MC8-Air leaks

[Sam 4106]

I am trying to fix the air leaks in the suspension so I can use my air bag leveling system. So far, I am working on the front and have found leaks in two of the air bags where the bag is supposed to seal to the block off plates. I have the bolts out of the top of one bag and was wondering if there is any kind of sealant that I could use between the rubber and the block off plate?
Any ideas would be appreciated. Thanks, Sam MC8

[RickB]

Sam,

I would bet that JD at C&J has some home brew fix it for that. Their # is 952-881-0034 give them a call tomorrow if you call earlier than 9-9:30 ask for Dan. Dan knows our buses inside and out.

How's Char and how's my 8V92 running???

Rick

[Sam 4106]

Hi Rick,
Thanks for your post. I will call.

Our 8V92 is running fine NOW! On our trip to North Dakota we had recurring starting problems again. I talked to a good two cycle Detroit guy in Dickinson about the problem and he told me it was a 12 volt power to the computer problem. He said to find the fuses that feed the computer and start checking from there. Well, that sounded like an easy thing. NOT! I couldn't find any fuses to the computer in the battery compartment, engine compartment, front electrical panel, or rear electrical panel. Finally, at Fargo on our way home the engine wouldn't start no matter what I did. I finally found the source of power to the computer in the rear electrical panel fed by three bus type self resetting circuit breakers, but no power to the breakers. An easy work around for that was to get 12 volts off the wire to the relays for the tow car lights. THEN the engine started.

When we got home I searched a long time to find where the 12 volt power came from to feed the computer. The previous owner ran a wire from the batteries to a cabinet above the drivers seat, through a relay, to the rear electrical panel to feed the three circuit breakers that feed the computer. The relay is powered by the master switch on the dash and the contacts in that relay were only making intermittent contact. That was the problem. I have talked to several qualified bus mechanics and all have told me that there should be power to the computer all the time. So, the final fix was to remove the relay from the circuit, replace the self resetting circuit breakers with the proper size fuses, and have 12 volts to the computer all the time. That sounds simple when I read it, but it was a real ordeal not knowing if the engine was going to start each time. This was another example of "Why did he do that?" But, he named the bus "MY WAY" so I guess I shouldn't wonder.

Take care and I hope to see you down the road

Thanks, Sam MC8

[steve wardwell]

maybe some sort of lockout ? For theft ?

[Sam 4106]

Hi Rick,

I called C&J this morning. Asked to talk to Dan but he was gone this week so I talked to Steve. He suggested silicone or gasket cement. I think I'll try gasket cement as I don't have much luck with silicone most of the time.

Thanks again, Sam MC8

[bevans6]

I'm thinking back a couple of weeks to when I changed my front air springs.  the clamps just pressed the rim of the spring onto the sealing surface of the frame mount, which was smooth and painted steel.  The rubber just sealed without any additional goo.  So I would think of just taking the bag off and cleaning, painting and trying again.  You would definitely want a sticky, non-setting, non-slippery goo if you used anything, so I am thinking some kind of tacky gasket cement, definitely not any kind of silicone.  Are you springs the stock double convoluted or are the they the rolling lobe type with a blocking plate?

Brian

[Sam 4106]

Hi Brian,

My air bags are the double convoluted type but there are block off plates between the bag and the mount connected to the air beam. The air beams are not used. The block off plate is machined aluminum and there is no corrosion on the sealing surface, yet there was a leak between the bag and the block off plate. The bolts were very tight so I don't think I could get them to seal without some sealant in the joint. The leak was small enough that if I weren't trying to use the air bags for leveling I wouldn't have worried about it. When I sprayed soapy water on the joint bubbles formed right away. When using the bags for leveling the air went out in about 30-45 minutes but that was with a leak at the accessory tank connection too. That leak is now fixed and the bag leaks will be too with the right sealant. I don't think the air bags have many miles on them since the undercarriage was completely rebuilt at the time the bus was converted. The bags show no weather checking or cracks and are very pliable. The bus has about 86,000 miles since converted.

Thanks for your response, Sam MC8

[Sam 4106]

After further examination, I now know the source of the air leak at the block off plate. There is a crack in the aluminum plate in line with the air hole that supplies the bag. I took the plate to a local welding shop to get advise about welding the crack. He said there would be some warping if he welded the crack and the bag may or may not seal. So, I called US Coach and ordered two new block off plates. Hopefully that will solve the problem.
Thanks for the advise, Sam MC8

[JackConrad]

Sam,
   If the crack started at the threads, it is possible the fittings were overtightened when installed. Use thread compound or teflon tape to prevent leaks and do not overtighten.  If threads were not involved, it must have been a fatique crack?  Jack

[Sam 4106]

Hi Jack,
The crack appears to start at the inner end of the air hole into the bag, but extends far enough out to be past where the bag seats. The area where the fitting screws into is much thicker than the plate so you would really have to overtighten the brass 1/8" pipe thread fitting to cause a crack.
Thanks for your thoughts, Sam MC8

[Chopper Scott]

Glad you found the problem Sam. For what they cost versus what it takes to change them regardless of any repair you are a wise man to get the new ones!! Hope you got the new bolts and nuts also.