The Stovebolt Site Forums The Shop Area Driveline Confused About Types ? SAE 90 GL Number

Hello Everyone

I am based in the UK and own a 1953 Chevy 3600 with 4 on the floor.

Looking at my owner manual it say I need Multipurpose SAE 90 oil for gear box and transmission. This term multipurpose does not appear to track back to an actual specification i.e GL-1 or GL-5

I would say the most common type of gear oil in the UK is EP90 some supplier sites say that this is equivalent to SAE 90 GL-5 which is an EP extreme pressure lubricant but some site also say it is not suitable for yellow metal bushings or bearings. I actually don’t know if my gear box has bronze bushing etc. it does say its suitable for transmissions and Hypoid usage,

I can also buy oils in the UK that have the SAE 90 GL-1 specification, these are still classed as gear oil but tend to state for manual transmission and worm boxes. They don’t mention suitability for Hypoid use which I am guessing is the differential. It says suitable for historic vehicles and tractors

https://www.ryeoil.co.uk/shop/vintage-gear-oil-90/


Thirdly I can buy from miller oils SAE 90 - GL-5 / EP90 this oil say it’s safe to use on yellow metals,

https://www.opieoils.co.uk/p-69297-millers-oils-pistoneeze-classic-differential-oil-90-gl5.aspx

Can anyone help advise me on what I actually need.

Thanks Regards Chris

Hi Chris, the correct oil for your trans if it is a sm420 4sp granny low trans is the GL1 mineral based oil. You also run this in your differential. Anything other is not needed or correct either. Some talk that your other GL5 oils are too slick to use effectively on the sychros to slow the cone down to make a smooth shift. Others will argue that GL5 will work. I personally assembled more than 1/2 dozen sm420s this last year and all got the GL1 oil and no complaints either. The trans will take 6.5 pints, if you have an enclosed ujoint make sure you get some oil in there too, there is a small 1/4" plug to remove on top of the rear bearing housing used for this purpose.

Cheers,
Steve (roots from Norfolk in East Anglia)

Thanks Steve

Thats the answer I wanted so that going to be the Ryeoil

https://www.ryeoil.co.uk/shop/vintage-gear-oil-90/

Best Regards chris

That is confusing. Rear ends (hypoid gears) must have GL-5 or equivalent. Practically all syncro trans. have bronze syncro rings.
George

I just read that George, says no mineral oil in truck rears. Thanks for the clarification.

Oops confused again by the last two comments are we saying that the rear differential needs a GL5 specification oil ? I’m wondering where the comment came from about no mineral oils in truck rear end. I have ordered the GL1 spec for the gearbox anyway.

I did get confirmation from miller oils that the SAE 90 / EP90 GL5 is specifically blended for yellow metals so it shouldn’t corrode anything

Regards Chris

Here is a few truck links shows you my junk - these are unusual in the U.K. so not completely sure what I have regarding engine and transmission etc.

I misspoke on the mineral oil in the rear, George is correct, GL5 or equivalent in hypoid rears. Mineral is good in the transmission though.
Here is an excerp in the GM repair manual:

http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0005.htm

Ok thanks for the explanation I have ordered the miller classic oil for the rear. It’s hypoid rated and yellow metal safe so should be good to go.

Now im going to stick with the above two types of oil for transmission and rear better to be sure etc But looking at the term straight mineral oils shall not be used in the rear. Now both oils are minerals oils as would be most hypoid oils excluding the modern synthetics. So I’m guessing the use of mineral oils is fine in the transmission and rear. So it comes back to the word “Straight” My understandings of the word straight is it means a pure mineral oil without additives. Now going back to the two oils I listed both are mineral oils and neither of them are straight mineral oils as they have extreme pressure additives. I suspect both oils could be the same thing. Anyway just thought this was interesting if there are any oil experts reading this. I could be totally wrong but it would be nice to know either way.

I guess back in the day there were just less types of oil around and you probably had straight mineral oils and then everything else under the multipurpose label. It must be a common question as multipurpose oils don’t exist as a specification


Thanks for the advices. Best regards Chris

Plus keep in mind that the link I provided out of the truck manual was written in 1947, a lot has happened to oils in the last 70 plus years. Try not to get to consumed in it, if it says for hypoid or multipurpose gear oil it will be just peachy, most off the shelf stuff here in the states that says multipurpose gear oil are a GL5 rating