| Author |
Message |
Jack Conrad (Jackconrad) (207.30.189.17)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 23, 2002 - 7:55 pm: | |
I can feel/hear air leaking from exhaust port on service brake application valve when parking brake is applied. No leak when parking brake is off. Service application valve is less than 1 month old. Any suggestions where to check for problem? Thanks in advance, Jack |
dougthebonifiedbusnut (24.218.119.24)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 23, 2002 - 8:18 pm: | |
it sounds to me like you have a leak in one of your diaphrams if you are going to service the spring brakes yourself be sure you know exactly what you are doing if you dont have someone else do it the spring brakes are under tremendous spring pressure and will do you damage if you dont know how to repair them |
George Myers (12.85.13.196)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 23, 2002 - 9:22 pm: | |
~~~~~~~~~~~~~~
March 23, 2002
Do I read you correctly???
I can feel/hear air leaking from exhaust port on service brake application valve when parking brake is applied.(All air to the spring brake is released and the spring has applied the brake)
No leak when parking brake is off (Air applied to cage the spring)
If this is correct, check to see if you have an SR-1 valve. This is about 4 inches across and installed in the line between the spring brake control valve and the spring brakes. Unless you have a DD-3 parking brakes, It is the only place I can think of where air pressure, a line to the treadle valve, and a line to the spring brakes are all in the same place when the air is dumped to lock the parking break.
If I do not read you correctly, (it leaks then air is applied to release the spring) it probably is in the seal between the air chamber for the spring brake and the air chamber for the service brake. Remove the hose for the service brake and listen.
You did not say what kind of coach you have and I do not remember. If you have DD-3 parking brakes, the problem is probably in one of the chambers. Remove the service line to each chamber and see if that is where it is.
George Myers |
Jack Conrad (Jackconrad) (209.26.42.60)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 24, 2002 - 7:04 am: | |
I guess I should have mentioned that this is on a MC-8. and the leak is when parking brake is applied with no service brake application. If parking brake knob is pushed in, leak stops. Thanks for suggestions i have received so far. |
George Myers (12.85.0.134)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 24, 2002 - 10:16 am: | |
There are other valves used between the spring and service brakes. Since your leak only occurs when there is NO air pressure on either the spring or service brakes, you need to find another source. Looking through the book, the SR-1 Spring Brake Valve is the only one I can find. |
dougthebonifiedbusnut (24.218.119.24)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, March 25, 2002 - 7:35 pm: | |
jack please dont be offended but i just want to know what you mean by the parking break is applied do you mean when the button is pushedin or when the buton is pulled out |
Jack Conrad (Jackconrad) (204.193.117.66)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, March 25, 2002 - 7:58 pm: | |
No offense taken. When parking brakes are applied (Knob is pulled out) As soon as knob is pushed in (parking brake released) leak stops. I am going to check "cans" on drive axles, inversion valve and relay valve next weekend, when I have time. I will post if I find problem. Jack |
Don KS/TX (205.187.92.4)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, March 26, 2002 - 5:52 am: | |
I had a similar problem on my DD3 equipped bus. After using wheel chocks to park and having people tell me it was various valves, I found it was only a cheap and easy to replace parking brake diaphram in a rear wheel DD3 chamber. When the parking brake valve routes air to that diaphram, it leaks thru the diaphram and comes out somewhere else. |
Roger Jendrusina (Rogerj) (67.217.14.125)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, March 28, 2002 - 7:34 am: | |
Jack,
I also hear some leaking from the park brake valve when the knob is pulled out (brakes applied). But my leak is from the stem on valve. If I move the knob a small amount it will stop.
Roger
4104-Michigan |
Steven Gibbs (12.148.43.8)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 04, 2002 - 6:25 am: | |
I have also discovered air leaking at the push/pull (parking brake) valve and at the exhaust port on the service brake valve when the parking brake is applied. Now I know why my air drops off so fast when I shut down.
I also seem to have some air leaking out of the parking quick release valve.
