Posted by Bruce Mitchell on Friday, January 30, 2004 at 9:54PM :
In Reply to: Oils to use in gearboxes posted by Matt Wilson on Friday, January 30, 2004 at 7:25PM :
your new tranny has tighter clearances and was built with the idea of installing the lighter oil. Some manuals will tell you to change the oil to 80 or 90 weight if you are doing alot of hauling or "Severe duty "
Your old tranny was not built with the clearances to handle the auto oil. It will leak and the gears and bearing will wear out quickly.
Two tricks you can try - Add moly slip to the tranny- this will provide great easy shifts for about 10,000 miles after that it forms up into little balls in the bottom of the tranny which does no harm but does no good either.
Or go synthetic. The trick here is to find a real synthetic and not some dressed up oil with the synthetic tag.
Auto trans fluid was added to standards to reduce friction and improve gas milage.
hope this helps
BAM