65 corsa 4-speed transaxle fluid question

[MR65Corsa]

Good Day All,

Just a quick question regarding changing the transaxle fluid in a 65' 4-speed. Are there two separate fill holes or just one to fill both? I had always assumed that there would be just one since they shared the fluid but after reading some threads on this forum it leads me to believe there may be two. Can someone please clarify this.

I purchased the car last fall and noticed the fluid was low on the transaxle dipstick so I want to change it and get it back to full again. On another forum I read that after 64' GM quit putting a drain plug on these units so to do a change on later models the fluid had to be manually suctioned out. Is this true? Based on what I've read here, I plan on using the synthetic Amsoil Manual Transmission & Transaxle Gear Lube 75W-90 unless someone has a better suggestion.

Thanks,
Mario

[bbodie52]

Welcome to the Corvair Forum!

I would like to encourage you to expand on your post and tell us more about yourself, as well as about your Corvair. Your personal assessment of your mechanical skills and abilities helps a lot. Members of the Corvair Forum love to be helpful in assisting other Corvair owners with technical support and advice, but it helps a lot if we have some understanding of your technical background and mechanical abilities, your Corvair-related knowledge, etc. Helping us to know more about you, your Corvair, and you plans for your Corvair will help us to write comments to you that are tailored to your needs and experience. Knowing your home location may also suggest some possibilities.

https://www.corvair.org/index.php?optio ... crmSID=3_u

You might consider joining CORSA (Corvair Society of America) and seeking out the nearest local club chapter, if there is one near your location. While the Corvair Forum can be very helpful as you work on your Corvair, having local friends and contacts in your region who are knowledgeable about the Corvair can also be very helpful. These family-friendly CORSA club chapters often offer picnics, group scenic drives, technical training and assistance, car shows, and competition events that can greatly enhance your enjoyment of Corvair ownership.

The link below will provide you with a list of useful websites that are Corvair-related. Some of the links will lead you to an extensive technical library that will allow you to download shop manuals and other technical references in Adobe Reader format at no cost. There is also a link that will help you to locate nearby CORSA (Corvair Society of America) club chapters. You will also find a list of essential Corvair parts suppliers.

Common and Useful Corvair Websites

http://www.corvairforum.com/forum/viewt ... 225&t=6007


As to your transaxle gear lube question...

I guess when GM engineers dropped the transaxle drain plug to simplify production and to save a little in the cost of manufacturing the Corvair, they assumed that Corvairs only had a life expectancy of 10 years or so and would be junked before they needed a change in transaxle gear lube. History has proven otherwise! Unfortunately, there is no easy way to drain the differential and manual transmission in many Corvairs, which literally sucks!

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.

I did not know that about their gear lube products. The bottle lable states that it is suitable for transaxles, but the website states otherwise!

https://www.redlineoil.com/mt-90-75w90-gl-4-gear-oil

Since most GL-5 gear oils for differentials are too slippery for manual transmissions, Red Line offers these products that ensure proper shifting while providing ultimate wear protection

Appropriate coefficient of friction for most manual transmission synchronizers (other's synthetic gear oils are often too slippery for proper synchro engagement)
Red Line offers lubricants to pinpoint nearly every transmission application
MTL, MT-85 & MT-90 are not for use in differentials with hypoid gears
Excellent gear and synchro protection, balanced slipperiness for easier shifting in cold climates
Excellent for high- and low-mile transmissions
Compatible with petroleums and other synthetics

Red Line MT-90_GO_PROD_INFO.pdf

(290.63 KiB) Downloaded 30 times

And you are using GL-4 gear lube to fill your transaxle, right? NOT GL-5!

My research indicates that Red Line makes two separate gear lubricant products. One is specifically for use in manual transmissions, that include YELLOW METAL synchros. The Red Line gear lube manual transmission oils are rated as GL-4, but the fine print also specifically states that this GL-4 gear lubricant is NOT FOR USE IN HYPOID GEAR DIFFERENTIALS (the Corvair differential uses hypoid gears). The other Red Line gear lubricant products are GL-5 and are for use in differentials, but are not for manual transmissions. Because of this, neither of the Red Line series of gear lube products are suitable for use in a transaxle that shares fluid between the manual transmission section and the differential section.

See the material at the bottom of the following thread: http://www.corvairforum.com/forum/viewt ... ne#p106565

As mentioned in the above thread...

MAX GEAR – HIGH PERFORMANCE SYNTHETIC GEAR OIL
Max Gear – High Performance Synthetic Gear Oil
Max Gear is recommended for use in truck and automotive front or rear differentials, manual transmissions and lower gear units of marine engines that specify 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.

The above product line is from Royal Purple and is a synthetic product. It is not cheap but should work well in a Corvair manual transaxle.

75W-90 Long Life Synthetic Gear Lube

Use AMSOIL Long Life Synthetic Gear Lube in differentials, manual transmissions or other gear applications where one or more of the following standards are specified: API GL-5 & MT-1, MIL-PRF-2105E, Dana* SHAES* 234 (Formerly Eaton* PS-037) for 250,000 miles, Dana SHAES 256 (Formerly Eaton PS-163) for 500,000 miles, Dana SHAES 429A, Mack* GO-J & GO-J+, Meritor* 0-76N (75W-90) & 0-80 (80W-140) plus hypoid gear oil specifications from ZF TE-ML 07A and 08 foreign and domestic manufacturers such as GM*, Ford* and Daimler* Chrysler*. It can also be used in rear axles where API Service GL-4 lubricant is recommended.

So a non-synthetic GL-4 or some of the more-expensive synthetics, like Royal Purple, will do the job for you. The above material should help you to make a selection for your Corvair manual transaxle. Read the fine print carefully! As you can see, many modern products are GL-5, but not necessarily GL-4 for manual transmissions. Some GL-4 transmission lubes are not OK for hypoid differentials. Since the Corvair transaxle needs combine the two, many products will not work. I believe the Royal Purple synthetic gear lube is OK for the Corvair, but somewhat expensive.

[joelsplace]

Yes, there are 2 fill holes. The passage between the transmission and differential is small and cold thick oil takes a while to equalize so it is easier to fill with 2 locations.

[MR65Corsa]

Thanks for the answers, that's exactly what I needed.