| Author |
Message |
Stan
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, February 23, 2006 - 3:44 pm: | |
Supposedly everything can be found on the internet. A lot of searching found this on a Bendix site. Everyone can do their own math to compare spring brakes to DD-3 brakes.
Q. I WANT TO KNOW MEANING
OF TYPE 24-30 ( CHAMBER BRAKE )
A. The first number represents the rated area of the service portion of the brake actuator in square inches. The second number represents the rated output of the spring brake portion of the actuator. A Type 24/30 would have an approximate area of 24 square inches on the service side and would have the output for a Type 30 spring brake. The force exerted by the service portion is approximately the pressure at the chamber times the area of the chamber. A pressure of one-hundred pounds-per-square (PSI) times 24 square inches (area) would result in approximately 2,400 pounds force at the chamber push-rod. The spring brake output for standard actuator is just over one-half the output for the same size service actuator. The output for a Type 30 spring brake would be approximately 1,600-1,800 pounds force at the push-rod. |
Donald Lee Schwanke (Dontx)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, February 23, 2006 - 3:58 pm: | |
Good job, great info! I looked and failed. |
t gojenola
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, February 23, 2006 - 6:33 pm: | |
Stan, I don't doubt the authenticity of the information quoted, but it is confusing. The square inch area of the diaphram in the spring brake portion does not represent the force applied by the spring. It merely indicates how much force is available to release (compress) it at a given air pressure.
If Bendix is saying that their springs are rated to provide 1600 to 1800 pounds of force, that is another matter. But it also bolsters the arguments made here in past years that the DD3 chamber gives superior stopping power in emergencies, which I don't believe to be true.
Bendix is not the only product on the market, and I have never seen a spring-force graph which they have published. On the other hand, the MGM site does. Their graph shows forces more than double those quoted above.
In every spring brake chamber, the actual forces will change over the length of the stroke, so this tends to support the necessity of proper adjustment.
Read the force graph on this document, page 2:
http://www.mgmbrakes.com/products/documents/5031_002.pdf |
John MC9
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, February 23, 2006 - 6:38 pm: | |
Does that mean that it would take more, or less volume of
air to operate a spring brake canister? |
Donald Lee Schwanke (Dontx)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, February 23, 2006 - 6:45 pm: | |
Yes John, it does. |
niles steckbauer (Niles500)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, February 23, 2006 - 6:47 pm: | |
DON - ROTFLMMFAO |
John MC9
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, February 23, 2006 - 7:37 pm: | |
Doesn't take much, ehh Niles? |
Marc Bourget
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, February 23, 2006 - 7:54 pm: | |
JohnTCG,
The volume of air required is dependent on a host of interrelated factors. Without narrowing the options, Dontx's comment was appropriate - albeit, tongue in cheek!
Methinks Niles was laughing "with" the fact that you kinda stepped in it! (I think you really have to rile niles before he gets rude or nasty!) |
Donald Lee Schwanke (Dontx)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, February 23, 2006 - 8:21 pm: | |
Sorry John, the devil made me do it. |
John MC9
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, February 23, 2006 - 8:37 pm: | |
Yeah, yeah... blah blah blah..
(HAR HAR)
Ahh... I had asked at a local bus garage, about changing
out the dd3 to truck spring types (less $$$), and had been
informed that there was a difference in the amount of air
volume needed. That difference (I was told), would change
the timing of the brakes. And that timing difference could
toss the bus into a skid on slippery roads.
So, the doubting fool that I am, I asked at a local truck
garage and had it explained essentially the same way.
So of cuz, when I read about swapping parts in the air brake
system, without regard to the engineering behind the system
as a whole, I become curious if those that may deem it proper
and honky-dory, really know if it is or not.
I don't, so I continue to ask..
(Hopefully Luke and Rich will explain in depth, if any "swaps"
should be made from a DD3 canister, to the spring type..) |
Stan
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, February 23, 2006 - 8:38 pm: | |
t gojenola: I don't see any spring force chart on your site link. There is a chart for the service brake force which is quite straight forward and provides much the same info as other manufacturers. The only difference in this one is it is a long stroke chamber. Bendix recommends a minimum of 1/2" and a maximum of 2" so one shouldn't really be concerned about stroke out at the margins where you get pulled of the road in a safety inspection
For several years I have been searching for the actual spring force in a spring chamber and yes, bendix is quite clear that a size 30 has 1600-1800 pounds of force. The above post is pasted from the Bendix site. Read the authors credentials here:
http://expert.fleetowner.com/brakes/
With a 1800 pound spring it will take 60 PSI on the 30 square inch diaphragm to release the brake. Do you suppose that is why your {push-pull valve is set not lock in until you have 60 PSI in the tank?
