GM #1052271 substitute - Ancient posi trac juice

[GS380T]

What would be good to use as a substitution? This is a pretty rare 1970s posi equipped gearset I'm dealing with and I want to make sure I'm doing a good job. I've attached a page from the service manual and it seems that I would need to use SAE-80W and some friction modifier.

From what I understand the gearset would not do well with synthetic or anything like that. I think I can find the acdelco friction modifier, where can I find straight 80w?

When I checked the fluid level it appeared to be ancient and black, some say to just top it off with some friction modifier and call it a day, the seals indeed are holding, and everything seems fine except for what I think is a clutch hangup when taking off from stopped while turned.

Any thoughts or ideas are appreciated thanks.

 

[Gimpy1]

Torco makes some non synthetic gear oils. Alot of the guys on the GTO forums use it after putting in a tru track. If you want reglar non synthetic Toro RGO 80W90 GL-5 is available at Sumit racing, walmar online and Amazon, its anywhere from $13-16 bucks a quart, its not cheap but it works well. I've used the RGO 75W140 in my GTO and it worked very well in my diff that was designed for a 6 cyl car with 200 hp, that GM thought would be a great idea to use in a 400Hp car that weighs 4000 lbs. Be warned tho used, old diff fluid smells awful.

 

[zrxkawboy]

I would use a quality dino 80W90 and a bottle of limited slip additive.

 

[skyactiv]

It appears that manual says 80W90 is okay minus Canada.

Forget the fact there are parts of British Columbia Canada that have warmer winters than some places in the lower 48.

Napa is the go to brick & mortar for gear lube. They sell Valvoline 80W90 which will be better than anything GM
used in the factory over 40 years ago.

 

[slacktide_bitog]

Welcome to BITOG

It sounds like "controlled" is just an LSD. Does that sound right?

If so, you can use any 80w90 or 75w90. The Walmart brand 75w90 synthetic is a quality gear oil at a great price

 

[SoNic67]

That spec sheet says GL5 80W90. That's what is I would use, there are plenty alternatives, including AC Delco:

https://www.amazon.com/ACDelco-10-4051-GL-5-80W-90-Axle/dp/B007Q10F3S/

 

[MParr]

Pretty much any 80W90 GL-5 with limited slip modifiers.

 

[GS380T]

Thanks for the warm welcome and all the advice!

 

[PontiacHO]

Run 80w90 Amsoil synthetic with Classic Industries additive G7103.
done

 

[RyanY]

https://www.redlineoil.com/75w90-gl-5-gear-oil
Scroll down and check the OEM compatibility link.

 

[Oro_O]

This is my preferred LSD additive; can be had in most auto parts stores, not special order. The ester base would help the older seals. Add one bottle, give it a drive and see if the chatter is gone. If not, add a little more and repeat. And as above, 80w-90 is going to be just fine.

 

[Snowflake White]

Interesting that you can see that the original printing information was changed (newer changed font and print ) in that owners manual later on.
I wonder what is said about the controlled LSD and Power Steering Fluid on the original printing version?

 

[GS380T]

Interesting that you can see that the original printing information was changed (newer changed font and print ) in that owners manual later on.
I wonder what is said about the controlled LSD and Power Steering Fluid on the original printing version?

Good eye! Here is a picture from the previous year service manual. Maybe it holds the answer.

 

[Greasymechtech]

If not rebuilt, posi is well worn out. Surprised you notice it grabbing, but that is normal starting from a stop in a turn.

Prefix only grades are meaningless and pretty much pathetic without any details.

Since an 80w90 can be used, you can find one at malwart or any auto part stores. Most come with LS additive. If you get posi chatter, then add ANY of the available LS additives from your local autopart store, a little at a time with some parking lot left/right circles or figure 8's to make sure there isn't excessive chatter and to work the LS additive in.

Found an 80w GL5 and it was 11.1cst.... making it an 80w85, and would probably shear into an 80w80. So, I wouldn't bother looking for it. The automakers are now using 75w85 GL5 and available at most dealerships in OE form, Mopar, GM, Ford, Toyota, Honda...

No need for synthetic since seal/gasket integrity is unknown. But, any 75w90, 75w110, or even 75w140 GL5 is an option.

 

[kschachn]

What would be good to use as a substitution? This is a pretty rare 1970s posi equipped gearset I'm dealing with and I want to make sure I'm doing a good job. I've attached a page from the service manual and it seems that I would need to use SAE-80W and some friction modifier.

From what I understand the gearset would not do well with synthetic or anything like that. I think I can find the acdelco friction modifier, where can I find straight 80w?

When I checked the fluid level it appeared to be ancient and black, some say to just top it off with some friction modifier and call it a day, the seals indeed are holding, and everything seems fine except for what I think is a clutch hangup when taking off from stopped while turned.

Any thoughts or ideas are appreciated thanks.
View attachment 47508

What leads you to believe this?

 

[Greasymechtech]

Because its pretty rare

 

[benjy]

Redline lubes for sure! if their web dont show recommendations give them a call!! not cheep but VERY good real synthetic ester with proper additives!!

 

[GS380T]

What leads you to believe this?

Someone's response from a vintage Cadillac forum

Because its pretty rare

The sentiment isn't because it's rare it can't use synthetic. It's because due to the fact it isn't easily replaceable means don't mess around and only use what the factory calls for or the equivalent of that.

 

[Greasymechtech]

What the factory calls for was obsolete decades ago

Times change. Get over it.

 

[kschachn]

Yeah, that doesn't make much technical sense at all.