| Author | Message | ||
| james dean boggs (Jd_boggs)
Registered Member Username: Jd_boggs Post Number: 146 Registered: 11-2004 Posted From: 71.102.82.199 Rating: N/A |
That scared the cr** out of me! While driving south on hwy 99 in Bakersfield CA. Just had enough time to pull to the right after braking hard to avoid another car cutting in front of me. No it wasn't the S-cam. It was the R8 relay valve. Soon as I relieved the air pressure from the main brake system, it let go until it regained pressure again and locked up again. So, if you're going to break down Bakersfield is great place. There are truck and trailer parts places everywhere eager for your business! PS In my air diagram there is an item called brake modulator. What is it and what does it look like? | ||
| Clint Hunter (Truthhunter)
Registered Member Username: Truthhunter Post Number: 331 Registered: 1-2009 Posted From: 24.129.232.232  Rating: N/A |
not familiar with Gruman, but a brake modulator sounds like the function in the anti-lock system (if yours has one), function is to reduce pressure and prevent lock up by control of the anti lock computer, perhaps not far from the rear axle , with air lines going in & out about the size of a toaster oven. Hope this wild guess doesn't add to your confusion. Perhaps a good nights sleep will see someone that actual knows gruman pipe in. ...A good incident is one you live to learn from ... | ||
| R.C.Bishop (Chuckllb)
Registered Member Username: Chuckllb Post Number: 887 Registered: 7-2006 Posted From: 75.208.81.25 Rating: N/A |
Amen, Clint ! RCB | ||
| Clint Hunter (Truthhunter)
Registered Member Username: Truthhunter Post Number: 332 Registered: 1-2009 Posted From: 24.129.232.232 Rating: N/A |
??? have you got your laptop in church this morning old chucky? Sacrilege "I-a-sayzha", sacrilege ! ??amen, wasn't it one of those egyptians gods, that didn't like "mass transit" or something not trying to sharpen your horns, just seeking the truth... old friend -IF ONLY they had had laptops in the pews in my day's as a unwilling make believer, just might have kept me awake a little longer; but then crowds always had either that effect on me, or I on them!!! ~Once traded a fellow a propane schooly for a unsalvageable generals car, under the stipulation he only use it as a portable church hall (my specification); needless to say he sold it for cash within days of the deals close. That is what eye get's for handing a bus over to a non-bus nut, or so it would seem! live and learn!!! | ||
| larry currier (Larryc)
Registered Member Username: Larryc Post Number: 258 Registered: 2-2007 Posted From: 205.188.116.203 Rating: N/A |
"It let go until it regained pressure again". Sounds like you have a serious air leak on the service side. You should have plenty of air for more than one emergency stop if you don't have a big leak. | ||
| Clint Hunter (Truthhunter)
Registered Member Username: Truthhunter Post Number: 334 Registered: 1-2009 Posted From: 24.129.232.232 Rating: N/A |
...then you might hear/see (spray with soapy water) air escape from the TR valve when in the releases position , assuming you have DD 3 . A little detail would assist in making wild assumptions from my limited "data base of the imagination" | ||
| Chuck Newman (Chuck_newman)
Registered Member Username: Chuck_newman Post Number: 388 Registered: 1-2005 Posted From: 99.153.84.192  Rating: N/A |
James, Not sure if this is the same thing referenced on your air diagram, but the Bendix Air Brake Handbook shows and describes the R-7 Modulating Valve. It is described as having 4 functions, one of which is to apply the spring brakes "should a failure occur in the service brake system". It is designed for spring brake actuator, not DD3. What does the Grumman use? | ||
| james dean boggs (Jd_boggs)
Registered Member Username: Jd_boggs Post Number: 147 Registered: 11-2004 Posted From: 71.102.82.199 Rating: N/A |
My bus has 2 R8 valves and one SR1 valve. Upon further reading another manual it says that the SR1 is there to modulate the spring brake should the service brake fail. But I still don't know what caused the service brake to activate itself while on the road at high speed. I replaced the R8 valve and worked fine all the home to about 250 miles of mostly freeway. | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1672 Registered: 12-2000 Posted From: 76.68.122.101  Rating: N/A |
So you are saying that the brakes stuck on when you made a heavy application? For the learning of the rest of us, how did you determine that it was the relay valve? You want to be sure that the crisis didn't just self clear along with your parts changing, and isn't still present. An SR1 valve, more specifically, will modulate the spring brakes on the rear axle, via the brake pedal, if there is a significant loss of air from the rear service tank. It is controlled by a signal line from the front part of the dual brake system. The coach will stop as normal, via the brake pedal, and the driver is none the wiser, the low air alarm blaring away, you pull over and stop, unaware what part of the machine actually did the stopping. happy coaching! buswarrior | ||
| Tim Brandt (Timb)
Registered Member Username: Timb Post Number: 399 Registered: 10-2003 Posted From: 66.165.176.62  Rating: N/A |
Just as another data point when I first got the Flx I had a situation where the front brakes wouldn't release after an application. I had to trigger the ICC valve to remove presure from the front side of the system to get them to release. In my case it was a bad treddle valve | ||
