MCI 9 Rear air bag

[jmblake]

I had the drivers side drive axel rear air bag leaking, it had air coming out the bolts and around the ring, I tried tightening the bolts and it leaked worse and when I loosened the bolts it didn't leak as bad. So I ordered a new bag and rings and took every thing apart and cleaned the plate's and every thing looked good and clean no rust pits or anything. When i put it back together and aired it up and the same thing, bubble's coming around the bolts and the ring and the aluminum plate that blocks the air to the air beam. The same thing the tighter the bolts the more it leaks, So I loosened the bolts to finger tight and no leaks. Any idea's what I am doing wrong. Thanks Jason

[jjrbus]

Jason, you have come up with a tough one. Because you replaced one that was doing the same thing it may not be you!
You mentioned new bags and rings, these also take a special bolt, did you order those also? Is ring installed right side up? Not insinuating you are stupid, the po may have installed it wrong!! Just look at a non leaking bag.
One way I like to create problems for myself is overtightening things. IIRC they use a 1/4 or 5/16 28 threads per inch bolt. it should be torqued to 10/12 pounds.  See chart.  http://www.machinetoolhelp.com/Repairing/bolt-torque-chart.html
You should not tighten the first bolt all the way down and then the second etc. The ring should be brought down evenly tightening in a criss cross pattern so as not to distort the ring. Similar to torqueing a wheel.
That is all I can think of at the moment, I'm sure others will chip in. Let us know how you make out.   HTH Jim

[JackConrad]

Jason,
   Another thing I found that helps is to use "Tire Grease" on the air bag to help get a good seal. As was mentioned, tighten gradually going around to pull the clamp ring up evenly. Only other thing I can think of is possibly a bent/warped surface?

[roadrunnertex]

Let me step in with my 2 cents worth.
You make mention that the aluminum air beam block plates are installed on your bus.
There is a good chance that the block off plate might be corroded or might have a small crack that opens up when the bolts are torqued down tight.
A new block off plate is not that expensive if the above is the case.
FWIW
jlv

[Hartley]

I was going to say that about the block-off plates.

Mine looked OK visually but were porus and allowed air to leak
right through. 83 model NJT MC9.

I got new plates and looked at the old ones. Tapped one with a hammer and
it fell apart due to corrosion in the grains of the metal.

Most are made of a poor grade of aluminum casting material ( Sand Casting )
it absorbs moisture and degrades if not sealed well.

Dave....

[jmblake]

Thanks for the input I didn't get a chance to work on it tonight but maybe over the weekend. I did tourqe to 10ftlb but it still leaks, I am going to take back apart and dbl check every thing, I may try a little silicone around the seal, The alum plates looked realy good and smooth I Didnt see any cracks put any thing is posible Thanks Jason

[jjrbus]

I would not use silicone. If it does not solve the problem it is too hard to remove. There must be a better sealer. Jack mentioned "tire grease"??

[JackConrad]

Tire Grease is what tire shops use when installing heavy equipment tires.  It looks like axle grease, but I do not know what is in it.  Jack

[Hartley]

The "Tire Lube" that I saw used on mine was made by Murphy's Oil Soap people.
If that helps any...


http://www.jtmproductsinc.net/NewSite/TireMountingLubricants.htm