DIFFERENTIAL OIL QUESTION.

[Kellison Jim]

Quick question regarding my Corvair powered dune buggy build. What type of fluid/oil/gear lube do I use on my 4 speed, 140 hp differential and transmission? The more I research it, the more confused(doesn't take much) I get. Do I use the same for both?
Thanks, Jim C.

[bbodie52]

Yes, you use the same for both. The differential and manual transmission are not isolated from each other and lubricant can pass from one component to the other. Here is some information I posted a while back on this subject...

I tend to prefer synthetic motor oils and synthetic gear oil. HOWEVER... whatever you choose be sure to stay away from GL-5 gear oil. GL-5 would be OK in the differential, but not in a Corvair manual transmission. Since the lubrication contents of the transmission and differential are shared between the two components in the Corvair manual transaxle, you definitely do not want to use GL-5 in a Corvair manual transaxle.

Question:
Clarify Comments on Use of GL-5 vs. GL-4 Gear Oil

Concerning the GL-5 gear oil, on your website you state the following: "Mobil 1 Synthetic Gear Lubricant LS 75W-90 can also be used in rear axles where API Service GL-4 lubricant is recommended." However, you also say in this "Ask Mobil" section that: "Mobil 1 Synthetic Gear Oil is recommended for all applications where a GL-5 lubricant is specified. GL-5 type lubricants, which have a higher level of additive chemistry, can be corrosive to yellow metals such as copper, brass, etc., and in these applications a GL-4 product is usually specified." Can you clarify this disconnect here? Thank you.
-- John Goetz, Newport News, VA

Answer:
There are transmission applications that recommend API GL-4 type products where we would not recommend using an API GL-5 fluid because transmissions typically have components made from “yellow” metals. However real axles where GL-4 fluids are recommended do not have “yellow” metal components. As a result, the application of an API GL-5 fluid is acceptable.

http://www.mobiloil.com/USA-English/Mot ... r_Oil.aspx

Mobil 1 Synthetic Gear Oil appears to be a GL-5 lubricant, and therefore should not be used in a Corvair transaxle. It could be used in a Corvair automatic transaxle, since the differential would not be damaged by GL-5 lubricants.

Pennzoil produces both GL-4 and GL-5 synthetic gear oils. The bottle with the blue top is clearly labeled GL-4. It is a high-quality lubricant and would work well in a Corvair transaxle. The bottle with the yellow top is GL-5, and using it in a Corvair manual transaxle could damage the transmission.

Whether you choose a brand of synthetic or non-synthetic gear oil, always be sure the gear oil is rated GL-4. If you have a Positraction Limited Slip differential, also be certain that the gear oil you choose is designed for use in a Limited Slip (LS) differential. (LS gear oil will also work OK in a non-limited slip differential).

SYNTHETIC SAE 75W-90 GL-4

Long Service Life, Wide Temperature Use Gear Oil

PRODUCT DESCRIPTION PENNZOIL® SYNTHETIC SAE 75W-90 GL-4 combines a premium performance gear oil additive package with high-quality synthetic base stocks. The result is a gear oil that provides excellent low temperature fluidity for safe lubrication during very low temperature transmission and transaxle startup, and also maintains a thick protective oil film during extremely hot operating conditions.

PENNZOIL® SYNTHETIC SAE 75W-90 GL-4 is formulated with all the performance additives necessary for outstanding
protection of gears and bearings. It contains extreme pressure agents which protect against shock loading and wear. It is formulated to be compatible with copper containing alloys and soft metals found in synchronizers. Foam inhibitors protect against oil aeration and foam, which can rupture the lubricant film and cause wear due to lack of lubrication. Special rust inhibitors are incorporated into PENNZOIL® SYNTHETIC SAE 75W-90 GL-4 to protect against corrosion than can result from condensation. Oxidation inhibitors are included to further enhance this synthetic’s inherent oxidation stability, resulting in a lubricant with exceptionally long service life and excellent resistance to deposit and sludge formation during high temperature operation.

PENNZOIL® SYNTHETIC SAE 75W-90 GL-4 meets all the requirements of API Service Classification GL-4 .

APPLICATION
PENNZOIL® SYNTHETIC SAE 75W-90 GL-4 is designed primarily for the lubrication of manual transmissions and
transaxles requiring an API GL-4 lubricant. It can be used in passenger cars, light trucks, sport utility vehicles, and vans.
It continues to flow at very low temperatures, providing especially good protection of gears and bearings in extreme cold
weather. It also provides excellent service in hot climates by not thinning at high temperatures, thereby maintaining a full film of protective lubricant on gear teeth. In hot running gear boxes, it allows longer service due to the excellent stability of the synthetic base stocks used in it. It can be used in applications that call for General Motors part number 12345371 gear oil.

http://www.amazon.com/Pennzoil-56076-75 ... B00C43BLLS

The shop manual indicates the rear axle (differential) has a capacity of 4½ pints. It also states that the 3-speed manual transmission has a capacity of 2.2 pints, while the 4-speed transmission has a capacity of 3.6 pints. So the combined capacity of the 4-speed transaxle would be approximately 8.1 pints (4.05 quarts). NOTE: In 1966-1969 the Corvair 4-speed manual transmission changed to a Saginaw unit, which might have a slightly different capacity than the earlier four-speed. I don't have a 1966 or later supplement, so I'm not sure of the lubricant capacity for the 1966-1969 transmission.

