| Author | Message | ||
| marvin pack (Gomer)
Registered Member Username: Gomer Post Number: 44 Registered: 3-2007 Posted From: 76.4.142.242 Rating: N/A |
hey have a mci-8 and would like to upgrade the parking brakes since they have become a little pricy. what is an acceptable replacement? The ones on it are dd-3's | ||
| larry currier (Larryc)
Registered Member Username: Larryc Post Number: 147 Registered: 2-2007 Posted From: 152.163.100.13 Rating: N/A |
The only other replacement available is truck style maxi cans aka spring brakes. You can pay between $40 and $100 each for them depending on where you are and what price you get. If it says Bendix on it you got the best. DD-3s were mandated on passenger buses in the old days for fire safety reasons. A DD3 won't drag the brakes, heat the drum and maybe burn the bus. If you get a leak in the emergency side diaphram with a spring brake, the emergency spring will overpower the leaking air supply and the brakes will drag. If you do not notice an air loss or see smoke and stop, eventually some one will stop you. Unfortunately by this time the 100 lb brake drum will be cherry red. The tires then catch on fire and you get to watch it burn. The made in China thing is here in a big way. If I didn't buy Bendix from a genuine dealer I would at least buy from a big dealer like Freightliner, KW, Pete, in hopes I'm not getting a forgery. DD-3s are a thing of the past. Everyone needs to know the faults with the alternative and keep up with the maintence procedures on the spring brakes. You have choices to make about stroke, my Eagle has 30-36 cans on it. Most trucks use 30-30. I think if you replaced a 36 diaphram with a 30 it would push out and leak, so keep track of what you are running. | ||
| Kyle Brandt (Kyle4501)
Registered Member Username: Kyle4501 Post Number: 346 Registered: 9-2004 Posted From: 65.23.106.193 Rating: N/A |
I think the number is the size of the diaphram in square inches. The first number refers to the service diaphram & the second is the spring brake release diaphram. If you have the room, put on the larger spring brake cans (to have more stopping power from the spring.) But you should usually keep the same size service brake diaphram. If you change from the DD3, you may need to change some other parts of the system too. A GOOD repair/ parts shop should be able to help you with the parts needed. Go to the Bendix web site & look at their schematics. Good Luck! | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 618 Registered: 10-2003 Posted From: 71.58.117.21 Rating: N/A |
If you have mechanical skills and buy the repair parts from Mowhawk (about $200 for both ) they are pretty simple to repair if the insides are in good condition.Change to other brake chambers, if you have the clearance will probably end up costing you as much or more till everything is done. Rebuild them once and you shouldn't have to do it again. | ||
| Jim Wilke (Pd41044039)
Registered Member Username: Pd41044039 Post Number: 151 Registered: 2-2001 Posted From: 69.77.144.142 Rating: N/A |
I can't believe you guys are back telling someone they can just replace the DD3s with spring brake cans or that this would be an easy conversion. First, the DD3 designed bus has an ENTIRELY different air brake system, period. To change over, you will need to replace most of the brake components. There are all kinds of relay valves, check valves and double compartment tanks. The system is a split front/rear system like a modern car. If one side develops a leak, the system diverts to use the highest remaining pressure. If there isn't full air pressure, you can't release the brakes. Your dog or an untrained person can't accidentally release the brakes. This system was designed so well that Eagle designed their system to mimic it using spring brake cans. But worst of all, you are advising someone to re-engineer the brake system on a "commercial" class vehicle that may well weigh 20 tons. IF THERE IS AN ACCIDENT AND IT IS DISCOVERED THAT YOU HAVE CHANGED THE BRAKE SYSTEM YOUR INSURANCE WILL NOT PAY AND YOU WILL NEVER CRAWL OUT FROM UNDER THE JUDGEMENT $$$$$$$!! It costs about $100-200 for the parts to overhaul a DD3 can. There is no dangerous spring involved. When the DD3 system works right, it works very well. In my opinion, we should advise other busnuts to maintain the basic platform of the bus just as GM, MCI, Eagle, etc. designed it. There is no REAL savings to taking the liability on ourselves & WAY too much potential tragedy possible. Think about your feelings if your mods allow someone to be injured or die. Any of us would carry that to our graves. | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1039 Registered: 12-2000 Posted From: 74.12.88.37 Rating: |
