Allison trans is jumping around

[Scott & Heather]

So my Allison 748 has been starting to jump in and out of gearish for the past month. Actually it feels and sounds like the torque converter is losing lockup and slipping in and out of it. It's not constant and not often but it's definitely happening. Of course I had a trans fluid and filter change this past spring. (April). But it hasn't done it until just about a month ago. Fluid level is good, already checked that. Anything else easy I should check?


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[Bill Gerrie]

If you have an ATEC transmission computer it is possible that wire 201 (K2) which goes to chassis ground is a bad connection. If it is corroded or lose it will cause the symptoms you describe.

[Scott & Heather]

I do indeed have an ATEC trans. I'll see if I can chase down wire 201 and be sure I have a good ground. Thanks Bill.


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[luvrbus]

Could be a solenoid getting weak also 

[thomasinnv]

No stored codes? You can pull codes through the shifter pad.

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[Scott & Heather]

Guys, my jumping in and out of lockup is getting worse. Driving past mount Shasta on the way to Portland it just kept popping out of lockup and then when I would stop at a truck stop right after exiting the HWy, bus would be sluggish to move and then trans would seem to "catch" and then go. The next day, drove fine for hours and then started acting up. Drives fine mostly on the flats but get in the hills and she starts getting jumpy. Fluid level is good, fluid color and smell are good. No shift malfunction lights or anything. No engine codes being thrown. I'm at a loss here.


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[luvrbus]

Basically you have a 740 with 5 or 6 solenoids on the valve body you are losing lockup pressure could be the solenoid,springs,governor,the lockup valve going bad or the torque converter have a transmission shop check your pressures it not that expensive and time consuming and stop looking for a code   

[Scott & Heather]

Lol. Ok cliff. I'll see if I can sneak the coach into a shop somewhere near Indianapolis.


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[sledhead]

mine did somewhat the same thing and it ended up being a broken wire from the ecm to the transmission ( ht740 ) I had to leave the coach at leids diesel when the turbo went bad and when I returned to pick it up they had a new wire run along side the wiring harness and a rebuilt turbo to boot at no charge . great guys

dave   

[Scott & Heather]

Dave you can't remember which wire right?


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[sledhead]

to be honest it started on the trip to lieds diesel 11 hour drive and they didn't even tell me that they had fixed it until I asked about the added wire

so no I do not know what it fixed but never had a problem shifting  in the 6 years after that

dave

[Scott & Heather]

Ok thanks. To the shop she goes.... again sigh


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[bigred]

Scott:My American Coach has the six speed Allison tranny .Three years ago after having the fluid and filters changed it started acting squirrely coming out of lock up slamming from one gear to the other and all sorts of crazy things .After spending almost 4500 dollars with Clark Power starting with 2800 dollars for a TCU .Took the unit back to them four times and they charged me every time .I finally took it to their shop in Greensboro and the guy's down there got it fixed .According to what the tech told me,there is a gasket that people who are not familiar with Allison sometimes mess up during fluid and filter changes creating a low pressure condition on "port 5 " .Before you get into a big drawn out affair with yours have them check the pressure on ports .This cost me 800 dollars (which I also had to pay) .If I had known about this ,I would be 3500 dollars better off.I am trying to find the invoice where they did this work .Had it just a while back but danged if I know what I did with it!!! 

[luvrbus]

Pressure is the key to a Allison for sure

[Scott & Heather]

Thanks a bunch bigred. I'll check into this. And if that turns out to be the case, I'll be in contact with Stewart and Stevenson in Texas to rectify this.


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