-
Do I have a problem or is this normal?
Hi guys,
I was over at my coach today, started it up and set it on high idle. While on high idle every once in awhile there is an air sound like the air built up to its max and expelled some. Is that standard?
When I shut the coach down and went back to turn off the coach batteries. I heard a faint air noise coming from the engine compartment that I hadn’t noticed before. I opened the engine compartment and now the air noise was both obvious and constant. It seemed like it was coming from around the electrical box above the engine. I put my hand all around but I couldn’t feel any obvious air movement. It lasted every bit of 10 minutes and then slowly diminished.
I had a guy come over who has an Alegro Bus and he didn’t know what it was nor could he figure the source. All my gauges were normal, the coach was at drive height and performed the DOT brake test and it passed with flying colors.
I should also mention the Jeff just installed new airbags, brake chambers and Norgren valves. I sure hope this is normal!!!
Harry
-
77 Replies
-
The big PSSSSTTTT sound is normal. All air brake vehicles that I have do that. I only have 4… in case you’re wondering….
I’ve never noticed a hissing sound like you’re talking about though… my novice opinion is it’s a leak. But a small one that’s not affecting your brakes.
-
Harry,
Does your bus have air bags to tension the engine belts? If it does then you may have been hearing a leak from the pressure release valve or regulator. On my bus it is mounted above the rear engine doors in the engine compartment. Look up and to the rear. Assembly has a check valve, pressure regulator and the release valve. Maybe the valve is just not closed all the way.
Good Luck
Doug
-
Hi guys,
I don’t know anything about the “air bags to tension the engine belts?” But I’ll look to see if there’s a check valve. Do you think a 91 would have this feature? I think I would have felt the air located where you mentioned because I had my hand all over that area!
Harry
-
Harry has an 8V92, no belt air bags.
-
Harry,
Your coach is likely set up like my 93. Your belts are tightened with 2 air cylinders (not bags like the newer coaches). Only 1 cylinder if you don’t have over the road air conditioning. The air passes thru a regulator and 3 way valve on the way to the cylinders which are mounted on the back wall of the cap above the rear doors. The valve has 4 ports and one is a vent.
If the cylinder seals are leaking air will come out the vent. Those valves are also known to leak. I have replaced my valve ($165 worth of pricey for a Whitney valve) and rebuilt the cylinders. The end seals are no longer available so the o-rings are all you can do. Until the air is gone from the belt tension air lines you may hear the leak.
On our vintage, this will bleed the air out of the wet tank. The Primary and Secondary Brake Tanks should not be effected. If they stay up up and you stay level (no leans) Jeff done you right.
Your Aux pressure will drop to about 75psi backfeeding the wet tank until the pressure protection valve closes. After that any drop in Aux pressure is aux system leaks.
Unless that leak is very large, use the coach.
-
Harry,
Your coach is likely set up like my 93. Your belts are tightened with 2 air cylinders (not bags like the newer coaches). Only 1 cylinder if you don’t have over the road air conditioning. The air passes thru a regulator and 3 way valve on the way to the cylinders which are mounted on the back wall of the cap above the rear doors. The valve has 4 ports and one is a vent.
If the cylinder seals are leaking air will come out the vent. Those valves are also known to leak. I have replaced my valve ($165 worth of pricey for a Whitney valve) and rebuilt the cylinders. The end seals are no longer available so the o-rings are all you can do. Until the air is gone from the belt tension air lines you may hear the leak.
On our vintage, this will bleed the air out of the wet tank. The Primary and Secondary Brake Tanks should not be effected. If they stay up up and you stay level (no leans) Jeff done you right.
Your Aux pressure will drop to about 75psi backfeeding the wet tank until the pressure protection valve closes. After that any drop in Aux pressure is aux system leaks.
Unless that leak is very large, use the coach.
-
Hi Joe, I was surprised how long the hissing air lasted. If it is the cylinder you mentioned, shouldn’t I be able to feel the air being expelled with my hand? I know you can’t always identify where sounds come from, but it sounded like it was coming high above the engine and to the rear.
If I read your post correctly you’re saying it’s not of great concern?
Harry
-
Harry: Did you take the coach for a ride? Get it all warmed up? Or just start it up and let it idle?
