The Stovebolt Site Forums The Shop Area Driveline Transmission Gear Oil

I'm looking at buying a rebuilt SM420 for my '51, and I've been doing some research on gear oil. From what I can glean from the internet, GL-5 oil is out. I have read some good reviews of Sta-Lube 85W90 GL-4, but it seems a bit pricey at almost $38 a gallon. Then I found that Coastal has 90 weight in both GL-4 and GL-1, at about $10 a gallon . Does anyone have any experience with the Coastal oil? Any opinions on GL-1 versus GL-4? GL-1 seems like it would be more in line with what was available 50 years ago, but that may not be the best.

Hopefully, things here don't get as heated as they do over motor oil preference.

I saw that Quick silver Marine SAE 90 is the best for our SM420'S--Bill.

Coastal is fine.

SAE 90 "multi-purpose" gear lubricant was specified.

Any brand should be OK. I have used Coastal.

NAPA carries a GL-1, and I recently got some Lube King GL-4 90W in a 2 gallon container for a very good price even with shipping.
(Google it)In fact I bought two!

Valvoline Synchromesh is a GL4 oil. They claim to be good for pretty much everything.

Thanks for the replies, everyone.

The Quicksilver looks good, but a bit much for my current budget, Bill. I can order a gallon of Coastal for what a quart of the Quicksilver costs. With having two kids and three grandkids under my roof, I have to really watch the dollars.

I'm not sure that Valvoline has Synchromesh available anymore, Whitedog. I searched their website, and it wasn't found. What they did have on their site was rated GL-4/GL-5, which from what I've read is the same as using GL-5.

Thanks for giving me a bit more confidence about the Coastal, Tim. If I can't find anything at NAPA like Ed suggested, I am planning on ordering the Coastal I found online.

Any discussion about GL-1 versus GL-4 in our applications?

The GL-4 has a few more additives for anti-rust, anti-foam, etc. which might not be absolutely necessary for use in a transmission, but "nice to have". The main concern is to avoid the extreme pressure additives the GL-5 has which can attack bronze parts such as synchronizer rings. I used to do a lot of business with a Fuller Roadranger transmission rebuilding shop in San Francisco when I ran a truck shop out there. They had 55-gallon drums full of trashed synchronizer rings caused by people running hypoid gear lube in Roadranger transmissions.
Jerry

I was able to check a couple of places in town today. From what I saw, straight SAE 90 is still safe. All multi-viscosity oils I found today were either GL-5 or GL-4/GL-5. AutoZone had Pennzoil Synchromesh, which is GL-3, for $8.99 per quart. Our local farm store had Champion SAE 90 GL-3 for $27.99 per 2-1/2 gallon jug. NAPA was closed by the time I got there. At least I have options locally.

My local Tractor Supply carries SAE 90 GL-1 labeled Ford Tractor Gear Oil...was about $18.00 for a 2-gal jug.

NAPA has SAE 90 GL-1 in a 1-gal jug for about $13.00, I just bought some last week for my Bolens Garden Tractor.

Mike B

Thank you very much, Mike

I hope this information is read in the future.

SAE 90 GL-1 will work very well, and the price is right.
hmmm, there must be a more expensive, synthetic, multigrade, race-car-rear-end replacement?

Would the Tractor Supply GL-1 SAE 90 Ford tractor oil be good to use in the 4 speed transmission of my '51 2-ton? It has a PTO attached, if that makes any difference. Or would something GL-4 be better?
The truck doesn't see a lot of use, but when it does, it's usually hauling about 12,000 lbs of grain, so I imagine there's some strain on the transmission that would need a pretty good lubricant, which might call for the GL-4? Tell me if I'm wrong, and if so, what the best option would be.
Thanks!

SM420 transmission?

GL-1 SAE 90 is OK - SAE 90 was original spec.

Novak Transmissions: "An 80W-90, API-GL5 or MT-1 rated fluid is very good. Some claim faster shifts from using a 50W engine oil in their transmission and we do not consider this to be contraindicated unless you operate your vehicle in a very warm environment."

I'm still pretty green, so how do I tell what transmission I have? All I know is the truck is a 6400, 4 speed, with a hi/lo rear axle.
Thanks!

GM switched from the SM-420 4 speed to the SM-435 4 speed and NP-540 series 5 speed in 1967/1968.

Ed

235Kidd - always list the year (with the make/model - which is apparent in your post).

According to Novak's website, 67 was the last year for the SM420, 1968 was the first year for the SM465. The SM420 was still used in some Military trucks into the early 80s though.

http://www.novak-adapt.com/knowledge/transmissions/manual/sm420

http://www.novak-adapt.com/knowledge/transmissions/manual/sm465/