1970 mci7 brakes

[moose]

Hello all
my mci 7 is vin # 8350 i have it in the garage in calgary ,Today i just completed my air brake course
i find out in 1975 it became law here in canada to have dual air brake system a 121 system ,when did this become compulsary in USA and i hope ,i will ask my garage on monday ,do you think greyhound would have changed this to a dual air brake system
trevor

[gumpy]

Hello all
my mci 7 is vin # 8350 i have it in the garage in calgary ,Today i just completed my air brake course
i find out in 1975 it became law here in canada to have dual air brake system a 121 system ,when did this become compulsary in USA and i hope ,i will ask my garage on monday ,do you think greyhound would have changed this to a dual air brake system
trevor

Explain dual air brake system.

[moose]

dual air brake system is a an air pod with 2 lines in one to release the spring brake when parked   and one to apply brakes from service foot brake 

[luvrbus]

A dual air system here in USA is 2 separate systems with one compressor and pedal one for the front axle and one for the rear.
A dual air system will have 2 gauges I believe 1989 was when the DOT required the system on buses not real sure about the date but the 1989 Eagle had the dual air systems


good luck

[TomC]

If you have the 121 brake system, disconnect it-it has caused more accidents then not.  Good Luck, TomC

[Stormcloud]

Hi, Moose:

Im also in Canada, also with an MCI-7 (in Manitoba).

Mine was formerly a hound in USA, then charter coach, then a church bus in Canada (where the engine was rebuilt, but they cant find the paperwork on it    ), then became mine.

When I bought it 3+years ago, I had a commercial vehicle safety done in Edmonton.
It needed minor repairs, but nothing on the brakes at all.

I would doubt if the brake system was reworked when it came to Canada as a church bus...it likely would have been cheaper for them to buy a bus already with 121 system.

Also, we dont have spring brakes on our busses..we have DD3. Dont know it that makes any difference.


Regards

Mark

[buswarrior]

Ummm....

No, Greyhound most certainly would have NOT changed your brake system.

The "121" standard does not have to be retrofitted.

It came into being in both Canada and the US at much the same time in 1975, with small differences in requirements, most notable, Canada did not require anti-skid control.

Your 1970 DD3 brake system already incorporates a "split system" of sorts that made it superior to the spring brake single circuit systems of the day in 1970. The Parking and Service circuits are isolated via check valves in a similar fashion to the post 121 circuits.

MCI coaches with DD3 continued to show only 1 needle on the dashboard gauge well after the "121" compliance, a second needle not appearing until the ?? 102 series of buses, IIRC?? Dashboard needles alone do not indicate the plumbing compliance.

I am concerned about the description of dual system... Perhaps you recall two isolated sources of air, typically one for the front axle, one for the back axle, both feeding the spring brake circuit via double check valves.... it has nothing to do with the presence of a spring brake chamber and it's two airlines.
Whose course did you take?

Also, your air brake course will lead you astray if you start applying what you learned to the plumbing of a DD3 brake system. Bendix has a number of DD3 publications to start the process of de-programming the spring brake propaganda. In the document library at Bendix.com.

The thing I think TomC is referring to is the US requirement of 1975 to have anti-skid control. The technology of those systems was simply not ready for prime time, the government wouldn't listen, and then there were a number of catastrophic collisions caused by the failure of the anti-skid control systems. The US legislation was quietly and embarrassingly reversed shortly thereafter for the anti-skid requirements after these problems came to light (not being reinstated until sometime in the mid 1990's when the technology was far superior and sorted out).

The manufacturers of the day ordered the anti-skid controls to be disconnected immediately by the fleets that owned them. Compliance with the request is thought to have been quite universal, due to the serious safety concerns that the systems would be directly responsible for collisions.

In my years on the boards, I have yet to hear of anyone having stumbled on an operational system.

happy coaching!
buswarrior

[bevans6]

When I took my air brake course a year ago, a Ontario Government recognized  course for drivers to get their Z endorsement, there  was a single paragraph in the manual about DD3's, and that basically said they were obsolete.  The instructor said I was on my own, so I embarked on a study of the DD3 and my buses air system.  it's my understanding that the DD3 system, at least as installed on my 1980 MCI, meets the dual system requirement by having a separate emergency brake tank (also operates as the parking brake tank) that can operate the braking system via a shuttle valve could pressure fail in the dry tank.  It is fed from the dry tank, but has a one way check valve to protect it.  it is supposed to give at least three full pressure brake applications to the rear brakes, which should be enough to stop the bus safely. 

Brian

[DaveG]

I am not sure that we are all talking about the same thing here. Dual air brake system is for application brakes, and there are  other requirements for releasing parking brakes after loss of air pressure.

Someone with some good word speak should spell it out for all to understand. I'd do it but I don't have a bus!

[bevans6]

Dave, your thoughts are relevant to spring brake type systems that do have dual air systems, one for the front brakes and one for the rear.  the MCI in question has DD3 rear brake chambers and, on my bus at least, the dual tanks are the dry tank, for all normal braking air front and rear, and the emergency  tank, which supplies air to the rear brakes when the dry tank is low on pressure.  Still two tanks, still operating the foundation brakes while moving, not a parking brake application or release operation.

I have thought that one of the significant benefits of the DD3 system is the ability to have operator controlled emergency brake application, but I also think that the simple, "it's gonna come on when the air pressure is gone" action of the spring brake, even though the spring brake application isn't all that strong, has great benefits too.

Brian