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|Allison 740 shifting problem||Bob||1-24-10|
I just purchased an MCI model 9 bus with a 6v92 dd with an Allison 740. The bus sat for the last five years with a rebuilt engine sitting in the frame not hooked up. We got everything humming on it and took it for a test drive. Runs great except that the Trans is not shifting out of 3rd gear. I thought it might be the cable driven modulator valve, so I took it apart and everything seems to be working fine in it. Also did 8 different adjustments from tight to super loose with no change. The cable is in good shape and working good. Changed the ATF and Spin on Filter with no change. I haven't dropped the pan yet, because I'm by no means a trans expert and don't know what I'm looking for. I'm likely to take it to an Allison tech on Monday, but wanted to see what I might be in for before I did that. I'm suspecting (or really just hoping) it's something to do with the valve body which can be accessed once the pan is dropped.
thanks for any info
|Re: Allison 740 shifting problem||BUBBA THE BUS TECH||1-25-10|
|Its allready monday but here we go. The most common problem I have seen that causes this is the trans is not in the drive or 4th gear position, usually due to a stretched and sticky shift cable making it a pain to select. An Alison guy will put hydraulic pressure guages on the test ports and tell if it has an internal or control problem real quick and that is probably your best bet before deciding what to do next. He may want to run his guages up through the floor plat and go for a drive. Thats the way I did it. Good Luck|