| Author |
Message |
MikeM (24.70.128.130)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 30, 2003 - 1:30 am: | |
I am having troubles getting enough air pressure in my GMC 5307 (6V71).
All was fine on the drive to her new home, good air pressure of 120psi. However, since then Air Pressure has not gone above 80psi.
I have replaced the governor.
Pressure rises to 80psi then stops and holds. I can drop it to about 60psi and it will kick in and build back up to 80 again.
I have verified the pressure reading at the wet tank and it reads the same as the dash gauge.
Pressure holds at 80psi for several hours after shutting down engine so I don't see a huge leak anywhere.
I have piped air into the rear air chuck and I can pump it up from an external source to about 110psi (limit of my shop compressor).
What do I need to do to isolate the governor and get it out of the system to let the compressor pump full time to see if it can actually keep up and pressurise over 80psi?
Any troubleshooting tips appreciated.
Thanks guys.
Mike |
two dogs (67.30.23.81)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 30, 2003 - 5:36 am: | |
Wow..that's a brain twister...you put on a new D-2 air governor, still 80...worked fine on the way home..compressor wouldn't just go out overnight......a 'guess' would be rings might be bad and at hiway speeds it kept-up..that's just a guess |
FAST FRED (67.75.105.248)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 30, 2003 - 6:05 am: | |
Most Govs can be adjusted for higher pressure ,
FAST FRED |
two dogs (67.30.23.81)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 30, 2003 - 6:16 am: | |
never heard of that..I never did anything except put a clean one on..can't imagine why, if it was the gov. Two in a row would give same pressure... don't see how it'd be the gov..still points to weak rings in the comp. But I did say I was guessing |
BrianMCI96A3 (65.41.249.165)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 30, 2003 - 8:39 am: | |
Mike,
when you first got her, did she build to 120 before you drove away? At this point, messing with the governor isn't going to help. I hate doing it but I tend to agree with dogs that it's in the compressor. |
Bill Gerrie (65.49.74.228)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 30, 2003 - 8:40 am: | |
Mike
Take the cap off the new govenor, loosen the lock nut and turn the screw till you get the cut out psi to rise to 120. Lock the nut. The cut in psi is not adjustable. It is set by the cut out psi. If you cannot get the psi to rise you may have a defective compressor or even though the govenor is new it could be defective also. You might also try reving up the engine to see if at an increased speed you can get the pressure up. If you can than the compressor is no good. Drain your wet tank to see if you get a lot of milky looking junk out of it. If you do it could be the rings on the compressor are gone. It is easy to rebuild the compressor. Just go to your nearest Bendix dealer and get a set of rings and gaskets. Make sure the cylinder is not to bad before you spend the money on the parts. You could also get an exchange one. Hope this helps you. Bill |
Buswarrior (Buswarrior) (64.229.209.250)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 30, 2003 - 9:57 am: | |
Hi MikeM.
I'm suspicious of this problem showing close to 80 lbs. The pressure protection valve will be set close to there, isolating the brakes from the rest of the air powered accessories.
For instance, if you were to burst a bellows, the pressure protection valve will close and isolate the brakes from the loss of air, as the pressure falls past it's set point, usually in the 70 to 90 lb range.
I'd go out and around checking carefully for air leaking while it's running. (Just to make it difficult, it'll more than likely be somewhere in the engine room, where the noise of the motor and fan will hide it!) Things like control lines, the shutter stat system, the suspension is still up?
It doesn't take much of a hole to defeat the compressor's ability to build air. A perished seal or diaphragm in some regulator or valve leaking out the backside vent hole will do it. (and the hole will only be the size of the lead in a primary pencil) Since this has happened suddenly, I'm thinking sudden failure, not a wearing out type scenario.
The fact that the pressure builds well from 60 to 80 really makes me think the compressor is not the culprit.
Have you confirmed the pressence of your 80 lbs of air in EVERY part of the system when it's shut down?
good luck, and let us know what you find!
happy coaching!
buswarrior |
MEL 4104 (208.181.100.16)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 30, 2003 - 10:13 am: | |
Mike, check your gauge with one you know is working. If you have an outlet that you can plug into. Some have an outlet that you can use a tire gauge on in the engine compartment. When you have the air built up, check the front and the back and if they are not the same, change the gauge.
Let us know what the trouble was.
Tks. Mel 4104 |
MikeM (24.70.128.130)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 30, 2003 - 10:35 am: | |
I have tried adjusting both the old and the new governor.
Can I check for leaks and possible protection valve probs as Buswarrior suggested by filling up the system with an external source, hooking up at the air chuck in the engine bay, or does the engine need to be running to check. Very noisy to tell if air leaks while the engine is running.
There was some sludge out of the tanks, but who knows how long it has been since they were last properly drained?
