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lfr101 Dale Hatch
Beamsville, ON, Canada   CAN
Hi everyone this site looks like just what I need. I am working on a 76 spitfire for a friend and her son. We taken the body off the frame , repaired some rot and had the tranny rebuilt and installed a new clutch at the same time. Body work is next . My first question of what will be many is the company that rebuilt the tranny said to use GL4 75w90 gear lube . All I can find is GL5 75w90. I am told that using GL5 will cause the new seals to leak . Does anyone know were I can get GL4 lube in southern Ontario or can I use GL5 lube . Thanks for the advice in advance

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spitfire50 Avatar
spitfire50 Paul Mugford
Rochester, N.H., USA   USA
A synthetic oil may leak from the freshly rebuilt gearbox, but GL-4 or GL-5 wouldn't have anything to do with that.
The big reason to avoid GL-5 oils is that some of them are hard on copper alloys. Some important parts inside e gearbox like synchronizer rings are copper alloy. You may have to order GL-4 oil to get it. If you are near an agricultural supply they may have it, but then again it may only be in five gallon /20 liter buckets.
All the best,

Voda2000 Avatar
Voda2000 Andrew McMillan
Winnipeg, MB, Canada   CAN
Try MT-90 from Redline.

I’m in the process of switching to it but I’ve heard good things.

1978 Triumph Spitfire

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Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
I could bore you to death with the details on this, but basicly oils have changes formulations over the years to meet the requirement of modern manufacturers.

Gear oils have changed in order to deal with the increasing loads and extended service life now expected from our 'gears' in modern vehicles.

At the time our cars were made the same lubricants (available at that time) were suitable for gear boxes AND differental gears.
This lubricant was rated as GL4, it contained sufficent extream pressure additives (EP) to deal with the requirements, tolerances, and gear angles then common, and was also tolerant of yellow metals (Alloys containing Copper) that were commonly used in bushings and thrust washers at that time.

Now fast forward to the 1990's. Manufacturers were imposing higher loads on differentals, they also wanted them to run quieter.
GL5 lubes became available, and fitted the requirments, BUT they tended to contain additives such as sulphur that could attack yellow metal components when subject to heat. But that was OK as modern diff no longer used yellow metal.

However Gearboxes DID use yellow metal, at least in their syncro rings. Also the additives in the latest gear lubes were also too slick for syncro rings to grip properly.

So MTL's (manual transmission lubes) were developed. These provided all the protection that non Hypoid (sliding ) needed but had friction modifiers that could better enable syncros to grip.

These MTL are commonly available as Red line MTL , MTL 90, Pennzoil Syncro and many others.

Diff lubes are also changing. Where we HAD to use GL4 lubes in order to protect thrust washers that are often used in our diff, the latest GL5 formulations are buffered and quite compatable with yellow metal components. BUT NOT ALL!

So what BEST to use in your gearbox?

Many owners (like myself) favour an MTL such as Red line.

arturo64 Avatar
arturo64 Arthur T
Billings, MT, USA   USA
I had to ask for the MTL options at my parts store, they didn’t have them on the shelf! Weird.

68 spit
70 gt6+

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