GL5 vs GL4 Compatibility

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Are most brands in the USA yellow-metal friendly now, or is care in selection still required? Question involves replacing the diff lube in a Rolls-Royce Silver Shadow, and a couple other older cars.
 
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Originally Posted By: Buick8
Are most brands in the USA yellow-metal friendly now, or is care in selection still required? Question involves replacing the diff lube in a Rolls-Royce Silver Shadow, and a couple other older cars.


For what it's worth.

I rebuilt my Triumph Spitfire 20 years ago, the diff was fine, but I did change the lube, I used GL5.
After about 5 years the diff is getting noisy and there is a lot of slack in the gears. When I reboved and dismantled it, the gear lube was a Green colour and there was NO trace of the planetary gear thrust washers (they are/were yellow metal.

On rebuilding the diff again, I used GL4 and have not had an issue since.
 
GL-5 will likely never be 'yellow-metal friendly.' If you have yellow metal to worry about, GL-4 is the answer if you need hypoid protection as you do in your case. For gearboxes without hypoid gears, there are lots of manual-trans lubricants available- Redline's MTL/MT-80/MT-90 series and Royal Purple's Synchromax, for example.
 
Originally Posted By: Buick8
Are most brands in the USA yellow-metal friendly now, or is care in selection still required? Question involves replacing the diff lube in a Rolls-Royce Silver Shadow, and a couple other older cars.


I wouldn't risk it. Personally I don't believe the 'yellow metal friendly' claims for GL-5 lubes.
 
Originally Posted By: Whitewolf
Originally Posted By: Buick8
Are most brands in the USA yellow-metal friendly now, or is care in selection still required? Question involves replacing the diff lube in a Rolls-Royce Silver Shadow, and a couple other older cars.


I wouldn't risk it. Personally I don't believe the 'yellow metal friendly' claims for GL-5 lubes.


The companies claim that they use advanced "buffers" that protect the yellow metals from the other friction modifers (with high sulfur content) but I too have my doubts especially when you CAN find GL-4 available if you look a bit.

The official view from SAE is that GL-5 is NOT a successor or replacement for GL-4 fluids.
 
Copper corrosion per ASTM D130:

GL-4: 3b max after 1hr. @ 121C
MT-1: 2a max after 3hr. @ 121C

Even the cheap Super Tech on the shelf of your local Walmart meets both GL-5 & MT-1.

Please stop with the fear-mongering, folks.
 
Issues are that gear oil isn't changed regularly, or has excessive moisture, or excessive temp caused by low level.... so, its not fear mongering.

But, over the last 20 years, gear oil tech has improved and I don't worry about GL5 in components. I only worry about excess LS additives when not needed.

Doesn't the RR get GL5 in the diff anyway? If no LS diff, use a non-LS fluid.

Another thing to worry about is 'blender accuracy'. When Amsoil did their gear oil test, some fluids failed tests that the manufacturers claimed that their fluid would meet.
 
Most Euro transaxles' use GL4+ these days. With those you get best from both worlds, yellow metal friendliness and hypoid gear protection.
 
With Gl-4 available, why take a risk with Gl-5?

I will continue to use the proper gear oil, which is what I would recommend to anyone who asked me.
 
Originally Posted By: Ramblejam
Copper corrosion per ASTM D130:

GL-4: 3b max after 1hr. @ 121C
MT-1: 2a max after 3hr. @ 121C

Even the cheap Super Tech on the shelf of your local Walmart meets both GL-5 & MT-1.

Please stop with the fear-mongering, folks.



thumbsup2.gif
 
Given the cost of a RR diff, I would not use a GL5 lubricant without getting some comfort from the manufacturer. I would also reach out to RR as I'd be curious to get their take.

I prefer synthetics and I had a long talk w/ the folks at Redline a while back and use their 75w-90 or Heavy Shockproof in my diffs. Redline indicated that their EP additives are yellow metal safe....well at least they were last I checked. Redline has new ownership, so I would confirm.

Beautiful car Sir. I have always admired their craftsmanship and elegant (and distinctive) engineering.
 
I used supertech gl5 in the trans and diff of my old ford truck because it said its safe for top off or refill of manual transmissions and differentials. Also says protects from corrosion of yellow metals. Truck shifts 100 times easier than it did before the change. I don't know what came out but it was really nasty.
 
Reading the labels at WalMart this weekend: all the GL5 on the shelf included the statement that it was yellow metal safe.
I also learned my diff does not have any yellow metal in it, so it's OK anyway.
Thanks.
 
From everything I have read GL-5 is for differentials while GL-4 is for manual transmissions.

Since GL-5 typically comes with friction modifiers and EP additives, these can play heck with manual transmission synchros.
 
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