| Author | Message | ||
| Chuck MC8 (66.156.56.211)
Rating: |
I've been in the process of finding and repairing air leaks on my MC8. Here's a biggie and I'm stumped. I've removed, serviced and replaced the diaphrams in my DD3 chambers. Also replaced a leaking supply air line on one of the chambers. I use my 5hp electric shop compressor to air up the bus so I can hear without the engine noise. With the "push-pull" controll knob in the out ( or parked position) I have a severe air leak from the bottom of the Brake Application Valve. (brake pedal valve) Push in the knob, and it stops completly. This is with 120 psi in the system. If I air the system up from zero psi with the knob in the park position, it dosent make the super loud "hiss", just a constant leak from the bottom of the brake valve. Is the Brake valve defective? It appears to have been recently changed. (Looks New) It was doing this same thing before I rebuilt the DD3's. I had suspected a blown diaphram. (and one was certainly suspect) Any Ideas? PS: the bus is properly blocked and secured, and is not in service | ||
| two dogs (66.90.211.109) Rating: N/A |
is it comeing out of the exhaust "port"...you always have an air release when you apply your parking brake..and...if you have a constant air supply (air comp.) the leak will always be there.."IF" I understand your statement...will the bus run & make it's own air..? I'd say try it & see if the bleed-off stops.. | ||
| Buswarrior (Buswarrior) (64.229.209.205)
Rating: N/A |
Hello Chuck. You have dealt with the first place for this symptom, the diaphragms in the DD3 chambers. My air schematics are off site with the bus, so I'm going from the dark recesses.... If we assume that the DD3 chambers have air integrity, IIRC, perhaps an inversion valve failure will manifest itself with air exhausting from the brake pedal? All the airlines were before and now are attached to their proper locations? May I assume that this problem has happened along the way, and you didn't inherit this with the bus? Former owner done something unconventional? If someone else doesn't nail this, I'll bring the books home this weekend and post early next week. Keep us informed! happy coaching! buswarrior | ||
| BrianMCI96A3 (65.173.65.147) Rating: N/A |
Actually, unless I miss my guess, this was a problem that came with the bus. It has been mentioned a time or two... sometimes you run into parts changers, not mechanics... I'd be willing to bet that the parts changer who worked on your coach was told there was a leak in the treadle valve (service brake valve) and it got replaced, but that wasn't the problem... as for what the problem is...looking at a Bendix schematic just now, I'd be looking and listening to check valves between the treadle and the reservoirs. Hard to make a good diagnosis from here, but thats where I'd start. Brian | ||
| bluegrass (216.207.2.145) Rating: N/A |
You said that your DD3's has been changed, maybe you have a bad rebuild on one or someone has a line on In the wrong place. Tony | ||
| Chuck MC8 (66.156.56.211)
Rating: N/A |
Heres more info, Yes, it's a problem that came with the bus, (Thanks a lot) and I think Brian is right about the parts changer instead of the true mechanic. I've stopped all the air leaks (with the execption of the tag axle valves)in the rear half of the bus. So, with the push pull valve in the down or "travel" position, I'm not losing much air at all from the system. But in the "UP" or park position, It will exhaust the air reservior quickly ( without the engine running or the shop air supply connected). So as it stands, It wasn't a problem (I suppose)going down the road, or with the bus running, It could keep up air pressure. The noise of the air leak is not nearly as noticible with the engine running, as opposed to the shop air doing the supply duties. When I drove the bus home, I noticed the brakes would stop it, but not well. Aslo, another symptom is while backing up to move the bus around in the driveway, an application of the brakes would make a loud "chatter" noise from the front brakes. But, only in reverse. In the process of maintainence, so far I've removed and either replaced or serviced all brake componets on the tag and drive axle. The slack adjusters were nearly frozen on all four of these wheels, and were badly out of adjustment. The steer axle is next for this treatment. I suspect that the adjustment of the front brakes has been neglected as well, and that may indeeed be the cause of the brake chatter whilst backing up. My MCI manual sez that the Immersion Valve needs to be removed,disassembled, cleaned and lubricated every year or 50K miles. The manuals description of this objects purpose goes right over my head-----. I plan on doing that service, but if it's not a possibility of being a culprit in my brake valve mystery, I'll leave it alone untill I resolve the problem, rather that making another variable in the situation (crossed air line or assembly error, etc) The manuals service reccomendation regarding the check valves is to R&R them every 6 months or 50K miles. I think they have never been off the bus. Again, before I remove anything, I want to be certain I'm heading in the right direction. Doing the brake maintaintence according to "Da Book" is a big job, but if it had been done correctly and at the prescribed intervals, I'd be doing something else now.....Thanks for the help | ||
