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Old 10-26-2020, 02:32 PM   #1
Bus Nut
 
Join Date: May 2017
Location: Houston TX
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Year: 1998
Coachwork: Amtran
Chassis: International
Engine: dt466e
I think I have a air brake pressure leak

I went to start my bus today after months of it sitting and when I want to put my foot on the brake and release the brakes the brake pressure light came on and started buzzing. I figured I'd let it run for a bit to let the air pressure build back up but I found that it wasn't going up at all. After a while I went to take a look under the bus to see if I can spot anything obvious and I noticed a mild smell that I never smelled before. Also, I wasn't for certain but it sounded ike it was making a noise that wasn't there before too.

I climbed under to try to get as close to the sound as I can and I moved my hand around and found that there was some air shooting out from somewhere. It wasn't a big amount of air and I'm not sure if that's just something that's always been but I recorded video of where the air is coming from to see if anybody will be able to tell me if this is a air leak issue. Also, I took more video of the same area of something that looks like it was bubbling

Any help would be appreciated. I have to move my bus from where it's stored at before tomorrow or I get charged the monthly rate. Hopefully this is easy to fix on my own it's a 98 International 3800 dt466e Amtran

Here's a link to the video

https://streamable.com/fmvxux


Thanks
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Old 10-26-2020, 06:04 PM   #2
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That's the air dryer. Where it's leaking at is the exhaust of the air dryer. If yours is leaking out of the exhaust all the time like that, you need to either rebuild or replace it the air dryer assembly.

That exhaust has a valve above it that is supposed to seal up and allow the compressor to push air through the desiccant(drying material) and into the wet tank. If that valve is broken or stuck open, it will continuously push air out of the dryer and never build pressure.

Take a picture of the whole dryer assembly and we'll see if we can figure out which dryer you have and what rebuild kit/reman'd assembly you need.
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Old 10-26-2020, 06:05 PM   #3
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It looks like an ad9 dryer, but I'd like to see a clear picture before I send you on a wild goose chase.
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Old 10-26-2020, 07:05 PM   #4
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Booyah's right. These are somewhat common failure items, usually when the "filter"/cartridge is never replaced. The cartridge should be replaced at least annually on a "daily driver".
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Old 10-26-2020, 08:04 PM   #5
Bus Nut
 
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Quote:
Originally Posted by Booyah45828 View Post
It looks like an ad9 dryer, but I'd like to see a clear picture before I send you on a wild goose chase.

Thanks for replying. Someone else also bet on it being an AD-9. I'll take pictures when the sun comes back up. He also said there's different configurations so you gotta be careful when determining the replacement
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Old 10-26-2020, 09:10 PM   #6
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Either of you know what the bubbling is all about in the last part of the of the video?
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Old 10-26-2020, 09:21 PM   #7
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The bubbling is air bypassing one of the o-rings on the purge valve assembly. pull it apart and see if you need an entire valve or just a rebuild kit. Unclip the heater connector on the bottom, and then remove the 3 bolts and the valve should pop out.

Here is a video that kind of shows it. It isn't mine, and there's minimal audio, but you can get a idea from it.

https://youtu.be/sBwKvY8e-Pg

I seen on amazon they had an ad9 purge valve maintenance kit and new cartridge bundle for 63 bucks. Definitely replace the cartridge because most skoolies neglect to do so.
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Old 10-27-2020, 02:28 PM   #8
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Thanks a lot!
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Old 10-27-2020, 02:34 PM   #10
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sure looks like a Bendix AD-9 or AD-4.. both were used on school busses.. and both pretty common.. judging from the outside of that one the dessicant cartridge hasnt been changed in a long time..



I would replace it with a reman unit..



since bendix recommends swapping any AD-4 for an AD-9 as a replacement, its a good bet to get an AD-9 reman unit..


yours is a Heated air dryer . . be sure to get a heated one as the replacement..
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Old 10-27-2020, 02:53 PM   #11
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It's an ad-9 based off the exhaust housing in the pictures. The ad9 has a 3 bolt whereas the ad4 has a 4 bolt.
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Old 10-27-2020, 08:55 PM   #12
Bus Nut
 
Join Date: May 2017
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Good news!... I think..

