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Old 09-20-2021, 05:03 PM   #21
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Well I'm at the bus now, it's been running over 10 min and only at 70 psi . I have been able to hear any air leak. I'm running the eng at high idle to see how much pressure it will build. I drained the tanks already. Today's it's worse then Sat. Alarm won't shut off so doesn't want to reach 75 psi even.

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Old 09-20-2021, 05:42 PM   #22
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I wound up crawling all along the power train, front to back. The 3 tanks are under the nose. I traced the lines all the way to the back, no sounds. My hearing isnt that great however.

The Thomas cat c7 engine is in the back. Any clues as to what the part is I'm looking for? Maybe a picture ?
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Old 09-20-2021, 05:53 PM   #23
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No idea of the specifics of your bus, but here's an example of an air dryer:
Click image for larger version

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And here's an example of an air governor:
Click image for larger version

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These are pretty standard models, but I'm sure there are oddball ones out there that look different. I'd try to track down something that looks like one or the other, then start spraying sudz like crazy.
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Old 09-20-2021, 05:53 PM   #24
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This is a picture of a Bendix governor.
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Old 09-20-2021, 05:56 PM   #25
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Quote:
Originally Posted by flattracker View Post
This is a picture of a Bendix governor.
Ok, thanks flattracker : )
I'll be out there again Wed for the suds part.
Keep the clues coming and thank you!

Peter
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Old 09-20-2021, 07:16 PM   #26
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Was your air slow to build when you first got the bus last year?
If you don't find any leaks with your ear or spray you may have a weak inlet valve. compressors need to pull air in through that valve then it closes for the compression cycle. If that valve is weak the compressing air can be forced back out through that intake valve and cause a slow pressure build until it gets to a point where it can't build any higher pressure.
Good luck.
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Old 09-20-2021, 08:21 PM   #27
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Quote:
Originally Posted by Oscar1 View Post
Was your air slow to build when you first got the bus last year?
If you don't find any leaks with your ear or spray you may have a weak inlet valve. compressors need to pull air in through that valve then it closes for the compression cycle. If that valve is weak the compressing air can be forced back out through that intake valve and cause a slow pressure build until it gets to a point where it can't build any higher pressure.
Good luck.

Hey Oscar,
I drove the bus to its new parking spot 2 weeks ago, and it was fine. Popped up to 100 psi or whatever like a champ. Im trying to recall if perhaps during my construction phase, im working on the bus electrical, as in AC, breaker panel etc, I could have done something to have caused this. But I dont think I did.
Im going to try and find a schimatic for the C7 engine so I can figure out where these parts are bolted on to the engine or frame. Id hate to unbolt something I shouldn't.


Heres some pics from the engine compartment and the air tanks.
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aittanks.jpg   eng_center.jpg   eng left.jpg   eng right.jpg  
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Old 09-20-2021, 09:06 PM   #28
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Hi Peter
Your motor, when in the rear is installed opposite to the front installation so it is in backwards. So your compressor will be on the passenger side just above and in front of the starter.
There is a lot going on when the bus is running and a lot of noise, years ago when I took my class 1 driver training I refused to move the truck because I could hear what I thought was a serous air leak, the instructor couldn’t hear it and was major pissed at me for refusing to drive. I said to him I’m behind the wheel and it’s my ass on the line, I parked and made him call a supervisor. Turns out he is almost deaf and couldn’t hear a thing, the leak was so bad the truck was towed in to service. trust your gauges and your gut, you may not hear it but if it’s trying to tell you something pay attention.
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Old 09-20-2021, 09:18 PM   #29
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also gauges can lie/fail so that’s why a pre trip inspection is so important every time you move the bus.
Look up on line what’s involved in a pre trip for a semi then modify that to your vehicle specifics
Cheers
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Old 09-21-2021, 01:09 AM   #30
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I suggest always keeping a spare D2 governor in the bus - they're cheap insurance. If the air dryer is iffy, just replace it, or at least get the rebuild kit for it and replace the dessicant and seals. Sometimes the reed valves that are the unloader valves in the head of a typical Bendix air compressor can stick, but again there are rebuild kits for most of the Tu-Flo compressors.

