Need Help with Secondary Air problem

[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!!

 

[EASYTRADER]

I believe your leak is so severe your truck should be out of service. But you can check your cdl handbook I think no more than 10 psi in 1 minute is allowed.

Having said that, the way to solve the problem is as you have, spray the whole system with soapy water and check again. Spray down everywhere not just connectionns, wet the hose and the tanks, wet down the connections in your air seat as well as the hoses.

Also, check the spring brake housing, they contain rubber bladders which fill with air to release the springs.

If you don't leak when parked, but do leak when the parking brake is released the leak is most likely in the spring brake housing or hoses which feed it.

If you have a tractor, it may be leaking at the glad hands.

 

[jjoerger]

Check your seats, gauge connections and tractor valve. Finding leaks inside the cab is not unusual.
We just had 1 rear air bag replaced, brought the truck home and found the other one was leaking. Had to take it back to the shop for a second time.
If I remember right Layoutshooter was having problems with a leaky valve on an M2.

 

[layoutshooter]

It is likely going to be one of half a zillion, AMU's, air management units. They go bad all the time. I have replace 20 or so. There is plenty of post in here on that subject. IF you can't do them yourself, like me, take your truck to a Freightliner shop. While I know that they are NOT VERY GOOD, they have a warranty. I just had ANOTHER one replaced under that warranty, saved me over $200 bucks.

It is a never ending problem, get used to it.

UNLESS

You are good with a wrench. There is one guy in here that knows how to fix them, it is a problem with poor installation. Maybe he will see this.

OTHER WISE

Have fun, sorry to be the bearer of bad news.

 

[busop1]

I believe your leak is so severe your truck should be out of service. But you can check your cdl handbook I think no more than 10 psi in 1 minute is allowed.

Having said that, the way to solve the problem is as you have, spray the whole system with soapy water and check again. Spray down everywhere not just connectionns, wet the hose and the tanks, wet down the connections in your air seat as well as the hoses.

Also, check the spring brake housing, they contain rubber bladders which fill with air to release the springs.

If you don't leak when parked, but do leak when the parking brake is released the leak is most likely in the spring brake housing or hoses which feed it.

If you have a tractor, it may be leaking at the glad hands.

I was told that as long as primary is not leaking while driving then I have not to worry about being in service with this secondary air loss?? And isn't my compressor doing exactly as it should in rebuilding the pressure that is bleeding off??

And as for the parking brake leak you suggest - wouldn't any brake air loss be losing off the Primary side?? I'm not losing air on Primary side but only on Secondary side.

 

[layoutshooter]

It is likely a AMU leaking, they will put you out of service. IF that secondary leaks down far enough, and it will, it will engage your spring brakes. Been down this road MANY times. JUST had one replaced, for the 5th time, yesterday.

 

[busop1]

Just spent 45 minutes on phone with Freightliner service dept - Person I spoke with said it sounds like air governor on the compressor. He said that AMU's wouldn't leak slow when parked then leak fast like my problem when driving. He took the time to look up some troubleshooting checks on my problem and his computer seemed to suggest he might be right may need air governor rebuilt??

What say you guys??

 

[layoutshooter]

Been watching them AMU's doing what you say they are for more than 5 years.That's all I know.

I can watch the gauge drop enough to set off the compressor, every 3 to 5 minutes. The compressor kicks in, brings it up. Then it repeats.

Got the offended AMU replaced yesterday, It stays above 100PSI for several hours.

Don't know what else to say.

 

[busop1]

Been watching them AMU's doing what you say they are for more than 5 years.That's all I know.

I can watch the gauge drop enough to set off the compressor, every 3 to 5 minutes. The compressor kicks in, brings it up. Then it repeats.

Got the offended AMU replaced yesterday, It stays above 100PSI for several hours.

Don't know what else to say.

Layoutshooter - That's good enough for me. I just didn't realize from your earlier posts that yours was doing exactly same as mine. Am I looking at $300 range on this repair you think??

 

[layoutshooter]

Layoutshooter - That's good enough for me. I just didn't realize from your earlier posts that yours was doing exactly same as mine. Am I looking at $300 range on this repair you think??

Yesterday's repair WOULD have been around $240. It all depend on which one, or multiple AMU's are our. It can be, and often has been, more than one that was out. It is likely more than one if you have not keep up with them. They SUCK. Freightliner is aware and is doing nothing. Their new trucks no longer have them on.

That is not to say you don't have other problems but the AMU problem is VERY common, good luck. Let us know how it comes out.

 

[zorry]

Pickup an air govenor. $35 ??(about $20 last time I bought one.)
Switch out about 20 minutes. Good to have spare anyway.
Layout is probably right. He the Freightliner air leak expert. Lot's of experience.

