Trans Axle Fluid

[Joeatty]

I have a 66 Monza with auto trans. Leaking axle fluid. What type of fluid do i need to refil once repaired and where does it go in?

Thanks!

[Frank DuVal]

A Powerglide transaxle does not share fluid between transmission and differential, so you can use GL-5 gear lube.
90 or 80-90 SAE is a good choice. 90-140 only if operates only in hot weather. This is my opinion, others will chime in.


Manual transmission transaxles on Corvairs do share gear lube between differential and the transmission, which has brass synchronizers, so a GL-4 is the fluid those use! GL-5 may harm the brass faster than the GL-4 lube. And SAE 90-140 or 90 will make a hard shifting transmission. Try something with 75 or 80 as the first number in GL-4.

[Joeatty]

A Powerglide transaxle does not share fluid between transmission and differential, so you can use GL-5 gear lube.
90 or 80-90 SAE is a good choice. 90-140 only if operates only in hot weather. This is my opinion, others will chime in.


Manual transmission transaxles on Corvairs do share gear lube between differential and the transmission, which has brass synchronizers, so a GL-4 is the fluid those use! GL-5 may harm the brass faster than the GL-4 lube. And SAE 90-140 or 90 will make a hard shifting transmission. Try something with 75 or 80 as the first number in GL-4.

Thank You!

[bbodie52]

Although it is somewhat pricey, I have come to believe that these Royal Purple motor oil and gear lube products are a good match for the Corvair engine and manual transaxle.

HIGH PERFORMANCE ENGINE OIL (WITH SYNERLEC®)

HPS is recommended for use in gasoline and diesel automotive, commercial fleet and stationary industrial engines. Royal Purple® HPS® Series motor oil is specifically formulated to maximize performance and meet the demands of high performance and modified engines. HPS is recommended for vehicles no longer under manufacturer warranty and for those seeking a higher level of performance and protection. Royal Purple HPS oils are fortified with a high level of zinc / phosphorus anti-wear additive and a generous dose of Royal Purple’s proprietary Synerlec® additive technology. These unique formulations enable HPS oils to outperform leading synthetic and conventional lubricants in both gasoline and diesel engines.

PERFORMANCE ADVANTAGES

• Exceptionally high film strength for dramatic reductions in engine wear and reduced engine heat to extend the life of your engine
• Improved sealing between the piston ring and cylinder wall maximizes horsepower and torque and optimizes fuel economy
• Exceptional oxidation stability extends oil life and allows for more miles driven between oil changes saving you time and money
• Advanced synthetic solvency reduces engine deposits and keeps engines clean
• Outstanding wear protection for valve train components, including performance roller lifter and high lift flat tappet camshafts and lifters
• Superior corrosion protection

https://www.royalpurple.com/product/hps ... motor-oil/


This synthetic gear lubricant appears to support both hypoid differentials and, unlike GL-5 lubricants, is safe for "yellow metal" synchros.

Special gear oils are required for hypoid gears found in Corvair differentials because the sliding action requires effective lubrication under extreme pressure between the teeth. ... They are considerably stronger in that any load is conveyed through multiple teeth simultaneously. By contrast, bevel gears are loaded through one tooth at a time. Hypoid gear oil is formulated with extreme-pressure (EP) additives to protect and operate effectively with hypoid gears.

EP additives which contain phosphorus/sulfur compounds are corrosive to yellow metals such as the copper and/or brass used in bushings and synchronizers.

A traditional GL-4 gear oil of any given viscosity has about ½ of the level of sulfur/phosphorous additive that would be in the GL-5 product, so the bond is not as strong, and therefore can be peeled off without peeling a layer of brass (or less brass). This means that the GL-4 product provides a little less extreme pressure protection, so in the differential of a high-powered car, it would not be the ideal product in the differential. To understand this need we should be aware of the fact that the differential is where the final torque is applied to the wheels (in most applications)...

---Some cars (including later Corvairs) came with military specs instead of API gear oil specs. So we should consider that MIL-L-2105B is an equivalent to GL-4, and MIL-L-2105C, 2105D, and 2105E are GL-5 gear oil lubricants.

Tue Nov 07, 2017 11:32 am

... DO NOT USE Redline MT-90 in a Corvair transaxle. Redline's site specifically states that MT-90 is NOT approved for hypoid gears (differential). So it is NOT acceptable for use in a Corvair transaxle since protection for the ring and pinion differential gears is inadequate. Redline does make a modified GL-5 lube that is suppose to work with brass synchronizers called - 75W90 NS GL-5 and states it's approved for transaxles with brass parts. NOTE: Redline NS GL-5 is different vs. their GL-5 which is NOT approved for transaxle use.

Basically, Corvair transaxles share the lubricant in the transmission portion and the differential portion. So it is necessary to compromise and select a gear lube that will protect the hypoid gears in the differential and not harm the "yellow metal" synchronizer components in the manual transmission. A good quality GL-4 Hypoid gear lubricant (SAE 75W-90) in your Corvair manual transaxle is the way to go.

