brake air system Mc5A

[skihor]

I have a question about the air system in my bus. It airs up fine and maintains air fine around 110-120 lbs. What bugs me is I don't hear any air "dumping" like every other air brake vehicle does. While at the rear of the bus I can hear the air commpressor cycle on and off but that's all. Is this normal??
The air bag system doesn't ever leak down and the brake air system leaks down to O within 16 hours with no audible leaks than I can detect.
Thanks,
Don & Sheila

[Dallas]

Don and Sheila,

It's quite possible you don't have an air dryer which is what makes that distintive sound.

It's also possible that if you do have an air dryer it is non functional due to being crdded up with oil, water and junk.

I hope this helps.

Dallas

[Ncbob]

Hi Don & Sheila.   As another paranoid MC5 owner, I too worry about why, from time to time it doesn't make the wonderful Whoosh, Whoosh noises I expect.  Does it cycle from the parking brakes properly?  When you're driving down the road and you put your foot on the treadle and the brakes go , Whoosh, Whoosh?  Does the bus stop when you ask it to do so?

Understand, MCI didn't put a foot valve in their buses that would have to stop a dump truck loaded with 50M lbs.  They designed the package so that, if the drivers were properly trained, the customers would have a pleasant ride without having to come out of the bus with those collars you see on TV all the time.

Those if us who are fortunate to own MCI's have to learn to live within the ideas that the Design Engineers built into the system.

Now, that's not to say that your bus might not have a problem...that's up to you and 'Da Book' to determine.  

But rest assured that whatever problems you might run across...there's help here...based on experience, and we will be here when you need us.

Thanks for your inquiry...we're the 'Good Hands" people.

And if you'll read through the lines and forgive me 'tongue in cheek' humor you realize that we're all interested in Buses and safety for all.

Bob

[JackConrad]

The sound you are describing is the air dyrer. Many of the MC-5As did not have them.  Our 63 4106 did not have one OR your has one and it is not working. Have someone that knows what an airm dryer looks like to tank a look under your bus. The first step to to determine if you havean air dryer.  Jack

[Ncbob]

The air dryer should "dump" when the compressor come to the end of the cycle.  MC5's did not come with a dessicant fliter...hence no "dump".

Is this a new bus to you?  Do you have "Da Book"?  You need to know how to empty the 'wet tank' and the first drain in the R/R
compartment...otherwise you'll build up too much H20 in the system.

We're here...for whatever you need.

Bob

[skihor]

We've owned this bus for two years now. While we haven't been able to put the travel miles on we would like to, (around 12,000 so far), we enjoy it. We live in it full time in Golden Colorado. I do have Da Book and I do drain the tanks every time I start and or drive it. The air is so dry here I rarely get anything out. I have what appears to be a water trap at the right rear of the engine compartment on the bulkhead which reads "drain daily", I do. I also drain both air tanks after every days drive or it's Bi-Monthly start-up.
Can I put on an air dryer? Cost?? I have experienced parking brake freeze-up twice now, although it was 10 F or 12 F below.

[Sojourner]

Can I put on an air dryer? Cost??

Yes you can....all passenger buses should be equips with automatic air-dryer in freezing climate. Perhaps your MCI-5's came from local that never enter non-freezing area.

However it a big plus to have automatic purser with screw-on desiccant dryer cartridge.

System Saver 1200  link to manual;
http://www.meritorhvs.com/MeritorHVS_Documents/mm34.pdf

Cost about $150.00 plus fitting & lines with free or no labor.

Major truck repair shop can install it...better yet bus repair shop.

One less thing to worry about freeze-up brake-pedal control "hang-up air valve".

Now enjoy the sound of Piiissssaaaaww....after compressor unload.

FWIW

Sojourn for Christ, Jerry

[ceieio]

Don & Sheila - Your bus may have had had an alcohol system for cold weather operation (in slang, a whiskey sniffer).  My 73 MCI has one and it is located inside the right engine hatch down low, slightly to the front.  Mine is a small metal can that threads onto the mount from below.  The mount clearly has an air line running through it.  My bus did not come equipped with an air dryer.