| james dean boggs (Jd_boggs)
Registered Member Username: Jd_boggs Post Number: 148 Registered: 11-2004 Posted From: 71.102.82.199 Rating: N/A |
Buswarrior, Q:So you are saying that the brakes stuck on when you made a heavy application? A:Yes. Q:For the learning of the rest of us, how did you determine that it was the relay valve? A:I don't know it was the relay valve or the treadle valve. That's what I'm trying to determine. I could still have an unsafe situation and not know it. I would like to know. I know it wasn't the spring brake because it was compressed by air and I could tell because I tried to push the bolt into the hole to compress them. They were already compressed. Q:You want to be sure that the crisis din't just self clear along with your parts changing, and isn't still present. A: Correct | ||
| larry currier (Larryc)
Registered Member Username: Larryc Post Number: 259 Registered: 2-2007 Posted From: 207.200.116.13 Rating: N/A |
Compressing the spring brake with air takes care of the emergency side unless the air pressure drops below the strength of the spring. Does it hold air on the service side when you hold the brake pedal to the floor, with the brakes released, or is it dumping your air? If it's dumping your air, (service) then it will set the emergency side when the air gets low. Thats kind of what I thought you described. Sometimes the spring breaks and you can't push a bolt into the hole! If you break a spring a piggy back can be dangerous to replace even if you are used to working around them. A broken spring also often pokes a hole in the service diaphram, sometimes setting up a senario something like you have described. | ||
| james dean boggs (Jd_boggs)
Registered Member Username: Jd_boggs Post Number: 149 Registered: 11-2004 Posted From: 71.102.82.199 Rating: N/A |
Larry, I may have a broken spring. When I tried to push the bolt in the piggy back spring I noticed that one side had the holes miss aligned and could not get the bolt inside. I'm going to stick this camera I have into the whole and see what caused this problem. Yes, the service brakes hold air when the treadle is pressed. But I cannot tell if it exhaust because I can only hear the front brake exhaust. I have heard that these coiled springs have lots of force. One mechanic told me that he had one go through the ceiling tiles at the shop. (Message edited by jd_boggs on August 11, 2009) | ||
| Clint Hunter (Truthhunter)
Registered Member Username: Truthhunter Post Number: 346 Registered: 1-2009 Posted From: 24.129.232.232 Rating: N/A |
...ain't them little camera thingys handy as snot; I had the shop picked up the snapon electic model with the narrow head, last year! +so handy for so many diagnostics problems , especially chasing leakes and lost parts where you can not get your eyes or old mirrors. Still kind of expensive, but then so is pulling the head to peak at the valves or cylinder wall on just one modern day crap mobile (cars & light trucks which are design to not be work on, but go together well on the assembly line) | ||
| Clint Hunter (Truthhunter)
Registered Member Username: Truthhunter Post Number: 347 Registered: 1-2009 Posted From: 24.129.232.232 Rating: N/A |
RCB: dearest old chucky my friend, in public response to your private email , responding to my public request,a few post ^up: -you typed " Not real sure what I said to you to deserve the public lambasting, but ...have it you way, friend!" & " Sorry you took such strong offense at an Amen.....By the way, how are you doing re my "challenge"? ending with I am still praying for you...and that, is a promise. )!! Your BNO "friend???" RCB" = yes I asked you once in private , and once on board & now above I have told you not to include me as your prey or in your prays a few posting above .^ + Having told you this on the board, it would seem I own all readers closure on this subject , if I read your email correctly, that they may get on with more pressing bus business, as some atheist might chose to politely express about keeping a bus in working order , you do your praying then, your way & let me continue fixing the bus, my way (or was that rowing to shore my way). >anyhow, many many times in life I failed to help believers of many things, gods, devils, deities and well about all things make believers are told to imagine & forced to believe, I always respond with the same thing : I am not your prey , nor any group you might desire to subjugated into your flock of sheep, then later into wolf in sheeps clothing, nor those that actual may willing concur with your beliefs; as it is my will not to be forced into a corner, only to become a hunter of predators by those that would treat me as there prey, upon realizing that I was only able to truthfully not give them mutual confirmation through capitulation & conversion into there flock. < If others, anywhere or anytime are of the will to be self emancipate or conversely willing to endure your thoughts & beliefs, even to willing have your thoughs & beliefs become theirs, then that is truly there will, not mine & not yours, then that is thier way. So if you chose not too follow your gods way (amen ray or what ever you call it)and respect all others free will , well then your whole gig falls apart in the face of truth. I decline to be use as a part of that. I hunt only truth , not belief. Final appeal in your good books venaculer: ~I am neither hot nor cold, so don't be puting your god's mouth upon me,I be not food for your belief or your god. ~~ I am trying to retire from the god hunting habits & stick merly to hunting for the truth... but if there be even one that intends to feed me to there god or any such notion, well then you do so without my consent or respect, though in the end , regreatable with my resiprocity your sincerily & peacefully clinton hunter my deepest appology to all other bus nuts that had to get pulled into this none bus bussines nonesense. May it not happen again! | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1674 Registered: 12-2000 Posted From: 76.69.143.97 Rating: |
