Community Forums

Jf57 · 03-17-2025, 09:19 PM

Hi, anybody knows why my rear air gauge is always higher than my front one, 125# in the rear while 100# in the front. Is it normal ?
Best regards

Skip426 · 03-17-2025, 09:43 PM

Not normal .

Most Freightliner chassis the front tank serves the front brakes and the air suspension .
Does your air suspension leak down quickly with the engine off?

Defective gauge of pressure sensor also possible.

Lv2Roam2 · 03-18-2025, 04:10 AM

Probability for air leaks would be high on my list - Gaffney Freightliner chased down multiple leaks in two visits on my rig. We tracked 'air up' time from a cold start - it was ~ 3 minutes when new, became 5+ over the years.

JNSNWT · 03-18-2025, 07:59 AM

Just to flesh this out a little would it be a true statement that “when it left the factory both gages read within a pound or two of each other “?

wolfe10 · 03-18-2025, 08:04 AM

Wonder if this could be a gauge/sender unit issue instead of actual PSI difference???

Try swapping the senders and let us know what you find.

SafariBen · 03-18-2025, 08:08 AM

Since they're filled from the same compressor, if they're ALWAYS the same difference in pressure, then it would have to be a plugged valve between them, or more likely, a bad air pressure gauge. I'd start with the gauges, either swap them, or add a schraeder air valve temporarily in place of the drains, and measure the pressure independently of the dash pressure gauges.

Kurtis Vogue · 03-19-2025, 07:51 AM

Hello Lv2Roam2,

I have an older diesel pusher. My air up times have increased significantly over the past couple years. You mentioned your air up times have increased and you traced down a couple leaks if I understand correctly. How did you go about doing that, as I suspect I also have leaks somewhere?
Thanks,
Kurt

Lv2Roam2 · 03-19-2025, 10:08 AM

Kurt Started by airing up the coach (full bags), then turning the wheels all the way to a left stop (and later to a right stop), shutting down and immediately looking in the wheel wheels to trace the tank water purge lines and listen to the top of the tank (where many of the lines are). You may also be able to get to the airbag valves. Did not go under the coach front. Then went to the rear to check air bags and air manifold. I tightened 2 airbags valves and heard more leaks above the tanks but couldn't (wouldn't) get at them. Freightliner Service Center in Gaffney, SC traced down those leaks and another that a previous service center had 'mucked up.'

If you have a diagram of your chassis find the air manifold(s). If you have an airline added for your toad braking look that over carefully.

A spray bottle of soapy water and a quiet location helps - some of these leaks are small and fairly soft sounding (especially for my hearing). Key leak symptoms were 1) increased air up time, 2) about 10# lower pressure in the primary tank, and 3) perception that the compressor was running longer with more frequent 'blow-offs.'

Let us know what you find - we all learn...

SafariBen · 03-19-2025, 10:09 AM

I'd look for some youtube videos to show what to look for and how to fix. Many of the control valves are standard and relatively cheap, but that still doesn't mean you want to replace every one of them that shows some bubbles, focus on the big ones. You're not going to get an old vehicle to hold air overnight without a lot of effort.

The air up time is one measure, how long it holds air and how often the compressor cycles while sitting are two other measures of "leakiness". They don't all show the same thing, air up time getting longer could be compressor output, if it still holds air the same as it always did.

DarkSideJeep · 03-19-2025, 10:37 AM

Quote:

Originally Posted by Jf57

Hi, anybody knows why my rear air gauge is always higher than my front one, 125# in the rear while 100# in the front. Is it normal ?
Best regards

I have noticed that my rear gage always shows about 130psi while the front varies between 130 and 110 as I am driving down the road. I believe this is because the front tank also drives the air suspension. The suspension is constantly making adjustments while driving down the road, so it uses more air.

mlh2013 · 04-12-2025, 06:30 PM

Quote:

Originally Posted by DarkSideJeep

I have noticed that my rear gage always shows about 130psi while the front varies between 130 and 110 as I am driving down the road. I believe this is because the front tank also drives the air suspension. The suspension is constantly making adjustments while driving down the road, so it uses more air.

This is exactly how my gauges act. I was wondering why, thanks for the information.

DarkSideJeep · 04-12-2025, 08:33 PM

Quote:

Originally Posted by mlh2013

This is exactly how my gauges act. I was wondering why, thanks for the information.

I suspect the front tank is where the air to maintain the ride height comes from. As you drive down the road the constant changes as the suspension works results in air used.