After reading the replies here and another place I asked, something made me twist the bolt where I guess the "cartridge" is (?) And from what I can tell it seemed to have moved up slightly. I decided to start the engine and see if that helped and low and behold, the air pressure gauge started climbing! And quite quickly. At about 60 or 90 psi the light and buzzard went off.

Few questions: Should I twist it more until it stops? Is it supposed to be easy to turn? It wasn't loose loose but not tight as one would think. The bolt itself wasn't turning. Well it was but along with the white disc looking thing right above it.

I wanted to get some feedback at this point before I drove it to where I'm taking it, which is not that far at all.

Thanks for all of your help guys!
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Old 10-27-2020, 09:13 PM   #13
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Here's an image to point out what I twisted clockwise

Also, typo in the pics text. *Bolt, not but.
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Old 10-27-2020, 09:26 PM   #14
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In your case I'd feel OK moving it a short distance while the thing is building air pressure, but I'd plan on changing the air dryer before too much longer. Sounds like maybe you dislodged whatever was making it stick open and it's likely to do so again at some point in the not-so-distant future.
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Old 10-28-2020, 12:53 AM   #15
Bus Nut
 
Join Date: May 2017
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Quote:
Originally Posted by Brad_SwiftFur View Post
In your case I'd feel OK moving it a short distance while the thing is building air pressure, but I'd plan on changing the air dryer before too much longer. Sounds like maybe you dislodged whatever was making it stick open and it's likely to do so again at some point in the not-so-distant future.
Yea, I was anxious and just moved it. When I first tried to drive it it wouldn't move. Forward nor reverse. I tried a decent amount of times and then started researching what could be wrong. I found nothing so I tried again and noticed the bus moved forward "very" little and vice versa backwards but like it was chucked or had a really strong emergency brake applied. Kinda like it was stuck. I tried one more time in reverse and then drive and it kinda mad a tank sound and drove forward as usual. Sounded like it released itself from a chain or something. It wasn't attached to anything BTW. What do you suppose caused this? Hopye it's not a sign of transmission issues to come ��

Anyways, I took another look at the air dryer and it seems kind of wet. Either way, s you suggested, I will replace it since it seems like easy task and the part is cheap. What do you think that wetness indicates? Also, do you think twisting that nut some more will make it go away? Aside from one drop, there was no liquid leaking from it. Kinda like condensation. I took a pic.

Since I've had the bus, after shutting the engine off I've always heard like a long faint hiss. More audible when I stick my head under the bus. I figured it's just how the air brake system works but with this situation I found it's actually the air dryer (I think). Is that normal? It goes away after a short while.

Air pressure seem great BTW

Thanks again guys
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Old 10-28-2020, 07:57 AM   #16
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Quote:
Originally Posted by Booyah45828 View Post
It's an ad-9 based off the exhaust housing in the pictures. The ad9 has a 3 bolt whereas the ad4 has a 4 bolt.



ha! cool stuff I always went by heated or not but I learned that both can be heated.. now I know what to look for when determining AD-4 vs AD-9..
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Old 10-28-2020, 08:18 AM   #17
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If the bus has sat for a while, the shoes/rollers/s-cams might be frozen because of rust. That essentially means the brakes are still applied, so you're not going anywhere. To free them, you can push in the parking brake release, chock the wheels, and then whack the brake drums with a big hammer. You could also try and rock it back and forth like you did and that will sometimes free them too. Don't forget to chock the wheels, your life depends on it. That simple step should be done anytime your working under your bus.

As far as the faint hissing, that further points to the fact that you need to rebuild or replace your air drier. The condensation on the bottom shows that the air drier is working. Everytime the drier purges, or goes whoosh, it's blowing dry air past the wet desiccant purging the moisture out of the desiccant and out the exhaust into the environment.

This whole bus sounds like it needs gone through before you plan on driving it anywhere. Filters need changed, driers need fixed, and hit every grease zerk you can find with grease.
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Old 10-28-2020, 10:45 AM   #18
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Quote:
Originally Posted by Booyah45828 View Post
If the bus has sat for a while, the shoes/rollers/s-cams might be frozen because of rust. That essentially means the brakes are still applied, so you're not going anywhere. To free them, you can push in the parking brake release, chock the wheels, and then whack the brake drums with a big hammer. You could also try and rock it back and forth like you did and that will sometimes free them too. Don't forget to chock the wheels, your life depends on it. That simple step should be done anytime your working under your bus.