| Chuck MC8 (66.156.56.211) Rating: N/A |
Bluegrass has mentioned a possibility....I marked and replaced the air lines when I did the R&R on the DD3's. One was original and the other a recent(In bus years)&(new when installed, I suppose). I'm sure the factory chamber was plumbed correctly, but the replaced chamber may have had a line crossed and I carefully put it back the same way. I'll take my book and have a close look and will post that result this morning. | ||
| Chuck MC8 (66.156.56.211) Rating: N/A |
OK, I've checked the air lines (On the DD3's) and they are in the correct positions on each side. | ||
| Ian Giffin (Admin) (64.228.55.184)
Rating: N/A |
Hi Chuck, It sounds like you have been thorough with the DD3s but in your original post you said the brake valve "appears to have been recently changed (looks new). It was doing this same thing before I rebuilt the DD3's". Could it be that the brake valve (or fittings) was re-installed incorrectly? As well, have you checked the proper operation of the quick release valve, the relay valve and the two-way check valve? A question to all - would the "immersion valve" have anything to do with whether or not this bus has s-cam or wedge brakes? (Buswarrior, are you there???) Ian www.busnut.com | ||
| BrianMCI96A3 (198.81.26.104)
Rating: N/A |
Not being as familiar with coach brake plumbing as I am with truck brake systems, there may be valves and connections I'm not aware of on a coach, but according to the Bendix truck schematic, as I remember it, the only physical connection between the parking brake valve and the service brake treadle valve, are via check valves. Brian | ||
| Chuck MC8 (66.156.56.211)
Rating: N/A |
Ian, it has "S" cams on the brakes. I'll pull and service the check valves and report what effects that has. I'll also take my air line schematic and check the brake service valve to confirm that its plumbed correctly. I truly appreiciate all the help | ||
| Stan (24.67.44.50) Rating: N/A |
The 'inversion valve' is a double ended valve with a larger piston on one end of a common shaft. This valve moves when you apply service brake to release the DD3 brake. The smaller piston end is connected to the DD3 park port. The DD3 is applied with about 80 PSI and when you apply the service brake pressure to the larger piston the valve switches and dumps the DD3, if the Dash valve is in the release position. This is a simplified explanation of how to release a DD3 brake. BTW if you replace the DD3 with spring brakes you can remove the inversion valve. | ||
| Buswarrior (Buswarrior) (64.229.213.59)
Rating: N/A |
Hello all. Ditto what Stan just wrote above. The inversion valve will not be found on a spring brake system. It is the centrepiece of the "Double Diaphragm, 3 airlines, Safety Accuator" braking system. DD3 for short. As you have already alluded to Chuck, you want to move through the entire system and replace or rebuild it all. Check valves, filters, seals, the works. Your system sounds like it has been poorly maintained, and at this point, I'd just do it all. The design and built-in safety of the system depends on everything working properly, and you have already figured out that none of it or those who worked on it before can really be trusted to have done things properly. A DD3 is able to fulfill the same regulated requirements for emergency braking that a spring brake system does, which is the bus industry's attraction to it originally. To Ian's question, I'm not sure whether anyone has actually used a DD3 system on a wedge brake wheel end, but I don't see why it wouldn't work. Might even be better, from a packaging standpoint since a DD3 has a somewhat tapered profile towards the end, where the spring chamber is fat to the end? DD3's weren't very popular outside of the bus industry, and even inside it, MCI are the only ones who made it standard and kept on with it for so long. The rest offered it as an option. If someone else doesn't beat me to it, I'll write up a functional explanation of the DD3 system features over the weekend and post early next week. Off to Michigan, all hail CCO! happy coaching! buswarrior | ||
| Chuck MC8 (66.156.56.211) Rating: N/A |
In removing the inversion valve this afternoon, I broke it while trying to remove it. The nut holding it onto the bracket had corroded to the breaking point. So, It's off to Atlanta tommorrow for a replacement. The dual air check valve is attached to the Inversion valve, which was my target. So, I did get the check valve removed also, but it will prove costly to the sum of $87.oo for the new inversion valve. Perhaps it was defective anyway. I checked on the possibility of replacing the DD3 chambers with spring brake canisters. At least on my MC8, Theres simply not enough room for the spring brake can. The DD3 chamber nestles very close to the air bag, Shock absorber and the rod for the leveling valve. I would have made that change in a heartbeat. A new spring brake chamber would have cost less than the large diaphram in the DD3. Another suggestion has been made that the push-pull selector could be defective. I'll remove that and service it according to "Da Book" At least I'm getting an education in Air Brakes, So maybe I can help others in the future with similar quandries.... | ||
