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Author Topic: Where to buy parts (wet tank) and is my troubleshooting (air level) good?  (Read 3345 times)
philiptompkjns
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« on: February 28, 2010, 05:01:26 PM »

Well, I drove the bus today and it's leaking a lot of air, the compressor ran most of the time.

Can ya'll confirm that the wet tank (MCI 102a3) would only leak when the compressor is on?
And where is the cheapest place  to  buy one of these?

Also, about the leveling valves.....
My bus has always had a case of the  "leans".  I unhooked the line coming off the leveling valve going to the airbag and no  air  was coming out, I disconnected the leveling arm and moved it around, still no air. There is air at the  line coming into the leveling valve though.   Is this normally how leveling valves fail?
What would happen if  I just did a U with the air line, and cut the leveling valve out of the system, does the bus air pressure need to be regulated at that point, or is it regulated already?  Also, what is the pressure range that the airbags are supposed to operate at?  Like could you blow one up by giving it the full 120psi? 
Ya'll are always really helpful and have great  advise, so thanks in advance.
-Philip
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1990 102a3... Just got started, don't  know  what I'm doing.
RTS/Daytona
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« Reply #1 on: February 28, 2010, 05:22:05 PM »

Caution - There is a DELAY built into HEIGHT CONTROL VALVE  typically 2-9 seconds (more if cold)

My RTS fronts run at about 60 psi   and the rears about 80 psi - when aired up and runiing straight and level  on the road

Bringing  the air bags up to 120 psi will raise them fully and to they limits  - I've done it many times on my RTS  -- BUT Huh

YOUR RESULTS MAY VARY !!!!!!!


« Last Edit: February 28, 2010, 05:25:30 PM by RTS/Daytona » Logged

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bevans6
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« Reply #2 on: February 28, 2010, 07:21:05 PM »

The wet tank is under pressure all of the time, unless the check valve between it and the air dryer is leaking.  Under normal conditions, it maintains very much the same pressure as the dry tank does. 

I've been led to believe that the air bags on an MCI are looking for around 60 psi at ride height. 

brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
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JackConrad
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« Reply #3 on: March 01, 2010, 04:55:39 AM »

On our MC-8, the air bags are usually around 55-60 PSI when driving down the road using the OEM leveling valves.  I know some that have replaced the OEM leveling valves with adjustable pressure regulators (then change the pressure settings when camping to level the coach).  When we installed our leveling system, I called Mohawk Industries and asked about maximum pressure in the replacement air bags we purchased from them. They recommended a max of 85 PSI. I have found that at 85 PSI, we have lifted the bus as  high as it will go.  Jack
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zubzub
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« Reply #4 on: March 01, 2010, 05:43:05 AM »

If you're new to this...remember not to climb under the bus untill it is safely blocked.  This means having the body supported high enough that if the air bags empty the bus will not descend and crush you.  There are numerous way to do this, check the archives.....just don't go under there untill you understand the safety implications. 
Re: the air leak, once safely blocked, air up the bus and work out where the air is leaking from, (could be many things).
I find it easier to find leaks using shop air.
If you need air tanks etc...you can buy them at truck part stores but I have found that old transits have all sorts of tanks.  I imagine original matching tanks will either cost$$$ or be hard to find....expect to do some  plumbing mods and you can fit decent used tanks where you need them, though it sound like it's too early to be condemning tanks.
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philiptompkjns
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« Reply #5 on: March 01, 2010, 06:45:13 AM »

If you're new to this...remember not to climb under the bus untill it is safely blocked.  This means having the body supported high enough that if the air bags empty the bus will not descend and crush you.  There are numerous way to do this, check the archives.....just don't go under there untill you understand the safety implications. 
Re: the air leak, once safely blocked, air up the bus and work out where the air is leaking from, (could be many things).
I find it easier to find leaks using shop air.
If you need air tanks etc...you can buy them at truck part stores but I have found that old transits have all sorts of tanks.  I imagine original matching tanks will either cost$$$ or be hard to find....expect to do some  plumbing mods and you can fit decent used tanks where you need them, though it sound like it's too early to be condemning tanks.

Thanks, I did use jacks/jack stands when crawling under the bus looking for air leaks with it somewhat aired up.... luckily I can crawl under the bus when its aired down though, so it's not too big of a problem.

And I'm pretty sure  of the wet tank leak because I actually crawled under there and could hear it, then hear the leak get worse as a picked the rust off, haha.
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1990 102a3... Just got started, don't  know  what I'm doing.
philiptompkjns
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« Reply #6 on: March 01, 2010, 06:49:10 AM »

The wet tank is under pressure all of the time, unless the check valve between it and the air dryer is leaking.  Under normal conditions, it maintains very much the same pressure as the dry tank does. 

I've been led to believe that the air bags on an MCI are looking for around 60 psi at ride height. 

brian

thanks, this may be the case, or the leak in the tank is so massive that it just empties  very quickly?  After I replace the tank I'll check it again after the dryer purges and  see if  it still had pressure.
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1990 102a3... Just got started, don't  know  what I'm doing.
trucktramp
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« Reply #7 on: March 01, 2010, 06:55:13 AM »

You may want to consider putting soap and water on the suspected tank to see if your assumption is correct before spending the money since, as you said, it may be leaking somewhere else. 
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Dennis Watson
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zubzub
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« Reply #8 on: March 01, 2010, 07:30:46 AM »

Forgot to mention, on my bus it was a major PITA to change out 2 air tanks, close quarters and the designers probably were not thinking it would be necessary.