If I have to do the math for anyone: A size 30 DD-3 with a 80 PSI regulator will have 2400 pounds of force compared to 1800 in the spring brake. In other words the spring brake is 25% less than the DD-3.
1800 pounds of force is a lot and before the advent of welded top chambers you could take the clamp ring off to replace the diaphragm. There were regular reports of death and serious injury when done without the proper equipment. |
Jon W.
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, February 23, 2006 - 8:53 pm: | |
Maybe there is a recognition of the presumably lesser force of a spring brake. At least in my coach it seems. They always go bigger for the spring brake than for the service brake.
My original coach weighed 42,000 road ready. My driveway ascends 80 feet in elevation in a 300 foot length of driveway so brakes are critical. My emergency brakes were on the drive axle only, and they were 30/36. They would hold the coach on the hill.
My current coach weighs 47,000 road ready and it has 30/36 on the drive alxle and 16/24 on the tag. The spring brakes hold it on the hill.
As just a piece of information the front axle brakes were size 30. |
Donald Lee Schwanke (Dontx)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, February 23, 2006 - 9:21 pm: | |
Before we get to saying it won't work, lets be clear that MANY buses have converted from DD3 to springs, and I have never heard of someone having a problem with it. In fact, in todays world finding someone that even understands DD3 is an accomplishment, and also the reason many are changed over. Having something that is readily serviceable at most truck shops, and is cheap and easy to replace on the road, HAS to count as an advantage if you don't do all your own work. After all, just how many times have your brakes failed, and you had to use the park/emergency stopper, and hit something solely because you did not have DD3's to stop you a few feet sooner than the springs? I thought so. |
John MC9
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, February 23, 2006 - 9:33 pm: | |
Donald -
I know that some manufacturers have moved to the spring
type, and have re-engineering the entire brake system in
doing so.. Are you saying that some companies have simply
swapped DD3 cans with spring cans?
(On another thread, that was the plan..) |
Donald Lee Schwanke (Dontx)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, February 23, 2006 - 10:35 pm: | |
I have not kept up with companies John, just individuals, just being busnuts. |
Gary LaBombard (Garylee)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, February 23, 2006 - 11:53 pm: | |
Lets keep this thread going, (Please), my question about changing over to a new system a couple of days ago in an earlier thread seems to have gone down the crapper, but now I see you are seeing my point (I think) and the Reason ($$$$$$$$$)I want to research if this can be done.
A better question would be, if your bus had the original (DD3) chamber design had been changed on your air brake system was it done by you? I am only familar with (Eagles) but this would also include any bus model if they were fitted with the (DD3) chamber. If you changed from a (DD3) drive chamber and it worked would you tell us if it did please? If you did do this, do not give me the drawing information for the change right now, (before the Liability) issue comes up, I just want to know if it worked safely? Did you do all the work yourself?? Did you have to change the entire air system (valves etc) to have the entire air brake system compatable when the brakes were applied or released?? I think most of us want to know if this is possible to do even though the original design was engineered over 30 years ago to be efficient and it is not recommended today by many to change?? To Me There is just nothing in this world that can justify the prices I have seen for the replacement of the original design (DD3) from a price of $450 ea. on ebay and approx. $650 each in my area brake supplier to fleets!!!!!! None!!
All you experienced converters with the full knowledge of what you have done and what has actually worked could really help out on this issue to a lot of us just getting more frustrated over this issue. I know I am talking about a lot of us that would be appreciative of any of your actual use feed back. If you had bad experiences because of it as well!!! I am sure all owners of the (DD3) would like to have this feed back from actual users of a changed over air system and then if this information is needed perhaps it can be archived so we all can use it in the future if needed.
Thanks so much again for your help from many of us.
Gary, (Rustless Money Pit) |
John MC9
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 24, 2006 - 12:01 am: | |
Gary -
Luke mentioned something about you calling him for info?
Have you done so, and what was the verdict? He did
stipulate, that you'd share the info; your conversation with
him, with the rest of us.
