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Bus Discussion => Bus Topics ( click here for quick start! ) => Topic started by: richard5933 on November 29, 2020, 11:23:57 AM
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Went out today to air up the bus with the shop compressor and check on a few systems, only to hear a new hissing sound after I was done. It's normal to hear some suspension venting up front as things even out and find their level, but now I'm hearing a leak coming from the rear axle area. Oh oh.
I did the best I could to check things out with my limited abilities right now. I was able to slide the jack stands under the bus and slide under enough to listen more closely, and the leak doesn't appear to be coming from either of the brake canisters from what I can tell. Sounds much more like it's coming from the center of the bus, around the area of the air tank back there. Lots of other things that it could be, including what looks like miles of air lines and a few valves. Or maybe the tank itself.
I did my best to check for obvious cracked air line and didn't find any. Also checked the function of the brakes, and they appear to be working right now. The compressor can overcome the leak pretty easily at idle, so I'm pretty sure it can make it to the shop on its own, but it really isn't ideal.
Any thoughts?
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Plastic dip the entire bus?
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Plastic dip the entire bus?
Huh??
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Does it change by applying or releasing the parking valve? I would suspect leaking out the bottom of the relay valve exhaust port. Bunch of valves there. All mounted to a plate. Relay, inversion, check valves, qr valves. I know because I rebuilt or replaced ever one of them 2 years ago. Nothing like a pit for that kind of work.
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Take the bus for a drive, 2 hours, 100 miles, before emptying your wallet...
Sitting is no place for a bus and its air system.
On your return, report back that silence has returned to the Ponderosa?
Happy coaching!
Buswarrior
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Does it change by applying or releasing the parking valve? ... Nothing like a pit for that kind of work.
Best I can tell is that it leaks with the parking brake applied. With the brake released it doesn't appear to be leaking, at least not that I can hear.
However, I think I can also hear something when I depress the service brake pedal. Not sure from where though, and no one was home to help at the time. The brakes do work, so for now it's driveable.
I'm still recovering from surgery, so my ability to crawl around under a bus working on things is minimal. I'm thinking that if the shop can get it in this week I'll take it up there for them to put on the rack and inspect, at the least. It's about 40 miles away, so if driving will help things then maybe it'll be better by the time I get there. If not, then I'll let them check out and tell me what's going on. The guy there is familiar with DD3 brakes, so hopefully he can get things sorted out and diagnose.
Pit? Sure do wish I had one right now. Indoors even better.
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It's at the shop. They were able to get it in right away and hopefully it will be back home before the snow begins to stick.
Pressure held fine during the drive, but once at the shop and shut off the pressure dropped from 120 to 90 in just a few minutes. That would normally have take overnight to happen. Now the waiting begins, but at least it's there and not broken down in my driveway.
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heres some pics of mine
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more
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if your plumbing is the same as mine, there are two relay valves. the one at bottom of vertical tank controls the service brakes and the one on upper left side controls dd-3s and lock ports.
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due to your coach age, consider new dd3 diaphragms. Not that costly.
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The leading theory right now seems to be leaking diaphragms in the parking brake side of the DD3 brakes, at least in one side. Luke agrees. Guess we'll see.
If it is the diaphragms, I'll probably have the shop do both diaphragms on both sides and be done with it.
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That is what was leaking on mine that got me into doing it all, including rebuilding the dd3's. Luckily yours is in nice shape with low miles.
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Yeah - the DD3 canisters themselves appear to be relatively clean and in good condition with most of the original paint in place. I'm sure that servicing them with new diaphragms won't be that difficult of a project.
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Pretty easy actually. No giant spring to take your head off, just a lighter pressure one.. Good idea to lightly lube inside of clamp V's with some antiseize so they can seat nicely when tightening the little bolts, which, of course should receive some also.
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Sounds like I might have escaped major problems this time... They're thinking it was just a faulty tank drain check valve.
Will know more tomorrow.
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Great!! More money to spend on other things : ;)
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Funny, I had a pull cord one on the 4104. It developed a pinhole through the ball. Had to be a mfg defect.
Glad you got lucky...this time🤫
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Even funnier is I only had this drain valve replaced three years ago when I got the bus. Guess not even new parts are any guarantee against issues like this.
They're going to give the entire system a close look tomorrow to make sure that the tank drain leak isn't masking another problem. Hopefully this is all there is.
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Further update...
Back of the bus appears to be holding with just the tank drain valve being replaced. No problems with the DD3 chambers. However, I wasn't crazy when I said I thought I heard something up front with service brake application. Both front chambers are leaking. The fun never stops. The shop is working with Luke right now to get the parts to them.
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The maintenance manual indicates that the front diaphragms should be replaced at 100,000 miles or annually. No reference made of a schedule for replacing diaphragms in the DD3 chambers. Not sure if it's wise to service the rears right now as a precaution or to wait. Either way, I'm going to have Luke send the parts so they'll be on hand whenever necessary.
Also, when the tech initially reported the need for front chambers/diaphragms, he made a comment that one of the front chambers had two air lines going to it. Luke is not sure what he means? I'll have to drive up there this afternoon to see for myself.
Anyone know of a GM front chamber that has two airlines? I'm thinking he's seeing another air line in the vicinity, not one going directly to the chamber. Always something, isn't it?
Edit...
Apparently both front chambers are the same. Must have been a communications mix up or something.
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Glad I had the forethought to have Luke send all the diaphragms, not just the front. After the front were done and sat overnight, the shop called to let me know there is a leak in one of the rear diaphragms. Now they're going to be changed out and hopefully I'll be good to go for another few years, at least. Will feel much better knowing that the diaphragms are all new and (hopefully) up to the task at hand.
