No air pressure!

[Mtrdrms]

Is this it? It doesn't sound or feel like it's leaking...

 

[Mtrdrms]

Guys. Solved.


It was a sticky brake pedal valve. I jammed the brake pedal a few times and she came right up.

Can't thank you all enough. This was a wonderful learning experience for me.

 

[Wornout Wrench]

Enjoy your ride! 50k! Wow

Made it, and still breathing.

And I see while I was out you figured it out, cool.

View from the seat during a water stop.

Stats are.
52 Km
2:05 duration
Average speed 26 km/h

 

[Booyah45828]

Guys. Solved.


It was a sticky brake pedal valve. I jammed the brake pedal a few times and she came right up.

Can't thank you all enough. This was a wonderful learning experience for me.

Great to hear!

But, sorry to say, its still not solved. Those valves shouldn't be leaking and the compressor should have been able to build up pressure even with the pedal applied.

You still have problems.

So, the next step is to run the engine until the compressor kicks off, shut the bus off, turn the key back on and then have a buddy apply the brakes. While your buddy is applying the brakes, go underneath and listen for air leaks. Your buddy must maintain even pressure on the pedal. Any air leak you hear is either caused by a faulty component, or your buddy not maintaining even pressure.

If those modulator valves are leaking with air applied, they're junk. The only time they should leak air is when the abs is activated and they're freeing up a locked wheel.

*Brad, I don't think I've ever seen a dump valve and a quick release valve all in one unit. Even with these dump valves, it will still have a qr valve. The dump valves will be on the frame rail, near the hose to the chamber, while the qr valve will likely be located more towards the center.

 

[Mtrdrms]

Ok, thats good to know. I will test it.
So, maybe a silly question but how will i know when the compressor kicks off?

 

[Booyah45828]

You'll hear a psshttt out the air drier, and the air gauges will read anywhere between 100-150 psi.

 

[Brad_SwiftFur]

Guys. Solved.


It was a sticky brake pedal valve. I jammed the brake pedal a few times and she came right up.

Can't thank you all enough. This was a wonderful learning experience for me.

But, sorry to say, its still not solved. Those valves shouldn't be leaking and the compressor should have been able to build up pressure even with the pedal applied.

On this I agree, I'd be rebuilding/replacing the brake pedal valve. This is one very critical piece and the last thing I'd want at this stage is to chance it on something that has already given problems once. I don't think they are very expensive.

So, the next step is to run the engine until the compressor kicks off, shut the bus off, turn the key back on and then have a buddy apply the brakes. While your buddy is applying the brakes, go underneath and listen for air leaks. Your buddy must maintain even pressure on the pedal. Any air leak you hear is either caused by a faulty component, or your buddy not maintaining even pressure.

If those modulator valves are leaking with air applied, they're junk. The only time they should leak air is when the abs is activated and they're freeing up a locked wheel.

*Brad, I don't think I've ever seen a dump valve and a quick release valve all in one unit. Even with these dump valves, it will still have a qr valve. The dump valves will be on the frame rail, near the hose to the chamber, while the qr valve will likely be located more towards the center.

Ok, thats good to know. I will test it.
So, maybe a silly question but how will i know when the compressor kicks off?

The compressor kicks off around 120 PSI. Often (on vehicles equipped with one) it will purge the air dryer when this happens.


It's good to test these valves for leaks as Booyah explained but don't be surprised if they don't seem to be leaking when you do. It was explained to me once, long ago, but I forget the exact how and why it happens. ... basically the brake valve is a pressure regulator - it's letting air in but regulating it to 0 PSI or something like that, which would explain why air is(was) coming out all those other valves.

 

[Wornout Wrench]

I'm assuming that it is a floor mounted treadle valve. Have had lots of issues with those in the past.
Nothing really wrong with the valve itself. But they will get jammed up with crud right at the bottom and it will hold the pedal slightly applied.
If there is a floor mat or something on the floor, make sure that it can't slide forward and get under the pedal. Make sure there is no accumulated dirt built up around the pedal.
You have a compressor, get in there with a blow gun and get it all cleaned out.
Then make sure that it is moving easy and that it is returning all the way by itself.
A bit of WD40 or something like that can help out lots here.

Besides the problem you are having, even if it is applying even just a tiny amount of air to your brakes, it will cause a drag and the brakes will heat up. YOU DO NOT WANT YOUR BRAKES TO HEAT UP. Enough drag and they can catch fire, not to mention the horrible amount of brake fade that is going to happen.

If in doubt, throw it out.
Get a rebuild or even a new one. If you have never rebuilt an air valve you should not start on one now, not a good place to learn.

Booyah once again nailed it about those leaking valves.
There should be no air leakage at all.

It seems strange that they were all leaking, but it is an older bus and the only way to repair will be to replace. Once again, not something to fool with. Aluminum valves corrode.

Do the tests that Booyah has set out, good start.

And my mind must be turning to mush.
Yes there are combinations of ABS modulators and QR valves, we had them on our logging trucks.
The QR is mounted in the middle with the left and right module mounted to the QR. It all very nicely bolts together.
We found that if one modulator was having issues, we changed the complete valve, found that spending the time to take all apart and change one side and in a month or so the other side would have issues. Not cheap, if I recall correctly $800 CDN but that was new, not rebuilt.

google Wabco Merritor ABS valves, it will come up.

 

[Brad_SwiftFur]

I've had a couple trucks with the floor mounted valves, and I can attest that crud builds up around them. In one case, it made brake application require much more pedal effort than should have been necessary.

 

[CHEESE_WAGON]

Guys. Solved.
It was a sticky brake pedal valve. I jammed the brake pedal a few times and she came right up.

Glad you found the problem, but I would invest in a replacement in the near future. Shows a lot of wear on the brake pedal treadle valve internals, which is a sign of heavy use. Problems like that may or may not be that common, and tend to come back eventually.

 

[Mtrdrms]

Glad you found the problem, but I would invest in a replacement in the near future. Shows a lot of wear on the brake pedal treadle valve internals, which is a sign of heavy use. Problems like that may or may not be that common, and tend to come back eventually.

I think its a good investment also.
Where is the best place to get such a part?