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Old 08-14-2018, 09:53 PM   #1
Join Date: Jan 2017
Posts: 25
AT545 acting jerky, weird shifting

Hi guys, looking for help again!

2000 3800 international, 8 row bus, DT466e, attached to a AT545. 137K on engine, just recently serviced by a shop after I bought it from a school. Bus sat for one year before I bought it. Only driven it about ten miles so far.

The bus shifts somewhat hard into gear, going up and down, but feels very jerky, like she is never happy in one gear or another. As soon as I let of the gas, she downshifts, lurching me forward, and probably scaring the willies out of any driver behind.Nothing is remotely smooth about driving her and, with the air seat, its making me kind of sea sick.

Since the bus is new to me, I am still trying to work out if the jerky up and down shifting is me getting used to driving this type of vehicle, OR, if there is an issue with the transmission.

Don’t know what rpms I am shifting at, since I have my eyes glues to the road to make sure I don’t hit anything (still getting a feel for driving her).

Don’t think it is gear slip, but I don’t know if I would recognize gear slip anyway.

A few possible issues I see pop up when researching what could cause the effect I am feeling are (1) stuck governor, (2) modulator and modulator wires to the AT545, and (3) valve body issue.

Any thoughts on this one would be greatly appreciated!!

Douggy is offline   Reply With Quote
Old 08-14-2018, 10:35 PM   #2
Bus Geek
Join Date: May 2009
Location: Columbus Ohio
Posts: 15,813
Year: 1991
Coachwork: Carpenter
Chassis: International 3800
Engine: DTA360 / MT643
Rated Cap: 7 Row Handicap
it DOWNshifts when you let off the gas? they normally upshift. and they do have a bit of a think when they shift up.. if it is hunting.. meaning you hold the pedal in one spot and it goes up-down-up-down-up. then that usually means the line pressure is low in a higher gear sao it drops down.. which raises pressure and the cycle continues..

if you can let off the gas and it upshifts then you punch it and it drops down a gear then your modulator is working properly.. thats what it does.. the computer enables the modulator to downshift if you press down in the area of 50-70% throttle.. if you hold it near the floor it will eventually upshift as it reaches max RPM (2600) for that gear..

the original design of those transmissions was to have a progressicve modulator.. it was a cable that moved with your foot pedal.. your 466E is a cable-less pedal.. so the modulator us simply on or off... at part throttles letting on and off it results in some pretty rough shifts at times...

the air seat takes awhile to get used to... if it is bouncing too much you can let it all the way flat or pump it all the way up and you womnt get the extra bounce.. as you get more comnfortable driving a bus you can introduce small anounts of "bounce" into your seat.. you'll find once you arent going crazy moving your head up down and back N forth constantly at a rapid rate like when you are learnming the bus, that the air seat wont bother you

cadillackid is offline   Reply With Quote
Old 08-15-2018, 09:49 PM   #3
Join Date: Jan 2017
Posts: 25
Hi Christopher,

Thanks for the response.

Did a bit of digging and experimenting…..

What I did was hook up a 12V light bulb to the modulator input wiring, and played with the accelerator pedal.

I get no 12v signal when the accelerator pedal is not touched – which is what I expected.

But I notice I get a 12V signal once the accelerator pedal is just barely touched – I’d say way less than 10% pressed down.....just off idle, basically.

Everything I read, including your note, mentioned that a 12v signal to the modulator should not occur until around 40-60% travel on the accelerator pedal – yet I am getting mine at waaay less than 10% pedal travel.

So, with the 12V signal going on early, is this a faulty relay, or a faulty switch on the accelerator pedal mechanism??......

As always, any input from anyone is greatly appreciated!

Douggy is offline   Reply With Quote

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