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Old 02-03-2024, 12:16 PM   #1
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1996 Thomas RE Cummins throttle issue

I have 96 Thomas and it runs great, it's currently stored in LA and I am in New Mexico. we flew out there to drive it back home, when we started it there was zero throttle response. I know this bus is air throttle and the pressures in my tanks were 110 psi so air pressure isn't a problem, and I noticed that even my air door wouldn't work. it was like I had no air going to the front of the bus. Im new to buses and air system like this so Im not sure if there's an air valve someone could've turned off while in storage to cause this problem or if there is a bigger issue. I'm planning on flying back out there in a couple weeks to fix this issue and drive it back, so I won't be able to send pictures or antything like that. any ideas would be greatly appreciated.

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Old 02-03-2024, 02:33 PM   #2
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Year: 1999
Chassis: Amtran / International
Engine: DT466E HT 250HP - Md3060
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I have 96 Thomas and it runs great, it's currently stored in LA and I am in New Mexico. we flew out there to drive it back home, when we started it there was zero throttle response. I know this bus is air throttle and the pressures in my tanks were 110 psi so air pressure isn't a problem, and I noticed that even my air door wouldn't work. it was like I had no air going to the front of the bus. Im new to buses and air system like this so Im not sure if there's an air valve someone could've turned off while in storage to cause this problem or if there is a bigger issue. I'm planning on flying back out there in a couple weeks to fix this issue and drive it back, so I won't be able to send pictures or antything like that. any ideas would be greatly appreciated.
Are you 100% sure it is air throttled?

My 99 int-amtran is not. Has a sensor in the foot pedal.

Have you confirmed there is no sensor on the foot pedal ?
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Old 02-03-2024, 02:46 PM   #3
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Yes I am positive, bottom of the pedal has two air lines going to it, and if my research is right those years for rear engine buses only came with air throttle.
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Old 02-03-2024, 08:32 PM   #4
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Engine: DT466E HT 250HP - Md3060
I myself have never had the opportunity to work on an air throttle system and quite honestly, I know nothing about them.

First thing I would look for is air leaks.

That being said, looks like a good time to learn something about air throttles!

I did a quick google search and here is something I found that might or might not help.

Thomas Buses - Air Throttle Repair

SOURCE

During most of the 1990's before the electronic age the engine throttle was air controlled on Thomas Bus Saf-t-liner models. The high idle was a welcome addition since it was operated with the flick of a switch on the dash.
In the photo the air line can be loosened while the engine is running where there should be no air with the high idle switch turned on. The throttle linkage is moved into high idle with spring pressure[no air]. The regular foot throttle air line is attached to the underside of the cylinder.

The air is controlled with an electrically actuated air valve that is normally open with full air pressure and no power from the switch. The air pressure moves the internal piston to the idle position compressing the internal springs. When the high idle switch is turned on, battery power closes the switch and blocks air pressure to the air throttle allowing spring pressure to kick the throttle linkage up to high idle[around 1000 rpms].
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Old 02-03-2024, 09:04 PM   #5
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What throws me is that the air actuated door also quite working the exact same time the throttle stopped. Looking into air systems it seems like busses have a wet tank, a primary tank for rear brakes a secondary tank for front brakes and an accessory tank for everything else including throttle, door and what not. And not being there looking at it is there a valve that can be shut off to stop the flow from the accessory tank?

I have had several air brake trucks and this is the only vehicle I’ve had that will hold 90 psi for months with out dropping pressure so leaks is not an issue
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Old 02-03-2024, 09:17 PM   #6
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I do not know if your bus has a valve like you ask about on the tanks. You will have to go underneath and look but in other busses with air operated doors, I know of no valves between the tanks.

what I would do though is grab your vin number and call a Thomas bus dealer and ask them to send you the diagrams/schematics for the air system on your bus.

If anything, at least you will know know how the air system is built on your bus.
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Old 02-03-2024, 09:50 PM   #7
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on the side of my bus there are bunch of air valves, do you know if those are just bleeder valves or do they actually send air tho the bus?

I didn't look into them because I had no reason to cause everything worked flawlessly.
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Old 02-03-2024, 10:00 PM   #8
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on the side of my bus there are bunch of air valves, do you know if those are just bleeder valves or do they actually send air tho the bus?

I didn't look into them because I had no reason to cause everything worked flawlessly.
Impossible to answer this question the way it is asked.

Pics would be helpful !
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Old 02-04-2024, 09:22 AM   #9
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I know, I wish I was next to it. just sucks that it broke in LA
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