I tried AMSoil 75W 90 GL-2 -- GL-5. It is safe for all metals.
But when I removed the left driveshaft I noticed gear oil in the inner c.v. joint. The c.v. flange seal had been leaking. Since synthetic oil will leak through small holes easier, I got paranoid and, after replacing both c.v.flange seals, drained the expensive AMSoil gear oil and refilled with a conventional 85W 90 GL-4 gear oil.
Should I be concerned over this? I miss the AMSoil gear oil. It really made it shift easier. As Castrol has blended and filtered castor beans in it, AMSoil had blended and filtered sea weed in it. That stuff is green and surely is slippery.
Which synthetic lube do you recommend? Thanks! jplikesm73vwbttl
If it is rated GL-5 MT-1, its fine for your car. Go to Amsoil's site and read the product information to find this.
GL5 MT-1 is fine for the yellow metals in our VW trannys (unlike GL-5). It discovered shortly after GL5 came out that it was not good for the longevity of the yellow metals, and that brought GL5 MT-1, which is what most of the new gear oils are.
Dane Tyler
Sleepy Joe wrote: > I tried AMSoil 75W 90 GL-2 -- GL-5. It is safe for all metals. >
By the way, I use Mobil 1 75W-90. It is rated GL5 MT1 and according to Mobil 1's website, is safe for all metals. It made a difference in the smoothness of the shifts in my car ('69 Bug). I have not had a problem with it leaking, matter of fact I checked last month and it was full, just as it was 1 year (and 10,000 miles) ago when I changed it.
I used Redline in mine. They all will seep. But in the trans is one of the only places I would not worry. Not much heat as in an engine and it synthetics work well in gearboxes. No worry about it being able to carry the heat as to an oil cooler as in an engine. Joe
What about the gear oil leaking past the c.v. flange seal on the transaxle into the inner c.v. joint? Won't that be bad for the c.v. joint? Well, the swing axles use gear oil to lube the inner c.v. joints right? I thought since conventional gear oil is thicker than synthetic gear oil, it would be better to lube the inner c.v. joints with than the synthetic gear oil will? If it doesn't matter, I think I might run over and get some Mobile 75W 90 GL-5 MT-1 gear oil. Any comments on this will be appreciated! Thanks! jplikesm73vwbttl
Joe, I use syntec synthetic and love it but if you are not comfortable with sythetic don't use it because if something goes wrong, I'm sure the oil would be the prime suspect in your mind.
I think I will try it. It is less expensive than AMSoil gear oil.
I found the FAQ for it.
Mobil 1 Synthetic Gear Lubricant LS 75W-90 API Gl-5/MT-1 X
Mobil 1 Synthetic Gear Lubricant LS 75W-90 can also be used in rear axles where API Service GL-4 lubricant is recommended
Product Description Mobil 1 Synthetic Gear Lubricant LS is a supreme performance, synthetic, multi-purpose, SAE 75W-90 automotive gear lubricant designed to meet the highest level performance requirements of modern passenger vehicles in all types of operating conditions including limited slip applications, as well as, deliver outstanding power transfer performance. Compared to conventional hypoid gear lubricants, Mobil 1 Synthetic Gear Lubricants LS 75W-90 performs exceptionally over a wide range of temperatures. Mobil 1 Synthetic Gear Lubricant LS
75W-90 achieves this through a unique proprietary formulation, that deliver optimized viscosity-temperature properties together with the highest level of inherent formulation stability and protects against thermal and oxidative degradation, wear and corrosion, viscosity loss associated with premature shearing. It also can be used in extended service and for aiding in fuel economy performance.
Mobil 1 Synthetic Gear Lubricant LS 75W-90 meets the most severe API Service MT-1 and GL-5 EP gear oil service classification.