A broken spring would only put the brake on weakly on that wheel end, maybe a little pull to one side, maybe not.. However, you need an air leak out of that chamber to explain an unintended brake application, and it wouldn't go away by itself, and a broken spring doesn't apply very hard. Continue the unrelated investigation into broken springs, but I'm thinking it isn't the culprit. Spring chambers are cheap, how old are they? preventive maintenance justifies putting a fresh pair on, dispose of the old ones properly! If accidentally let go, they'll go through a cement block wall, never mind the ceiling tiles Also from a preventive maintenance standpoint, why not change out the treadle valve too and that can be ruled out also? Sticking internals are just another symptom of an old valve, and it cannot be returned to anything that might be called reliable in busnut service without taking all the time/tools/materials to tear it down and rebuild it. Cheaper to replace. When will it stick again? Busnuts, as they can, should work through the coach replacing the air system components that have unknown ages in order to freshen up air retention and maintain reliable service. For an important system, a relatively cheap investment in the driveway versus a roadside di$ablement. happy coaching! buswarrior | ||
| larry currier (Larryc)
Registered Member Username: Larryc Post Number: 260 Registered: 2-2007 Posted From: 205.188.116.203 Rating: N/A |
JD, If you get some help, check to see if the drivers are releasing air after application. Maybe you have a bad Quick Release Valve holding the shoes on after you release the treadle. You can just watch the slacks and if they are releasing right away the QR is OK. | ||
| james dean boggs (Jd_boggs)
Registered Member Username: Jd_boggs Post Number: 150 Registered: 11-2004 Posted From: 71.102.82.199 Rating: N/A |
Larry, Buswarrior, all The QRV was replaced 2 years ago. The old part looked original to me same for the SR1 which was replaced this past trip. Both R8 relay valves were replaced 4 years ago and now one was replaced again this last trip. As for air leaks, tanks will hold 120 psi for months. I will check the slack adjuster movement after releasing the brake treadle. Question: Is there only one QRV for both front and rear brakes? Or does the R8 relay valve have QRV function built in? PS The springs in the brake cans are NOT broken. I saw them with this fiber optic cable light and viewer. BTW Thanks to all who have helped me along. Planning a trip from Southern California to Portland OR and would like to drive this old bus with some confidence. hehe | ||
| Clint Hunter (Truthhunter)
Registered Member Username: Truthhunter Post Number: 349 Registered: 1-2009 Posted From: 24.129.232.232 Rating: N/A |
MCI specified disassembly of TR valves needing service once per year, inspect and wash internal part as regular service in my 1975 MC 8 service manual PM schedule if I recall. - This may not translate to your gruman directly as this was specified for pre nineteen-eightys 0-rings , with air dryer system. Yours is much newer, so two years ago and 4 years ago may or may not be considered brand spanking new in your application. You may not be wise to rule out those parts as possible problems. Do the PM as scheduled & in the process you will likely element some more doubt, if not find the most likely cause. + but might be of noteworthiness for others that will read this thread in the archives, in the future. ... Brakes are not a option , unless perhaps you have one of those rocketfied coaches or hover buses "they" are flogging stock shares for ... | ||
| larry currier (Larryc)
Registered Member Username: Larryc Post Number: 261 Registered: 2-2007 Posted From: 207.200.116.13 Rating: N/A |
JD, I prefer R6 valves because they are simple and I understand them. They work good too. An R8 may be able to exhaust like a QR, I don't know. The Bendix book shows 5 different R8 valves and 2 of them leave the factory without an "exhaust cover". The book also shows a 6th valve a R8P that looks like it has a built in porportioning feature. No matter where the release of air is comming from, if the slacks bounce right back when you release the brakes, you should be OK. The last time I had a bad release valve issue, the brakes acted like I dynamited them after application and continued to drag until the air could escape the diaphrams some other way. Not everyone likes airbrake alcohol, but I have used it without issues for many years and it is great at keeping valves clean and working in my personal opinion. You should also check all of your air tanks for water if you haven't already done that. |