I'm nervous when I hear that someone starts their bus engine and then only idles it. You're possibly creating more long-term problems that way. The general rule with big diesels is to not start them unless you're going to get them to full operating temperature. Even at Fast Idle, diesels don't build much heat. In addition, you need to get some heat into the tires to help keep their rubber from drying out prematurely, and it's also better for the transmission, hydraulic and steering systems to keep their seals supple, and this means driving the bus for at least 20 miles. So saying, don't even think of moving the bus unless you can meet DOT Air Brake standards - if it won't pass, fix it!

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Old 09-21-2021, 03:02 PM   #31
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Thanks John,

I'll be at the bus Wed looking for the governor next.

Any recommendation where to order parts from ? This is a 2005 C7. Id like to get a governor and a air drier.
If I was going to replace parts, cheap to expensive, would I replace the air drier, governor, then compressor, in that order ?

Thanks Oscar:
>compressor will be on the passenger side just above and in front of the starter.
So as Im looking at my motor, it on my right hand side.
>you may have a weak inlet valve....
Im guessing your talking about the compressor?

Since the bus was delivered to me this time last year from AZ, Ive kept it in a lot to build it up. I cant license it and drive it till that happens, IL laws, so I just start it sometimes, just to know it still starts. I run it for a few minutes and shut it down.
I understand about running diesels at idle too long is bad, glazing the cylinders etc. When I was a kid, I did drive a little, some straight-trucks, and a 53' Freightliner, so still have my class A, just dropped the X.

Peter
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Old 09-21-2021, 03:17 PM   #32
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Any truck stealership should work. Pacar, Freightliner, Navistar, Mack/Volvo or Fleetpride.
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Old 09-21-2021, 03:20 PM   #33
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Try to avoid Chinese made replacement parts. Most are not that good and have QC issues.
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Old 09-21-2021, 03:58 PM   #34
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Quote:
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If I was going to replace parts, cheap to expensive, would I replace the air drier, governor, then compressor, in that order ?
Stop.

You start with troubleshooting. You replace parts after you find what's wrong. Throwing parts at something is never a good idea, especially if you throw a compressor at it, and it will likely be more expensive then if you had a mobile mechanic come out and check for you.

On a normal bus air pressure should build to full pressure in less then 10 minutes. Your's running that long and only getting to 70 is telling. What's the air pressure gauges read after you turn the engine off? Steadily drop or is it a rapid drop? No movement at all? You could have a faulty governor causing cut out to be low, but you'd still get a dryer purge with that, and you've said you're not getting that.

Air leaks might not always be heard, especially if you're hard of hearing and the engine is running nearby. A soap and water mixture in a spray bottle can be your best friend. Spray any of the air components under the bus. Douse them liberally. If it's under the bus, it can get wet, so don't be afraid to get it wet.

S2mikon mentioned air suspension leaks, but you never responded if you even have an air suspension. Do you?
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Old 09-21-2021, 04:10 PM   #35
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Originally Posted by booyah45828 View Post
stop.
> Roger : )

you start with troubleshooting. You replace parts after you find what's wrong. Throwing parts at something is never a good idea, especially if you throw a compressor at it, and it will likely be more expensive then if you had a mobile mechanic come out and check for you.
Ive been reading air driers should be replaced once a year and figured id start looking for a governor too.

me > Wednesday ill be out at the bus getting wet, yes.

On a normal bus air pressure should build to full pressure in less then 10 minutes.

> Mine now can run all day and only hits 50. Last week it was 70, week before that it was 120.

Your's running that long and only getting to 70 is telling. What's the air pressure gauges read after you turn the engine off?

> Right now 50, cant tell if its dropping, seems no drop, just cant build pressure.

