ever complete the restoration of my TF.

I trust anything that Tom Lange recommends, including Red Line 75/90 for T-series diffs. I used it right up until I disassembled my car. However, the description on the Red Line web page is confusing to me, so I'll switch to regular GL-4.

Lonnie
TF7211

LM Cook

Some GL5 oils are suitable for use with yellow metals (like Millers), according to the manufacturers.
Dave H

Dave Hill

Going back a very good number of years it has been considered that GL5 is ok to use in diffs as diffs should not get that warm for the potential harmful interaction of materials and product.

For at least 10/15+ years when going into most MG specialist suppliers in the UK buying axle oil with numbers of 75,80, 85, 90 would get you a GL5, not GL4, spec oil whether the buyer realised or not, although it would be printed on the label.

GL4 and GL5 are standards not strict lists of ingredients, what's in them is up to the blender. Some engine, gearbox and axle (re)builders are very strict about what they recommend but like major car manufacturers there are many reasons for their recommendations which might be for many reasons far too restrictive.

More generally many fear putting GL5 in gearboxes as they get hotter (with help I'd guess from dissipated heat from engine and perhaps exhaust) and the yellow metals might be affected by GL5 - it depends on what the oil blender states and your belief (in what they tell you, what you've heard or read, what you previously knew and hold on to).

A good oil is a good oil regardless of its description but some oils are better than others, depending on your vehicle (and your) needs a range of options are generally available and suitable. A better oil will perform and protect better over a wider range of environments and use (and misuse) and help with protection when other components and systems on the car begin to deteriorate or fail.

Personally I use higher priced fully protective oils in my road (only) going 1973 Midget, all from Millers, with their GL5 in the Ford T9 gearbox and original rear axle, as I believe what Millers have said about their GL5 being suitable and because I have a (vastly) disproportionate amount of components and systems failures and like to drive in a spirited manner so believe in greater protection than general requirements.

Nigel Atkins

ETA: by axle oil with numbers of 75, 80, 85, 90 I meant the various two-number-ranges over the years between 75 and 90, for example 80w-90 and what was before and after (sorry can't think of the number combinations at the moment).

Nigel Atkins

I might be a little dense, but where is there brass/bronze in the rear differential? I have a rebuilt 4.1 rear and I can't figure out where there was any brass in it. PJ

PJ Jennings

The rear end has copper thrust washers and the sulphur compounds in GL-5 rated oils will ruin them as well as bronze. I have seen examples of at least one synthetic gear oil advertised as safe for yellow metals that certainly was not.

L E D LaVerne

PJ,
Maybe the thrust washers. The angular contact bearings can also have brass cages.
Regards
Declan

Declan Burns

OK, Thanks fellas I never gave that a thought, I think I put Lucas 75/90 in it, I'll have to check the lable on the can again, if it's wrong I'll change it. Thanks again. PJ

PJ Jennings

L E D LaVerne,
which synthetic GL5 is this please so that it can be doubly avoided?

Nigel Atkins

Just read an article from the Chevy club and they say do not use Lucas 80/90 oil in the diferentials due to bronze spacers used in older Chevys! I'm dropping it out and getting some GL-4 to put in the rear. The Lucas oil is a non synthetic oil and specs are slightly confusing as some folks say it can be used in anything, aparently that isn't so. PJ

PJ Jennings

It was the Royal Purple syn gear oil Nigel. They claim it is safe for yellow metals and I had used it in the past but no more. I saw several images on line a number of years ago in an article that I did not save but the oil was causing damage to the copper thrust washers in a rear end. The sulphur compounds in GL 5 rated oils adhere to soft metals and the shearing action tears pieces of metal away from the base material which is why you should stay away from GL-5 rated gear oils in our cars.

L E D LaVerne

Thanks for your reply.

You do need to be careful about tarring all GL5 oils, or any standard of oils, together. The standard is a rating and can be achieved using different blends/make-up/additives so a modern made oil may not have the same effect as an older formulation.

Damage in those photo may have been from other than the oil used at that time (was that oil a GL5 from Royal Purple?).

There are some oft quoted examples of some in the business going against their competitors products without full disclosure, that's not to say one of these was what you are referring to as obviously we don't know..

If you are concerned and do not believe the manufacturer then go with a GL4 to save hassle.

Decades ago I was told using Mobil 1 (and synthetic oil) in my MGBs and Spridget would ruin the engines and I'd lose me teeth, looks and charm. I done very many tens of thousands of miles and the engines were fine for me and following owners - and I've kept my teeth, looks and charm (and modesty :) ).

Nigel Atkins

What a mess. I guess I will stick with trashing the environment with traditional based oils, which probably have the same compounding issues. :-)

Christopher Couper

https://groups.google.com/forum/#!topic/rec.autos.tech/jM9m87kbi00
Good read. George

George Butz III

Here's a couple non sulfer gear oils, GL-4 rated.