| Author |
Message |
Larry K Dixon (Larry_d)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, October 17, 2005 - 1:00 pm: | |
Finally got a better look at the coach, it appears to be the parking brake locking up and there must be an air valve or something under there. Have to push main brake peddle very hard and a couple of times, making the brakes squak and squeel before ther release. Thanks everyone for all of the help. Drove 200 miles with no brake heat and seemed to work very well. larry 4905 |
RJ Long (Rjlong)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, October 17, 2005 - 1:12 pm: | |
Larry -
4905s came with DD3 brakes on them. Don't know if you're aware, but there is a correct procedure to release the parking brake on these units, which is as follows:
1. Build coach system air pressure to normal governor cut-out (about 120 psi).
2. Lightly cover the service brake pedal, weight of foot only, no additional pressure.
3. Release parking brake knob (usually push in).
4. Apply FULL service brake application (push pedal to floor) and HOLD IT for approximately 3-5 seconds.
5. Release service brake, and you should be good to go.
If the parking brake does not release after this procedure, then you need to have your system checked by a qualified BUS mechanic. Call your local charter bus outfits and talk to the shop foreman. Explain your situation and ask him if they do outside work, or ask him for a referral to a qualified shop. If you get referred to the same shop by several companies, then you know you've got a good source.
FWIW & HTH,
RJ
PD4106-2784
Fresno CA |
Brian Brown (Blue_velvet)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, October 17, 2005 - 6:47 pm: | |
DD3s are complicated to diagnose because of the inversion valves and double diaphrams. I had to replace a parking diaphram on my old MC8 last summer before I horsetraded it (loong story).
It took about a day to rebuild and about $100 from Mohawk for the various parts. Of course, it took three days of frustrating head-scratching to figure out where the faiure was. The cans are very pricey to just buy outright (~$500, IIRC), so I rebuilt the bad one.
To save time, I'd go ahead and pull both cans and check the rubber in them. If there's a pinhole leak on one of the parking diaphrams you will have trouble releasing 'em. There's also the inversion valves, the relay valves, the foot treadle, AND the parking brake valve itself. There's also some quick-release valves in the system, as well. (I told you it'd be fun!)
But... it's most likely in the cans, I'd guess.
BTW, did Stan ever write up a primer on DD3's? I seem to remember him promising to do so not too long ago...
HTH,
BB
PD4106-1175 (just a Johnson bar!)
Longmont, CO |
Buswarrior (Buswarrior)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, October 17, 2005 - 10:10 pm: | |
Hello DD3 fans.
RJ and Brian's posts are solid.
There is also a critical pressure regulator in there, in the parking application side, that if it has crept up in pressure, will make the parking brake impossible to release. If it has crept down in pressure, the parking brake application weakens.
Order of operations, it might be easier to pull the lines and check the pressures, before removing the chambers?
I was also making a move to write a DD3 thingy. Life keeps getting in the way of my hobbies!
Stay tuned, have to get this back on the front burner. I'm going to see what the good folks at Bendix might do special for the busnuts...
happy coaching!
buswarrior |
John MC9
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, October 17, 2005 - 10:20 pm: | |
Larry -
"Have to push main brake peddle very hard and a couple of
times, making the brakes squak and squeel before ther release."
Like they said, that's the way you release the parking brake.
Some truck mechanics don't know bus brakes and think it's
faulty if the brakes don't release without having to depress
that brake pedal to the floor for a second or two. |
Larry K Dixon (Larry_d)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, October 18, 2005 - 12:42 pm: | |
Hello everybody, what world of information. There is no way Thank you will cover. I was not informed any of this (just to push peddle and knob and go) Thanks again have printed all of this will try again. busy to day with dogs.
larry 4905 |
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