GMC 4104 Front Air Bags

[gus]

Has anyone replaced the front air bags on a GMC 4104? I just replaced one today and will do another tomorrow. After reading a post recently by someone who said he could replace air bags on the side of the road I expected it to be not too bad. Well, I had a big surprise-this is a tough job. He sure wasn't talking about original GMC bags with air beams when he wrote that!

It is tough enough getting the two mounting rings over the bags but the really hard part is getting those 16 mounting ring bolts through the holes in the mounting bases and getting nuts on the mounting ring bolts. One ring went not too bad but the other one was hell. Those bolts are just about three threads too short to get the nuts on-I had to draw the nuts up tight then loosen them one at a time to insert the lock washers.

Does anyone have any good ideas for making this a bit easier, I still have three bags to go!

[Sojourner]

I am not sure on 4104 GMC....if ever had air beam then maybe yours is equips with metal blocker plate that cause your replacement bolt to be too short. If so get longer class "2" bolts.

FWIW

Sojourn for Christ, Jerry

[JackConrad]

Make sure if you get longer bolts, they have the proper type head so they do not ruin you new airbags. I think the problem is the thickness of the lip on the new airbags. I had the same problem on our MC-8. I used several pair of vise grips to clamp it all together to get the nuts started.  Jack

[Stan]

I don't know the part number, but MCI sells a longer bag bolt. It is used on the rear bags where the leveling valve bracket is bolted to the top mounting plate. Ironically, if you order a rear bag assembly complete with rings, bolts, nuts and washers,  they don't include the two longer bolts.

[bernie]

when you get to the rear bags, then the fun starts, they will be rusted in place and the bolts will tough to remove.when we replaced the bags on my 04 the rear ones were full of mud or rusty water. it took 12 hrs to replace the rear bags. they had been in place for a long time
good luck
         Bernie

[Fredward]

I have a rear bag that i need to replace on my MC-5. The guys at C&J bus in Mpls sold me the air bag and bolts. THey also gave me some longer bolts to use temporarily to pull it all together. What you experienced must be what they were preparing me for. Also they said (carefully) torch the old bolts off. Additionally they said before you install the new one to be sure and clean up the mating surfaces and even paint them with a good oil base primer. I haven't torn into that project yet but I think I smell what you're stepping in.
its great having a really good bus garage within shouting distance.
Fred

[gus]

This is the front only;

They are the original Firestone bags with cast rings and L head bolts. These rings and bolts won't work with the new Goodyear bags. The Goodyear bag mouth is slightly thicker and 1/4" larger diameter? It sure would have simplified everything if they were the same size.

The original air beams still hold air, no bag plates yet!

Had no problem getting old bolts or bags off.

I cleaned the bag bases (Mating surfaces) and applied rust converter, they look like new. This is the air sealing surface so it must be smooth. Rust converter is much better than paint, it makes the rust into a very hard substance. I think paint will come off when the bag rings are tightened down, the rust converter won't.

The hardest thing is to get the nuts started, some long bolts sure would have helped. Also, the bag mouth is just large enough to push the bolts into a slight angle so they won't go straight into the base holes-frustrating. They have to be pushed into the base holes one at a time.

Another problem is that the upper and lower bag bases are not parallel, just a slight angle between them makes getting all the bolts into the holes even more difficult.

I got the front one in ok yesterday but finally gave up on the rear one today. I'll tackle it again in the morning.

Getting the rings over the bag mouths is no picnic either. I finally did it using four motorcycle tire irons and lots of soapy water.

Those new bolt heads are a real pain keeping properly oriented when trying to get the bolts into the holes. It is very easy to get one misaligned. The old L head bolts were much better, once they were in they were in to stay.

One tip; hit a bolt head with a hammer into every ring hole before installing the rings on the bags, the heads do not fit flush unless you do this and that will make getting the nuts on even harder.

Fred,

I would strongly recommend doing both bags on one side while you have everything apart unless they are relatively new. Once you're in there with the wheel off is the best time to do it. I'm going to replace the two on the other side in a short while, don't have time to do it now before my next trip. The one that had to be changed was separating between plies where it fit into the base ring. It appeared that half the plies were separated but it still held.

Bernie,

Luckily the rears were replaced just before I bought the bus, they will probably last longer than I will!

[gus]

Well, I finally finished the job early this morning. I had to completely remove the rear bag because one rear side bottom bolt was crooked and I could never get it straight. I first tried to pull the bag base down with four bolts and then insert the other four because it is so hard to get eight bolts into the holes. This didn't work, I couldn't get the other four bolts into the ring holes with the bag bolted down, the bag mouth is too wide to allow the bolts to go straight into the ring holes.

I had already bolted the top but couldn't get the bottom bolts in. The second attempt I bolted the bottom first, the top bolts are easier to reach, and I inserted all sixteen bolts into the rings before placing them onto the base plates. One bolt head was twisted and was a real pain to turn but all the others went right in.

Now I have to do the other side but I have learned a bunch so it shouldn't be as bad.

[Fredward]

I suppose you are right. If I'm going to do one, I might as well do both. Its just that one has a little chunk of rubber loose on it. The rest of the bag looks fine and so does its mate. I think that the one with the chunk of rubber lose must have gotten pinched at the truck garage that replaced king pins and tie rod for me. They jacked the front end way up and squished the air out of the rears. Bent the right rear leveling arm which is the side that has the damaged bag. We've used the coach since then but I'm afraid to go far with it. But also afraid of tackling the project because I can't get the inside dual off of the hub.
Fred

[tekebird]

good example of why truck mechanics  does not equal bus mechanic

[gus]

fred,

I don't see how you can possibly do the job without removing the inside wheel unless you have a pit or lift. It was hard enough with just the drum and hub in place. I spent a lot of time hanging over that drum. Recommend finding a mover's pad to drape over it.

[gus]

After completing the job I aired it up with shop air. Now, three days later, it is still up.

Talk about being happy. I knew the old bag had deplied slightly but didn't think that caused a leak. It has been a long time since the suspension would stay up more than a few hours.