SM465 Oil Type - Yes it Makes a Diffference

[cleszkie]

Just wanted to share my experience with using different types of gear oil in my SM465.

Got my SM465 professionally rebuilt by very reputable shop (Anaheim Gear in SoCal) about a year ago. They did all the little tricks to improve the detents, and to improve shifting. I installed it and filled it with 80W-90 Hypoid gear oil with GL4 and GL5 rating (before I recently learned that oils with GL5 rating are mildly corrosive to yellow metals such as the brass synchros in the SM465). The tranny shifted great for the past year until it recently began acting like the synchros were not working properly. Shifting was getting harder and it was wanting to grind during shifts at times. Long story short, I drained the old oil out, removed top cover and side inspection cover to take a look at the synchros. The oil looked good (a little dirty but no brass dust, shavings, or chunks), and the synchros looked good. I had to look long and hard, but finally found a 85W-90 gear oil that was only rated GL 4. It actually stated on the side of the bottle that it was not corrosive to brass! Filled the tranny with this oil and my shifting issues immediately went away. It now shifts much smoother, like when it was just rebuilt. This is just my personal experience, but it seems to support the fact that this tranny is intended for GL 4 rated oil, and that GL 5 rated oils can cause problems. Hope this helps someone out.

[B. W.]

Would you mind sharing the info, I did a quick search & everything I found was rated GL5 or GL4 & GL5 except some of the boutique oils that had no rating at all!

[jeffahart]

What did Anaheim Gear say to use? I was thinking about taking my tranny and transfer to them. I was hoping after rebuild I could just dump in the new gl5.

Here's what I have now. But I think they have a new bottle for the gl4.

['68OrangeSunshine]

Thanks for that tip Cleszkie. I was buying GL-5 90 weight so only one oil type was necessary for both the transmission and Posi rear-end [and transfer case on the Jimmy].
I have noticed shifting issues on one SM465 in the '68 C/10 -- hard shifting, 3rd popping out, etc. I will have to get some GL-4 just for the 4-speeds.

[cleszkie]

Originally Posted by jeffahart

What did Anaheim Gear say to use? I was thinking about taking my tranny and transfer to them. I was hoping after rebuild I could just dump in the new gl5.

Here's what I have now. But I think they have a new bottle for the gl4.

jeffahart - This is exactly the oil I found. The Sta-Lube 85W-90 Hypoid GL-4. Came in a black 1 gallon jug. I am pretty anal about following proper lubrication instructions. I don't recall that Anaheim Gear made any recommendations. However, I could be wrong. Those guys really know their stuff over there and have done a lot of work for me on other gear boxes in the past.

[B. W.]

Thanks for the info guys!

[rsavage]

I use this in two muncie 4 speeds and a BW T10. I will be using it in the sm465 Blazer project.

https://www.summitracing.com/parts/bpo-023-7729

[D.PASSMORE]

Originally Posted by cleszkie

Just wanted to share my experience with using different types of gear oil in my SM465.

Got my SM465 professionally rebuilt by very reputable shop (Anaheim Gear in SoCal) about a year ago. They did all the little tricks to improve the detents, and to improve shifting. I installed it and filled it with 80W-90 Hypoid gear oil with GL4 and GL5 rating (before I recently learned that oils with GL5 rating are mildly corrosive to yellow metals such as the brass synchros in the SM465). The tranny shifted great for the past year until it recently began acting like the synchros were not working properly. Shifting was getting harder and it was wanting to grind during shifts at times. Long story short, I drained the old oil out, removed top cover and side inspection cover to take a look at the synchros. The oil looked good (a little dirty but no brass dust, shavings, or chunks), and the synchros looked good. I had to look long and hard, but finally found a 85W-90 gear oil that was only rated GL 4. It actually stated on the side of the bottle that it was not corrosive to brass! Filled the tranny with this oil and my shifting issues immediately went away. It now shifts much smoother, like when it was just rebuilt. This is just my personal experience, but it seems to support the fact that this tranny is intended for GL 4 rated oil, and that GL 5 rated oils can cause problems. Hope this helps someone out.

I appreciate you sharing, funny - I'm dealing with the same symptoms that you described with my SM465/Blazer. I drained and was looking at refilling with full synthetic gear lube. Currently having the motor rebuilt and changing all the fluids. Hopefully this solves the hard shifting and sometimes grinding that popped up recently. Its been a few years since I changed fluids. I like Brad Penn products, might look at that first.
Thanks David

[El Dorado Jim]

thanks for the info....

[toiletbowl54]

If you dont mind spending a few bucks on oil, Redline has GL-4. And yes it does make a difference which oil you use GL-4 or GL-5. I have an old 1978 harley with brass bushings in the tranny and use GL-4.GL-5 would attack the brass bushings.

[toolboxchev]

I change all my fluids according to schedule, and even before. I would more than speculate that its the main reason to and for longevity in these older vehicles.

Some folks just do not understand what the wise farmer knew.

[BCOWANWHEELS]

I,ve run 50 weight SYNTHETIC gear lube for several decades now. The kind semi trucks use