SAE paper #982674 is simply packed with interesting data about the development of ATF+4. Here are a few tidbits:
The initial development was done using Shell's XHVI base oil. Only much later were other Group III oils approved.
Lubrizol developed a shear-stable VI improver specifically for ATF+4. The initial tests of this VI improver in the test fluids was so remarkable that Chrysler modified the then current ATF+3 spec (MS7176D) to include it. Thus Type 7176E fluid was born, which remained the factory fill until the introduction of ATF+4. In testing done during development of ATF+4, Chrysler noted the following viscosity loss from shearing for the following ATFs (20 hour KRL Shear Test):
Dexron III - 40.1% loss
Mercon V - 18.6% loss
Type 7176D - 32.4% loss
Type 7176E - 14.2% loss
Type 9602 - 9.9% loss
You can see what a significant impact the new VI improver had on ATF+3 when you compare the 7176D and 7176E numbers.
One of the stated goals of Type 9602/ATF+4 fluids was that it would have the same frictional characteristics as ATF+3. The paper explicitly stated that this would be a performance criteria because new clutch materials would not be introduced for this fluid and it had to be backwards compaitable with ATF+3.
Overall, the goal in developing ATF+4 was to create a fluid that would match the performance characteristics of the then current fluid (Type 7176D), but that would retain those characteristics for at least 100,000 miles. The article specifically noted that the anti-shudder properties of ATF+3 were usually seriously degraded by 30,000 miles.
The initial development was done using Shell's XHVI base oil. Only much later were other Group III oils approved.
Lubrizol developed a shear-stable VI improver specifically for ATF+4. The initial tests of this VI improver in the test fluids was so remarkable that Chrysler modified the then current ATF+3 spec (MS7176D) to include it. Thus Type 7176E fluid was born, which remained the factory fill until the introduction of ATF+4. In testing done during development of ATF+4, Chrysler noted the following viscosity loss from shearing for the following ATFs (20 hour KRL Shear Test):
Dexron III - 40.1% loss
Mercon V - 18.6% loss
Type 7176D - 32.4% loss
Type 7176E - 14.2% loss
Type 9602 - 9.9% loss
You can see what a significant impact the new VI improver had on ATF+3 when you compare the 7176D and 7176E numbers.
One of the stated goals of Type 9602/ATF+4 fluids was that it would have the same frictional characteristics as ATF+3. The paper explicitly stated that this would be a performance criteria because new clutch materials would not be introduced for this fluid and it had to be backwards compaitable with ATF+3.
Overall, the goal in developing ATF+4 was to create a fluid that would match the performance characteristics of the then current fluid (Type 7176D), but that would retain those characteristics for at least 100,000 miles. The article specifically noted that the anti-shudder properties of ATF+3 were usually seriously degraded by 30,000 miles.
