| Author |
Message |
Henry 96A3 (Hank)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 10, 2006 - 12:46 pm: | |
A while ago I posted this topic and after a lot of sluething I discoverd a few leaks here and there that I tightened up. Rate of charge is much improved. Brake chambers don't leak, compressor passes DOT with flying colors (85 to 100psi in 30 seconds). Had airdryer rebuilt a few months ago, had brakes checked and adjusted by a good truck garage. Here's the one thing I can't figure out. The pressure quickly builds to around 65, then just hangs there for about 7 minutes and then starts climbing quickly again to cut out. Does the same thing with shop air. I can hear air moving (not leaking) in the front bogie area-like a tank filling. I assume it's the wet tank, air springs, etc filling? Does this sound "normal"?
Thanks,
Hank 96A3 |
Craig (Ceieio)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 10, 2006 - 12:52 pm: | |
Henry - that doesn't sound right to me. I am sorry I don't havea solution to offer you. My bus is ready to roll from 0 pressure in 2-3 minutes and yours has to have significant engineering improvments over mine.
Craig - MC7 Oregon |
Dale Waller (Happycampersrus)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 10, 2006 - 1:12 pm: | |
My GMC does the same thing If it sits a while and all the air leaks off.
What it does is it gets to around 70psi (check valve opens)then it starts to air up the suspension air ride and other stuff.
Mine has done that for years with no problem. Just check it out for leaks if you have a tight system it will still take a few minutes at engine idle to fill a empty system.
Dale |
Pete/RTS Daytona (Pete_rtsdaytona)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 10, 2006 - 2:00 pm: | |
RTS's have a "pressure protection valve" just ahead of the suspension air tank
It opens to fill the suspension tank at about 50 lbs on an RTS
It purpose is to prevent a major suspension leak (Air Bag / kneeling / wipers / etc ) from letting the Brake pressure primary and secondary tanks go below 50 lbs in an emergency
Dash Air Gauges on an RTS are only hooked to the Primary/secondary brake tanks - there is no gauge on the suspension tank
so there is a quick rise to 50lbs in both gauges then a delay as the suspension tank catches up
Pete RTS/Daytona |
John MC9
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 10, 2006 - 6:50 pm: | |
Henry -
"The pressure quickly builds to around 65, then just
hangs there for about 7 minutes and then starts
climbing quickly again to cut out. Does the same thing
with shop air. "
Mine's the same. When all the air's out, it's going to take time
to air back up. Dale is absolutely right, it gets to 65-70 and
begins airing up the rest of the system. |
Henry 96A3 (Hank)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 10, 2006 - 7:51 pm: | |
John & Pete,
That's pretty much what I figured. What got me concerned about this in the first place was hearing people (like Craig) say their buses inflate from stone cold zero and are ready to roll in a few minutes. Is it that some units have bigger tanks and suspension parts to fill than others? BTW, it takes about 12 hours for my bus to completely deflate when off so I think it's fairly tight. It seems that these rate of charge figures would be relevant and in the manuals but nowhere is it mentioned in mine. When Ian flamed me a little about throwing around the word "normal" I had nothing to compare to. Knowing now that everything else in the system seems okay it's reassuring to know that this is comparatively "normal"....I think.
Henry 96A3 |
Stan
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 10, 2006 - 8:25 pm: | |
The operation of your compressor is normal, but why does your bus lose all its air in 12 hours? Bus companies are reluctant to pay a mechanic by the hour to look for small air leaks. If you have enough spare time to play with a conversion, you must have enough time to fix the leaks. |
John MC9
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 10, 2006 - 9:26 pm: | |
Henry -
Stan's 100% right. Fix the leaks and you'll be much better off.
My MC9 also loses air quickly; too, too quickly. I've been too
short for time to do a thing with the bus this past season, but
fixing air leaks is high on the priority list of things to do. If mine
took 12 hours to leak down, I'd be a little happy, but mine
will drop down within hours, and it's got to be corrected.
The guys that say their bus can be stone cold zero and air
fully within minutes, are.... well...
The most common complaint, is having to run the engine so
damned long at the campsite, just to build enough air to release
the brakes. Most guys will suggest using a small quiet 110v
compressor to charge the system, just for that reason. That
"within minutes" is in the minority.
If you play some random harp music, I'll go back in time, to
my own driving days... There wasn't a bus aside from the
Eagle (60s vintage/mechanical hand brake)... , that ever aired
up within minutes after sitting off all day during a charter, or
prior to a trip after it sat in the barnyard all night. We fired it
up, did the paperwork, swept, adjusted seats, did the
walk-around, flirted with the blond tha.... (ooops)... and maybe
if and when the buzzer stopped, we'd get rolling. My memory
ain't all that great, but I can't remember it ever being "a few minutes".
And contrary to Stan's comments, the outfits I drove for, didn't
take air leaks all that lightly. But leaking down during the off
period, was common. With the leveler valves trying to keep
the bus level even while off, I wonder if it's at all possible to
not use up the air? |
Tom Caffrey (Pvcces)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 10, 2006 - 10:56 pm: | |
Henry, one other thing. When we pick up our coach to go on a trip, it's usually been sitting unused for about 2 1/2 months. Whenever the engine is shut down, the air goes pretty fast.
After we've been using the coach for a week, we usually have some air pressure after being shut down overnight, even though nothing shows on the gauge.
That's because the auxiliary system has some leaks, but the minimum pressure valve is 65 psi, so once the brake system is down to that, the supply to the auxiliary system is cut off.
There is also a check valve in the system that allows air to flow from the auxiliary to the brake side, so the auxiliary system pressure will never be very much higher than the brake side.
