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Curtis B.
Curtis B., Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 26033
Experience:  Technician turned service manager on multiple lines of trucks and engines, used in industry.
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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:  Curtis B. replied 1 year ago.

Governor is under four bolt cover, on the tailshaft section

Expert:  Curtis B. replied 1 year ago.

Remove the governor and work the weights in and out, and watch the small valve through the slots. valve has to move up and down with weights.

Expert:  Curtis B. replied 1 year ago.

The gear can also strip, but the governor is the place to start!

Expert:  Curtis B. replied 1 year ago.

680 in picture.

Expert:  Curtis B. replied 1 year ago.

http://www.makcotransmissionparts.com/mm5/graphics/Catalog-pdf/Allison-AT540.pdf

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