| Author |
Message |
Glenn MC-9
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 11, 2005 - 11:20 pm: | |
OK fellas, I need some help here.
Our singing group is running a 1984 MC-9 "New Jersey Transit" coach.
Last weekend I went out to do my "pre trip" before pulling out. My air pressure guage was reading around 60 psi, with no air in the suspension.
Note:It use to be that the suspension would stay up for about 3 days before leaking down.
What happened next has me baffled. After I cranked up the engine I got the normal lamps and buzzers. Then the air pressure built up to around 90 psi and stopped. I flipped the "fast idle" switch hoping that would speed things up.
After several minutes of waiting the pressure built up to about 95 psi and stopped again.
By this time I'm getting concerned and decided to try to release the brakes. When I did, the brakes released and the air pressure dropped back to 60 psi and stayed there for a minute or so. Then all of a sudden the air started building back up and the body started raising. When the pressure got back up to 90 psi, the pressure switches were satisified and silenced the buzzers and lights. The air then continued to build on up to the normal 125 psi.
Everything looked OK, so I left. When I got to the church, I let it idle for several minutes to let her "catch her breath" and then shut her down.
After about 45 minutes I went back out to move from the front of the church and my air pressure had dropped back to 60 psi.
I had to repeat the entire process mentioned above to get it moved.
I've been had a small air leak on the bi-fold doors, but it's been leaking about the same for the last several months.
Sorry for the long post.
Anybody got any ideas on what may be the problem?
Glenn
Tallulah Falls, Ga.
glennvin at alltel.net |
TWODOGS (Twodogs)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 11, 2005 - 11:42 pm: | |
you have a leak....get a young person,with good ears to find it |
Tim Strommen (Tim_strommen)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 12, 2005 - 12:05 am: | |
Step 1) Put soap and water in a spray bottle.
Step 2) Spray soapy-water at air lines, fittings, and major hardware.
Step 3) Look for bubbles and "spitting" on air parts (use a mirror to see the hidden sides of things) this is a leak.
Another possibility for your loss is a faulty govenor, bad skinner valve for high-idle or engine shut-down. You also my have a clogged purge valve on your air dryer, or a dump valve on your air tanks that's not fully closed...
The list goes on and on... Start with the soapy water.
Cheers!
Tim |
Glenn MC-9
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 12, 2005 - 6:31 am: | |
Yea I realize that I've got a leak.
But what I don't understand is why releasing the brakes makes a diference. It's acting a though a valve is sticking. But on the other hand, it's not just dumping a lot of air when I shut it down either.
I'm going to get it over a pit this weekend and hopefully find the problem.
Glenn |
TWODOGS (Twodogs)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 12, 2005 - 7:41 am: | |
when you release the brakes ,it suplys air TO the brakes |
Doug Dickinson (Dougd470)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 12, 2005 - 2:12 pm: | |
Glenn
You didn't mention if you have removed the kneeling on the coach. If not, do so immediately. I had a similar experience and removing the kneeling feature fixed one of the two problems.
You also have a leak somewhere, but the kneeling feature can hide some of the problems.
Doug
83 MC9 (NJT 6442) |
Glenn MC-9
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 12, 2005 - 4:02 pm: | |
Doug,
I haven't at this time removed the kneeling feature. As a matter of fact, I've been scared to even see if it works. I heard of these things going down and being a nightmare to get back up.
But I have thought about disabling it but wasn't sure what I'd run into. From what I understand there is some safety interlocks involved. I sure wish there was sombody nearby that had done this before. LOL
My learning curve on this MCI is sort of slow. Before we purchased it we had a 4104...entirely different!!!
Thanks,
Glenn |
Jon W.
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 12, 2005 - 4:48 pm: | |
There may be a combination of problems. Start looking at the brake chambers because when you release the emergency brakes as was posted air goes to compress the spring brakes. When you put on the emergency brake you dump all that air pressure so you will not hear the leak. Chock the wheels and release the brakes. If it is a diaphragm in the emrgency brake chamber you will hear it.
I would also spray that soapy water around the bottoms of the air bags. Unless those air bags have been replaced I would suspect corrosion has created pin hole leaks around the bottom steel portion of the air bags. |
Jack Conrad (Jackconrad)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 12, 2005 - 5:46 pm: | |
MC-9 does not use spring brakes, it uses DD-3 parking brakes. This system uses air pressure to apply the brakes and rollers to lock the pushrod in the applied position. To release the brakes, you have to apply a firmer application to allow the rollers to release their hold on the pushrod. There is a little more to it than this, but basically this is how it works, Jack |
Buswarrior (Buswarrior)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 12, 2005 - 6:03 pm: | |
Hello Glenn MC-9
First of all, Jon W, an MC9 does NOT have spring brakes, it has DD3 chambers.