Maybe an 8V92 owner could comment on firing the engine up and just letting it run. I’ve seen comments from both 8V92 and Series 60 owners that it isn’t a good idea to fire up the engine to just let it run for the sake of running it or letting it needlessly idle for any length of time. Getting either engine up to operating temperature before hitting the road is a different story.
-
Hi Dick,
This day I didn’t take it for a run. I started it and ran it on high idle for 30 minutes, took it off high idle and had it run on idle for a minute. I then shut it down and turned off the power sources. I also had the generator on and ran all air conditioners to put it under load.
Harry
-
HJarry: Are you plugged into 50amp shore power now?
-
Before Harry gets more confused here are some facts. His vintage coach has OTR so he has two pneumatic brass cylinders that provide belt tension to his OTR A/C compressor and his fan drive.
He has the same set up as far as regulator and valve to provide the correct tension and to release air so belts can be replaced.
But Harry isn’t helping us to help him because he is in the dark as to what we need to know to steer him in the right direction. For example, I think we all believe the hissing noise he hears is the air dryer cycling. He needs to verify that by being very specific about where he hears the noise, and to tell us if he is seeing his gauges on the air systems provide him with information about cycling, and if they are cycling on which circuits and how often.
Without some solid information anything we say can be misleading and wrong.
Regarding noise from the rear of the coach…….again Harry needs to get far more specific. Feeling around for an air leak may only work if it is within reach, and of such a volume it can actually be felt. I know from experience air leaking in an area such as around the engine bounces off of various surfaces to such an extent we have no clue where its origin is. This is where a stethoscope or leak detector aids in providing some clues.
If it relates to something other than brakes that means Harry needs to advise if he has an aux gauge and if he shows the accessory air cycling up or down. Accessory air leaks can come from many sources. Maybe it is important, maybe not.
Harry, do some digging and get specific and maybe we can help.
As to just running the engine……..I am not the expert but I believe we can do more damage over the long term by failing to get everything heat soaked such as we would do if we did a 30 to 50 mile run. It takes more than just idling in place to drive out moisture from the crankcase for example.
-
10 minutes may be about right if you are draining the wet tank. The leak is downstream of the regulator and it has to pass around the o-rings in the cylinder so it is throttled pretty good. I don’t think it can overcome the air compressor supply like a failed air bag but I would try and have it fixed at a convenient time. It can go on your list for the next trip to Jeff.
It could be the regulator, the valve or the cylinder o-rings. I know I could hear mine but don’t recall if I ever felt it. I know I replaced the valve and rebuilt the cylinders don’t recall about the regulator without checking my log book.
Based on your description, I think the big swoosh your hear is the air dryer cycling. Next time see if it happens when the air pressure is about 120. The air dryer purges to drop pressure in the dryer housing and drive the moisture out of the dryer material. That is normal expected behavior.
-
I forgot to mention that with a leak so big you can hear it the gauges are going to show it unless it precedes the wet tank.
A report of what the gauges show after the pump cycles off would help.
-
Hi guys and thanks,
Tuesday I’ll be taking “The Beav”, (that’s original) out for an hours run and will pay attention to all gauges. What they say when I start and what they say when I get back?
When I shut down I’ll go back and open the engine bay doors. If I hear the same noise (it be weird if I didn’t right?) I’ll see if I can determine exactly where it’s coming from.
Oh, and before starting out I’ll take the chrome covers off the belts.
Anything else you recommend please let me know before Tuesday.
Thank you one and all,
Harry
-
I would strongly suggest you develop a pre-trip inspection procedure that works for you. What makes this important is the more you do inspections the more likely you will quickly spot something that is not normal. I am not suggesting the air leak you describe is normal and if it is an indication of a needed repair it is good you caught it.
Because air and brakes are vital to your safety do a complete pre-trip brake and air check and pay close attention to the gauges so you verify no brake system leaks, all warnings and buzzers come on as required, the parking brake comes on automatically, and the protection valves are working. You not only need to know the procedure what is more important is you understand what each step in the procedure tells you.
Then when you do get on the road and everything is warmed up, not all your gauge readings, their upper and lower readings and what they are telling you. Again, because you have an air leak note how often the air system gauges cycle up and down. I hope you have an accessory system air gauge because that may be the one that might provide clues regarding your leak.
Log in to reply.