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Pete, Automotive Mechanic
Category: Medium and Heavy Trucks
Satisfied Customers: 28319
Experience:  Performed various automotive repairs on several light duty and medium duty vehicles over 15 years of service.
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I have an Allson AT540 in my 76 international dump truck. I

Customer Question

I have an Allson AT540 in my 76 international dump truck. I was driving back home with it in 4th at 55 mph and it abrubtly downshifted into 3rd. I eventually messed with the lever enough and got it to shift back into 4th then a minute later it abrubtly downshifted into 3rd again and wouldnt go back. I got to my turn and it abrubtly downshifted into I believe 1st or 2nd and it wont upshift anymore. I can go about 25 mph and thats it. I still have reverse and it shifts into both gears the same as it did before. Transmission never slipped, always nice firm shifts. I checked the vacuum hose to the modulator and its fine, i sucked on the end of the hose and it holds vacuum and i can feel the modulator click if i suck hard enough. I cant find much info online? I found a troubleshooting manual that said possibly governer or range valves but im thinking if it did this as i was driving down the road it would be the governer. Any idea? Does anyone have an exerpt from a book that shows troubleshooting and removal of the governer?
Submitted: 1 year ago.
Category: Medium and Heavy Trucks
Expert:  Pete replied 1 year ago.

My name is ***** ***** I am a professional here at Just Answer. I noticed that your question was not getting a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.

My info is limited on your model here but I see no one else has responded and thought I would see if I can help here.I see no one has replied with the info you are looking for here on this.In some cases this is due to the info being difficult to obtain.

I suspect this may be a fault with the transmission range sensor or a mechanical fault with the transmission valve body itself.Unfortunately I don't have any info on the trouble shooting on this here myself.These should be checked into though to see if any of these are found to be the cause needing repaired or replaced.

Thanks Pete

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