Also glad I've got a shop that I trust to do the work and that's actually willing to break open a brake can and replace the diaphragms.
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Spring brakes are the only chambers that can hurt you,that spring can bite you big time
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Spring brakes are the only chambers that can hurt you,that spring can bite you big time
Guess I was thinking more about shops that are into just replacing parts nowadays instead of rebuilding things, whether from lack of skilled techs or liability issues. Jack has been working on buses for 40+ years from what I've heard, so I'm sure this is not the first set of DD3 cans he's ever opened. May have been a few days since the last one though.
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Guess I was thinking more about shops that are into just replacing parts nowadays instead of rebuilding things, whether from lack of skilled techs or liability issues. Jack has been working on buses for 40+ years from what I've heard, so I'm sure this is not the first set of DD3 cans he's ever opened. May have been a few days since the last one though.
He probably has open a few DD3 chambers in his life lol I was throwing out some old paper work and seen a bill for a set of diaphragms for the DD3's the set (2) cost less than 6 bucks in 1983 times have sure changed since Bendix dropped support of the DD3's ,if they ever do need replacing you can install spring brakes on the 4107 and 4108 MCI guys are not that lucky
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Guess I was thinking more about shops that are into just replacing parts nowadays instead of rebuilding things, whether from lack of skilled techs or liability issues.
OR cheaper to swap parts. #1 reason
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OR cheaper to swap parts. #1 reason
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So true it adds up at over a $100.00 per hour shop rate to rebuild parts
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DD3 cans are not cheap, so even an hour or so each is still cheaper. I've had some things rebuilt over the years that would have been cheaper to replace just because the OEM parts were better than the current production replacements.
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DD3 cans are not cheap, so even an hour or so each is still cheaper. I've had some things rebuilt over the years that would have been cheaper to replace just because the OEM parts were better than the current production replacements.
Only new DD3 chambers you can buy now are aftermarket made who knows where for 600 bucks ea,spring brakes are around 100 bucks ea and all truck stop carry them
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He probably has open a few DD3 chambers in his life lol I was throwing out some old paper work and seen a bill for a set of diaphragms for the DD3's the set (2) cost less than 6 bucks in 1983 times have sure changed since Bendix dropped support of the DD3's ,if they ever do need replacing you can install spring brakes on the 4107 and 4108 MCI guys are not that lucky
I thought there was a clearance problem putting them on the 4108?
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I thought there was a clearance problem putting them on the 4108?
There is with some models of spring brake but you buy the spring brakes with the rotatable chambers and they clear,MGM was supposed to start manufacturing a direct replacement for the DD3 before the CV-19 hit
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currently, none will work on 4107, 8, 4903 and on up. Not enough room without body clearancing. Even if they would fit, the caging bolt would hit the bulkhead. Also the plumbing would require some significant rework that would be beyond the general owner or shop.
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I installed spring cans on River Bill's 4905A 6 years ago the cage bolt is a simple deal and the plumbing is just reversing the air supply with 2 lines from the brake relay just like you do on a 4106,The MaxiBrake spring brakes from a older R600 Mack Truck are easier if you can find a set
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Final chapter of the saga...
The original problem was a failed tank drain which I had the shop install about three years ago. This is on the rear tank which is mounted above the rear axle and not accessible at all without getting under the bus. They installed the drain with a pull cable. Worked great until last week.
They replaced the drain valve, and then went on to replace the diaphragms in all four brake cans since they were leaking as well. Everything was great and the bus held air all weekend. Then I picked it up this morning and drove it home. Then that new drain valve proceeded to leak even worse than the first one.
Took it back. Apparently the tank drains being made in China have a sketchy track record. New valve installed, and it appears to be good for now.
Question...
With that tank being above the rear axle, was it ever intended to be drained daily? No way to get to it without a pit, and I seriously doubt that these buses were all put on a pit daily. Am I to assume that this tank was not intended to be drained other than when in for service?
The rest of the repairs (diaphragms, etc.) went without a hitch. The original diaphragms are actually in good shape and could probably have been reused. The problem with the brake cans was solely due to corrosion on the mating surfaces of the cans forming leaks where the diaphragm mounted. New diaphragms were installed for good measure though, after the cans were given the once over and had the mounting surfaces cleaned.
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My bus came with a rebar T handle that the PO made for reaching in to drain the tanks. It worked but i never cared for it so put cable pull drains on all of them.
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I replaced all my pull drains and installed small 4"-6" pull cable loops that I can get at with the old awning rod . even the drain between the drive tires if I reach through the tag and drive opening . works every time . so yes I can drain all the drains from standing beside the coach with the help of the awning pull rod . no squashed bus nut to drain the tanks
dave
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I'm surprised you haven't installed an air drier yet.
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No air dryer yet. Not sure when. I asked at the shop today when I picked up the bus and the answer was pretty much there was no immediate need unless I was going to start traveling more in freezing weather. Otherwise just keep draining daily.
All my tanks have accessible drains except this one over the rear axle. That's why I had them put the pull-cable on it so I can drain it safely.
Still confused as to what the plan would have been for this bus in revenue service. Clearly they didn't intend for every bus to be put over a pit every day to drain this tank, so how/when was it drained?
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The wet will be in the wet tank, the rest should be dry.
First tank after the compressor.
I doubt you get anything out of the rest?
Happy coaching!
Buswarrior
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The wet will be in the wet tank, the rest should be dry.
First tank after the compressor.
I doubt you get anything out of the rest?
Happy coaching!
Buswarrior
Thanks - that's been my experience so far.