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If you have a GM Muncie M20/M21/M22, SM465, Older Toyota syncro manual etc. , you must use the obsolete GL-4 oil. The reason for this is two fold:
1. GL-5 is CORROSIVE to yellow metals such as bronze, brass and copper. This will quite literally corrode your syncros and bushings due to high sulfur content which is acidic.
2. It may make the transmission grind or have problems synching due to having 50% more extreme pressure additives than a GL-5. These additives prevent proper synchronization and may cause premature wear and failure of the syncros. The GL-5 is also more slippery and may not provide proper lubrication.Good GL-4 oils still in production are Sta-Lube and Redline MT-90. Make sure that any oil you buy says it is safe for yellow metals.
GL5 is marketed as “multipurpose” when in reality it is most suitable for differentials.
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Good info to know. I didn’t realize that was a problem. Any idea if the older B-W trans fall under this as well, like the granny low T-18?
[quote=”nickwarner” post=135404]Good info to know. I didn’t realize that was a problem. Any idea if the older B-W trans fall under this as well, like the granny low T-18?[/quote]
[quote=”nickwarner” post=135404]Good info to know. I didn’t realize that was a problem. Any idea if the older B-W trans fall under this as well, like the granny low T-18?[/quote] Indeed, the t18 is synched 2nd through 4th and uses yellow metals if memory serves correct. Sometimes even an outdated manual may say GL5 however at the time of the manuals printing, the adverse effects of GL5 were unknown.
As I understand it, it’s the copper specifically that corrodes. I rand into that with my BMW E30, which has factory ATF and copper/brass alloy synchros. My solution ended up being BG SynchroShift II:
It’s a great full-synthetic gear oil for that stuff, and a great upgrade to wear resistance and shift feel if you have ATF in it from the factory. It’s not publicly available however, you would need to buy it from a shop (typically a dealership, but sometimes independents) that uses BG products.
[quote=”Fopeano” post=135417]As I understand it, it’s the copper specifically that corrodes. I rand into that with my BMW E30, which has factory ATF and copper/brass alloy synchros. My solution ended up being BG SynchroShift II:
It’s a great full-synthetic gear oil for that stuff, and a great upgrade to wear resistance and shift feel if you have ATF in it from the factory. It’s not publicly available however, you would need to buy it from a shop (typically a dealership, but sometimes independents) that uses BG products.[/quote] Indeed, yellow metals are alloys that the main ingredient is copper. For example bronze is an alloy of copper and tin. Brasses main base is also copper. Copper as an element is a soft yellow metal, prone to corrosion and distortion without an alloying element such as tin for strength. Even then, it still is susceptible to corrosion.
The BG syncroshift, never heard or seen that one, but it’s far too thin for the transmissions of old(at least US domestic trannies and many Jap trannies). German trannies have closer tolerances typically.
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