Allison Transmission Problems

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Shane Hamilton

New member
Oct 23, 2012
Hi Guys, I'm a new member from Australia. I have an Allison 4 speed T Bar, Auto with Retard function attached to a Cummins 5.9 230 engine. My problem is that my truck dosen't want to go fast. It labours to get to 35mph maybe taking 500 yards to get there. Then it hits a wall at 55mph and is hard to get to 60mph. Being an ex Fire Truck I would expect it to go like a cut snake but its more like a turtle. Has anybody have any ideas as to what may be wrong.
Cheers from down under, Shane.
late model? some of the late model box trucks i use will reduce power if brake light switch sticks. try lifting brake pedal with your toe next time, if that works it's just a brake light switch adjustment.
Why do you think it is a transmission problem? Could it not be that the engine simply isn't producing its full rated power? A dirty fuel filter(s), faulty fuel lift pump or faulty injector(s) would have the same symptoms as you describe.
Shane Hamilton said:
Thanks for that, I'll give it a try.

Thanks Gary, have thought of changing filters etc. I think I'll try that first before looking at the transmission.

A new fuel filter is the automatic first step for any diesel performance problem. A new air filter is close behind. Eliminate the common causes before you start diagnosing more complex - and expensive - problems.

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