Craig - MC7 Oregon

[Ncbob]

We, some BusNuts and myself, have kicked this can called "Parking Brakes" all over the lot and have come up with the conclusion that 'Parking Brakes' we designed by the Engineers for a temporary safety measure for the driver to 'Park' the bus while exiting passengers and luggage, and boarding passengers and their luggage in the Terminal.

They weren't designed for a 'months long' parking situation in your dooryard or your bus barn.

And we wonder why we have problems releasing them?  Let's face it....in most cases these are old buses and the Lithium grease in the 'caging' mechanism is probably harder 'n a Honeymoon hard-on.  (excuse, if it get's through)

Let's take a collective look at our equipment and start using chocks, that's what they were designed for, to block the tires and save ourselves a bunch of aggrevation!

FWIW,

Bob

[Len Silva]

We, some BusNuts and myself, have kicked this can called "Parking Brakes" all over the lot and have come up with the conclusion that 'Parking Brakes' we designed by the Engineers for a temporary safety measure for the driver to 'Park' the bus while exiting passengers and luggage, and boarding passengers and their luggage in the Terminal.

They weren't designed for a 'months long' parking situation in your dooryard or your bus barn.

And we wonder why we have problems releasing them?  Let's face it....in most cases these are old buses and the Lithium grease in the 'caging' mechanism is probably harder 'n a Honeymoon hard-on.  (excuse, if it get's through)

Let's take a collective look at our equipment and start using chocks, that's what they were designed for, to block the tires and save ourselves a bunch of aggrevation!

FWIW,

Bob

But how would you keep the "parking Brakes" from coming on anyway, unless you kept shop air on all the time?

Len

[Ncbob]

My guess, Len, would be whether you have the DD-3 system or the 'Spring brake' system.  I thought we were talking about the MC-5's.
Which have the DD-3 system....

For those of you who are in the latter part of the 20th Century...it might be different.  But we still believe that 'Parking Brakes' are for a temporary situation....not long term.

It all boils down to opinions, based on the best information you can garner.  And you know about opinions...I'm sure.

Just mine......

Bob

[JackConrad]

My understanding is that the DD3 brakes will set automatically when the air pressure gets down to about 60 PSI.  Try leaving the parking off overnight, then go try to move the bus. You will find the parking brake knob has popped up overnight as the air pressure leaked down. You cannot make the knob stay in the down/depressed position until you get about 65 PSI air pressure (unless your DD3s are differnet than the ones on my MC-8).  Jack

[Ncbob]

By Golly, Jack!  I'm going to have to look tomorrow when I go down to the barn!   I'm not so smart that I have all the answers so I'm going to have to check that one out.   I left the P/B valve off when I put the bus up a week or so ago!

Unlike 'Spring brakes", It's my understanding that with the DD-3's, air (according to "Da Book") must be applied via the P/B valve @ 85PSI.  And with the release (or discharge) of the P/B valve the Operator should apply the 'Service Brakes' at or above 90 PSI to 'uncage' the mechanical lock and release the P/B.

I will always give a nod and a tip o' the hat to those who are more learned than this 'newbie'.

May we talk again about this topic, please?  I'm sick and tired of them suckers locking up and I can't get 'em off!

Bob

[Stan]

The PP valve is spring loaded and automatically pops out and sets the park brake when the air pressure drops to about 60 PSI.

BTW: I had a MC-5A for about 10 years and even if it sat for six months the park brakes released the normal way. I would suspect something is wrong mechanically in your brake system. Take the DD3 cans apart and clean and lubricate the moving parts. Pull the brake drums and inspect all the moviing parts in the brake linkage. Pay particular attention to the cam shaft bushings and the brake shoe rollers. Too much wear at these points will make the brakes bind. Brake blocks (lining) that are nearly wore out will also cause problems if the cam get almost to the point of turning over. HTH.

[JackConrad]

I don't have my air schematic in the house by my computer, but I seem to recall a separate air tank dedicated to the parking brake system so that in the event of a catastrophic air loss, this tank can set the drive axle brakes to stop the bus. (no parking brake system on front wheels, so you will still have steering).  Perhaps someone with an air schematic handy can chime in.  Jack