Can you run Schaeffer 50W oil in a SM465?

[SquareRoot]

So, it sounds like the consensus for SM465 is SAE-80W-90 GL4. But @AuroraGirl posted a picture from the 1980 owners manual on Oct 9, 2021 in the "2wd SM465 Speedo Gear Problems" forum, which shows SAE-80W-90 GL-5, or in Canada (like me), use SAE-80W GL-5. Why does the manual specify that if GL-5 is actually harmful?

Also, that forum seems to conclude 85W-90 GL-4 CRC gear oil should be used (what is CRC?). So that forum disputes this forum?

Do we have consensus? What about NP205? The same?

Ohhhh...sounds like we got ourselves a conundrum! All I have to add is be glad ya'll don't have NV4500's. That oil is harder to source than Unicorn piss and pricier than liquid gold. Ahhh, but she shifts like melted butter.

 

[DoubleDingo]

I'll be sticking with GL4 in my old manual transmissions.

 

[Ricko1966]

So, it sounds like the consensus for SM465 is SAE-80W-90 GL4. But @AuroraGirl posted a picture from the 1980 owners manual on Oct 9, 2021 in the "2wd SM465 Speedo Gear Problems" forum, which shows SAE-80W-90 GL-5, or in Canada (like me), use SAE-80W GL-5. Why does the manual specify that if GL-5 is actually harmful?

Also, that forum seems to conclude 85W-90 GL-4 CRC gear oil should be used (what is CRC?). So that forum disputes this forum?

Do we have consensus? What about NP205? The same?

I don't have the pic you are referring to and not going to spend a bunch of time looking for it. Screenshot it,put it up for us. In the mean time do a search "does gl5 damage shift syncros" Now to make it more fun all gl5 is not the same. Some is safe,some is not.

 

[Mark80K15]

I don't want to reproduce a pic from an existing post, so here is the link, look for the @AuroraGirl posting on Oct. 9, 2021:

2wd SM465 Speedo Gear Problems

This is the only GL-4 lube that I've been able to find for the last few years. Been running it for several years in my SM465, and in the Super T-10 in my Chevelle. https://www.amazon.com/gp/product/B000M8RYMC/

www.gmsquarebody.com

 

[Mark80K15]

I found an short post outside of GMSquarebody.com that states "most GL-5 lubes are now compatible with yellow metals IF it has a rating of "MT1". Early GL-5 lube may have been corrosive, but, most of the new GL-5 lubes have counteractive agents to any sulfurs that reside in the oils".

This post didn't provide anything to back up this suggestion. Does anyone have anything else to add? I'm still struggling with the idea of using GL-4 instead of GL-5, when the 1980 GMC Service Manual explicitly states on Page 0B-16 "SAE-80W GL-5 or SAE-80W-90 GL-5 gear lubricant" for "Manual Transmission, Conventional transfer case".

 

[Hunter79764]

When I had my SM465 rebuilt for the first time in the early 90's the builder told me to us SAE 50 ND. He told me the non detergent oil won't suspend the dirt in the oil. Dirt collects in the bottom of the case. Ran the transmission on the road until 2002 when I started bogging the truck, so it has seen some abuse. I tore it down in 2020, there was a lot of sludge in the bottom and around the magnet, but very little wear on the gears and syncro's. Only wear I had was from me grinding gears when throwing it in reverse

Maybe not directly applicable, but I was recently told by an industrial expert in the field to use non detergent oils in gearboxes, as the detergents that are often found in motor oils contribute to foaming as well, which can cause all sorts of issues. Sounds like it might be X2 on Non-Detergent oil use in a conventional gearbox, unless of course the OEM calls for it. I would ASSUME that ATF detergents don't have the same tendencies, since ATF is sometimes called out for certain manual transmissions, but who knows?

 

[DoubleDingo]

Maybe not directly applicable, but I was recently told by an industrial expert in the field to use non detergent oils in gearboxes, as the detergents that are often found in motor oils contribute to foaming as well, which can cause all sorts of issues. Sounds like it might be X2 on Non-Detergent oil use in a conventional gearbox, unless of course the OEM calls for it. I would ASSUME that ATF detergents don't have the same tendencies, since ATF is sometimes called out for certain manual transmissions, but who knows?

Never knew that, but now I understand why the gear oil in my saginaw 3 speed was foamy looking when I had to drain it. I used Valvoline 80w90 gl5 because that was the "newest" gear oil the place had. I now have gallons of NAPA 90w Mineral Oil on hand and will only use that in my old gear boxes.

 

[cvanerstrom04]

Has anyone ever used AMS OIL Severe Gear 80w-90? says its a GL5 but works for GL4 applications. stuff is kinda spendy but seems like a decent oil to run. any input?

 

[Mark80K15]

Actually, that's what I wound up getting. Partially because Amsoil has an excellent reputation, partially because when using the Amsoil website and specifying "1980 GMC K1500 4WD PICKUP 5.7L 8 -cyl Engine [L]" and "For Manual Transmission: 4-SPD GL-5 All TEMPS 80W-90,80W", it tells me to use SEVERE GEAR® 80W-90. As I mentioned above the 1980 GMC Service Manual also explicitly states "SAE-80W GL-5 or SAE-80W-90 GL-5 gear lubricant". Also, I read somewhere that the MT-1 specification that this product meets eliminates the concern about GL-5 being corrosive. Sorry, don't remember where I saw that.

If I remember, I'll let you know in a month or two where I'm at.

​

 

[metal tech]

When I was stationed in Idaho, I had a 76 GMC and used the Amsoil in the trans. With regular gear oil it was really hard to shift in the winter. I swapped to the Amsoil and it was so much smoother in the cold, summer time it was even lighter shifting, but it did make a little more noise. I put the Amsoil in my 85.

 

[Mark80K15]

Thanks @metal tech , can you please tell us what grade of oil you used?