Reference: Manual Transmission Oil

[leo tomaiolo]

on my 41 ford with the marmon herrington 4x4 i filled my drive line with modern GL-5 fluid. went out for a ride and the drive line was real noisy and the transfer case got real hot. checked the manual and it specified sae 140w GL-3. GL-3 is for mild extreme pressure. i was able to find it (Summit racing). the GL-3 lube made a huge difference in driveabilty. note the modern oil i originally used said it covered GL-3 but was EP. after looking in to it the modern oil did not have enough suspension (MEP vs EP) to stay in the void of the gears resulting in not enough oil cushion between the gears.

[Les Kovacs]

Hi Wayne & Rob.

Great post Wayne.....Rob sent me a similar explanation many months ago as I was looking for a suitable transmission/transfer case oil.

At the time I settled on Redline MT-90. It states that its....

•Safe for brass synchros, as it lacks the reactive sulfurs found in most GL-5 oils that cause damage
•Recommended for GL-1, GL-3 and GL-4 applications, as well as where most special synchromesh fluids are specified.
•Satisfies the gear oil viscosity requirements of 75W90, 80W90, 90 and motor oil viscosities of SAE 40, 10W40 and 15W40

Unfortunately its $25.00 CAD/liter as it is a synthetic.....but shift feel is fantastic.

if you have found a cheaper, safe & local (Canadian sourced) alternative please let me know as its not stated in your post.

Regards to both...

lesk

[Alex van de Wetering]

EP doesn't necessarily mean it's not compatible with yellow metals! I recently bought "Penrite Mild EP Gear oil" for my Chev steering box. It's safe to use with yellow metals. The C8 steering box has a washer and a bushing in brass. The box still leaks though.....so I am now also looking at the 0 or 00 grease, which is what is used in hydraulic systems on trucks here.....I wonder, is it safe for use with yellow metals?

https://www.penriteoil.com.au/produc...ar-oil-sae-110

Alex

[Wayne Hingley]

Originally Posted by Alex van de Wetering

EP doesn't necessarily mean it's not compatible with yellow metals!

You are correct Alex. There are several specialty oils with EP additive packs that are yellow metal "friendly".

Les: I have decided to use Royal Purple MaxGear 75w90. It is available through Canadian Tire.

Below is some info from their website:
Max Gear is recommended for use in truck and automotive front or rear differentials, manual transmissions and lower gear units of marine engines that specify use of an API GL-5 or GL-4 fluid. It is non-corrosive to soft yellow metals (brass, bronze, copper, etc.) and synchronizer safe.

[Les Kovacs]

Thanks Wayne....its now a matter of price....if the Royal Purple product is cheaper than the Redline MT90 I will switch.

Regards,

lesk

[Jacques Reed]

As I am about to swap the gears from one transmission case to another on my Ford F15-A I thought it would be a good time to revisit the type of gear oil to use.
After reading this thread I started hunting around on the net for more info. A lot of info that I read about EP additives to gear oil dealt with damage to bronze synchronizers in synchromesh transmissions or bronze worm gears.

In a Ford CMP truck with a non-synchro transmission my main concern however is possible deterioration caused by those additives to the reverse slider gear bronze bushing and the bronze thrust washers in the end gears in the differentials

Extreme pressure rating GL-4 gear oils have about half the quantity of buffered sulphur phosphate EP additives as GL-5 rated oil so is less harmful to yellow metal. As the rating indicates however, GL-4 Extreme pressure protection of gears is less than GL-5 rating.

The next question: Is GL-4 rated 80W-90 gear oil equivalent to, or even better, than the wartime SAE 90 gear oil as far as gear tooth protection goes? If so only GL-4 rated gear oil seems the obvious choice.

Ford gives a spec in their Special Pattern Vehicles manual as Ford spec MC-568A and call it “Extreme Pressure Gear Oil”. Haven’t been able to find a copy of it. It would probably be difficult to relate it to modern extreme pressure ratings anyway.

I have been using Castrol EPX 80W-90 in my CMP truck but it is GL-5 rated so it would have double the yellow metal damaging EP additive compared to a GL-4 gear oil. I found 3 suppliers of only GL-4 rated gear oils in Australia. Penrite, Hi-Tec, and Shell make them and market them here.

On the positive side, the reverse slider gear bushing seems fine even after being immersed in GL-5 oil for 10 years but then again I cannot see micron size damage! Hopefully ditto for the end gear thrust washers.

Any ideas on the subject gratefully received.

Have attached the link to the paper written by Richard Widman a Chevy Corvair enthusiast and a link to a Machinery Lubrication article on EP additives. Both are very informative on this subject.
https://www.widman.biz/uploads/Transaxle_oil.pdf
https://www.machinerylubrication.com...itives-effects