Hello First, there is no room to fit anything but a DD3 in your MCI. Second, it would require a fair bit of re-plumbing to the existing system. You can't just plug a spring brake in, if you made the extensive modifications to fit them. Third, there is nothing wrong with the DD3 system. It was used most appropriately by MCI up to a couple years ago, when even they finally succumbed to the market forces of supply and demand ($$$$) and changed to spring brakes. Fourth, the only thing wrong with the DD3 system is the lack of maintenance done by the former and present owners, often through the ignorance that a shortage of good maintenance and training materials brings on. There are two diaphragms per chamber, the chamber needs the occasional squirt of grease for the locking mechanism to stay free, there is an inversion valve, and a pressure regulator that all need to have vintages of known quantity. As noted by john w. do the maintenance, change out the parts and that'll be it done and move on to worrying about other things. And fifth, a DD3 is quite capable of setting the tires on fire by dragging, if it has not been maintained and it does not fully release from parked. Some might suggest it is more prone to hanging up! DD3 full name is "Double Diaphragm, 3 Air Line, Safety Actuator" It became available back when all the trucks and buses only had service brake chambers at all wheelends, and the most awful collection of poor parking brake contraptions. Driveshaft mounted mechanisms and so on. A 1960's bus with DD3 had two isolated supplies of air, one to stop normally with, and the other to apply the Safety Accuator in times of air loss or to park. That was quite a performance and safety design compared to the single air source, 4 service chambers and a handbrake to the driveshaft set up that was far more common. What happened in a single source air system if you blew a hose on some road debris? The rest of the world eventually caught on, and in 1975, dual air systems, along with greatly improved parking/emergency brakes were mandated in the manufacturing standards. Fear not, the DD3 was, is, and would continue to be, fully compatible with the current design criteria for brake systems. Like many products before, it has suffered the fate of not being popular enough for cost competitive pricing and will fade from view. Best to get your spare parts now? The clock is ticking on the commercial demand for these things. happy coaching! buswarrior | ||
| Kyle Brandt (Kyle4501)
Registered Member Username: Kyle4501 Post Number: 347 Registered: 9-2004 Posted From: 70.153.19.15 Rating: N/A |
RE: IF THERE IS AN ACCIDENT AND IT IS DISCOVERED THAT YOU HAVE CHANGED THE BRAKE SYSTEM YOUR INSURANCE WILL NOT PAY AND YOU WILL NEVER CRAWL OUT FROM UNDER THE JUDGEMENT $$$$$$$!! ??? Really? or are you exagerating to reinforce your point? If you modified the brake system properly & to a current dot approved system, it would be easy to argue you upgraded the old system to a current system that was easier for shops to service & therefore safer. If you had a DD3 system fail. It could be argued that you are liable since you didn't upgrade to a current standard that was widely understood by all repair shops. You see, some damn lawyer will find a way to reach inside your pockets. As I posted earlier: "If you change from the DD3, you may need to change some other parts of the system too. A GOOD repair/ parts shop should be able to help you with the parts needed. Go to the Bendix web site & look at their schematics." That is what I did to add spring brakes to my old dump truck. The parts shop even provided me with the bendix schematic & all parts needed. Yes, it cost $$. But now, the durn truck stays where you left it  If you UNDERSTAND how all the components work in both systems, I don't see how changing from one to the other will effect the safe operation of the coach. Personally, I respect compressed springs & compressed air, & I prefer relying on springs, NOT air & wedges, to keep my vehicle parked. I also prefer the 'softer' application of the spring brake in a loss of air failure. The DD3 can lock up the tires & that may prove to be problematic in certain situations too. but that is MY choice. Each should make an informed decision for themselves. It's all a compromise. Educate yourself & choose what is best for your application. PS, FWIW, 3 of my scenicruisers have the spring brakes, not DD3 for park brakes (I haven't looked under the 4th. From what I remember, there was plenty of room for them. | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 218 Registered: 8-2006 Posted From: 207.231.81.59 Rating: N/A |