Enquiring minds are hungry! |
Gary LaBombard (Garylee)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 24, 2006 - 12:27 am: | |
John MC9
I emailed luke my phone number and photo's of my situation, he wanted to call me and as yet has not probably had the time. As soon as I get good information I will post as it as I do like everyone to have the same knowledge if it helps in making an important decision in particular and something as important as our air systems.
Gary |
t gojenola
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 24, 2006 - 1:07 am: | |
Well, guys - I apologize about the former post. I picked up the wrong reference. The correct one on the MGM site is this one:
http://www.mgmbrakes.com/documents/Section10-Tech.Info.pdf
And, it confirms spring forces very similar to the Bendix data.
Just to throw something else into the discussion:
The DD3 system requires a dedicated "reserve" air tank to supply it in any situation where the service brake supply is interrupted, or falls below a set psi. This means that emergency brakes will be fully applied instantly in such an event. The valves that cause the reserve tank to cut into the system are a little more complicated than I can explain. Good - or bad? You decide.
Spring brakes (with lesser force) will, on the other hand, be similarly applied in the event of a sudden and catastrophic air loss, but less violently. If the spring brake air supply is through a quick release valve, the reaction might be quicker than a DD3. Good - or bad? You decide.
By the very nature of the two systems, conversion from DD3 to spring brakes should be very simple.
tg |
Tom Caffrey (Pvcces)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 24, 2006 - 3:16 am: | |
Gary, we converted to spring brakes, but we did it for a different reason than you. Our coach came with a Johnson bar and ICC valve, a combination some people seem to accept, but I couldn't.
As I undertood the emergency brake operation, the ICC valve would remove all the air from the rest of the system and apply it to the to drive brake cans.
If a rear hose blew or a diaphragm let go on a downgrade, you would lose any hope of stopping the rig unless you could do it with the handbrake and the engine.
The DD-3 was an option for our coach, but never installed.
The spring brakes have been everything I hoped for and we have never had any difficulty with them after the installation.
I would not want the spring beake to set any harder than ours does. THIS FORCE DEPENDS ON THE BRAKES BEING PROPERLY ADJUSTED.
If we were to lose our air on ice, it might be very difficult to keep it on the road until the rig came to a stop. For this reason, we retained the Johnson bar and we have used it many times.
JohnMC9, the extra volume of air required by the spring brakes should only be needed by the parking brake, not the service brake. Service brake timing should not be affected appreciably.
For what it's worth.
Tom Caffrey PD4106-2576
Suncatcher
Ketchikan, Alaska |
Stan
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 24, 2006 - 8:47 am: | |
Gary: In one of these threads I said that I had changed DD-3 cans to spring brake cans on my MC-7 Combo and why.
My understanding of the bistory of these brakes was the US government had concerns about passenger buses having air brakes without any backup system. I think they mandated the ICC (Interstate Commerce Commission) brake found on early GM buses and maybe others. This was only an alternate air supply than the one supplying the treadle valve.
Bendix developed the DD-3 and it was used on virtually every bus (highway and transit) being built in North America. The bus chassis was designed around the DD-3 system and certainly GM and MCI did not have room to mount the spring brake chamber when it came on the market. That made it easier to continue to use the DD-3 and only have one system to deal with. I also expect the cost of getting approval from the regulators to use a different system entered into their decision.
In the meantime everything else changed to a spring brake, including disc brakes and industrial machinery. Gradall excavators continued to use the DD-3 for some time because they were controlling the brakes from both the driver's cab and the top operator's house and they were designed around the DD-3..
Most of the brake manufacturers web sites refer to the DD-3 as a brake sytem from the 1960s used mostly on highway and transit buses. On one site it says that four milliom 30-30 spring brake cans are sold in the US each year. Compared to virtually no DD-3s that likely explains the drastic difference in cost.
Like Sony and Apple found out, being better doesn't guarantee success. The world has moved on and DD-3 brakes sytems are like a Sony video recorder. |
Gary LaBombard (Garylee)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 24, 2006 - 9:58 am: | |
Stan,
and all other BNO posters.
Thank you so much for this insight and information, I am sure I am not the only newbie on this issue that is appreciative of you comment and yes comparison to the (DD3) pre-historic air system. Why isn't it still used "today" and on 80,000 lb. 18 wheelers as well??
Thanks again, I will wait for other information but at least I know what I want to do is not an impossiblity and not completely unsafe.