Glenn, two related strategies:
The kneeling is interlocked with the parking brake on many buses. Perhaps releasing the parking brake invokes something in your kneeling circuit to stop dumping air out of the system in a way that it isn't supposed to. On some buses, releasing the parking brake automatically raises the kneeling to drive height.
You might find that it only does it's misbehaviour under a slow leak down, and behaves properly once the bus is aired up and running.
What happens if you get the bus properly aired up using your discovered recovery method, park it, leave the engine running and then pump the brakes to get the air down below 90 again? air pressure stalls or builds back up?
I would strongly recommend that you get that kneeling feature figured out. As already noted, they are tempermental in the best of times, and with infrequent use, it will just fail and leave you stranded. I would fully expect the wiring in it to be a dog's breakfast of pierced wires and splices.
I'd bet there are members of the singing group who have little patience for the bus always screwing things up....
If you are able to rule out the kneeling circuit, I would focus on the parking brake related valving, if changing the parking circuit clears up the problem...
When air valves fail, sometimes they leak when they are "shut off" and hold air when they are "turned on" which seems a little backwards, if you know what I mean.
I have seen many parking brake circuits leak heavy enough to defeat the compressor while in the "parked" configuration, only to seal up perfectly tight when the parking brakes are released.
Let us know how you are making out!
happy coaching!
buswarrior |
David Hartley (Drdave)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 12, 2005 - 6:08 pm: | |
NJT MC9 Air problems can usually be traced to the rear air bags on the main axle. Many of the NJT MC9's had air beam leaks and NJT installed aluminum blocking plates on the airbags. These I have found out the hard way, Are subject to corrosion and pinhole leaks due to moisture, salt and other organic things going on between the aluminum and the steel mountings.
There are TWO plates on each side of the axle. A forward bag and a rear bag. IBP has the replacement plates in stock along with the longer bolts needed to install them. It takes about a day in the shop to have both sides done, or about 8 hours of labor. A very good investment and stops that 90 psi delay business in its tracks.
Soapy water in sprayer, air bus up and spray around tops and bottoms of air bags including the bolt areas. If you see a bubble, replace them all now and it will save you later.
One other item, the front air leveler valve on mine was leaking quietly and intermittantly. This solved yet another major air loss region.
If the fast idle doesn't let you build up air rapidly then the cylinder for it has a leak. mine does and I actually can lose pressure when in fast idle. I know where my leaks are now but it took me 3 months of searching.
Have Fun.... |
Tim Strommen (Tim_strommen)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 12, 2005 - 6:31 pm: | |
Step 1) Put soap and water in a spray bottle.
Step 2) Spray soapy-water at air lines, fittings, and major hardware.
Step 3) Look for bubbles and "spitting" on air parts (use a mirror to see the hidden sides of things) this is a leak.
Step 4) Fix leak (usually will need to replace a part)
I added step 4 because I may need to mention it. Glenn, you mentioned that you know you have a leak. As complicated as air systems appear to be, they were designed by people, and are repaired by people every day. Take your spray bottle and start on the major hardware (govenor, air tanks, air bags, relay/inversion valves etc.). It's rare for a DOT nylon line to just "spring a leak", go for places where parts come together, and you'll more than likely find your problem in a few minutes (but don't stop looking until you've done it all!!)
Tim |
Jon W.
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 12, 2005 - 7:45 pm: | |
My brain is thinking Prevost with spring brakes. |
Jtng
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 12, 2005 - 7:49 pm: | |
MCI brakes work, regardless of season. |
Buswarrior (Buswarrior)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 12, 2005 - 9:42 pm: | |
That's ok Jon.
There's more info on here than in several lifetimes of personal discovery.
Moments of confusion are a side effect.
happy coaching!
buswarrior |
Glenn MC-9
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, July 13, 2005 - 6:34 am: | |
Thanks for all the comments and information folks.
I'm hoping this thing won't be a "bugger bear" once I get under it.
Again, thanks.
Glenn |
Marc Bourget
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, July 13, 2005 - 8:17 am: | |
It bears repeating - before you get under it - BLOCK IT!!! |