Kyle, I feel your last post clarifies the whole thread. I also feel a couple of things should be added: 1. IF spring brakes caused all of this potential dragging=fires, why are they the ONLY system made on ALL new air brake equipped vehicles? It must be mentioned also that spring brake equipped vehicles are equipped with low air pressure protection, just as are DD3s. This means that when air pressure falls to the safety setting, the knob will pop out on the spring brakes, just the same as DD3s, and a full emergency application will occur. So, with the hypothesis of a leaking emergency diaphragm causing brake dragging, actually one of two things will probably occur. Either the bus air system will have enough capacity to keep the brakes released, or it won't, depending on the leak rate, and an emergency application will occur, keeping in mind that the emergency setting is above the minimum required release pressure! 2. "If you change from DD3, you may need to change..." should read: You WILL NEED TO CHANGE many of the other parts of the system too. 3. Can I use this post to ask another question? What if a DD3 has a leaking park/emergency diaphragm??? Answer: No pressure in it going down the road, released, so you don't know anything is wrong. But when parking/emergency is needed, the air leak will deplete the seperate emercency application reservoir quickly, and MAY NOT provide a full strength emergency application for the wedges to hold. KUTGW, & Happy 4th, George | ||
| Jack Conrad (Jackconrad)
Registered Member Username: Jackconrad Post Number: 602 Registered: 12-2000 Posted From: 166.165.232.171 Rating: N/A |
The MC-8 does not have room for the spring brake assembly without fabricating a new mount for the spring brake asembly. There is very little extra room for the larger spring brake assembly. I would not want to accept the responsibilty or liability that goes with fabricating a part used on the brake system of a 15+ ton vehicle. Jack | ||
| Kyle Brandt (Kyle4501)
Registered Member Username: Kyle4501 Post Number: 348 Registered: 9-2004 Posted From: 70.153.19.15 Rating: |
Jack, you are a good man, & a good man always knows his limitations. (Thanks Clint) You bring up a key point - Stay within YOUR abalities! I wouldn't be worried about redesigning my brackets if I needed to - But that is along the lines of what I do at work. And I have access to all types of fabrication tools. Our own level of experience should guide us in the choices we make. | ||
| marvin pack (Gomer)
Registered Member Username: Gomer Post Number: 45 Registered: 3-2007 Posted From: 76.4.142.242 Rating: N/A |
you guys always bring a new meaning to busnuts. I am just so proud to be here, and be able to look at what is the real truth. I think that I will just stay with my dd3's and dig a little deeper thanks Gomer | ||
| Kyle Brandt (Kyle4501)
Registered Member Username: Kyle4501 Post Number: 349 Registered: 9-2004 Posted From: 65.4.179.235 Rating: N/A |
If you can't have fun with your hobby & friends, - you might need to get a new hobby & friends. One advantage of dd3's is that they can be cheap to repair the diaphrams & there is no big spring wanting out. | ||
| David Dulmage (Daved)
Registered Member Username: Daved Post Number: 169 Registered: 12-2003 Posted From: 142.46.199.30 Rating: N/A |
While DD-3 brake chambers are expensive, rebuilt ones are available on an exchange basis from MCI parts on overnight delivery (and likely available from other suppliers) for about $500.00 plus core charge. Considering the fact the spring brake chambers won't fit without modifying the mounting the bus, its possible that the cost of changeover from DD-3 would outweigh the cost of direct replacement and the replacement chambers will likely last a long time and you can be assured that the bus braking system continues to comply with the design and manufacturing specifications that were the basis of its certification to FMVSS requirements. In addition, the diaphragms in DD-3s can be replaced at a moderate cost if a complete rebuild isn't required. FWIW Dave Dulmage |