 

[zorry]

Layout. They are doing something.
They decided that crap didn't work. That's why they don't use them anymore.
They just aren't helping you(and previous buyers.)
They got your money,why spend anything pleasing you now ?

 

[jjoerger]

When our fan hub had a leak it would sometimes run the pressure down enough for the compressor to kick in every 3-5 minutes. Other times it would go for 30 minutes. It seemed to be worse while we were moving.

 

[layoutshooter]

When our fan hub had a leak it would sometimes run the pressure down enough for the compressor to kick in every 3-5 minutes. Other times it would go for 30 minutes. It seemed to be worse while we were moving.

Good catch, had THAT problem 2 years ago. Mimicked the AMU leaks.

 

[Refer Hauler]

I would pull the "Pop Off" valve off the compressor and spray it with carb cleaner or something like it to remove the gunk that can build up and cause these to stick. It is usually covered by a small plate with two Torx screws holding it down. Make sure you bleed your air down to ZERO as it may be under pressure and might fly out of there. This is the cheapest and easiest way to fix or discount this as an item needing repair

 

[RETIDEPXE]

There is one guy in here that knows how to fix them, it is a problem with poor installation. Maybe he will see this.

I just checked, my last AMU replaced due to air leak was on 03/24/09 at 236,590 mi.s. Just turned 780,000 mi.s with no AMU problems since then. Screw Freightliner, they don't want to hear what the fix is, it's easy money for service. It really is not hard to diagnose and replace AMU's. Here are the threads I posted in explaining my AMU fix. I would also suggest bypassing the sleeper leveler valve in favor of a manual switch and gage (Donvel can fix you up there); http://www.expeditersonline.com/for...rking-brake-light-low-air-buzzer-issue-2.html

http://www.expeditersonline.com/forum/truck-talk/52431-another-air-leak-2.html

Good Luck!

 

[skyraider]

Hey cv'ers and sprinter drivers, see what you missing.................

 

[layoutshooter]

I just checked, my last AMU replaced due to air leak was on 03/24/09 at 236,590 mi.s. Just turned 780,000 mi.s with no AMU problems since then. Screw Freightliner, they don't want to hear what the fix is, it's easy money for service. It really is not hard to diagnose and replace AMU's. Here are the threads I posted in explaining my AMU fix. I would also suggest bypassing the sleeper leveler valve in favor of a manual switch and gage (Donvel can fix you up there); http://www.expeditersonline.com/for...rking-brake-light-low-air-buzzer-issue-2.html

http://www.expeditersonline.com/forum/truck-talk/52431-another-air-leak-2.html

Good Luck!

I was hoping you would post again. I could not remember who it was who had a 'fix' for this. I hope someday I can meet up with you. I need to be shown what you are talking about. I am NOT, by ANY means, the most handy guy with a wrench.

 

[RETIDEPXE]

I was hoping you would post again. I could not remember who it was who had a 'fix' for this. I hope someday I can meet up with you. I need to be shown what you are talking about. I am NOT, by ANY means, the most handy guy with a wrench.

Yeah, I didn't realize how much the AMU's do until I read up on a couple links. They do have a benefit, according to Freightliner, by reducing the amount of air lines in the dash thereby reducing the chance for air leaks....huh, if installed right, right?

This guy had a problem with the low air press warning and A/C in op. chassis..air press warning light and buzzer stay..gauges..100-125 psi - JustAnswer

Referring to the tech's link here; http://ww2.justanswer.com/uploads/budnshe/2010-06-16_045405_ma4219100wm.pdf

Fig 2 shows the "L-bracket" (4), nothing but a piece of angle iron that holds the AMU's in place and the "locking keys" are nothing but a large "C" clip that slides in and out locking the AMU's side to side. Fig 1 shows an AMU by itself and on the left side see the 4 hooks the C clip slides into, making sure it is hooking all hooks on the two AMU's the clip holds together (one clip between each AMU), then give the C clip a light tap with a small hammer to seat it completely. Then put a wood worker's slide clamp on the entire bank of AMU's squeezing them together to fully compress the rubber gaskets between them, o-rings are molded in these gaskets, then install and tighten the 4 bolts found in the "L-bracket" or angle iron, whatever you want to call it. With the rubber gaskets, cleanliness is your freind. Remove wood worker's clamp and walla, good for the next 500,000 plus mi.s.

Follow at your own risk/
Hope this helps.

 

[layoutshooter]

I got a good look at that bracket the other day when it was off. I will look more at it next time I am home. Weather permitting.

They were telling me at this last shop that the AMU's are no longer used on the new trucks due to all the problems they were having. Don't know if that is correct or not.