Our air gauge is on the auxiliary system. This means that you can use the gauge to figure out which side of the system is losing air.
If no pressure shows on the gauge, but you hear air when you step on and release the treadle, the auxiliary is leaking down first.
If there is no air noise when you step on the treadle and release it, that means that the brake side may be leaking down first.
I hope this helps.
Tom Caffrey PD4106-2576
Suncatcher
Ketchikan, Alaska |
Henry 96A3 (Hank)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 10, 2006 - 11:02 pm: | |
John-Thanks to you and some others who take the time to put up a helpful (and polite) post and for helping me keep things in perspective. I've read a lot of conflicting thoughts about this topic on this board.
I've read some of the threads that discuss the small compressor idea. It's actually on my laundry list for the tools I'll need on board.
Stan-conversion of my coach is a long way down the road. Getting it mechanically sound is my first concern...and that's why I'm asking the questions. As for having all that time on my hands? I should be so lucky. |
Craig (Ceieio)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 11, 2006 - 12:25 am: | |
Henry - one question, do you have the fast idle on when airing up? Mine airs up considerably slower at the normal idle speed. The old warhorse has been setting in the driveway for a little over a week since last started; I could go out this weekend and time various points (pressure, bumper height) it if that is helpful. I know from looking at it the rear is fully down.
I agree with you, it is puzzling that that rate to charge the system up is not specified. I guess it is too hard to tell if "empty" is "empty" so your result would be misleading.
Tom, neat troubleshooting idea, I think I will use that on my coach to see if there is still air in it when it reads zero. My assumption has been that my bus is old and couldn't possibly hold air for a couple of months, anywhere. Since it seems to air up at the same rate no matter how long it has been sitting, I assumed that the air was flat everywhere. The possibility that the thing actually held air somewhere never occured to me, but if it did, I would observe the same thing! Wow, the old tub may be better than I thought!
I guess I better watch that 'old' thing too... even though I was in grade school when my bus rolled off the line, that still makes me older. I think I need an oil change.
Craig - MC7 Oregon |
John MC9
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 11, 2006 - 12:37 am: | |
"I was in grade school when my bus rolled off the line,
that still makes me older. I think I need an oil change. "
HAR de HAR HAR!! |
Stan
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 11, 2006 - 8:32 am: | |
Henry: If you are just starting your conversion, now is the time to check all the air lines that will be hidden after you are finished. People with airbeam buses should lift the floor and check the beams while the bus is empty. It can take a lot of hours to check every fitting on a bus and the ones underneath can be done after the conversion is completed. There are several systems and each one can be isolated and pressure tested with shop air.
John MC9: Leveling valves do not react instantly if they have the correct damping fluid in them. When a bus rocks in the wind there should be no change in the suspension system. You have to change the distance between axle and body and hold it there while the piston slowly moves inside the leveling valve before the air valve opens. I have only worked on older model buses and this system may have changed but that is the way the older leveling valves worked. |
Henry 96A3 (Hank)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 11, 2006 - 1:01 pm: | |
Stan, yes I agree. It's an ongoing process. Like I said, conversion is a long way off. I'm picking away at the mechanicals with all that free time I have. Air beams and bags are next. Thinking about buying one of those portable mangnaflux kits to check for stress cracks while I'm at it. Anyone have experience with them? http://www.magnaflux.com/spotcheck.stm
Tom, I will definitely check that out. Good idea.
Craig, my fast idle kicks in around 80 psi-and that probably explains in part the slow buildup @ 65psi. From what I gather this is not right. My throttle lockout cylinder leaks pretty bad when the fast idle switch is on which I think explains why it doesn't kick in sooner? I've got parts coming to fix it (plunger dried out). |
Craig (Ceieio)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 11, 2006 - 3:51 pm: | |
Henry - I just ran a test because I was curious (and I got my scout troop off to snow camp without me!!)
My guage read flat, 0 PSI. The bus has not been started in over a week. To make sure that there was no air in the brakes, I pumped the foot brake until the brake release knob would not stay down (it pops up on low pressure). Granted there is still residual air in there but there can't be much.
I measureed the bumper height front and rear to see how much that moved. This should tell me if there was air in that system.
I fired the engine:
Nothing much happens for the first 30 seconds.
At 50 seconds, there is 30 PSI on the guage and I kicked on the fast idle.
At 1 minute 20 the bus starts rocking from the bags airing up.
90 PSI was reached at 3 min 10 seconds.
Govonor cut out was at 4 minutes and seven seconds with the guage reading slightly over 120 lbs.
The point on the rear bumper I had chosen to measure rose about 3 1/2 inches. (Measured after govoner cut out).
The point on the front bumper I checked didn't move at all??? I am not sure what that means... was there air in the front bags (is that possible?)
On the local truck scale, my front axle carries a little less than 10,000 lbs, I think it read 9900 last year when I checked it, the drivers and the tag came in a about 21,000, so maybe being tail heavy makes a difference?? I don't have a clue on that.
Anyway, that is my numbers with my '73 MC7 and it feels about typical for when she has been setting. I think it might go a few seconds faster, say 20 or 30 because I don't normally pump the brakes to nothing before I start it.
Your bus is a lot newer and doubtless there are design differences, so I think this is good only for Kentucky windage, but it is at least a real data point to compare to.
I hope this helps.
Best Regards,
Craig - MC7 Oregon |
Henry 96A3 (Hank)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 11, 2006 - 4:33 pm: | |
Craig-Thanks for that. I'm going to fire her up tomorrow and check it out. It's been sitting since Tuesday but I'll double check and make sure it's totally flat first.
Cheers!
Henry 96A3 |
|