Finally a short message,
Thanks Again
Gary |
John MC9
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 24, 2006 - 9:06 pm: | |
"Why isn't it still used "today" and on 80,000 lb. 18
wheelers as well?? "
Could it be as simple as the fact a trailer needs foolproof
brakes when the tractor isn't there? |
Stan
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 24, 2006 - 9:32 pm: | |
No! Trailers have their own air tanks and could dynamite or stay locked up with DD-3s if all the complex valves were installed. |
John MC9
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 24, 2006 - 9:54 pm: | |
Kids like to play; tanks are vulnerable, spring canisters are not.
You're right Stan. They're likely better, especially if
all the bus manufacturers are using them now. But the
initial "debate" involved the simple swapping of a DD3
with a spring canister. I think you would agree, that's
it's not a simple swap; more has to be changed and
taken into consideration to accomplish a safe swap.
The "timing issue" shouldn't be taken lightly, if it
does exist.. having the rear brakes grab while the
fronts are not yet engaged, even for a split second,
can cause problems on slippery surfaces. Ever down gear
on ice? Bad news! A rear lockup will cause you to see
the back passing you.
Funny ain't it? Here I am, a guy that argues about the
correctness of "codes" and engineers not living in real life....
Insisting that the way the brakes were engineered should
not be re-designed by the home-brew hobbyist.... and
an engineer is arguing they should be...
Gads... I just gotta' start drinking again... |
Tom Caffrey (Pvcces)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 25, 2006 - 12:57 am: | |
JohnMC9.
Haw.
Tom Caffrey PD4106-2576
Suncatcher
Ketchikan, Alaska |
niles steckbauer (Niles500)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 25, 2006 - 4:16 am: | |
By niles steckbauer (Niles500) (71.100.175.122) on Thursday, December 08, 2005 - 8:20 pm: Edit Post
There are certain critical systems in our buses for which the unexperienced should not undertake to repair, maintain or modify - brakes, electrical, steering, etc.
By John MC9 (66.217.105.53) on Thursday, December 08, 2005 - 9:09 pm: Edit Post
The words, Niles.... Were akin to me telling you, that since
you had no prior professional experience driving a bus, you
should hire a professional to drive it for you.
No-one has to be an expert at anything, experienced at
anything, or all that knowledgeable about anything, to make
a motorhome out of a bus shell. Most here, learned about
one aspect or another, as they plowed through the debacle.
If you haven't crashed and burned due to lack of professional
driving experience, may I consider this matter settled and closed? |
Stan
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 25, 2006 - 8:55 am: | |
No John, I would not agree that it is not a simple swap. You eliminate all the complicated DD-3 components and put in a simple spring brake system.
I know you like to argue every point ad-infinitum so I have tried to explain everything you asked in very simple short words. Re-read my previous post abour some of things that affect brake timing and then tell me that you had control of each and every one of them or even any one of them every time you drove a vehicle. |
John MC9
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 25, 2006 - 9:58 am: | |
I think we have some sort of a language barrier, Stan.
Re:
(me)
"I think you would agree, that's it's not a simple swap;
more has to be changed and taken into consideration to
accomplish a safe swap. "
(Stan)
"No John, I would not agree that it is not a simple swap....
....I know you like to argue every point ad-infinitum..... "
No arguments here, Stan. I know little about the mechanics
and differences of the air brake systems. I would be willing
to wager a tidy sum, that very few commercial drivers can
explain each system in depth, as well as you can.
Stan, you seem to feel it's an easy swap. Please list all (each
and every) component that a reader will have to change, to
replace his (or her) DD3 system to a spring brake system.
There are many here (I'm very sure), that would love to
undertake this swap ASAP, and with a short list from you,
we can get started this afternoon. (I'm serious about this!)
Thank you. |
Donald Lee Schwanke (Dontx)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 25, 2006 - 10:44 am: | |
Not sure about other breeds, but the old GMC buses had the mounting bracket totally unacceptable for mounting a spring brake. The very first bit of engineering was to have to fabricate a new mounting bracket from scratch. This bracket would of course be a life or death situation if it was poorly engineered, and as we have seen, the forces exerted by the service brake can be huge. In many cases, the owner did not want to trust his engineering of a new bracket nor that of the fella next door that had a welder, since having the ability to destructive test the new bracket was usually not available. I did see one fabricated bracket that had failed from braking forces. |
Stan
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 25, 2006 - 11:01 am: | |
Dontx: You got that right. From the introduction of DD-3s until their use was discontinued there were literally hundreds of different mechanical designs and air system designs. In one of my first posts I pointed out that early GM and early MCI buses did not have enough room to mount a spring brake chamber. There is no one size fits all and if you don't understand how the system works and how to modify it correctly then you shouldn't be doing it.