Can I disconnect the governor from the compressor to let the compressor work full time? Do I need to block off the governor so it does not dump out all my pressure? |
Bill Gerrie (65.49.74.228)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 30, 2003 - 11:10 am: | |
Mike
You could fill up the system with an external air supply without the engine running to check for air leaks. This way you don't get the engine noise overcoming the air sound. If you can get the 110 lbs in that you said your air compressor will develope than listen and if you don't hear any air leaks and your gauge shows that your system is holding than it pretty well has to be a compressor problem. You might want to check the flexible connection right after the air compressor because if your system holds the air okay there is a check valve just after the flex line that if there is a problem there it will not show up when the engine is not running due to the check valve. Bill |
MikeM (209.52.92.132)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 30, 2003 - 12:19 pm: | |
I Will do some more troubleshooting tonight. I plan on filling the tank by external methods and checking for leaks. Then removing the governor and allowing the compressor to work alone.
I will post my findings.
Thanks for everyone's suggestions.
Mike. |
Gary McFarland (Gearheadgary) (209.128.99.4)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 30, 2003 - 12:21 pm: | |
Betcha five bucks Buswarrior's nailed it.
I'd hook up external air, I bet you find a whopping hiss somewhere.
Gary |
T Gojenola (24.237.70.61)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 30, 2003 - 2:53 pm: | |
Gary, I'd take you up on that bet, but it would not be fair. Mike said in his original post that the pressure rises to 80PSI, drops to 60, and then builds back up to 80. This indicates a problem at the governor, although it may be exacerbated by other problems, such as air leaks.
tg |
two dogs (67.30.23.102)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 30, 2003 - 3:03 pm: | |
yep....he also said it held air for hours after he shut it off...poor guy,...always wrong |
Gary McFarland (Gearheadgary) (209.128.99.4)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 30, 2003 - 3:33 pm: | |
But he's replaced the governor, Actually, did it hold shop air for hours?
Or did it hold at 80?
I did miss the kicks in at 60 part--that doesn't jive.
Sorry I don't make the grade for you two dogs, I know everyone is here just to gain your approval.
Gary |
two dogs (67.30.23.102)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 30, 2003 - 3:52 pm: | |
poor ol' gary,...born with a silver foot in his mouth |
jim mci-9 (209.240.198.60)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 30, 2003 - 7:24 pm: | |
you can remove the governor and run the engine... if the compressor build air past 80, then the compressor is good... the compressor should keep building air till a relief pops pff.... somewhere around 150.....how is the intake to the compressor plumbed?? does it share an intake with the engine???? check that.... and you can spray wd-40 into the intake of the compressor to free up sticking unloader valves.....hope it helps..jim |
ED-NJ (67.85.224.113)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 30, 2003 - 7:33 pm: | |
Ok guys on my MCI-9 the polyproplene air line to the piston for the rest room door was loose.It had the same symptoms, real hard to find. |
MikeM (24.70.128.130)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 30, 2003 - 9:39 pm: | |
Well, I think Buswarrior was pretty much on the mark.
I filled the system with external air and there is a major leak in the DS rear air bag. Can't really hear it too well, because it is such a huge leak. The bag seems intact, but the bottom can is leaking where the can is welded together. Leaking all around.
I didn't get a chance to test the compressor etc, but I figured this was a major enough event to stop here and repair.
By the way, this seems as though it may be a major repair, because it seems that can is welded to a big arm etc. Any suggestions as to how to proceed?
Once the air hits about 80psi on the gauge, the air gets shut off to the suspension and the pressure holds steady.
Not sure why it does not kick back in building pressure until it drops to 60, but I'll tackle this problem and see if it gets better.
Thanks guys for all your great advice.
I'm looking forward to more advice on where to go next.
Thanks,
Mike. |
Gary McFarland (Gearheadgary) (209.128.99.5)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 30, 2003 - 9:57 pm: | |
Bags are not a showstopper, it's been about 18 years since I changed one though--
Some folks carry spares, in case they need to change them on the road.
what's the "Can" you're talking about? is it rather the "Cup" sinks into the bag when the air goes down?
I believe, replacement is only jacking up the frame, supporting it with a jackstand, I think the bag and cups come out as an assembly (remember...18 years ago...), reverse order to install.
I guess the bad news is, if one has croaked, you should replace all of them ($).
Let us know what you find out.
(TG, Where's my five bucks?) |
Bill Gerrie (65.49.74.228)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 30, 2003 - 10:16 pm: | |
Mike
It is easy to replace an air bag on a GM. Block the body under the pads and make sure the air is all released from the suspension. Take the wheels off so you can get at it easier on the side where the leak is. The bag is held on by small nuts at the top on each side of where the air line connects and on the bottom. There is a metal piston inside of the aluminum piece that the bag rolls down over and a metal piece at the top. Disconnect the air line. When you buy a new bag make sure it is already formed as you need a jig to get the bag to form. It is almost impossible to get it to conform otherwise. I have changed a bag in about 15 minutes on a GM so you can see it really isn't too big a job. Bill |
Gary McFarland (Gearheadgary) (209.128.99.5)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 30, 2003 - 10:33 pm: | |
Bill,
It is SOP to replace all in this situation isn't it?
