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dougallman

Allison Transmission Lock-up

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Have just had a problem with a 2004 Beaver Marquis Allison 4000 6 speed trans at 42000 mi.

When coming to corner of highway and using engine brake noticed that engine brake did not engage. After stopping "check transmission" light came on and transmission stayed in 5th gear. When arriving at destination as few miles later shut Coach off and then restarted, all was OK.

On return to home same problem appeared 4 more times, did not use engine brake, so thinking that when down shifting to stop this occurred.

Does anyone know what solving this problem involves.

Transmission is at fullmark for the Transynd fluid.

One other symptom is that when initially engaging transmission to move forward there is a seemingly longer delay than usual for trans to engage and it comes into gear hard. In reverse there is no delay.

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Have you used this shift pad to check for diagnostic codes? What does it tell you? This is in your Allison manual and on Allison's website.

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Your Allison transmission has sensors to monitor its operation and detect possible faults before leaving you stranded on the side of the road. For example, it knows the speed of the input shaft and the gear currently selected. With this information, the computer knows what speed the output shaft should be turning. If the measured speed is not close, the computer will declare a fault and turn on the “check transmission” light. It will also put the transmission in “limp home” mode and lock the transmission in the last known “good” gear. It will stay this way until the next time the transmission passes its built in self test when the engine is started.

I had a similar experience to yours while traveling down a long grade on I64 in West Virginia. We had been traveling for several hours through the mountains using the engine brake and cruise control to when suddenly the “check transmission” light came on and the transmission locked in high range (6th on our coach). We had just started down from the top of Sandston Mountain traveling at about 65mph. Fortunately there was not much traffic and I was able to use the service brake to get us slowed down. At that time I had no clue about the “check transmission” light or the existence of a “limp home” mode. I turned to my wife and asked her to dig out the books and get on the phone. The Allison technician told us that it was either a “soft fault” in which case it would clear itself the next time we started the engine or it was a “hard fault” in which case the bus was not going to move until it was fixed once we turn the engine off. Since it was nearly 11:00pm we decided to stop for the night at the Walmart in Lewisburg, WV and see if things got better in the morning (we got sideswiped by a WM truck in the middle of the night but that is a different story). The next day we started right up, the fault had cleared, and had no more problems on our trip.

When we got home we took the bus to our local Allison repair shop. They determined we had two solenoid valves in the transmission that were in the process of failing and needed to be replaced. Our Good Sam Extended Service plan covered most of the cost and today, after 3 years and nearly 20,000 additional miles, it seems to be working as good as new.

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I will look in manual and then use pad to get me codes. I also discussed with local here and they indicated that had same type problem and was fixed by replacing solenoid.

THANK YOU All.

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You can always call Allison, they are very helpful...have the transmission serial number handy.

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