I finally figured out where the air leak is coming from on my bus..
if you look at pic below it is coming from the black thing in the middle.. yesterday when under bus I had my hand on it and the black area is rubber and is easily movable, looks like a release valve or something.. does anyone know exactly what that does and can it be fixed or do I need to replace entire blue thing?
(https://busconversionmagazine.com/forum/proxy.php?request=http%3A%2F%2Fwww.impaks.com%2Fimages%2Fken%2Fbus%2Fimg_1985.jpg&hash=6c09e54954c733afccd106bb8649a7ce68f4c48d)
If I'm not mistaken, that is a brake valve (E-10 maybe?). I replaced mine because it was leaking there also.
It still leaked afterward.
Turns out this leaking may indicate a bad brake diaphragm.
On my bus it looks like one or both drive axle brakes (brake cans) need to be repaired. That is my next big project.
If you search my name for posts, you can find a discussion on troubleshooting.
Hope this helps.
Steve
Your parking brake was still applied? No service brakes applied? Bob
As mentioned, I believe that that valve will exhaust air from an internal system leak like a bad diaphragm.
yes bus is parked with parking brake applied.. bus will not air up over 80psi
If you suspect that the relay valve is the problem, you can take out those four screws you see in the bottom. The interior parts can be removed and cleaned. There is a chance there is some crud in there causing the leak. Dump all your air first and chuck your wheels. Put blocks under the body so it can't come down on you. If it leaks really bad when applying the service brakes, it's most likely a diaphragm in a chamber. They are pretty easy to change yourself.
As for not airing up past 80lbs. Does the compressor cut out or does it just not go past that even if the compressor is pumping? If the compressor is still pumping, I would suspect a very major leak in the auxiliary air system. The valve for that opens somewhere between 65 and 80lbs.
Don and Cary
That is the E-8 Rely Valve. Like above check your brake diaphragm in the rear by carefully clamping each air line to the brake can off to see if the leak stops. If it does then it is a brake diaphragm. If not it is probably the valve. It can be rebuilt but for the price just get a new one. It will last as long as you have the bus most likely. I just replaced mine about 58.00 NAPA ;D
Dave5Cs
Do you have the part number ?
Rear brake Relay Valve - R-8 on a 5C
Page 4.1101 March, 1981 Parts manual
4R-11-1
Might check with your supplier to see if there has been an upgrade for the MC 9
Looks the same in the picture with the same amount of hoses etc.
You might also check your regular next to it and your inversion valve. I replace all just in case.
Dave5Cs
There is a chance that there isn't anything wrong with the valve. I would make sure it isn't something else first. Those are a bear to change. We chased a leak on that valve only to find out we had two leaks from someplace else that showed up at the valve. It doesn't look all that old in the picture. The little rubber is even still there.
Don and Cary
As noted, don't go changing parts until the diagnosis has been properly done.
None of us appreciate when the auto mechanic throws parts at our cars as a diagnostic effort, why would we throw parts at the coach?
Confirm or deny that the brake chambers are bleeding air back and out the exhaust on that relay valve.
The black rubber disc is to keep the insects out of the valve internals. Beware the mud building wasps, no disc, they'll plug it solid inside and you get functionality trouble with the service brakes. I've seen them plug 1/4 turn drain valves on tanks and opening the valve won't blow the nest out. Solid as cement those nests.
The exhaust is normally open on a relay valve, so any air in the service portion of the chamber can escape, but if any air leaks into the service side from the parking side, it shows as a leaking relay valve.
Relay valves are also capable of leaking internally on their own, as they are supplied with tank pressure for their job of applying the associated brake chambers when signaled pneumatically by the brake pedal.
And pay attention those with spring brakes, you can get the same symptoms, not just the DD3. A spring chamber can leak down the shaft seal into the service portion. The DD3, it will be the parking diaphragm leaking through.
happy coaching!
buswarrior
so been getting dirty laying on the ground under bus with not much luck..
I have read threw the manuals and the pictures are terrible..I can not find any other leaks and to be honest I can not see any other issues with brakes etc.. it does make sense that it is related to brakes, because I rev'ed up bus and it aired up and once I released the parking brake the bus could hold air pressure find and would actually air up to the point the front air regulator would let air out once it had full air..
so it is related to brake system..
so what should I look at directly? do you have any pics of areas to look at ? thanks
Okay, if I have this right, it only leaks when the parking brakes are applied. As I understand it, that would point to a bad parking brake diaphragm on a DD3. Do you have DD3's?
yes only when parking brakes applied and yes DD-3
Might want to check the park brake push/pull valve also. It feeds the air to the parking diaphram.
Those diaphrams are so easy to change. If you have any questions as to their age, why not just change them out? Half hour each. It's so much easier to do at home than on the road someplace. You can't believe how much air lose you can fix changing them even if there doesn't seem to anything wrong with them.
Don and Cary
so here is a question?
I got under bus to remove DD3 and I can not get to the one of the top bolts that holds the DD3 to chassis.
I can get all bolts off etc but the one bolt that is close to the tire I can not get off.
are you guys taking off your tires to remove the DD3?
thanks
ken C
On my 4905 I was having air issues and after fixing the governor problems it still didn't always air up past 90 psi. Sometimes I could hear the leak under the the front, at other times it was quite. Turned out to be the push/pull parking valve right beside the driver, exhaust was plumbed straight down thru the floor. Sometimes leaking , sometimes not. Replaced the parking brake valve , no problems since.
Mark
Sent from my iPad using Tapatalk
Yes, you need to pull off the tires to work on the DD-3's on an MCI. Carefully inspect all the hoses - if you are going to do some rebuilding, may as well do them too if they need it.
Brian
well tires had to come off and pulled dd3, put new parking brake diaphragm in it and put it back on and the thing still leaked :(
so had to order a new one and replaced it and bam air leak fixed and bus now airs up to full pressure :)
Did you replace the diaphragm with a second one, or get a new DD3?
Brian
Why would you want to take the DD3 off? We changed the diaphrams with it on. Taking hoses loose is just asking for more leaks to fix.
Don and Cary
Quote from: bevans6 on April 11, 2013, 09:28:50 AM
Did you replace the diaphragm with a second one, or get a new DD3?
Brian
Could not get dd3 open easily on bus. And this was my first one so i took it off and replace the parking brake diaphragm. After putting it back on had more leaks. So I replaced entire dd3 with a new one. Had to also twist caps due to air lines not meeting up correctly on new one.
MCI mounts have very little room to work, taking the can off is about the only possible way to do a quality job. There is barely enough clearance to get them out. Mine were very crusty and when I took them apart for inspection many little parts in the locking mechanism were failing, about to fail, or just plain broke on disassembly. I put two brand new ones on. Oddly, the old ones were still working perfectly but the rubber boots were missing, the shaft was a little pitted and the hoses were shot so I needed to service them at the very least. As it turned out the aluminium castings were very corroded and were not even good as cores. About the only parts that were good were the diaphragms...
Brian