HIGH PERFORMANCE GEAR OIL (WITH SYNERLEC®)

Max Gear is recommended for truck and automotive differentials, outboard motor lower units or in rear axles or manual transmissions requiring an API fluid. Max Gear is a high performance automotive gear oil designed to provide maximum protection to heavily loaded gears while increasing power throughput through the drive train. Max Gear virtually eliminates both gear and bearing wear—even under severe squeeze film conditions caused by extremely high loads, sudden shock loads or low RPMs. Slippery, synthetic molecules not only reduce wear and friction but significantly increase Max Gear’s cold weather fluidity and lubricity, making it the ideal choice for vehicles operating in cold climates. Gears run smoother, quieter, cooler and longer without overhauls. It is noncorrosive to both ferrous and nonferrous metals.

PERFORMANCE ADVANTAGES

• Maximizes horsepower
• Extends gear and bearing life
• Reduces operating temperature
• Lower coefficient of friction
• Superior corrosion protection
• Separates rapidly from water
• For use with open, limited-slip and locking differential
• Contains limited-slip friction modifier

https://www.royalpurple.com/product/max_gear/

Special gear oils are required for hypoid gears found in Corvair differentials because the sliding action requires effective lubrication under extreme pressure between the teeth. ... They are considerably stronger in that any load is conveyed through multiple teeth simultaneously. By contrast, bevel gears are loaded through one tooth at a time. Hypoid gear oil is formulated with extreme-pressure (EP) additives to protect and operate effectively with hypoid gears.

Max Gear 75W-90 is recommended for use in truck and automotive front or rear differentials, manual transmissions and lower gear units of marine engines that specify the use of an API GL-5 or GL-4 fluid. It is non-corrosive to soft yellow metals (brass, bronze, copper, etc.) and synchronizer safe. Specially designed to extend gear and bearing life, Max Gear provides superior corrosion protection over competing conventional and synthetic gear oils. We engineered this ultra-tough, high performance automotive hypoid gear oil to provide maximum protection to heavily loaded gears while maximizing power throughout the drive train. Above all, Max Gear outperforms ordinary gear oils by combining the highest quality synthetic oils with Royal Purple’s proprietary Synerlec® additive technology. As a result, Max Gear makes gears run smoother, quieter, cooler and longer without overhauls. A direct reduction of drag in the drive train has a huge advantage for trucks and other 4-wheel drive vehicles, therefore, better gas mileage. Formulated with a friction modifier additive, therefore no additional additives are necessary. Max Gear is available in the following viscosities: 75W-90, 75W-140, 80W-90, 85W-140 and SAE 90

The selected lubricant for the Corvair transaxle must also be rated for use in API/GL-4 applications. GL-5 lubricants are not to be used in Corvair MANUAL TRANSMISSION transaxles, as the GL-5 formulation will cause damage and corrosion to the internal "yellow metal" synchro's in the manual transmission. GL-4 Gear Oil lacks the reactive sulfurs found in most GL-5 oils that cause damage.

In Corvair manual transmission transaxles, the gear lubricant flows freely between the transmission and the differential sections, so only GL-4 gear lube (transmission) designed for use with hypoid gears (differential) meets all of the compatibility standards for use in both. Some synthetic gear lubricants, such as Royal Purple Max Gear 75W-90 Synthetic Gear Oil is promoted as safe for the yellow metal synchros in manual transmissions and provides full protection for the hypoid gears in the differential. Some other synthetic gear lubricants are not rated for use in hypoid gear differentials, or they are rated as GL-5 and can cause damage to yellow metal components in transmissions. Since gear lube in the Corvair transaxle moves freely back and forth between the transmission section and the differential section, be sure to check the full description and read the fine print if you are considering a synthetic gear lube for your Corvair transaxle.

Since Powerglide transaxles isolate the transmission fluid in the transmission from the differential gear lube in the differential, GL-4 or GL-5 gear lube is safe in Corvair Powerglide transaxles, since it only goes in the differential section. DEXRON ATF is for the Powerglide section!

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Most Corvair transaxles lack a drain plug for the differential. A suction gun like the one described in the video below is needed to remove most of the old gear lube...



How to drain oil without a drain plug - Harbor Freight Oil Suction Gun item 95468

Harbor Freight Item 95468 Oil Suction & Gun is a great way to remove oil from an engine that has no drain plug. Very useful on small mowers and small generators, or anywhere that doesn't have a way to drain oil easily.

To use the device you simply insert the tub into the fill hole of an engine and use the pull handle to suck the oil out of the engine. It can pump quite a bit of oil in one pump. Overall capacity is 16.9 oz.

Construction of the unit is all metal. The only external part that isn't metal is the flexible clear hose. Made by Harbor Freight and branded as a Pittsburg tool, this item has a lifetime warranty.