Need Help with Secondary Air problem

[Slo-Ride]

I am NOT, by ANY means, the most handy guy with a wrench.

Then go to a bigger hammer

Retidepxe, Thanks for the links. No time to read em right now, but will do so later.
Any chance you have a place to d/load free shop manuals for these M-2s? Only thing I find online is the operators manual not shop manuals.

 

[busop1]

I have a 2007 Freightliner M2 with a Cat C9. Bought truck month ago and have fixed 4 air leaks including:

Replaced all cab air bags one was leaking where you could hear it with truck off (count as 1 leak) and 3 quick connect air fittings in different locations changed to brass. I will gradually change all to brass.I know cab air bags are on Secondary air and I know at least 2 of quick connects where on Primary air...

Now in 48-72 hours parked the Primary air will drop from 125 down to 110 - I think that is ok. Use to drop down to 0-25 before repaired leaks.

Secondary air when parked will drop from 120 (that's all the higher it will build up based on gauge) down to 50. Use to drop to 0 prior to repairs. Now everything has been spray soaped and only minor leak still see is Fan Hub - very small bubbles which could account for Secondary air loss in 48-72 hours from 120 down to 50 I guess?? Am I right? I will replace the fan hub soon but mechanic (small shop not dealership) told me to just run it for now because the leak their is so minimal according to him. Also I hear pretty good and don't hear any other leaks when truck is parked.

When driving the truck Primary air stays right at 125 doesn't move unless braking then builds right back up and stays right on money.

Here's the problem though - Secondary air gauge when driving drops from 120 down to 97-100 EVERY TWO MINUTES like clockwork then builds right back up and spits at pop off I guess at the air dryer?? It has been doing this since I bought truck and the repaired leaks haven't changed anything.

The previous truck owner told me they replaced the front?? air dryer 6 months ago - now I thought the truck only has 1 air dryer - am I wrong??

Most importantly - what do you guys think is the problem why my Secondary air keeps doing this two minute bleed down and build up when driving????? Thanks in advance for any help!!

UPDATE: Picked truck up today from Freightliner service. They replaced the Secondary air tank saying it had a bad valve that was internal and required tank change out.

 

[GandJ]

Glad for you that it is fixed now. Thank you for posting the update, was wondering how it was going to work out..... A very informative thread and learned a lot from everyone's postings. Good information here.