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 Air Throttle Leak?
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Kodie
Top Member

United States
1994 Posts

Posted - 10/02/2012 :  06:38:18 AM  Show Profile  Reply with Quote
I've got a 98 TC/2000 RE with the air throttle control (Cat 3116) and previous inspections indicate a leak at the "throttle actuator", however I don't know much about them so I'd like some info.

When you're at a low rate of speed trying to feather it the engine seems to surge so to speak. I got down on the floor and put my hand on the "air bag" behind the pedal, depressed it slightly with the other hand and could feel a pulse of air when it was feathered. Holding it part way led to a "psss..... psss" type pulsing of air in the pedal, which in turn caused the engine to surge in unison with that. Could this indicate a leak? The bus is sluggish as all hell too but that might just be because it has a low powered Cat. Flooring it, which is almost necessary, does not have the same effect, it'll accelerate just fine and not have any surging, it seems to be mainly at low rates of speed.

In addition the bus loses about 100 lbs of air just sitting for a couple of hours. I can't seem to trace any leaks in the braking system, so I'm wondering if that leak is also part of the throttle.

Can this be rebuilt or would it need replacing entirely?

Thanks guys.

Thomasbus24
Administrator

USA
3336 Posts

Posted - 10/02/2012 :  11:47:22 AM  Show Profile  Reply with Quote
Sounds like a bad pedal for sure. The thing SHOULD exhaust under the bus, not inside the bus, and being that new of a bus shouldn't be that touchy at low speeds (the OLD ones were).

Could also be leaking at the throttle actuator at the engine (slave cylinder). Some of them were set up with two air lines to the rear...one was connected to the pedal, the other came directly from the air tank after passing through a solenoid. If that line is exhausted (by air loss or driver flipping the switch connected to the solenoid, the idle goes up, assuming everything is set correctly. So you have two air systems to check for leaks.

I never had a pedal, but had one slave cylinder go bad (leaking). Thomas just sent the entire assembly, so I've never attempted a repair on one. Get ready for sticker shock when you get the bill.
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Kodie
Top Member

United States
1994 Posts

Posted - 10/02/2012 :  4:25:10 PM  Show Profile  Reply with Quote
I appreciate the response. I guess I should clarify too that the leak can't be felt inside the bus, you can just feel the pulsing in the air bag behind the pedal. Sitting still idling, and then depressing the pedal usually leads to a sudden revving, there's really no easing it, though that just may be part of the air throttle design. You can back off a fully depressed pedal and bring it down to a lower RPM however.

Now figuring out exactly which part is causing the problem is the next fun step.

Edited by - Kodie on 10/02/2012 4:31:19 PM
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Thomasbus24
Administrator

USA
3336 Posts

Posted - 10/03/2012 :  02:56:12 AM  Show Profile  Reply with Quote
I don't THINK that there should actually be any air in what you are calling the air bag of the pedal. If memory serves, that is just a dust boot to protect the seals on the plunger the pedal pushes on.

Let me try to find some more info. I'm assuming it's a Williams pedal? (It would say right on the thing)

Edited by - Thomasbus24 on 10/03/2012 02:56:53 AM
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Kodie
Top Member

United States
1994 Posts

Posted - 10/03/2012 :  06:17:02 AM  Show Profile  Reply with Quote
Yes, it is a Williams pedal. Perhaps I should take the pedal itself off and take a look behind there to see what's really there. They have those pedals so jammed in there you can't get anything behind them.
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