As far as the faint hissing, that further points to the fact that you need to rebuild or replace your air drier. The condensation on the bottom shows that the air drier is working. Everytime the drier purges, or goes whoosh, it's blowing dry air past the wet desiccant purging the moisture out of the desiccant and out the exhaust into the environment.

This whole bus sounds like it needs gone through before you plan on driving it anywhere. Filters need changed, driers need fixed, and hit every grease zerk you can find with grease.



+1 on everything that BooYah said,
and, get into the habit of regularly blowing the condensate out of your air tanks. Most important if your bus is in a freezing climate.
Best
Rich
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Old 10-28-2020, 10:28 PM   #19
Bus Nut
 
Join Date: May 2017
Location: Houston TX
Posts: 344
Year: 1998
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Chassis: International
Engine: dt466e
Quote:
Originally Posted by Booyah45828 View Post
If the bus has sat for a while, the shoes/rollers/s-cams might be frozen because of rust. That essentially means the brakes are still applied, so you're not going anywhere. To free them, you can push in the parking brake release, chock the wheels, and then whack the brake drums with a big hammer. You could also try and rock it back and forth like you did and that will sometimes free them too. Don't forget to chock the wheels, your life depends on it. That simple step should be done anytime your working under your bus.

As far as the faint hissing, that further points to the fact that you need to rebuild or replace your air drier. The condensation on the bottom shows that the air drier is working. Everytime the drier purges, or goes whoosh, it's blowing dry air past the wet desiccant purging the moisture out of the desiccant and out the exhaust into the environment.

This whole bus sounds like it needs gone through before you plan on driving it anywhere. Filters need changed, driers need fixed, and hit every grease zerk you can find with grease.
Really appreciate all the info and tips. I've been looking to change the oil and filter among other maintenance tasks. Definitely gonna replace the air dryer and keep an eye on it for now. I was thinking to spray, not only the current air dryer, but the whole underside with degreaser letting it sit and then blowing it with an 1 hp air compressor. Sound ok?

Thanks!
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Old 10-28-2020, 10:40 PM   #20
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Quote:
Originally Posted by adic27 View Post
Yea, I was anxious and just moved it. When I first tried to drive it it wouldn't move. Forward nor reverse. I tried a decent amount of times and then started researching what could be wrong. I found nothing so I tried again and noticed the bus moved forward "very" little and vice versa backwards but like it was chucked or had a really strong emergency brake applied. Kinda like it was stuck. I tried one more time in reverse and then drive and it kinda mad a tank sound and drove forward as usual. Sounded like it released itself from a chain or something. It wasn't attached to anything BTW. What do you suppose caused this? Hopye it's not a sign of transmission issues to come ��

Anyways, I took another look at the air dryer and it seems kind of wet. Either way, s you suggested, I will replace it since it seems like easy task and the part is cheap. What do you think that wetness indicates? Also, do you think twisting that nut some more will make it go away? Aside from one drop, there was no liquid leaking from it. Kinda like condensation. I took a pic.

Since I've had the bus, after shutting the engine off I've always heard like a long faint hiss. More audible when I stick my head under the bus. I figured it's just how the air brake system works but with this situation I found it's actually the air dryer (I think). Is that normal? It goes away after a short while.

Air pressure seem great BTW

Thanks again guys

Yeah, as Booyah said, the brakes can stick after being parked for some time - or applied when the brakes were fairly hot. Sure, you could do as described and whack 'em with a hammer, or do what many drivers do and rock the vehicle forward/back until the brakes let go (my usual method if/when this happens).


The part is called an "Air Dryer" for a reason! It's supposed to take excess moisture out of the compressed air. Naturally there will be water in this part, which it's supposed to purge periodically with a nice reassuring "Pshhh!" (usually right as the air compressor cuts-out).


Quote:
Originally Posted by adic27 View Post
Really appreciate all the info and tips. I've been looking to change the oil and filter among other maintenance tasks. Definitely gonna replace the air dryer and keep an eye on it for now. I was thinking to spray, not only the current air dryer, but the whole underside with degreaser letting it sit and then blowing it with an 1 hp air compressor. Sound ok?

Thanks!

If you spray the underside with degreaser, why not go on and give the underside a nice bath while you're at it?
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