1972 MCI MC-7 ...air problems

Gerry4104 · May 01, 2012, 08:04:09 PM

Have an MC-7..the front air bags wont air...rear airs up just fine......

air pressure guage is reading faulty..but i am sure it is airing all the way....

is there a way to air the front bags off a shop compressor...

also the maxi's ar either stuck from sitting or it isnt getting enought air to release..is there a wya to air up te brake system off shop air as well..TIA

thomasinnv · May 01, 2012, 08:17:17 PM

Inside the right rear side engine bay door should be a drain valve that you can connect to and air up the entire system. For brake system only, the fill valve will be located in the side compartment under the driver seat.

Gerry4104 · May 01, 2012, 08:22:10 PM

i wonder why the rear bags air fine, but the fronts wont do anything....and i hear no leaking at the moment... HMMMM

but thatnks for the info....i will be giving that a shot ...

Stormcloud · May 02, 2012, 05:02:28 AM

I'm thinking the front leveling valve ( about mid-axle in front) will be plugged or disconnected, not letting any air through.

The brakes? Sorry, can't help there.

Mark

challenger440 · May 02, 2012, 08:13:55 AM

I think the dd3 needs more air pressure to disengage than you set them with. Dash info says you must have at least 100 pounds to release brakes. j m

thomasinnv · May 02, 2012, 10:30:19 AM

leveling valves can stick from time to time, especially if the bus is not used that much. If you can safely get under the front of the bus, disconnect the linkage to the leveling valve and exercise it manually and it might start filling again.

Busted Knuckle · May 02, 2012, 03:28:07 PM

I suspect that there is a problem in the AIR system where it's not getting full air all the way through the system.

If it were just the front air bags or just the brakes not releasing I'd maybe think other wise. But since both problems showed up together I lean toward the AIR system itself!

Could be water/sludge build up in the tanks/system or could be stopped up lines or valves somewhere.

Remember these things have check valves between systems that can get stopped up when the system as a whole is neglected.

BK

thomasinnv · May 02, 2012, 09:18:32 PM

BK, I would agree if not for the fact that the OP states that the rear bags air up just fine, and the two problems are on separate air systems. The suspension is aired from the auxiliary air system, which is the last to get air. Of course the suspension will be fully aired up long before the brake system has ample air to release the parking brake, so it is possible that the entire system is not being fully aired as you stated, but if the rear has enough air to bring it up, so should the front. IMHO, the first thing that needs to be done is he needs to verify what the air pressure actually is getting up to. put a guage on the aux tank drain and see what you get there to start with. (thats the one under the driver seat)

mikelutestanski · May 03, 2012, 05:36:18 AM

Hello; The air system fills from the compressor to the wet tank (rear wheel housing) then onto the dry tank (front wheel housing driver side) . From the dry tank lines to the brake pedal and other places. One line goes to a small filter then to the pressure protection valve then to the height control valve.
Begin with the filter to make sure air is getting through and the pressure protection valve is working. If so then the height control valve is the next place to check. If your bus is stock all the piping is copper and the fittings must be aligned perfectly to reassemble. The fittings and piping are almost 40 years old so take care .
The filter has a small element in it called a sock filter. Check valves are located off the dry tank and sometimes they stick. It would be best if you could locate an airline diagram. There are several versions depending on the serial number of your coach.
Regards and happy bussing mike

Oonrahnjay · May 03, 2012, 06:12:01 AM

Quote from: mikelutestanski on May 03, 2012, 05:36:18 AM(snip) It would be best if you could locate an airline diagram. (snip)

Yeah, that's a good point. I don't know anything about an MC-7 but if the rears are airing up and the front isn't, that implies to me that air is getting to the "aux" air system but not actually getting to or working at the fronts. It must be getting to the rears (and the rear valves and bags must be OK). So my first question would be whether air is getting to the front valves. If not, it's probably an obstruction in the line from where front and rear air splits; if air is getting to the front valves, check from there and "move downwards" through the valves, air lines, and bags.

Stormcloud · May 03, 2012, 09:01:49 AM

I had trouble a while back with one of the rear leveling valves not permitting air to pass through to the bags. The screen in the leveling valve was plugged with 'crud' from a neglected air system ( prior to me owning it).

I expect the front valve will also have a screen in it, and could be the cause of the un-infated air bags, especially if all 4 bags are not aired up.

Mark

mikelutestanski · May 03, 2012, 12:13:59 PM

Hello: I forgot to answer your other question about shop air. THe doghouse door under the driver side window has a fitting that can be used to air up the bus. I changed the fitting to a valve with a male fitting so that an airline could be plugged in and charge the bus. I did not have to hold the air chuck onto the airline . You can install whatever pleases you as long as it works for you. Another consideration is when you are on the road and under tow the tow truck will have to supply air to release the brakes and supply the suspension.
FWIW I also have a separate valve arrangement in the rear so that I can air up with the compressor I mounted in the rear compartment where the original bus air compressor was mounted.
If you have a repair manual the airline diagrams are located in section 4. THe same line that feeds the front height valve feeds the aux tank in the front and the front accessories including the gage in the dash. SO if the dash gage is not working check the front filter can and the pressure protection valve.
If as you say the rear bags are up then air has to be in the dry tank up front because that tank feeds the rest of the coach. You can check that by opening the drain valve on the lower part of the tank.
REgards mike

Oonrahnjay · May 03, 2012, 02:02:18 PM

Quote from: mikelutestanski on May 03, 2012, 12:13:59 PM(Snip) I changed the fitting to a valve with a male fitting so that an airline could be plugged in and charge the bus. I did not have to hold the air chuck onto the airline . You can install whatever pleases you as long as it works for you. (snip)

My bus didn't have an air fitting originally (and didn't have spring brakes) so I installed one inside each bumper. There is a fitting (like Mike, I used a male fitting compatible with the airline in my shop), a 90-degree turn valve, then 1/2" DOT-type air pipe, and a one-way check valve to the wet-tank; I installed two of them cause ya can't guarantee which end your bus will need to be towed from. The male fitting screws into a 1/4" pipe thread on the ball valve; I have a Schrader valve, a "Type A" (a "paint line" fitting) male fitting, and a regular truck tractor "glad-hand" connector that will also screw into that 1/4" pipe thread. The 90-degree ball valve is convenient (not needed but convenient), the check valves mean that any leakage in this part of the system can't lose all your air. (I'm told that tow trucks occasionally need these connectors.)

This system work really well for airing up with shop air. I can attach the air line, listen for leaks before I open the ball-valve, open the valve and give it some air, then stop the process anytime I want to to listes for leaks, etc. Also, when I'm finished, I know that all I need to do is close the ball valve, disconnect the air line (I put a little cover on the male fitting) and then the system works just like it always does with the engine compressor providing air.

Gerry4104 · May 03, 2012, 06:47:28 PM

I will be getting after this on monday or tuesday, and i will let you guys know how i made out....

gotta get i up on all 4's and get if moving and driving to its new destination...thanks guys for all the help...

carry on !

ol713 · May 08, 2012, 08:55:14 AM

Hi;
I also have a MC-7 and had the same kind of problem a number of years ago. You have a main and aux
air system on your bus. Like Mike mentioned you also have a front filter that probably needs changing.
Mine was probably not changed since day one.
It is located behind the front axel on the wall. There are two air tanks there. One is the main and the
other is the aux. Between the two tanks you will find a filter housing about the size of a baseball.
Inside you will find a "ball of yarn" kind of filter. Just be carefull when reassembling the filter not to
overtighten the bolts. I broke one of the ears on the housing.
Good luck
Merle.