  Also are you sure if the bus was fully aired down it wouldn't crush you?

Just because the wet tank, or any of the air systems show no air pressure does not mean the air bags have descended completely. 
The leveling valves isolate the air bags from the main  air system and can remain inflated or partially inflated when the rest of the air system is empty.
If for whatever reason the bus decides to lower an extra 6" that could be the end of you, especially if you were between the axle and body.
Most people run the bus up on wood blocking to get the extra height, I also put blocking between the frame and axles (where the air bags are to maximize working space/clearance.
If you are pulling tanks you will need all the clearance you can get, anyway.
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bevans6
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« Reply #9 on: March 01, 2010, 08:08:50 AM »

There are two check valves associated with the wet tank - one between it and the air-dryer so that when the air is delivered to the wet tank it cannot return, and one between the wet tank and the dry tank so that air cannot return from the dry tank to the wet tank.  If you had a leak in the wet tank such that the compressor was running constantly, then you really dodged a bullet by driving the bus!

You would have probably noticed this by timing the air up of the bus, and by doing the DOT required compressor recovery test, which is to air up the bus fully, fan the brakes to bring the pressure down to 80 psi, then time how long it takes the compressor to build pressure from 85 psi to 100 psi.  that should be less than 45 seconds or so, mine is normally around 20 seconds.  You look not only for the pass-fail, you look for any change from previous tests that might indicate a looming failure.  With a leak in the system in the wet tank, you would think that the compressor recovery time would be longer than normal.

Anyway, good luck with your repairs, I've never changed a tank so I have nothing there to offer!

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Vintage race cars -
1978 Lola T440 Formula Ford
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zubzub
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« Reply #10 on: March 01, 2010, 12:50:41 PM »

here's a horror story for you guys....when I got my bus the front (dry) tank had a rust hole in it and constantly pissed out air.  AT about the speed of a small nail hole in a car tire after the nail has been removed.  The system had no trouble airing up even with this hole.  In fact  I could watch the air pressure and see the compressor cycling about every 15 mins as I drove done the road as long as there was no other air usage going on.  I just figured I had enough in the 3 air tanks to create a nice buffer and as the emergency brake was working fine home I went.  Well when I got home I discovered that a PO had completely bypassed the wet tank (I guess that help rust out the front tank) so I had only 2 tanks of reserve air.  Moral of this story is you would be amazed what people will do (myself included) just to get home sometimes.  That was 1000 miles with a decent hole in the front main air tank, nice to know there is a little leeway in the system.
Oh yeah forgot to mention, I would never do this again, and consider myself fortunate that it worked out for me, I had planned on fixing the tank first but ran out of time.  I also would not suggest to anyone else to ever drive a bus with an air system that was not fully intact and operational
« Last Edit: March 01, 2010, 01:13:09 PM by zubzub » Logged

bevans6
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« Reply #11 on: March 01, 2010, 01:06:08 PM »

different buses have different setups, but my bus has check valves and the pressure protection valve that essentially isolate the dry tank from the downstream tanks.  While there may be some bleedback through the PPV if the pressure is over 65 psi, basically you had no reserve tanks of air if your bus is set up anything like mine.

Again, and without disrespect, I just get so upset reading stories about people driving the bus with such faults.  Maybe it's where I am on the learning curve...

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Vintage race cars -
1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
buswarrior
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« Reply #12 on: March 01, 2010, 05:36:40 PM »

Price the tanks from MCI and then take some measurements and off to the local large truck jobber to price some suitable replacements.

Be sure that you are equal to, or larger in volume to the stock tank. You may need to mount two traditionally shaped tanks to match the volume of the less orthodox MCI tank shape.

Using our school daze math, for a round tank, measuring in inches, circumference x circumference, divided by four, multiplied by 3.14 (pi), multiplied by the length of the tank, and then divide by 231 to get gallons. (231 square inches in a US gallon)

As for a coach recovery, or "get it off the road" trick for those pesky rust flakes, drive a big screw into it with a piece of rubber inner tube (or whatever) and some goop and hope there's enough bite.

Or, a piece of flat tin can cut to cover the now larger hole, same gig, goop, and a bunch of self tapping screws around the perimeter. The ribs will leak air, so it has to be FLAT.

And replace the tank, because if it flaked off and sprung a leak in one place....there's more to follow!

happy coaching!
buswarrior
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Depewtee
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« Reply #13 on: March 01, 2010, 05:58:13 PM »

Philip,

I had a similar problem with a rusty tank.  I was fortunate in that the shop where I had it for service had an old MC-9 they scavaged the tank from - charged me $100 for the tank and install.  See my saga here.

Brian
« Last Edit: March 01, 2010, 06:23:08 PM by Depewtee » Logged

Brian Shonk
Fort Walton Beach, FL (Florida Panhandle)
1981 Prevost LeMirage Liberty Coach
1984 TMC MC-9
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« Reply #14 on: March 01, 2010, 06:21:24 PM »

ZZ,

Same thing happened to my wet tank, completely bypassed and I didn't know it for a long time!!

I found a wet tank on ebay. Take measurements and the dimensions and locations of the holes and look for one that will work. Many air tanks have multiple holes for different applications. The prices from MCI or a bus supplier will make you sit up and take notice.

On the leveling valve problem; I just went through this last week. One side would take a very long time to rise properly. Turned out to be a clogged external check valve. Cleaned it out added some air tool oil and all is well.

The valve was not an original which has an internal check valve. Some original valves also have internal air filters which can clog. My external air filter was missing the pyramid shaped filter screen so I made another one.
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