I found a further discussion about GL-4 vs. GL-5 use in Corvairs on the Corvair Center website, should you wish to read it...

http://corvaircenter.com/phorum/read.ph ... 887,401578

Here is a list of other GL-4 products. They also mentioned that the Pennzoil GL-4 synthetic lube may be difficult to find in some retail outlets, as the product may be classified as a "slow mover" since it caters to manual transmission owners who need GL-4, but not necessarily to a majority of owners needing only lubricant for a differential in automatic transmission cars which are fine with a GL-5 product. If you want something like the Pennzoil GL-4 synthetic lubricant, you may have to call around. I simply order it from a source like Amazon.com and have it on my doorstep in a couple of days.

* Amsoil Synthetic manual Transmission and Transaxle Gear Lube 75W-90 GL-4
* Citgo Citgear Standard XD 75W-90 GL-4
* Pennzoil Gearplus 80W-90 GL-4
* Pennzoil Synthetic 75W-90 GL-4 (from the spec sheet, the best overall viscosity curve)
* Quaker State Multi-purpose Gear Lubricant 80W-90 GL-4
* Redline MT-90 Synthetic Transmission Fluid 75W-90 GL-4
* Shell Spirax G SAE 90 GL-4 (I do not recommend this due to it's extremely high low temperature viscosity.)
* Shell Spirax GX 80W-90 GL-4 ( do not recommend this due to it's low high temperature viscosity)
* Chevron had a product called Chevron Manual Transaxle oil that was excellent, but I cannot find it except in clearance sites. I don't know if it has been replaced.

By the way, you might find this to be a handy tool for filling your transaxle. It received an average of about 4½ out of 5 stars in consumer reviews from 209 customers. It is about $6.00 from Amazon.com...

Plews 55001 Lubrimatic Fluid Quart Pump, Fits Standard Quart Bottles
http://www.amazon.com/Plews-55001-Lubri ... JDNZQVJVBF

[Kellison Jim]

Brad, Thanks for the quick response! It doesn't get any simpler or clearer than that.
Jim

[azdave]

I use Sta-Lube API/GL-4 SAE 85W90 from NAPA. It's about $24 a gallon but recommended by many others as the best locally available oil for diffs and manual trannies on Corvairs.

[SfcColts]

Would you use the same product for a powerglide?

[Wagon Master]

http://www.amazon.com/Pennzoil-56076-75 ... B00C43BLLS" onclick="window.open(this.href);return false;

Brad, The Pennzoil syn. GL-4 lube on Amazon looks great until you read the description line. It has GL-5 rating listed several places.

[bbodie52]

Brad, The Pennzoil syn. GL-4 lube on Amazon looks great until you read the description line. It has GL-5 rating listed several places.

This was obviously a typographical error on the part of Amazon.com editors when listing this product. They apparently copied the text over from the Pennzoil GL-5 product into the page for the GL-4 product without noticing or understanding the differences. The same listing for the Pennzoil case of 12 GL-4 Synthetic has the correct GL-4 references in the narrative. (See the link below). The product is in-fact a GL-4 synthetic lubricant as identified on the Pennzoil bottle and on the Pennzoil website — notwithstanding the Amazon.com website error.

http://www.amazon.com/Pennzoil-56076-12 ... +Synthetic

[bbodie52]

Would you use the same product for a powerglide?

Either GL-4 or GL-5 lubricant would be satisfactory in a differential that is attached to the Powerglide automatic transmission, because the differential does not contain any "yellow metal" components. Only the 3 and 4-speed manual transmissions contain "yellow metal" components. In a manual transaxle, the transmission and differential share the same lubricant reservoir so both must contain only GL-4 lubricant. In a Powerglide transaxle, the Powerglide is filled with ATF and the differential is isolated from the lubricant in the automatic transmission. Since the components in the differential do not include any items made from "yellow metals", the differential portion of a Powerglide transaxle would be happy with either GL-4 or GL-5 lubricant, as mentioned in the "Ask Mobil" question and answer quoted below.

Question:

Clarify Comments on Use of GL-5 vs. GL-4 Gear Oil

Concerning the GL-5 gear oil, on your website you state the following: "Mobil 1 Synthetic Gear Lubricant LS 75W-90 can also be used in rear axles where API Service GL-4 lubricant is recommended." However, you also say in this "Ask Mobil" section that: "Mobil 1 Synthetic Gear Oil is recommended for all applications where a GL-5 lubricant is specified. GL-5 type lubricants, which have a higher level of additive chemistry, can be corrosive to yellow metals such as copper, brass, etc., and in these applications a GL-4 product is usually specified." Can you clarify this disconnect here? Thank you.
-- John Goetz, Newport News, VA

Answer:
There are transmission applications that recommend API GL-4 type products where we would not recommend using an API GL-5 fluid because transmissions typically have components made from “yellow” metals. However real axles where GL-4 fluids are recommended do not have “yellow” metal components. As a result, the application of an API GL-5 fluid is acceptable.

[miniman82]

On the other hand I've yet to see anyone on the interwebs post pictures of this elusive GL-5 damage to yellow metals, so that's what I put in my trans when I rebuilt it. Some early formulations did have high levels of corrosive additives in them, but those issues have been sorted now. Just don't buy old oil.

[bbodie52]

Attached is a detailed analysis and comparison of GL-4 vs. GL-5 lubricants, by Richard Widman...

The Difference between GL-4 and GL-5 Gear Oils.pdf

The Difference between GL-4 and GL-5 Gear Oils — by Richard Widman

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