Features & Benefits Mobil 1 Synthetic Gear Lubricant LS 75W-90 combines wax-free synthesized hydrocarbon base oils and a specially designed extreme-pressure, limited-slip, sulfur-phosphorous additive system to provide a significantly higher level of performance in rear axles and differentials versus conventional fluids. Greater film strength at higher operating temperatures, reduced fluid friction and low-temperature application down to -50ºC provides significant advantages versus conventional mineral oil formulations. It reduces wear and spalling under the high speed, high torque and high horsepower conditions in competitive racing and high performance automobiles. This unique, high technology final drive gear lubricant has demonstrated outstanding performance including; fuel economy, extended drain, long-term friction retention, low-temperature capability and improved differential/axle durability and cleanliness. Key features and benefits include:
 Features  Advantages and Potential Benefits Exceptional thermal stability and resistance to high temperature oxidation Extended gear and bearing life due to minimal deposits Longer seal life Potential extended oil drain/service intervals Outstanding protection against low speed/high torque wear and against high speed scoring Capability to handle the severest driving conditions while delivering smooth efficient and reliable performance Exceptional shear stability Retains viscosity and film strength under severe operating conditions to prevent wear Excellent rust, staining and corrosion protection of copper and its alloys Reduced wear Longer component life Enhanced frictional properties Improved fuel economy and reduced operating costs Outstanding low temperature fluidity versus mineral oils Reduced wear at start up and ease of start up even in arctic conditions Good resistance to foaming Maintains film strength for reliable lubrication Compatible with typical automotive seals and gaskets Minimum leakage and reduced contamination Excellent limited-slip performance Reduced chatter and improved traction
Applications Mobil 1 Synthetic Gear Lubricant LS 75W-90 is recommended for use in modern high performance automobiles like SUV's, Vans and Light duty trucks requiring API GL-5 & MT-1 level performance Mobil 1 Synthetic gear Lubricant LS 75W-90 is intended for initial fill, topping-off or refilling differentials, final drives, transfer cases and other gear applications where lubricants meeting API Service GL-5 and multi-purpose or mild EP gear lubricants are recommended Mobil 1 Synthetic Gear Lubricant LS 75W-90 can also be used in rear axles where API Service GL-4 lubricant is recommended Not recommended for automatic, manual or semiautomatic transmissions for which engine oil or automatic transmission fluids are recommended Where extended service intervals and warranties are required
Specifications & Approvals  Mobil 1 Synthetic Gear Lubricant LS meets or exceeds the following industry specifications: 
75W-90 API Gl-5/MT-1 X
Typical Properties  Mobil 1 Synthetic Gear Lubricant LS  SAE Grade 75W-90 Viscosity, ASTM D 445 cSt @ 40ºC 106 cst @ 100ºC 15.2 Viscosity Index, ASTM D 2270 150 Pour Point, ºC, ASTM D 97 -46 Flash Point, ºC, ASTM D 92 175 Density@15C kg/l, ASTM D 4052 0.859
Health & Safety Based on available information, this product is not expected to produce adverse effects on health when used for the intended application and the recommendations provided in the Material Safety Data Sheet (MSDS) are followed. MSDS's are available upon request through your sales contract office, or via the Internet. This product should not be used for purposes other than its intended use. If disposing of used product, take care to protect the environment.
The Mobil logotype, the Pegasus design, Mobil 1 Gear Lubricant are trademarks of Exxon Mobil Corporation, or one of its subsidiaries.
I do engineering for elevator companies in NYC and well before Sythentic oil was available to the automotive public we used the heavy weight oils for large motors that were prone to bearing failures. After we started using the Sythentic oils the bears problems went away. There has been many years of research on Sythentics. The thing you have to watch is, they lube too well. SO do not use for breakings. Also some motorcycle guys say it is so slick the roller bearing engines get flat spots on the rollers because the rollers do not turn. Or the stories ( which are untrue ) of the Sythentics not carrying heat the coolers. I run Sythentic grease in my front end and bearing and the oil in my engine and trans. Yes I too was careful but it paid off. JOe
I use Pennzoil Synthetic GL4 75W90. We got into a pissing contest before on whether GL5/MT1 was suitable for the soft metals in our VW transaxles. I still maintain that Pennzoil makes this expensive GL4 for a reason. Why wouldn't they simply phase it out if GL5/MT1 did it all? Nobody has offered up a plausible reason yet.
Click on this link and check out the data sheets on both GL4 and GL5;
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Here are a few comments from the PDF document on GL4;
"It is formulated to be compatible with copper containing alloys and soft metals found in synchronizers."
"PENNZOIL® SYNTHETIC SAE 75W-90 GL-4 is designed primarily for the lubrication of manual transmissions and transaxles..."
But the inner cv joint with the gear oil and grease should be ok since swing axle transaxles have gear oil in their inner cv joints. Sounds like it should be ok at least.
I wanted to get the Pz GL-4 gear lube but they do not sell it where I live and I could not find a place to buy it online.
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