What gear oil for 4 spd manual

[57rookie]

1971 1/2 ton with 4 spd manual trans. What gear oil / weight goes in the 4 spd manuals on these trucks??

[cleszkie]

85W-90 GL-4 Hypoid. Do not use GL-5 rated gear oil. The additional sulfur in GL-5 will slowly eat away your brass synchros.

[harpo231]

You can use the same oil you use in the rear-end differential. SAE 90 weight.
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[57rookie]

Thank you!! I really appreciate the GL 4 tip also. I will be sure to source the right oil. Much appreciated.

[Alex V.]

GL-4 75/80w90 is best. Amsoil makes a GL4 synthetic that I'm curious to try.

[Toms67]

cleszkie Is right. You want through GL4. They used bronze synchro gears in the older transmissions. They say the new stuff is OK to use. Not so. I’m sure this will start a debate. Couldn’t find any locally. I had to order mine through Amazon.

[wpavlis]

This is what I bought. Most local places Cary it.

https://www.summitracing.com/parts/p...oaAsFlEALw_wcB

[67chevemall]

Originally Posted by harpo231

You can use the same oil you use in the rear-end differential. SAE 90 weight.
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Yes sir and change them both at the same time.
All that new stuff is for new junk.

[57rookie]

So went shopping today and I can't find 85/90 GL4 - not available in my area....
Closest thing I can find is 80/90 that is GL4/5 compatible but I don't want to use anything with a GL5 on the label after reading the above info about bronze syncros.....
I did find a GM spec Penzoil for older manual trannies - it was 80W90 BUT it was GL3 spec- would this work???
Never thought looking for a GL4 spec gear oil would be so difficult....

[jeffahart]

Originally Posted by 57rookie

So went shopping today and I can't find 85/90 GL4 - not available in my area....
Closest thing I can find is 80/90 that is GL4/5 compatible but I don't want to use anything with a GL5 on the label after reading the above info about bronze syncros.....
I did find a GM spec Penzoil for older manual trannies - it was 80W90 BUT it was GL3 spec- would this work???
Never thought looking for a GL4 spec gear oil would be so difficult....

It's getting harder to find on the shelf. You can get this online. It's what I'm using. If you are looking in the stores look for a greenish or blue label white bottle or the new black too. The second link post #3.

You can get it on Amazon.

https://www.amazon.com/Sta-Lube-SL24...s=sta-lube+gl4

Old bottling
http://67-72chevytrucks.com/vboard/s...d.php?t=748768



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[MJN]

Not to hijack or cause an argument but the Service Manual calls for GL-5 fluid. You can download PDF's of them from this thread http://67-72chevytrucks.com/vboard/s....php?p=5781194

[Alex V.]

That page appears to be out of a Chilton's or Haynes repair manual - not sure I'd trust that over factory info.

I've had GL5 in my Suburban's NP435 for the last 7 years and it doesn't seem to be hurting it much, but there is credence to the GL4 argument. My local Napa keeps Sta-Lube GL4, but outside of that I'd just order some online. Very possibly cheaper that way, too.

['68OrangeSunshine]

The GL-4 should work fine.
I just dumped 1-1/2 gallons of GL-5 80/90 weight out of the SM465 on my '68 C/10 Stepside. I pumped a like amount of GL-4 SAE 140 back in. [Took forever.] Owner's Manual specifies "8 Pints" -- that's a gallon, but it took another quart or so to dribble back out of the refill plug.
I topped off the 465 and NP205 w/ the GL-4 on my '71 GMC Jimmy 4x4.
The differentials got topped off with GL-5 since the rears are Posi units on both. I didn't put a Posi in the front D44 of the Jimmy, but I don't think GL-5 will hurt it. No bronze synchros there.
SAE 140 was all they had on the shelf at O'R AP, but for the extreme high summer temps we get here, it should work fine.

[MJN]

Originally Posted by Alex V.

That page appears to be out of a Chilton's or Haynes repair manual - not sure I'd trust that over factory info.

I've had GL5 in my Suburban's NP435 for the last 7 years and it doesn't seem to be hurting it much, but there is credence to the GL4 argument. My local Napa keeps Sta-Lube GL4, but outside of that I'd just order some online. Very possibly cheaper that way, too.

This page is definitely not out of a Chilton or Haynes manual, try following the link I provided in my original post and you'll find the factory manuals in pdf form and this exact page. In fact, I'll post it again straight out of the 1971 Chevrolet Truck 10-30 Chassis Service manual for your convenience.

[bubbasimms]

What about Royal Purple 75w-90 synthetic gear lube with friction modifiers? You don't need the additive unless your running a posi but I was thinking of putting this in both my saginaw 3 speed and my open diff 12 bolt. It says it is both gl4 and gl5 and will not harm yellow metals. Any opinions on the Royal Purple?

[ElKotze]

Well, now I'm confused. I was running GL-5 until I read here I was supposed to run GL-4. After I put in the GL-4, the trans (SM 465) was shifting like new, so I thought: Good news! After a week or so it started to be hard to shift when cold, was fine after it warmed up, but it made me think. If the factory manual calls for GL-5, I will put that back in, it definitely shifted better with the GL-5 80/90 !!

[wpavlis]

I would think as long as it is yellow metal safe you should be fine. A lot of gl-5 rated oils are not yellow metal safe.

[cleszkie]

I think that not all GL-5 rated oils are yellow metal safe. Back when the service manual was printed, perhaps all GL-5 oils were yellow metal safe and it went without saying. However, it seems that some modern additives to some GL-5 oils have made them corrosive to yellow metals. If you find a GL-5 oil that says its safe for yellow metals, then by all means use it. However, if it does not specifically state this, I personally would not use it. The only oil that I can easily source is Sta-Lube GL-4 that states it is yellow metal safe. So that is what I use.

[bubbasimms]

I concur with the above. The Royal Purple states that it is yellow metal safe.

[HO455]

Assuming you have a SM465 here is Novak's data page on them. Down near the bottom they talk about lubricants.

https://www.novak-adapt.com/knowledg.../manual/sm465/

['68OrangeSunshine]

I notice on MJN's chart, it mentions GL-6 for 4x4 transfer cases. I never even heard of GL-6.

[54blackhornet]

I have been running 50/50 GL4 / Lucas Oil Stabilizer. Silky smooth shifting even when cold.