2018 Freightliner secondary air leak only when moving

My O-ring kit has arrived. I’ll try fixing,one this weekend. Eaton part # K-2908
On the UltraShift transmission is an electrical solenoid that operates the high-low range . Inside is two plungers with four o-rings. Looks easy to change, if it doesn’t work in my case then I’ll try the dealer.

 

Changed the o-rings, only a 15 minute job .but that wasn't it So it must be the range piston o-rings.

 

Have you checked your air dryer purge valve. It’s known for leaking irregularly? Put your hand over it while your truck is idling, and also while the engine is off. Do this throughout the day as it’s not a constant leak.

When you are checking for air leaks, it’s important that you are supplying air to your truck. Chock your truck or set the brakes on your trailer. If you want to check your trailer, set the brakes on your truck, and supply air to the trailer. You also want to lightly move the air lines around while spraying them with soap and water. It could be you have an air line that is coming off when the air is hitting it at highway speeds. Make sure your air tanks are completely full of air, typically around 130 PSI.

 

Cascadia 2018. I have the same problem. Tried everything, 5 times already at the dealer and still nothing. The secondary air gauge drops to 100psi and then builds back 125 every 2 minutes. Changed the purge valve etc. It starts doing that only when driving 30 mph and up. If the speed is less than 30 the truck works perfectly without any issues. After sitting overnight also works good for the first 40 miles till it heats up and then the secondary air gauge starts doing the same thing. There is air going to the axles differential, found a bad connection and change it but i still have the same problem. Please let me know if you fixed it.

 

Not a Freightliner guy, but usually air ride cab and suspension are usually from secondary air.

 

Hi, Do you have any updates on your problem?

 

Finally confirmed where my air leak is.
Just as a reminder, mine ONLY leaks when going down the road. And ONLY while the transmission is in HIGH range. However, I have an Eaton 18 spd Ultrashift MXP with the Freightliner paddle shifter on the steering column. You are not able to get it to shift into high range while parked.
Just a few minutes ago I found in the service manual for my FO-18E318B-MXP how to test it.
With the truck off, turn the key to the on possition but do not start. Once everything comes to life: Step on the brake, using the shifter select reverse R1. Low-Low reverse.
Step on the brake pull up on the shifter paddle to select second reverse R2. Split high low reverse. Still in the low range, still no air leak.
Step on the brake, pull up on the shifter paddle to select third reverse R3. High range reverse. Finally could hear the air leak.
Jumped under the truck and confirmed that the air was leaking from the bottom of the gasket of the range cylinder cover.
Looks easy enough to change, I'll see if I can get a new gasket tomorrow. But Easter Weekend most places are closed.