4R100 converter continues to frustrate rebuilders
A few rebuilders in the Northern part of the country seem to have one thing in common: Cold-weather morning clutch engagements on certain Ford trucks 2001-2003 can be abrupt or have a slide, bump feel for the first few miles.
It seems all Dextron III/Mercon IV transmission fluids are not created equal. If you speak to a Ford technician, he will insist that Mercon fluid is better than Dextron III fluid. This is true. There is a difference in the performance requirements of most Dextron III and Mercon IV fluids.
While most oil manufacturers combine the ATF into one category, there are small and subtle differences. The amount of friction modification is higher on the Dextron III fluid. Some minor additive differences are also found in the two fluids.
Although both perform within factory specifications, it may be necessary to try using the Mercon IV in the Ford transmissions only. Ford also does not recommend the use of additional additives in the Mercon IV fluid. It is unnecessary and even detrimental to the transmission and may void any warranties.
Midco Lubricants can explain the differences in detail if you come across this problem. Midco also makes a Mercon IV only synthetic ATF, which is found to relieve this.