Again, going back to one of my original posts, I still maintain that changing a DD-3 size 30 to a spring brake chamber size 30 does not have any effect on the service brake. It does make a simpler and cheaper park brake. I would be happy to hear from anyone with the facts and figures to refute those two statements and I would apologize for leading anyone astray |
Richard (Busnutrick)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 25, 2006 - 3:52 pm: | |
Reading this thread has alerted me to another area of concern with older bus conversions. I appreciate all of the contributors to the board regarding important topics such as this brake topic. My intention will be to have a professional mechanic inspect any bus that I am looking to purchase and this board will certainly give me an underlying knowledge of bus sytems and what modifications to be very cautious of.
Thanks to all,
Rick |
John MC9
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 25, 2006 - 9:25 pm: | |
Rick -
Very good observation! |
Buswarrior (Buswarrior)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 26, 2006 - 4:28 pm: | |
Egads! I snooze for a few days, and the trouble I come back to!!!
1) Where did the idea DD3 were stronger than spring brakes come from?
Be careful, those mathematicians in the crowd, the emergency portion of a DD3 has a smaller diaphragm area than its service side, and the strength of the emergency application is dependant on the proper setting of a regulator.
If anyone has an output graph for the emergency side of a DD3, I'd love to see it!
Never mind the theory, FWIW, I regularly have trainees practice using the parking brake at speed, and there is no difference of note in stopping between my MC8 with DD3 and the newest transit buses with spring brakes. The greater determiner is the state of adjustment.
2) DD3 are ancient devices from another era?
DD3 were the stock brakes on the latest MCI 102DL3 coaches up until a time measured better in months ago, not years. The E model has fancy extra long stroke spring chambers to go with the 6 wheel disc brakes.
DD3 is a compliant brake with the most modern of the safety legislation, and on coaches built prior to 1975, offered a level of back-up, due to the isolated plumbing, not available on most of the other systems being sold.
3) Prices are wacky?
Yes, absolutely! Very simply a supply and demand situation, where the purchaser has no real choice but to buy them at any cost, and pass that cost onto the riding customers, which a busnut doesn't have as a source of revenue.
4) Ease of retrofit?
As noted, most buses with DD3 won't fit a spring brake chamber in the space provided. The axle area was designed around the smaller DD3 chamber.
5) Why would you need new ones?
Unlike a spring chamber, a DD3 may safely be worked on by an informed busnut without fancy tools or a press. Once there are fresh diaphragms in the chamber, how long before you will have to think about them again, except to put a squeeze of grease in that zerk once every half a blue moon?
6) Brake timing?
As noted by others, the service brake performance will not be harmed by changing the chambers type for type. If going to all this trouble, I'd also replumb the service brake to a dual brake system, if it is a pre-1975 coach. The parking plumbing will have to be rearranged and some new valving installed, replacing the DD3 related ones.
You also want to be sure that your efforts do not unwittingly imbalance the tank volumes feeding the brake chambers, or the pressure available at each axle may differentiate if the brakes are being used more than the air compressor can keep up.
7) Why has it fallen into disuse?
It wasn't popular outside the bus circles, and it wasn't that popular beyond MCI, once it became clear that a proper parking and emergency brake system was going to be expected from the regulators. The price differential appeared a long time ago.
Once GM lost its strangle hold on dedicated busparts, the future started to become clear: The bus market is not large enough to support dedicated parts. Build a bus with what is popularly out there, which is truck parts. And truckers don't know DD3 from shinola.
Even MCI has caved in to the economics of the situation.
8) Strength of home-built brake chamber brackets?
Yup, best not to be doing your own modifications to the mounting points for brake chambers. There are manufacturers of buses right now, today, in the active fleets of this continent who can't get it right: brake chambers trailing by their hoses and clevis pins in a city or town near you...
