I finally was able to get one of my lubrication buddies at the SAE to look up GM's specification for its Synchromesh product.
"GM Synchromesh is formulated with high quality paraffinic base stocks, a multifunctional performance additive, a fluidity modifier, a shear stable viscosity index improver, corrosion inhibitors, and a foam suppressor. It offers excellent synchronizer performance, oxidation stability, yellow metal compatibility, and low temperature performance. This product will satisfactorily lubricate manual transaxles/transmissions from –40F to +300F."
So, this basically confirms my speculations that this is essentially a fortified motor oil, or can be viewed conversely as a light gear oil lacking EP additives conforming to GL-4 or GL-5 specs. It does not contain any synthetic lubricant components.
Let's look at its chemical properties:
cST 40degC: 41.6
cST 100degC: 9.08
Pour point: -50
Flash point: 385degF
Color: amber
Let's look at Red Line D4ATF (typical ATF formulation)
cST 40degC: 34.0
cST 100degC: 7.5
Pour point: -60
Flash point: 437degF
Color: Red
Let's look at Red Line MTL
cST 40degC: 50.8
cST 100degC: 10.2
Pour point: -50
Flash point: 450degF
Color: Red
Let's look at Amsoil ATF
cST 40degC: 36.0
cST 100degC: 7.5
Pour point: -69
Flash point: 432degF
Color: Red
************************************************
So what do we make of all this? Well, GMS is a non-synthetic formulation, so it can be expected to change its properties over time, due to less stable base stocks and shear strength, and higher volatility. This is partly reflected by its 50 deg lower flash point than the synthetic competition. It does have higher viscosity than the ATF's, but lower than MTL.
As I have previously stated, GMS (and other specialized gear lubes including a Mopar spec) were developed primarily to deal with the special needs of some GM transmissions, particularly ones (like the Getrag and the ZF) which use yellow metal synchronizers. GM found that conventional gear oils, especially ones with GL-5 specification, often contained active sulphur compounds, which damaged the synchros. Going to a specific GM specification ensured less warranty claims, less rejection of claims by the German mfrs, and less consumer complaints. A good idea.
Now, does that make it a good choice for the T-56? Well, according to TTC's own website, they recommend Dexron III (Mercon V) for the Cobra and Corvette, or Castrol Syntorque (Dodge Viper). Nowhere on the TTC site does it recommend GMS - that appears to be one of those Internet "somebody told my brother who told me" stories.
GM gets a lot of $'s for a mineral oil-based product. Red Line and Amsoil use Group V (ester) and Group IV (PAO) synthetic lubricants respectively. There is very little likelihood that GMS will have anywhere near the service life of the synthetic products, neither of which has any components which will harm any of the T-56's internals, includings its carbon blocker rings or metal synchronizers. GMS will likely thicken over its service life, due to evaporative factors, resulting in reduced cold-weather performance, and the greater likelihood of deposits. If you use it, change it every 30k miles would be my recommendation. It is also amber in color - a dead giveaway if the dealer checks it or if the tranny fails.
But why use it? If you want thicker viscosity and stronger film strength, there is Red Line's MTL - essentially a light gear oil with the component properties and additives of an ATF. It has a flash point 65degF higher than GMS.
Now, I cannot comment on the shiftability or "feel" of the various lubricants, other than to note that the TTC T-56 ostensibly was designed to use ATF-type lubricants, and that is what Tremec, GM, Ford, and Chrysler recommend. One would have to wonder how the "feel" and mechanical performance engineered into the product using the ATF-family of lubricants could be bettered by a lubricant designed for other applications, and not even recommneded by its distributor (GM) for its own cars using the T-56. Doesn't make sense, does it?
"GM Synchromesh is formulated with high quality paraffinic base stocks, a multifunctional performance additive, a fluidity modifier, a shear stable viscosity index improver, corrosion inhibitors, and a foam suppressor. It offers excellent synchronizer performance, oxidation stability, yellow metal compatibility, and low temperature performance. This product will satisfactorily lubricate manual transaxles/transmissions from –40F to +300F."
So, this basically confirms my speculations that this is essentially a fortified motor oil, or can be viewed conversely as a light gear oil lacking EP additives conforming to GL-4 or GL-5 specs. It does not contain any synthetic lubricant components.
Let's look at its chemical properties:
cST 40degC: 41.6
cST 100degC: 9.08
Pour point: -50
Flash point: 385degF
Color: amber
Let's look at Red Line D4ATF (typical ATF formulation)
cST 40degC: 34.0
cST 100degC: 7.5
Pour point: -60
Flash point: 437degF
Color: Red
Let's look at Red Line MTL
cST 40degC: 50.8
cST 100degC: 10.2
Pour point: -50
Flash point: 450degF
Color: Red
Let's look at Amsoil ATF
cST 40degC: 36.0
cST 100degC: 7.5
Pour point: -69
Flash point: 432degF
Color: Red
************************************************
So what do we make of all this? Well, GMS is a non-synthetic formulation, so it can be expected to change its properties over time, due to less stable base stocks and shear strength, and higher volatility. This is partly reflected by its 50 deg lower flash point than the synthetic competition. It does have higher viscosity than the ATF's, but lower than MTL.
As I have previously stated, GMS (and other specialized gear lubes including a Mopar spec) were developed primarily to deal with the special needs of some GM transmissions, particularly ones (like the Getrag and the ZF) which use yellow metal synchronizers. GM found that conventional gear oils, especially ones with GL-5 specification, often contained active sulphur compounds, which damaged the synchros. Going to a specific GM specification ensured less warranty claims, less rejection of claims by the German mfrs, and less consumer complaints. A good idea.
Now, does that make it a good choice for the T-56? Well, according to TTC's own website, they recommend Dexron III (Mercon V) for the Cobra and Corvette, or Castrol Syntorque (Dodge Viper). Nowhere on the TTC site does it recommend GMS - that appears to be one of those Internet "somebody told my brother who told me" stories.
GM gets a lot of $'s for a mineral oil-based product. Red Line and Amsoil use Group V (ester) and Group IV (PAO) synthetic lubricants respectively. There is very little likelihood that GMS will have anywhere near the service life of the synthetic products, neither of which has any components which will harm any of the T-56's internals, includings its carbon blocker rings or metal synchronizers. GMS will likely thicken over its service life, due to evaporative factors, resulting in reduced cold-weather performance, and the greater likelihood of deposits. If you use it, change it every 30k miles would be my recommendation. It is also amber in color - a dead giveaway if the dealer checks it or if the tranny fails.
But why use it? If you want thicker viscosity and stronger film strength, there is Red Line's MTL - essentially a light gear oil with the component properties and additives of an ATF. It has a flash point 65degF higher than GMS.
Now, I cannot comment on the shiftability or "feel" of the various lubricants, other than to note that the TTC T-56 ostensibly was designed to use ATF-type lubricants, and that is what Tremec, GM, Ford, and Chrysler recommend. One would have to wonder how the "feel" and mechanical performance engineered into the product using the ATF-family of lubricants could be bettered by a lubricant designed for other applications, and not even recommneded by its distributor (GM) for its own cars using the T-56. Doesn't make sense, does it?
