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Ted OShann · 11-22-2016, 04:41 AM

My excella motorhome that I imported to Australia has an Isuzu diesel motor and a chev 400 gearbox. The auto has no 'park position'. My roadworthy engineer needs an explanation why for his report. Is this how they came from the factort after vthey were reprogramed to match the diesel?
Ted

overlander63 · 11-22-2016, 05:02 AM

Welcome to the forums.
The heavy duty transmissions generally don't have a parking pawl in them, as it is too easy to damage or destroy it. Most use the parking brake, typically mounted at the rear of the transmission, as "park".

Smartstream · 11-22-2016, 11:57 AM

Your Airstream should have a TH 450 or 475 and it should have a park position on the gear selector. It also has a parking brake on the rear of the trans operated by a lever under the dash. If you have rear drum brakes the parking brake will be in the rear drums rather than the rear of the trans.

If you have no park position on the gear selector you may have an Allison transmission. They were rare but they do exist with the Isuzu diesel and they do not have an internal park pawl.

Good Luck,

Ted OShann · 11-24-2016, 03:51 AM

Thanks Dan and Terry,
I had assumed that it was a chev auto but I would be happy if it was an Allison. I will have to have a closer inspection. I just have to research the difference between the 2 so that I can recognise which one it is. It does make sense that it is a heavy duty box as there is definitely no park position on the gear selector.
Cheers,
Ted

overlander63 · 11-24-2016, 04:20 AM

Quote:

Originally Posted by Ted OShann

Thanks Dan and Terry,
I had assumed that it was a chev auto but I would be happy if it was an Allison. I will have to have a closer inspection. I just have to research the difference between the 2 so that I can recognise which one it is. It does make sense that it is a heavy duty box as there is definitely no park position on the gear selector.
Cheers,
Ted

It's been the better part of a decade since I was under one of those, but I remember the pan on the transmission of the THM 400 series having something like "Hydromatic GMC" stamped in them.