Dd3 brake chamber

[zukmancdr]

I have a 1987 MCI 102A3. I sure this is what's on my bus. I am having the right drive axle not releasing. I been doing some research and thank that one of the "role" lock is not releasing. I have not paid any attention if I push hard on the pedal to make the release.  Does this souls right.

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[RJ Long]

Dr Zuk -

The proper way to release DD3 brakes is as follows:

1. Build air pressure to governor cut-out, usually about 120 psi.

2. Rest your foot on the service brake pedal, but do not apply at this point.

3. Push the parking brake knob IN to release brakes.

4. Apply a FULL service brake application and hold for 3 - 5 seconds.

5. Release service brake, bus should now roll.

If brakes fail to release, repeat procedure.  If brakes still fail to release, it's time to do some troubleshooting.  There are some other "tricks of the trade," but try the proper procedure first.  Also, do NOT make the full service brake application until after you've fully pushed in the parking brake knob.  Doing so before can "corn-fuzzle the troops!"

The proper way to set DD3 brakes is:

1. Apply a very light service brake, only sufficient to keep coach from rolling.

2. Pull parking brake knob to set DD3 brake.

When setting the parking brake, anything other than a very light service brake raises the potential for difficulty releasing.  All you need is just enough brake to keep the coach from rolling, no more.

Easiest way to tell what brake chambers you have on the drive axle is to look and see how many air lines are running to the cans.  3 lines = DD3, two lines = spring brakes.

FWIW & HTH. . .

 

[zukmancdr]

Thanks

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[Brian Evans]

There is a grease nipple on the DD3 that lubricates the locking mechanism, a little grease might help.  The rubber boot needs to be there and be intact, or the mechanism will corrode and bind.  The air line from the inversion valve to the locking port needs to be in good shape, not leaking.  New DD-3 chambers are available from REI.

Brian

[eagle19952]

who/where is REI ?

[Brian Evans]

Sorry, they've been discussed here a couple of times so I didn't add a link.  http://www.rebuildersenterprises.com/  As far as I have been able to find out they are the only people supplying new DD3's.  They are aftermarket, not Bendix.

Some have had issues with compressor rebuilds, to be fair, but I had great service from them.  They had the components for the DD3's manufactured, some in Canada I think, some off-shore, and they can supply either rebuilt units or brand new units.  I bought brand new units since I wanted fresh castings as well as fresh wear parts.  They came on time, they looked fine, they installed fine, and they work fine.  I hope to be able to basically ignore them (aside from annual maintenance) for 20 more years   

Edit: from memory the brand new units were $550, the rebuilds were $450.  I think all they re-use in the rebuilds is the castings.

Brian

[luvrbus]

I was the one that told Brian about REI I don't say much about him his new stuff is and at a good price but I will not buy his rebuilt stuff you get no service and he is impossible to reach.

You never get your money back for shipping defective parts back and the core charge is another issue with REI you get it back after awhile I will say he never beat me on that part buy new from REI if you buy JMO

good luck

[Don4107]

Something else to check on a DD3.  I had to repair a DD3 for our 5B.  It was either clocked wrong at some point or was for the other side. Vent was up! It showed signs of liquid in the can.  Be sure the vent is down!

Luke will fix you up with the parts and advice. I now carry both diaphragms, lock rollers, lock collar, piston o-ring, and an inversion valve to make repairs on the road.  Should be enough to get rolling again.

When we bought the thing it had a spring chamber cobbled on it by a roadside "mechanic".  Not that I would recommend it, but in an emergency a spring chamber can be made to function, on the drivers side at least, on a 5B. 

The PO had saved the DD3 chamber so I had something to work with.

[Brian Evans]

Actually, come to consider it, if you truly lost one DD3 on a trip and the other one was serviceable, you could replace the bad unit with a normal, non-spring brake canister that would give you full braking capability, and by capping off the lock port and parking brake port air lines to the replacement can you would retain the parking and emergency brake function on the remaining DD3.  Not great but possibly a "get off the road" repair.  A normal 30 cannister would fit on both sides of the rear of an MCI.

Brian