GM Air Throttle Noise

[richard5933]

The air throttle pedal on my GM 4108 started making a noise today, a slight 'farting' sound when the pedal is released. I imagine that the cause is a dry seal or o-ring inside.

Anyone have information on the process? This is the OEM air throttle, and the book talks about rebuilding the assembly if it doesn't operate smoothly but contains no instructions on doing so that I can find.

The air throttle pedal on my GM 4108 started making a noise today, a slight 'farting' sound when the pedal is released. I imagine that the cause is a dry seal or o-ring inside. Not a major issue as the pedal still works okay, but I'm sure that it's not going to get better on its own, only worse, especially if the o-rings are getting dry.

The pedal itself seems like a bugger to pull off, with the two air lines being inward of the brake treadle and its maze of air lines below the floor. You have to be a contortionist to even put a hand on the air line fittings, let alone turn one.

Any advice or suggestions would be welcome.

[chessie4905]

Remove the panel between the headlamps. Behind it is a handhold, approx 4x6 held with 4 Phillip's screws. You can access those fittings through it. OR, you can remove spare, lay on your back in the hole and remove the large ceiling panel, about 8 or 10 small cap screws. I found this panel after cleaning and rebuilding my brake components through the compartment under driver. What a bitch that was.

[chessie4905]

Oh, if you need to order a kit from Luke, make sure it is the correct one. The one I got wasn't  correct. Fortunately mine was ok.

[richard5933]

Oh, if you need to order a kit from Luke, make sure it is the correct one. The one I got wasn't  correct. Fortunately mine was ok.

How do I know which one is the correct one? There are numbers on a tag on the valve assembly. Anything else I need to know?

How difficult is the rebuild once I get the kit? Anything that I should watch for that might shoot out of the thing as I open it up? Any secret sauce necessary?

From the parts book, it looks pretty simple, but I've never opened one of these before.

[buswarrior]

I am lazier than sin, and hate taking things apart when there's something else to try first.

If you think it may be dry... feed it a careful dose of air tool oil and see what happens?

You were all fired up to dig into it anyway, so nothing ventured, nothing lost?

Happy coaching!
Buswarrior

[richard5933]

Remove the panel between the headlamps. Behind it is a handhold, approx 4x6 held with 4 Phillip's screws. You can access those fittings through it. OR, you can remove spare, lay on your back in the hole and remove the large ceiling panel, about 8 or 10 small cap screws....

I found the access panel(s) from the front that you mentioned. Should make it easier to get the air lines removed, for sure.

...If you think it may be dry... feed it a careful dose of air tool oil and see what happens?...
Buswarrior

Air tool oil? Is this the best option? Is there anything that is close to Parker O-lube which will flow? (That stuff is more like thin grease). Is mineral oil compatible with the o-rings and seals? Just afraid to put something in there which would make things worse.

[dtcerrato]

Ditto what buswarrior said - lubricant.
I wouldn't think you could go wrong with introducing some air tool oil upstream... IMO

[chessie4905]

I wouldn't  try oil with that diaphragm.  But diya. You will need to disconnect the two lines AND remove elbows on end of extension nipples, unless they thread out easy. Pretty tight to get them loose. They are different diameters, so can't  be mixed up. Better to leave nipples on. You will need to remove bolts that attach unit through floor.

[buswarrior]

Your air tools have seals, etc in them, so one would hope it will be friendly to automotive air  valves.

I hope everyone is lubricating their air tools?

Happy coaching!
Buswarrior

[chessie4905]

Do mine occasionally. That air throttle doesnt see oil easily from the air routing. Mine was totally dry. Maybe the diaphragm is made out of air bag material.😊

[luvrbus]

The sleeve becomes pitted from moister over time and they need to be replaced,oil I don't know the repair kits come with a special grease for assembly,the bolts will break is why a kit comes with all new bolts.I get my kits from the manufacture Brake Service in Portland Or   

[richard5933]

I talked to Luke this morning, and he didn't think it would help to put lubricant in upstream. He had the correct rebuild kit in the shelf and is sending it out today.

The screws that come in the kit - I assume those are the ones that hold the two halves of the outer shell together. Will I need any special technique to get them out if they are prone to breaking? Don't want to make this more difficult than necessary.

Does look like the kits come with a bit of lubricant, but I've also ordered some pneumatic tool oil to have on hand for future use. Found one by Super Lube, a company I've generally found to have good products.

[chessie4905]

They either come with or you fabricate a ring from cardboard to assist in getting the bellows to fold over itself. Similar to how the air bags do on newer coaches. Those little screws should remove easily on yours since it is in such good condition.

[richard5933]

Bellows??

Searching online, this looks like the parts that come in the kit: https://www.accupart.com/wil417103-kit-major-wm90dx-type-valve-modulating/

Looks similar to what the GM parts book shows.

[luvrbus]

Bellows??

Searching online, this looks like the parts that come in the kit: https://www.accupart.com/wil417103-kit-major-wm90dx-type-valve-modulating/

Looks similar to what the GM parts book shows.

I

I don't know which throttle you have but I know what Chessie is talking about I call it a loader that comes in the kit,a different kit than shown