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Old 10-26-2022, 11:37 AM   #1
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Looking for a Freightliner front air gauge

The front air pressure gauge needle on my 2001 Journey 32T (Freightliner chassis) will sometimes start out just fine with the little wiggle and then register the correct pressure as it is building up, then it will flip all the way to the right (130 lbs.) and the low air pressure alarm comes on. Sometimes as I am driving it will return to normal. There is no problem with the air that I can tell.
It has a 5 pin oval connector (only 4 pins are used) and no air hose connection. I have switched the connectors on the back of the "front" and "rear" gauges and the problem stays with the same gauge. I have removed the gauge and the needle stays to the right. Tapping it makes no difference, but when I connect the wires again it usually returns to zero. I feel the gauge is defective but the Freightliner parts can't seem to locate one. I have searched RV salvage yards online but struck out on that too. It is a Freightliner gauge #7595-08100-01. I would sure appreciate any help I can get on this. Thanks, Gene in Idaho.
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Old 10-26-2022, 08:08 PM   #2
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It sounds like you've done due diligence, and the gauge package was in use in Freightliner chassis coaches from Jan, 4th 1999 till mid 2003.

Testing info mentions the original supplier and contacting them may be in order.

EDIT: The low pressure alarm, is not a function of the gauge. So you may still have a different issue in the system .
Attached Files
File Type: pdf Freightliner gauges operation , testing.pdf (127.9 KB, 8 views)
File Type: pdf Freightliner VDC_Repair FL VDU (1).pdf (235.5 KB, 8 views)
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Old 10-27-2022, 01:46 PM   #3
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When you say "Freightliner parts can't seem to locate one," was that Gaffney you contacted? If not, maybe call FCCC and ask them if they have an alternate gauge they recommend as a substitute. They may even be able to get it for you or at least recommend a vendor.

800-385-4357

fcccservice@daimlertruck.com

They'll ask for your VIN
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Old 10-27-2022, 07:12 PM   #4
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I just experienced the same and it was my VDC module.

My 2000 Disco has front and rear air bags. One of my two air pressure gauges suddenly started to bounce from zero to 130 psi. When the gauge would fall below 60 psi, the low air pressure alarm would sound.

There are lots of articles and a few videos on the repair. The issue is the solder joints on the VDC that connect to the pressure transducers fail (cracks) causing an intermittent connection. This is why the gauge bounces around.

Basically you need to repair the 8 solder joints. Not very difficult to repair so long as you make a clean repair.
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Old 10-28-2022, 11:23 AM   #5
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Thank you for your input, I do appreciate it. I did touch up those solder connections on the VDU thanks to the step by step instructions that someone had posted earlier but am still having the same problem. I just don't quite understand why I can change the electrical connector on the back of the "front air" gauge to the "Rear air" gauge and it works like it should. If I put the "Rear air" connector on the "Front air" gauge it makes some noise and then pegs to 130.
I have measured the input voltage on the connector with the key on and both connectors and they are the same.
I just thought the gauge would be an easy fix to try. Thanks again, Gene
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Old 10-28-2022, 11:27 AM   #6
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Thanks for your time in replying. I wasn't even aware of Gaffney. I will definitely give them a call and check out the link. I'll let you know what I find. Gene
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Old 10-28-2022, 11:44 AM   #7
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I so appreciate your input and the links. This spring I did use Jim and Jim's instructions on repairing the VDU cold solder connections (very good instructions and pictures) but my problem remains. I received a reply telling me who the original supplier of the gauges were so I shall try to contact them. Thank you for your time in responding to my post. Gene
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Old 11-02-2022, 10:17 AM   #8
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Quote:
Originally Posted by Journey32 View Post
I just don't quite understand why I can change the electrical connector on the back of the "front air" gauge to the "Rear air" gauge and it works like it should. If I put the "Rear air" connector on the "Front air" gauge it makes some noise and then pegs to 130.

I just thought the gauge would be an easy fix to try. Thanks again, Gene
Each gauge is tuned to a specific digital signal, all the signals for all the gauges are provided to all the gauges, the gauge will only respond to the signal that it's tuned for, no matter which connector is attached.
Swapping connectors is only a test for the connector and wiring.
The message center controls the buzzer, so if the gauge is acting up and the buzzer is going off, then the signal from the VDU to the message center is suspect.
JMHO: I believe that rechecking the solder joints in the VDU would be the first step.

This pdf shows the wiring from the message center to the gauges, all the outputs from the message center are spliced together, so every connector will have the same signal. I'm sure that testing with a voltmeter won't provide a clue to the issue.
Attached Files
File Type: pdf wiring diagram gauges.pdf (256.6 KB, 11 views)
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Old 11-03-2022, 11:22 AM   #9
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Thank you for helping me to understand what I'm dealing with. I can see that my electronics training from '64 is a little outdated. The digital world is a whole new ballgame. I will pull the VDU (VDC?) and re-solder those points again.
My grandson found the front air pressure gauge at RV Maintenance in the UK for $57 which looks identical to mine but different #'s. I sent them an email on how to order it but haven't received a reply. Maybe that's a good thing. Sure do appreciate your time and help!! Thanks again, Gene.
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Old 11-03-2022, 11:30 AM   #10
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To Skip246. Guess I still haven't figured out how to reply to someone. As I look at the thread, my replies are just all grouped together instead of to the individual. I'm still learning.
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Old 11-03-2022, 08:02 PM   #11
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Not a problem .

VDU (Vehicle Data Unit) and VDC (Vehicle Data Computer) are often used to describe the same module. Probably most often by me.

Sounds like you and I might be of the pre digital age, when we we're allowed to carry those newfangled pocket calculators in school, had to use a slide rule.
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Old 12-01-2022, 04:39 PM   #12
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Quote:
Originally Posted by Skip426 View Post
Each gauge is tuned to a specific digital signal, all the signals for all the gauges are provided to all the gauges, the gauge will only respond to the signal that it's tuned for, no matter which connector is attached.
I apologize for being off topic.

Is there a name for this particular gauge data bus?

Has anyone made an LCD screen/computer replacement?

I've seen a diagram that shows many signals going into the message center module, then essentially a single bus going to the gauges. It would be so cool if I could replace both the message center and the gauges with a computer and LCD.
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Old 12-02-2022, 11:30 AM   #13
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I apologize for being off topic.

Is there a name for this particular gauge data bus?

Has anyone made an LCD screen/computer replacement?

I've seen a diagram that shows many signals going into the message center module, then essentially a single bus going to the gauges. It would be so cool if I could replace both the message center and the gauges with a computer and LCD.
A number of years back a member posted about his " Glass Dash " (photo below).
Unfortunately, with a recent hard drive failure, I've lost info about his user name and e mail address.
I'll dig around in my old posts and see if I can come up with that info.
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Old 12-04-2022, 10:21 AM   #14
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That's a bluefire dashboard. Bluefire has an adapter that plugs into the 6 or 9 pin diag port (J1708/J1939) that probably comes straight from the engine and tranny. That data bus does not have air and fuel level, which are added by Freightliner to a different data bus that feeds the dash.

I am waiting for bluefire to report whether their adapter will plug into the dash bus that has the air and fuel, and hopefully that bus will still have the additional info that is on the J1708 bus.
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