| Ian Giffin (Admin) (64.228.112.157)
Rating: N/A |
Hi Chuck, Thank you for your answer. The reason I asked was I wondered where the immersion valve was and thought it might be a part of a wedge brake system. But thanks to Stan and Buswarrior, I have a better picture now (thanks, guys!). BW, if we ever get the time to put an Air Brake Course online here, I'll hand over the DD3 chapter to you :-) . Ya learn something new every day, don't you? Regards, Ian www.busnut.com | ||
| Don KS/TX (63.234.100.104)
Rating: N/A |
The DD3 was standard equipment on many buses, not just the MCI. Its far superior action as an emergency brake is what made it popular, a bit more than three times the action when it is panic time, as opposed to the spring brakes, which are hardly more than a parking brake. I guess people are more difficult to replace than a load of dog food. If cheap and less effective is what trips the trigger, by all means change to spring brakes. | ||
| Stan (24.67.44.50) Rating: N/A |
A sort of off topic comment on DD3 brakes. If anyone wants to get some real experience work on a Model 660 Gradall. This is the truck chassis mounted backhoe type of excavator. Not only is the machine operated from the house but the truck can be driven from the operator's position. The turntable sits centered over the tandem axle and all the lines (hydraulic, electric and air) go through a hole in the center of the turntable. On one machine I spent over eight hours trying to find the inversion valve. The eventual repair consisted of changing a shim in the pressure regulator feeding the inversion valve. Busses are probably the simplest and easiest vehicles to work on. If you have the manuals, they have all the line diagrams and even tell you where to find the part. BTW, the Gradall used a DD 4-53 on each end. | ||
| Don KS/TX (63.234.100.8)
Rating: N/A |
Wow. Do you have the ability to send me a photo of it? | ||
| Chuck MC8 (66.156.56.211)
Rating: N/A |
Well, I believe I may have the brake quandry solved... It's the Push Pull valve leaking. I removed it and tested it. Once I get the new unit and installed, I'll report if that fixes it. Thanks again to all who responded. Chuck | ||
| Buswarrior (Buswarrior) (64.229.210.88)
Rating: N/A |
Excellent news, Chuck! I'll save the long winded DD3 explanation for a better time and place. Ian, I'll e-mail you off the board. happy coaching! buswarrior | ||
| Carroll (68.155.52.251)
Rating: N/A |
When I bought my 04 it had both a handle for the parking brake and a push/pull valve. The airlines running to the valve don't look original or even a good copy. The valve is plumbed backwards I think because the positions for brake on and off are backwards. There is also air leaking when the brake is off and continues to leak for however long the vehicle is running. Whats going on with this mess? The brakes will stop the vehicle but not nearly as quickly as maybe needed in the future. Carroll 04 | ||
| Buswarrior (Buswarrior) (64.229.209.151)
Rating: N/A |
Hello Carroll. You've got a parking brake retrofit on your hands, and all bets are off. The old hand brake is the original, the push/pull air valve is the add on. It would be a very good thing if you carefully traced all the lines and confirmed every connection, every valve and every destination for the plumbing, to make sure that all the proper parts, and none of the wrong parts have been installed. Be sure you know what check valves look like, you need to know exactly which model of relay valves have been used and which brake pedal valve. Check that they are appropriate. Bendix is a great source of info. You also want to be sure that proper sized brake chambers have been used, as there are space restrictions in a stock '04 that make a proper spring brake retrofit quite a bit more complicated than just re & re and adding a few air lines. Smaller chambers make for less stopping power. Do you know how to adjust brakes, and to make the coach safe to crawl under? Please post your findings, so we can all learn! happy coaching! buswarrior | ||
| Carroll (68.155.52.251)
Rating: N/A |
At this time in my evolution from rider/driver to fixer of the bus I really don't have a clue what the situation is with the brakes. I had them looked at by a local mechanic who said the shoes looked good and that was all that was said. The brake holds when parked until the air leaks out (leaking beam rt rear) and releases for movement. I have put about a 1000 miles on it and have found all sorts of things that need fixing. Hope to find someplace to park it this winter to do some major repairs on steering components, shocks and airbags, engine oil leaks, etc. Will go over the braking system at that time. At this time I don't have a clue how to adjust the brakes but have read how to block it up. Once I get into this thing I am sure I'll be asking all kinds of questions (probably HELP??). Thanks Carroll 04 |
