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Old 08-01-2018, 07:14 PM   #1
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Allison Transmission Problems

looking for answers on problems with my allision trans. clunks when down shifting when stopping its a at 542n 3 speed

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Old 08-02-2018, 09:52 AM   #2
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Hi ! Welcome to IRV2! We're sure glad you joined the gang!

Can't help with that but noticed you are new and wanted to say hello!

Good luck, happy trails, and God bless!

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Old 08-02-2018, 10:26 AM   #3
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An AT542N is a 4 speed (no overdrive). Check the fluid condition and fluid level.

Is this a new problem or has it done it for a while? What type of engine do you have? It might be as simple as a sticking modulator. It's possible that you could have a valve sticking in the valve body. Dialing in a valve body is becoming a lost art with all of the electronics on the newer transmissions.

I'd call around your area and look for an Allison Transmission dealer/distributor. Possibly check with your local school district, find out what transmissions they are running in their smaller school buses. If the are running any version of the AT500 series of transmissions, see where they take their buses for transmission work.

I was an Allison Transmission shop foreman/field service tech, been out of that business for a while now. There is an Allison Transmission fluids engineer, and a district rep on this forum as well, hopefully they'll see this thread and have more advice for you.
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Old 08-02-2018, 10:41 AM   #4
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My 4000MH has been doing that too, but I had new house batteries installed right before it started so I'm hoping it is due to the batteries being disconnected.
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Old 08-02-2018, 12:21 PM   #5
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^^^^Your issue will be completely different as the 4000MH is an an "adaptive" electronically controlled valve body. It's possible that the transmission control module lost it's adaptive settings when replacing the batteries and went back to the baseline shift patterns.

One thing you can try (assuming you are talking about the 2-1 downshift) is use the throttle and the brake as you are coming to a stop. Slightly raise the engine RPM as you are coming to a stop. This procedure will essentially "teach" the transmission how to downshift. The shift may be a little harsh when you are performing this operation, and it may take a couple of tries for it to correct the downshift. The transmission should adjust itself over time if you don't want to try that procedure.
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Old 08-02-2018, 03:32 PM   #6
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Welcome to the forum!

We're sorry that it took a problem for you to join us, but we hope that you will stay engaged on the forum after you have a resolution.
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Old 08-06-2018, 07:25 AM   #7
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The first thing to check on an AT500 is the modulator linkage. It needs to be adjusted correctly. Do you have access to an AT mechanics tips booklet or a service manual?
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Old 09-16-2018, 12:26 PM   #8
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Allison wont shift into gear

2006 Winnebago Journey 36G, Cummins 300. Allison transmission wont shift into any gear. Engine starts. Engine monitor says "No Brakes" but brakes are fine. Any ideas what to check? Cant move it so cant take for service.

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