Help! Air Brakes

Curious Slug · 08-08-2022, 02:25 PM

Hey,

We’re stuck and hoping someone here can help. I’m not mechanically minded at all. We have a 1998 Thomas MVP ER with a 8.3l Cummins and a Allison MD3060.

We’re touring around the states, currently in Dillon, Montana. I started the bus this morning to move on to Yellowstone but the air pressure won’t build up and therefore I can’t get it into gear. I can’t hear any audible leaks and the tanks seem to maintain pressure fine. It’s got a newish compressor which seems super hot to the touch. It’s also covered in oil. I’ve attached a picture from above with the blue line and then two from below.

I’ve tried all the local mechanics and I’m not having any luck getting anyone out in anything that resembles a workable time frame. I’ve got 3 kids in here and I really need to get moving, so I’m hoping someone might be able to give me some help. Any advice appreciated, or if anyone happens to know anyone nearby who might be able to take a look at it then that would be amazing.

Thanks,

Sam

Booyah45828 · 08-08-2022, 04:07 PM

1st pic is of the compressor, next 2 are of the power steering pump mounted to the back of the compressor.

Hot, especially to the touch, doesn't mean much in a bus world, as anything over 120 degrees will feel hot, and a lot of things on a bus have a normal operating temp above that.

Odds are that you do have a leak somewhere, you just haven't found it yet. Gut instinct tells me you should look at the air dryer, as it's likely not been maintained since you've owned it, and would very easily cause a leak large enough to never build air pressure.

But, if you're not mechanically minded at all, you'll likely struggle to get this fixed. I along with many others on here can point you in directions to look, and walk you through fixing it, but you kind of have to be somewhat mechanically minded to know what I'm saying. And if you're not, then there's a good chance you could hurt yourself in the process.

Curious Slug · 08-08-2022, 06:42 PM

Thanks for the reply. Whilst I’m not that mechanically minded, I did build/kit out the bus so I’m not dangerously inadequate at this stuff… it’s just not my strong point. However, I do also have some guys on the campsite who are very kindly looking over it.

If you can point me/them in the right direction then that would be appreciated. Where abouts would they look for the air dryer and governor?

Booyah45828 · 08-09-2022, 07:12 AM

Follow the blue hose to the governor.

The air dryer should be at the end of that ptfe/stainless braid hose.

sportyrick · 08-09-2022, 08:14 AM

Possibly the governor is stuck. Does your bus make a huge hiss when the compressed air is at highest pressure? If so then you do have an air dryer and that is where the governor is. My bus doesn't have an air dryer so I never hear that hiss so if yours never makes that hiss then the governor is on the compressor and might need a love tap.

Curious Slug · 08-09-2022, 07:51 PM

Right, I’ve found the air drier (attached to the frame rail near the air tanks) and the governor (in the engine bay). Pictures attached below. The air drier looks pretty corroded but I don’t see/hear any air leaks at either component with the engine running. Any further suggestions?

What’s the usual test to check the compressor? I’d assume find a connection in the ptfe/braided hose, disconnect it and then start up the engine to see if it’s pumping air? Happy to be corrected.

Curious Slug · 08-09-2022, 08:34 PM

Quote:

Originally Posted by Curious Slug

Right, I’ve found the air drier (attached to the frame rail near the air tanks) and the governor (in the engine bay). Pictures attached below. The air drier looks pretty corroded but I don’t see/hear any air leaks at either component with the engine running. Any further suggestions?

What’s the usual test to check the compressor? I’d assume find a connection in the ptfe/braided hose, disconnect it and then start up the engine to see if it’s pumping air? Happy to be corrected.

It didn’t attach the images, which I’ve now done

Booyah45828 · 08-10-2022, 08:38 AM

1st is the governor.

2nd is not the air dryer. It's one of the valves, possibly a spring brake valve.

Follow the ptfe/stainless hose back again, as if it doesn't go to an air dryer, it's supposed to go to the wet tank.

And you're right, to check if the compressor is pumping, you'd pull the hose off the compressor, start the engine, and see if air is pumping out the fitting.

If the compressor is pumping, and you're not building pressure, the air volume that's leaking should be pretty noticeable.

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