Changing the line pressure modulator ratio to increase shift firmness is a very popular upgrade in Ford E4OD and 4R100 units. All too often however, the result is a transmission that shifts harder than expected. Choosing the right Sonnax kit for your application is key to achieving the shift feel you want.
The accumulator control body is very sensitive to changes, so it’s easy to go too far — or rather, too big — when choosing a line pressure modulator plunger valve kit. Very often when a .500" kit is selected, the results are much firmer shifts than anticipated. We can eliminate this by choosing the appropriate modulator based on vehicle application — see chart for the breakdown of Sonnax options.
|6-Cylinder & Small 8-Cylinder Applications
|Large 8-Cylinder Applications
|Heavy Duty/High Performance or Stock AX4N (’97-Earlier) Replacement
|Extreme Heavy Duty/High Performance
For many, the .500" and even .427" options are going to be too aggressive with modestly modified street performance vehicles. For this scenario, we have found that combining the .372" LP modulator ratio with the performance-rated accumulator spring kit 36948-18K and a line pressure booster kit 4R100-LB1 in the pump will provide a balanced, progressive increase in shift firmness without the side effects associated with a large-ratio LP modulator change.
For all heavy-duty builds, we also recommend adding Sonnax line-to-lube pressure regulator valve 36424-04K to ensure converter and cooler flow are maintained regardless of the pressure regulator valve position.
While Sonnax makes every effort to ensure the accuracy of technical articles at time of publication, we assume no liability for inaccuracies or for information which may become outdated or obsolete over time.