No air pressure!

[CMORGANSKOOL]

Time to pop a fitting off and see if you have air flow.

 

[Mtrdrms]

There are 2 lines coming in to the governor.. Are they both outputs?

 

[Brad_SwiftFur]

Hard for me to tell from the pic, but how "new" would you say it is? One of the bolts looks like it hasn't been turned in ages. Since you already have a replacement, and yours looks easy to access, why not go ahead and change it out anyway?


It might also be a good idea to make sure the air inlet lines are not obstructed - there may be a filter somewhere.

 

[Mtrdrms]

Ok, with the engine running, I pulled both lines off of the governor and neither was moving any air. What does that mean?

 

[Mtrdrms]

Hard for me to tell from the pic, but how "new" would you say it is? One of the bolts looks like it hasn't been turned in ages. Since you already have a replacement, and yours looks easy to access, why not go ahead and change it out anyway?


It might also be a good idea to make sure the air inlet lines are not obstructed - there may be a filter somewhere.

Inlet into the governor?

It looks very new. Within a year

 

[Brad_SwiftFur]

Really, there's not much to these things. The air compressor (is supposed to) suck air in from somewhere and pump it into the air tanks. The governor turns it on and off. It's either pumping or it's not. Kind of a true-or-false scenario. New governor - $20-25. New compressor - $250-1,000+ (rebuilt ones are fine). I know which part I'd try first.


If memory serves me correctly, the governor has a couple internal springs which make it work and if one fails, it stops working.

 

[Brad_SwiftFur]

Ok, with the engine running, I pulled both lines off of the governor and neither was moving any air. What does that mean?

I don't expect the lines to move any air, that's the compressor's job. But I'll assume you checked and the compressor isn't moving any air either.

 

[Brad_SwiftFur]

Inlet into the governor?

It looks very new. Within a year

The larger steel lines - are they air intake for the compressor? Do they go to the air tanks, or some air filters somewhere?


I've had brand new parts fail, so I wouldn't rule out a failed governor just yet.

 

[CHEESE_WAGON]

Ok, first, no flaming if there is something I am not aware of here -- I hold a Class A CDL, and the vehicles I'm used to driving have gear-driven compressors, not belt-driven.

Everything in my training specifically mentions to check that the air compressor is gear-driven. Keep in mind, the vehicles I'm trained on are 40-ton combination vehicles. Perhaps there are different rules for a single vehicle such as a skoolie, but I wasn't aware belt-driven compressors were legal for air-brake systems. Is it legal for a bus to have a belt-driven compressor? Seems kinda dangerous to me.

That being said, certainly sounds like a bad compressor. Can possibly be fixed on-site by a competent mechanic. Such a service call is expensive, but on the other hand, so is a tow bill... Just my $0.02.

I once had a compressor fail on a rig I drove while I was waiting in a dock. Four stops and the spring brake engaged. Road service was called, they had to overnight the part and I was blocking the driveway. Fortunately, their shop was only two miles away. Best they could do was charge my air tanks so I could drive the two miles on residual air pressure. Something I wouldn't recommend unless you REALLY know what you're doing. It's doable though.

 

[Jolly Roger bus 223]

my bus is a belt driven air compressor.
can put my hands on every piece of it without any issues.
air brakes lock at anything 60 or below.
dont have any airbags yet but will add an extra air tank with check and bleeder valves when i add them
dont like the idea of a gear driven compressor behind the timing chain cover?
what a pain in the ass that would be!
i will stick with my belt driven one

 

[CHEESE_WAGON]

my bus is a belt driven air compressor.
can put my hands on every piece of it without any issues.
air brakes lock at anything 60 or below.
dont have any airbags yet but will add an extra air tank with check and bleeder valves when i add them
dont like the idea of a gear driven compressor behind the timing chain cover?
what a pain in the ass that would be!
i will stick with my belt driven one

In driving 400,000 miles across 4 years with gear-driven compressors, I have had one fail, and the truck in question was a worn-out POS.

To each their own. Maybe it's because I'm a professional driver with a lot more on the line, but I don't like the idea of a drive-belt that can snap without warning and leave me running out of the one thing my brake system needs to function properly with a heavy vehicle such as this. It's no fun being stuck on the side of the road with a perfectly-good running vehicle that can't move because the brakes are locked down.

Not saying that to be condescending, I was just always trained with equipment with gear-driven compressors, because it is required for Class 8 combination vehicles. If you want a good idea of what that spring brake can do if it locks down at 60 mph from low air pressure, try nailing the e-brake in a conventional vehicle at 30-40 in an open area.

 

[Mtrdrms]

Ok, new governor. No different. So, how do I check the compressor? I dont hear any leaks.

 

[o1marc]

Belt driven compressor from the 87 BB. with the DD 8.2

 

[Booyah45828]

Ok, new governor. No different. So, how do I check the compressor? I dont hear any leaks.

Remove the air hoses off the compressor head and check for air flow out the large one.

 

[Mtrdrms]

Yes, thanks, I just pulled the coolant hose(doh!) But once I found the air hose, its moving air. Not super strong but I can't block it with my thumb or anything. Is it supposed to be powerful?
Also, I was poking around underneath and found a box by the rear axle with 3 red lights on it.
Does any of this help?

 

[Booyah45828]

It needs to build 100+ psi.

Holding your thumb over it isn't really safe, but the fact that you can't hold your thumb on it is a good sign.

Re-attach the hose and follow it back to the air drier and do the same thing. If it's building pressure there, reattach the hose to the drier and remove the drier outlet. If you're building pressure there reattach the hose to the drier and do the same test at the other end of the hose.

You're losing air somewhere, you just have to start at the compressor and move your way back to find out where.

 

[Mtrdrms]

Man, I wish it was that easy.
So I ran it and I couldn't hear or feel any leaks.
Oddly, I can hear one of the tanks (there are 2, maybe 5 gallon tanks under the drivers area) filling but it doesnt hold any air. Once I kill the engine, I can hear it slowly empty. Its not leaking itself but its leaking some down stream? There has to be a mile of airline in this thing. Now, keep in mind that according to the guage, it builds 0 air pressure. Maybe its the compressor? I have no idea...

 

[CHEESE_WAGON]

Man, I wish it was that easy.
So I ran it and I couldn't hear or feel any leaks.
Oddly, I can hear one of the tanks (there are 2, maybe 5 gallon tanks under the drivers area) filling but it doesnt hold any air. Once I kill the engine, I can hear it slowly empty. Its not leaking itself but its leaking some down stream? There has to be a mile of airline in this thing. Now, keep in mind that according to the guage, it builds 0 air pressure. Maybe its the compressor? I have no idea...

Could be pumping air, but not pressurizing. Maybe blowing back out the compressor?

 

[Mtrdrms]

Should I just replace the compressor? Is 0 pressure a sign of a compressor failure?

 

[CHEESE_WAGON]

Should I just replace the compressor? Is 0 pressure a sign of a compressor failure?

Bad compressor or one **** of a leak between the tank and the compressor.