When I move the valve stem on the push/pull valve I can stop the leak while I hold it but the quick release valve starts to vent.
I was just about to order a reman push/pull when I reread these posts and now I think that air is coming back some how from one of the DD-3's. I will check this out before I proceed and post my results.
Jack,
Looking forward to your results also.
Thanks,
Steve
MC-9
Pontiac, MI |
gatorbusman (64.12.106.52)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 04, 2002 - 7:59 pm: | |
Mr Conrad,Jendrusina and Gibbs. All three of you have a failed parking brake valve. The exhaust port of the valve is plumbed into the secondary (front) brake circuit. It is there to provide for an automatic release of the DD-3 chambers lock mechanism should someone apply the foot brakes without releasing the parking brakes. This prevents the DD-3 chambers from being applied so tight that they might not release.
The air inlet seat of the parking brake valve has failed and air will leak from the bottom of the foot service (treadle) valve, and if it is a bad enough of a leak, the front brake quick release valve. If the parking brake valve is still in the position the factory installed it, you will find it to be plumbed with copper line and the fittings can be a little hard to deal with. Suggest you loosely connect all lines to the new valve before you secure the upper retaining nut.
There is no direct connection from the treadle valve to the drive axle service portion of the
DD-3s on MC-8 and later model coaches. The air signal goes to a relay valve, which in turn operates the drive axle service brakes.
Easy way to see if the parking (auxilliary) diaphramn is leaking, air will probably be leaking from the exhaust port on the relay valve,(its the large valve directly above and in front of the differential) with the parking brake on/set, just use a large pair of Vise-Grips or Channel Locks and gently squeeze closed the large center air line to the DD-3s one at a time. When you squeeze one and the leak stops, that side DD-3 needs some attention. Look forward to seeing a notice of your success! Good Luck!!! |
Don KS/TX (205.187.92.86)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, April 05, 2002 - 5:01 am: | |
Hey, excellent post Mr Gatorbusman! First time in quite a while I saw that explained correctly and in understandable terms.
I am trouble shooting what I think may be a problem, can the relay valve fail in such a way as to NOT allow full application pressure to the rear brakes? My braking on a 4905 with DD3 has never seemed to be up to par and I suspect that to be the problem, that I am mostly using only front brakes. (I know, just put a pressure gage on it and find out, but I am old and stiff and only want to crawl under there once) |
Gatorbusman (152.163.204.193)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, April 07, 2002 - 9:28 pm: | |
Don KS/TX
Yes it is very possible for that type of failure to occur. Caused by accumulation of gunk and hardened lubricant under the operating piston. limiting piston travel. Also have seen where people have their coaches repaired in a truck shop and the incorrect type relay valve was installed. Relay valves can have up to a 14psi differential between control line pressure and delivery pressure. This differential is because some valves have a spring installed under the main operating piston. All of the external casting numbers and such will be the same across all of the valves from the same manufacturer. The small metal tag attached to one of the bolts on the cover of the valve will have the specific part number of the valve. With that number, a competant parts person can tell you if you have the correct valve in-hand. I can sympathize with the old and stiff part, but there is no sustitute for a little detective work, call me lazy, but I like to do the job correctly the first time, I've got other projects to throw my money and time @ |
Steven Gibbs (12.148.43.7)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 08, 2002 - 7:03 am: | |
Gatorbusman,
This weekend I traced the problem back to the anti-compounding port on the parking brake valve. Removed the valve and tried to clean and replace o-rings. Still leaking so new (rebuild out of stock) one is on order from MCI.
Your post confirms I'm on the right track.
Thanks,
Steve Gibbs |
evolution custom coach (Mcibus2002) (63.188.38.73)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, April 19, 2002 - 1:45 pm: | |
justed fixed a 1974 mci 8 with the the same problem we only had to replace the parking brake valve and it solved the problem. |
mcibus2002 (63.188.38.73)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, April 19, 2002 - 1:46 pm: | |
just fixed a 1974 mci 8 with the the same problem we only had to replace the parking brake valve and it solved the problem. |