A Few Mechanical Issues (mostly airbag ones)

Glennman · February 28, 2022, 01:11:12 PM

I feel terrible posting my miniscule issues after reading of fred's run in with a fire hydrant. However, I constructed a set of ramps so that I could get the bus (2002 MCI D4500) up high enough to give a good look underneath and see if I could find where the air is leaking on the passenger side rear airbags. The bus settles on the passenger side within minutes of shutting it off. While under there I discovered:
1. I have a flat tire (inner dual passenger side)
2. I have an oil leak at one of the NAPA 1971 oil filters (the entire filter is covered with oil and it's dripping off the bottom. There are 2 filters next to each other, one is clean and everything is clean above them, so I'm hoping it is just the filter).
3. The leaky air bag is at the passenger side tag axle. At least that is the only leak I could find.

On the airbag, the bag itself is in great condition (no cracks or checks). The air is coming out of the bottom of the plastic "cone" that is under the bag where it sets on the base. Is that plastic cone something that is replaceable/repairable, or does one need to replace the entire airbag? Also, from a cursory look at the airbags, I cannot find any air lines leading to the main axle airbags. Where in the world does the air come from? The tag airbags have a line leading to the top of each one.

Bustle · February 28, 2022, 02:30:09 PM

Sorry to hear it Glenn. My airbag also leaks. I thought boats were money pits. The air comes in from the top. There is a fitting on the top. I do not believe air bags are serviceable. They are consumable replacements.

niles500 · February 28, 2022, 02:31:52 PM

If it's leaking under the bag at the cone that indicates the bag is leaking (99% of the time) fwiw

Glennman · March 01, 2022, 01:15:33 PM

So if the tag axle airbag leaks, would that cause all 3 rear airbags to go empty? It seems like there would be some check valves in the mix.

richard5933 · March 01, 2022, 01:32:49 PM

Quote from: Glennman on March 01, 2022, 01:15:33 PM
So if the tag axle airbag leaks, would that cause all 3 rear airbags to go empty? It seems like there would be some check valves in the mix.

How many ride height valves control the tag axle? If all four are on one valve, then all four will likely deflate if one is leaking.

buswarrior · March 01, 2022, 02:32:58 PM

Check the schematic. Post a pic, we'll tell you!

Tags used to be separate, unless a previous owner tied them all together.

Newer things... much bigger loads on tags, than in days gone by... ability to dump either tag or whole side in some... we gotta check Da Book!

Happy coaching!
Buswarrior

Glennman · March 01, 2022, 11:23:56 PM

I'll see what I can find in the schematics and take some pictures. I need to clarify... when I said all 3 airbags, I was referring to the 2 on the main axle and 1 on the tag, all on the passenger side. They all lose air withing minutes of shutting it off. I believe there is only one leveling valve (at least that is what I recall); I think it only has one connecting rod on each side that in turn connects to the valve. I should be able to look at it this coming Thursday pm. Thanks.

richard5933 · March 02, 2022, 03:47:09 AM

Quote from: Glennman on March 01, 2022, 11:23:56 PM
I'll see what I can find in the schematics and take some pictures. I need to clarify... when I said all 3 airbags, I was referring to the 2 on the main axle and 1 on the tag, all on the passenger side. They all lose air withing minutes of shutting it off. I believe there is only one leveling valve (at least that is what I recall); I think it only has one connecting rod on each side that in turn connects to the valve. I should be able to look at it this coming Thursday pm. Thanks.

The check valve is in the ride height valve, not in the airbags, otherwise the ride height valve wouldn't be able to adjust them lower when necessary.

If you have a leak on the airbag side of the check valve in the ride height valve then all the bags controlled by it will go down. So if one leaks they all go down. Get the one air bag fixed and you should be good, unless of course you still have leaks in the other ones. Might be a good idea to get an extra air bag to have on hand.

Glennman · March 02, 2022, 12:23:24 PM

Quote from: richard5933 on March 02, 2022, 03:47:09 AM
The check valve is in the ride height valve, not in the airbags, otherwise the ride height valve wouldn't be able to adjust them lower when necessary.

If you have a leak on the airbag side of the check valve in the ride height valve then all the bags controlled by it will go down. So if one leaks they all go down. Get the one air bag fixed and you should be good, unless of course you still have leaks in the other ones. Might be a good idea to get an extra air bag to have on hand.

That makes perfect sense (how they would all go down together and on getting an extra airbag)!!!

dtcerrato · March 02, 2022, 05:09:48 PM

Quote from: Glennman on March 02, 2022, 12:23:24 PM
That makes perfect sense (how they would all go down together and on getting an extra airbag)!!!

We've always carried a spare air bellow for front & rear of our 4104 & has bailed us out a few times in 42+ years of ownership & on the side of the road - yes we have replacement down pat...

Busted Knuckle · March 04, 2022, 08:57:15 AM

I'm not sure in your application, but if my memory serves me correctly the 2 strokes used a 1970 & a 1971 filter not two 1971's. But once I thought I was wrong, and it turned out I was mistaken.

BK

Dave5Cs · March 04, 2022, 09:18:16 AM

Glen, unless your system can be independantely operated as in a seperate air line goes to each corner so that you can adjust each axle by itself and or with ride height valves too. Some of us have that kind of system and then not all bags would go down on that axle or side.

Glennman · March 04, 2022, 01:02:42 PM

Quote from: Busted Knuckle on March 04, 2022, 08:57:15 AM
I'm not sure in your application, but if my memory serves me correctly the 2 strokes used a 1970 & a 1971 filter not two 1971's. But once I thought I was wrong, and it turned out I was mistaken.
BK

I've got the Series 60 4 stroke. I climbed under last night and was able to unscrew the filter way too easily. I can see why it was leaking. This might be a good time to change the oil anyway.

Glennman · March 04, 2022, 01:13:18 PM

Quote from: Dave5Cs on March 04, 2022, 09:18:16 AM
Glen, unless your system can be independently operated as in a separate air line goes to each corner so that you can adjust each axle by itself and or with ride height valves too. Some of us have that kind of system and then not all bags would go down on that axle or side.

Thanks Dave. It looks like I would have to make a bunch of modifications to have a system you speak of, which granted, sounds pretty good. If I was going to get into all that (maybe after I get the thing usable) I would put a leveling system in that can be operated from the dash. That would be pretty nice!

Glennman · March 05, 2022, 04:49:21 PM

I got the passenger tag airbag out today. It has a blue (3/8") airline plumbed to the top which is fully visible. The other airbags at the drive axle do not have any visible airlines going to them anywhere. They do not appear to be a problem at this point, but it is very strange. All I can figure is that it comes in from the top and can only be accessed by dropping the bag assembly. I cannot find the pneumatic schematics in the online MCI publication. At any rate, I'll pick up a new airbag this week and hopefully that will take care of it for a while.