Gary |
Bill Gerie (65.49.74.228)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 30, 2003 - 11:13 pm: | |
Gary
I would at the very least replace the two bags on the one side when I had it apart. The bags on mine are at least 18 years old and are fine. They are dated on the bag. I got to admit that I do carry a spare one for the front and one for the rear. It isn't always too easy to find a replacement in the middle of nowhere. Bill |
MikeM (24.70.128.130)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, October 01, 2003 - 12:16 am: | |
Thanks guys.
If the nuts are rusted solid, is it ok to cut them off with a die grinder as long as I'm careful not to damage the housing. I assume the bags come as a self contained unit with new bolts and nuts etc.
Just to confirm, the air bag just sits in the cup at the bottom and the leakage I am seeing is just the air finding its way out of the bag?
Sorry for the dumb questions, this "heavy" kind of mechanic work is new to me.
Again, thanks for all the quick and helpful responses. You may be hearing a lot from me as I get deeper into this project.
I'll post again after I replace this bag, just to let you know if it goes all back to normal.
Mike. |
Richard Bowyer (Drivingmisslazy) (24.196.191.70)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, October 01, 2003 - 6:19 am: | |
If you are in the Southern California area, Leonards Diesel in Ontario can do this for you. His rates are very reasonable and he does good work.
Richard |
Gary McFarland (Gearheadgary) (209.128.99.5)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, October 01, 2003 - 12:12 pm: | |
Actually, it was Buswarrior that nailed it, I just agreed with him.
Gary |
MikeM (209.52.92.132)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, October 01, 2003 - 12:34 pm: | |
Anybody got a part number for that air bag?
I can't get in there to see any numbers on the bag. Don't have a service manual YET.
1981 5307N. Driver's side rear air bag.
Thanks. |
Buswarrior (Buswarrior) (64.229.211.97)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, October 01, 2003 - 9:18 pm: | |
Hello MikeM.
I phoned the shop just now and the parts person related this info to me, so I'm not 100% on the accuracy.
For a Firestone brand rear bellow for GM 5307, the sticker has on it: K00952185
There is a number in the casting: ITI5AA3
The "I"s might have been "1"s.
I would be inclined to try the sticker number. Numbers cast into metal parts are frequently just casting numbers and have no relationship to a parts numbering system.
Glad I've been able to help!
For your compressor, once you have regained air integrity, build up the air to maximum, lower the pressure using the brake pedal to below 85 pounds, time how long it takes for the compressor to build from 85 to 100 with the engine idling. Good ones do it in about 45 seconds. Up to 2 minutes is legal, but if my own took more than, say, oh, 80-90 seconds, I'd be wanting to do a maintenance job on it. You MUST have air integrity, or the results will be flawed.
happy coaching!
buswarrior |
BrianMCI96A3 (65.40.144.214)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, October 01, 2003 - 9:23 pm: | |
Hey, who WAS that masked man (buswarrior)?
:::grin::: |
John Rigby (24.174.239.244)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, October 02, 2003 - 9:18 pm: | |
Mike
Before I would order the bag I would drive (if possible )the bus onto a block/ block the three wheels you are not working on/ jack the axle up, jack the body up a little.block both the body and the axle VERY Carfully/SEVERAL BLOCKS.Pull the wheels on the air leak side, start the bus up and really find out where it is leaking from, it could be a line? After you find out call luke 1888-coach 34 discuss the part and he will help you with the correct one.
John |
Johnny (67.242.221.189)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, October 03, 2003 - 8:56 pm: | |
"For your compressor, once you have regained air integrity, build up the air to maximum, lower the pressure using the brake pedal to below 85 pounds, time how long it takes for the compressor to build from 85 to 100 with the engine idling. Good ones do it in about 45 seconds. Up to 2 minutes is legal, but if my own took more than, say, oh, 80-90 seconds, I'd be wanting to do a maintenance job on it. You MUST have air integrity, or the results will be flawed."
I was told that, for a dual air system (which I don't know if Mike has), any longer than 45 seconds from 85-100psi at idle is unacceptable. I was told this by a CDL road tester, so I'm inclined to believe it. |
HenryMC7 (142.59.71.18)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, October 04, 2003 - 4:27 pm: | |
The official standard in Alberta is 3 minutes to go from 50-90 lbs at up to 1/3 throttle. However, I agree with the others, I would repair long before it got that bad. BTW, if the bus was constructed after 1975 it will have the dual air system. We've got a lot of those 5307's here in Edmonton. They just keep going and going....
Henry |