Sometimes the smallest part in a big upgrade can cause the most confusion. That was exactly the case with a tiny relief port plug in the popular RevMax Valve Body for 68RFE transmissions. To clear the air, Wade from Thoroughbred Diesel addressed the one question that kept flooding their phone lines. As Wade put it, “Ever since we did our ZeroFlex valve body install on our 68RFE truck sometime back, we’ve just been flooded with calls about the relief port in the valve body.”

Finding the Port: Cast vs. Billet

First, Wade showed viewers exactly where to find the port on the two different versions of the valve body for the 6.7-liter Cummins. On the standard cast-aluminum model, the small M4 screw goes into a port at the top (widest part) of the channel plate, right next to two larger plugs. On the upgraded billet-aluminum ZeroFlex model, the port for the slightly larger M5 screw is in a similar spot, located at the top center of the channel plate.

The Golden Rule of the RevMax Valve Body Plug

The most important part of the video was explaining the simple rule that determines whether to install the plug or leave it out. The decision depends entirely on if the truck has a transmission tune. Wade laid it out in a simple, direct way. “If the truck is not transmission tuned, you are going to want to put the plug in the valve body,” he explained. Conversely, for trucks with custom transmission tuning, the rule is the opposite.

What Happens if You Get it Wrong?

To emphasize why following the rule is so important, Wade explained the consequences of getting it backward. If you leave the plug out on a stock-tuned truck, you could end up with erratic line pressures. On the other hand, installing the plug in a transmission-tuned truck will seriously limit its performance.

Clearing the Air

This follow-up video was all about making sure a customer’s new RevMax Valve Body works perfectly right out of the box. By clarifying the function of this one small plug, the team at Thoroughbred Diesel aimed to prevent frustrating diagnostic issues and ensure owners get the performance they expect. In a moment of honesty, Wade summed up the reason for the video perfectly: “I must not have done a very good job explaining it in the installation video, so we just want to back that up and give you that information today.”