Steadily drop or is it a rapid drop? No movement at all? You could have a faulty governor causing cut out to be low,
>Seems no noticeable drop

> That is what i understood as well from the conversation.

But you'd still get a dryer purge with that, and you've said you're not getting that.

> I was getting a purge 2 weeks ago when it was 120 since then i am not.

Air leaks might not always be heard, especially if you're hard of hearing and the engine is running nearby. A soap and water mixture in a spray bottle can be your best friend. Spray any of the air components under the bus. Douse them liberally. If it's under the bus, it can get wet, so don't be afraid to get it wet.

> I plan on getting wet

s2mikon mentioned air suspension leaks, but you never responded if you even have an air suspension. Do you?
> I believe i do yes, they sure looked like air bags. Everything under the bus looks solid, brand new even. No leaks can be heard.
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Old 09-21-2021, 04:17 PM   #36
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Okay.

Do me a favor and drain all of your air tanks. Then start the bus and see what pressure you get to, and if you get a purge from the dryer. If you do get a purge, and it's below 120 or so, then you can replace the governor because it's likely failed. If you don't get a purge, you likely have a leak somewhere and that needs to be found.
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Old 09-21-2021, 04:18 PM   #37
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Even a good reman air dryer is a couple hundred bucks, so I wouldn't be throwing one at it for giggles to see if it fixes your problem.
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Old 09-21-2021, 04:20 PM   #38
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Originally Posted by Booyah45828 View Post
Okay.

Do me a favor and drain all of your air tanks. Then start the bus and see what pressure you get to, and if you get a purge from the dryer. If you do get a purge, and it's below 120 or so, then you can replace the governor because it's likely failed. If you don't get a purge, you likely have a leak somewhere and that needs to be found.
>>>Thanks Booyah...
I already drained ALL the tanks yesterday. Started the bus, and it only got to 50. So no purge. I shut it down after 10-15 minutes.
So, prob a super silent leak somewhere, or a failed governor like you said.
In any case, its been over a year since anyone replaced the air driver so id figure on ordering one but Ill hold off till I slither around under the bus for a while first.
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Old 09-21-2021, 04:35 PM   #39
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Quote:
Originally Posted by Peterjk View Post
>>>Thanks Booyah...
I already drained ALL the tanks yesterday. Started the bus, and it only got to 50. So no purge. I shut it down after 10-15 minutes.
So, prob a super silent leak somewhere, or a failed governor maybe?
In any case, its been over a year since anyone replaced the air driver so id figure on ordering one but Ill hold off till I slither around under the bus for a while first.
Well, that answers that.

I've seen where a governor would be frozen off and wouldn't build up any pressure, and likewise would never purge. But if you've started at 0 and built to 50 without a purge, the governor likely isn't at fault.

A leak that large I wouldn't consider silent by any means, it's a rather large amount of air.

With the bus running, feel your hand near the exhaust on the dryer. If you feel air movement out of it, it might be your issue, but my gut is telling me that isn't where your issue lies, as if the purge valve stuck open, you're air pressure would read minimal.

If you don't feel air movement out the dryer exhaust, go back in the bus and turn the engine off and watch the air pressure. If it doesn't drop from 50, the air leak is likely on auxiliary circuits such as air suspensions, stop arms, etc.

A blown bag in the rear can cause a pretty large air leak, that might not be heard with the RE engine running nearby.
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Old 09-21-2021, 04:53 PM   #40
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I had what sounds like these exact symptoms and it ended up being the governor exhaust port stuck open. Must have gotten road grimed or something. This was in warm weather, progressively longer pressure build-up and lower max pressure over 2-3 startups. No air dryer purges. Thanks to an internet tip, I now have a downward-facing elbow on the exhaust port on the new governor to help from getting debris up in there.

Whatever the cause, you'll likely find it on Wednesday with your spray bottle. And you'll know a lot more about the underside of your bus!

PS Kudos for the nice clean engine bay. Maybe I'll get there someday
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