Air throttle air leak.

[somewhereinusa]

I have a Williams air throttle that has developed a bad leak on the inside. Air is coming from the dust cover. I assume there is an o-ring of some sort around a spool? I can't seem to find any info. From what I can tell Williams doesn't make them any more, at least it isn't listed oh their website. My bus is a 91 Bluebird, it's a through the floor model. Are they all alike or are there different models? Can I do the repair from the top without taking it out? It's a REAL bear to get out. Anyone have a breakdown picture or service manual? Where can I get parts?

Thanks,
Dick

[frankenboom]

Hey, did you ever figure out your problem? I'm having the same issue!

With any depression of the throttle, I can hear a whooshing sound from under the floor, which I'm guessing should not happen. The further the pedal is depressed, the louder this sound becomes.

If I'm running at low-ish speeds, say under 25 mph, the air pressure drops fairly quickly and I lose the ability to rev up the engine, and I slow to a crawl. I usually have to pull over and wait for a bit, then the engine becomes responsive again.

I think what's happening is that too much air is leaking from both whatever mechanism translates the input from the pedal to the engine, and the air tanks. As a result, the engine RPM stays low and the compressor works slowly as well, which starts a vicious circle.

Thanks for any help!

[somewhereinusa]

After further research I was able to find a rebuild kit. Do your own research before you order but, the Williams part number for the complete kit should be 117107. I'm pretty sure that kit will fitt all models. That kit had all o-rings, pivot pins, and bushings. I think there are also kits that just have the o-rings. If I remember someone else found a kit.
Someone else here found a kit perhaps they will jump in.

[frankenboom]

Thank you! At some point, when I know the bus won't have to move for a bit, I'll take the throttle out and see if I can figure out what the problem is.

Hopefully the rebuild kit will help. Thanks again!

[Rameses]

Before you order the rebuild kit, try to find the leak. It might be something as simple as a loose compression fitting on the line coming out of the air throttle assembly. Put something against the pedal to lightly depress it to where you hear minor leakage, then crawl under the bus and see if you can see/feel/hear where the air's escaping.

[frankenboom]

Actually, so this is interesting.

Previously, the leak from the throttle, as described above, was coming from the EXH (exhaust) port on the valve. The exh port is only supposed to emit air right upon depression of the pedal and upon its release, not whenever the pedal is depressed at all.

I took the throttle out today, which was a major chore since the mounting bolts are so hard to reach. No real problems, though.

Took it apart, wiped off a little bit of gunk from the inside, reseated all the rings, and reassembled. Leak fixed! I'm not even sure what I did.

BUT

now, the pedal has to be depressed at least halfway for the engine to "get the signal" at all - ie, it has to be depressed halfway before the engine revs at all.

Then, even if the pedal is floored, the engine only revs to about 1900 rpms. I have no idea what this could be a symptom of. I doubt anything "behind" the valve has suddenly sprung a leak, so I'm guessing it's in the valve.

The other possibility is that the company that previously owned the bus adjusted the tension spring in the control cylinder in the read of the bus (by the engine) to work properly WITH the leak, and now that it's been fixed, the tension is too high or something. This seems less likely.

I'm working on it today; if I get it working I'll post back with the results.