Air Leak up front - What is this?

Tikvah · July 05, 2011, 05:23:59 AM

I started the bus this weekend after sitting many months. I have a significant air leak up front, in the spare tire bay.
For reference, this is a 1989 MCI-102 A3 with a 6V92

The leak is coming from this gadget in the pictures.
The first picture is looking in from the front bumper, the second picture is the actual unit that is leaking. The leak seems to be coming from the base of the unit, where the round rubber thing is.

What is this gadget? And, how do I fix it?

Dave

rwc · July 05, 2011, 05:25:49 AM

Don't see any Pictures.

robertglines1 · July 05, 2011, 05:32:57 AM

Your two problems could be related. That is you brake activation system. It has a plunger going in the top from the foot pedal. Get it freed up and it may clear up also effected by parking brake operation. first things lets get brake pedal freed up and roller/plunger on top freed up. /un stuck

robertglines1 · July 05, 2011, 06:16:13 AM

WD-40 is Water Displacement -40 is that plus a little lube was intended to push water mainly out of the situation- has been used for everything. By my self also out of connivance. A better lubricant for freeing up stuck parts and lubricating like PB Blaster or a Silicone Bike Chain spray might be better in this application. Any other suggestions ?

Highway Yacht · July 05, 2011, 01:01:08 PM

Dave... My brake application valve is also leaking at the little rubber flap. I was told by several people that it was a bad rear park brake diagram causing the air leak. Seems the air escaping through the bad diagram will find its way back out through the application valve that you have pictured. I know I can park it on level ground and scotch the tires, release the park brakes, and the escaping air will stop. You might also want to perform that test and see if the leak stops when the park brakes are released. Just make sure you have it on level ground and the tires scotched so there is no chance it will roll.

Jimmy

Tikvah · July 05, 2011, 01:22:20 PM

Jimmy,
I assume you must mean that the rear system can "back-feed" to the front and force air out the "Brake application valve???" in the front?

Actually, when I moved the bus this weekend, I was loosing so much air that I had to keep my garage compressor attached to the coach to release the brakes and move the bus. When the park brake was released the air continued to leak.

I have pressurized the bus a few times in the last couple of months, but never with the engine running. I simply connect my compressor. That allows me to use my air door, baggage bays, etc. But, this is the first time I've leaked air that quickly.
Just for information, I have never been able to hold air very long, but could never find any significant leak. This time was different, the air leak is significant and the large garage compressor worked hard to keep up.

I'm all ears if anyone can contribute to this.

JackConrad · July 05, 2011, 03:58:56 PM

Clamp the rubber air lines one at a time on the drive axle brakes and see if the leak stops. When you clamp a line and the leak stops, let us know which line and we will tell you how to repair the problem. Jack

buswarrior · July 05, 2011, 07:35:48 PM

If you are getting air leaking out the exhaust of the brake application valve, (under the black rubber grommet) both with DD3 parking brake applied and released, the brake application valve requires replacing for starters.

And in looking at it, call it catching up on the preventive maintenance.

I would recommend purchasing a replacement, rebuilding isn't worth your time, and how do you know if it is within spec to rebuild? If there is a core charge, pay it, and turn in the old one AFTER you have used it as the model to get it all put back together in the correct configuration.

A leaking DD3 diaphragm will show itself via air leaking out the brake application valve exhaust when parked with air pressure present, not when released.

So, move to checking for that after replacement.

happy coaching!
buswarrior

Highway Yacht · July 06, 2011, 02:22:59 AM

Quote from: Tikvah on July 05, 2011, 01:22:20 PM
Jimmy,
I assume you must mean that the rear system can "back-feed" to the front and force air out the "Brake application valve???" in the front?

Actually, when I moved the bus this weekend, I was loosing so much air that I had to keep my garage compressor attached to the coach to release the brakes and move the bus. When the park brake was released the air continued to leak.

I have pressurized the bus a few times in the last couple of months, but never with the engine running. I simply connect my compressor. That allows me to use my air door, baggage bays, etc. But, this is the first time I've leaked air that quickly.
Just for information, I have never been able to hold air very long, but could never find any significant leak. This time was different, the air leak is significant and the large garage compressor worked hard to keep up.

I'm all ears if anyone can contribute to this.

Yes.. The air will back feed back to the Brake Application Valve when there is a hole in one or both of your park brake diaphragms. You might want to follow BW's advice since your air leak continues after the park brakes are released. My air leak quits as soon as the park brakes are released and resumes as soon as they are applied.

Jimmy

zubzub · July 06, 2011, 03:01:10 AM

Have you ried stepping on the pedal a few extra times? If it isn't the DDs could just be some crud .....