What else?
happy coaching!
buswarrior |
Donald Lee Schwanke (Dontx)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 26, 2006 - 5:02 pm: | |
Extremely well put Buswarrior, thanks! The discussion on DD3 brake pressures was NOT concerning service brakes, but came from the fact that the pressure on the parking brake is higher in the DD3, simple mathmatics shows that. Personally I have had a different result than you describe, my ol 89 Kenworth would not stop very well when applying parking brake when rolling, but my GMC DD3 bus would stop very well thank you. Granted this is not scientific, one truck against one bus, but that was the case. The pressure could have been turned up on my bus park system, the springs may have been weak on the Kenworth. Adding fuel is the fact that actual pressures do not seem to be accurately presented anywhere. I certainly agree that adjustment can make a BIG difference as well. |
Buswarrior (Buswarrior)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, February 27, 2006 - 10:30 pm: | |
Thanks Don!
On the power of the parking:
Offline, Stan was kind enough to remind me that Bendix quotes the parking side of a DD3 is 80% of the service side. (smaller area on the parking diaphragm) Coupled with the recommended setting of the parking regulator to 85 lbs, output force at the pushrod of a Type 30 DD3 would theoretically be somewhere around 2000 lbs.
Not far from the 1800 lbs usually quoted for a type 30 spring chamber, as it takes approximately 60 lbs of air to fully cage a spring.
Yes, that K-Whopper maybe had weaker springs?
So, there's some more!
happy coaching!
buswarrior |
Stan
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, February 28, 2006 - 8:31 am: | |
Just to add more fuel to the fire, I read an accident investigation report from the NTSB with major coverage on spring brakes. They claim that there is a potential problem with broken springs. They go into great detail on the causes of broken springs. The original one piece spring works as designed but the more fractures there are inthe spring, the less force it provides. A visual inspection of the system does not reveal this problem as the park brake appears to work normally. It is possible to check the springs with a boroscope but that is not usually done on a brake inspection. |
Donald Lee Schwanke (Dontx)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, February 28, 2006 - 11:26 am: | |
And who would even know if the springs were BOTH broken? Crawling under the bus and checking to see if they have engaged is not part of every bus owners checks each time he parks. Of course one could attempt to drive off after setting them, to see if they engaged. |
akrom
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, February 28, 2006 - 9:19 pm: | |
Whew!!! Possible can failure makes me nervous,-ergo I'm glad I bought the anchor off Fast Fred last year!!! akrom |
akrom
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, February 28, 2006 - 9:24 pm: | |
Whew!!! Possible can failure makes me nervous,-ergo I'm glad I bought the anchor off Fast Fred last year!!! akrom |
Buswarrior (Buswarrior)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, February 28, 2006 - 10:01 pm: | |
Hello parkers.
Test your parking brake by using it.
Drive down the street, nobody behind you, dishes off the counter, loose stuff stowed, brake adjustment has already been confirmed as safe and legal, 15 or 20 miles an hour and pull the knob. Faster is ok too!
No, not that knob....
Don't do it at creeping speed, the stop is abrupt, and it doesn't check anything. Even weak brakes will stop a creeping bus.
You won't hurt anything, despite what that poorly imformed driving instructor told you years ago, or maybe yesterday...
All you are doing is applying the rear brakes using the springs instead of some air pressure.
After all, they are called "emergency brakes".
The coach should stop as if you made a moderately heavy brake application. If the bus sails on, you have problems. If you are able to add some fuel and keep it moving, you have problems.
You are after a smooth, firm stop, with a little jerk at the end, since the springs don't ease up at the end, the way you do with your brake pedal.
Go ahead, it won't hurt, you might even have fun!
And then get back on here and tell the world you did it!
happy coaching!
buswarrior |
john w. roan (Chessie4905)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 04, 2006 - 10:08 pm: | |
Luke told me a couple years ago that Bendix ( Allied signal now?) doesn't manufacture new DD-3's anymore...All you can get are rebuilds at like $450 a piece. You would think Bendix would start having them made in China, but probably love making a fortune rebuilding the old ones instead. I wonder what the price point will be when people decide to change over to spring brakes. BTW my 4104 has spring brakes and work fine; glad to have them. My 4905 doesn't have room for ANY brand of spring brakes; would have to modify rear baggage compartments to provide enough room...too much bother. You should only have to rebuild your DD-3's once at the most unless you keep your coach for a very long time.If you change a coach over to spring brakes, the other associated components needed are going to close the price gap a lot, esp. if you pay someone for the work. |
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