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Old 04-09-2012, 01:44 PM   #1
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Allison 2500 5 speed transmission converted to a 6 speed

Has anyone used Suncoast Transmissions 6 speed valve body and TCM to convert an allison 2500 5 speed transmission to a 6 speed? If so, is it working ok? Did it help fuel consumption? Does it have an economy mode?
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Old 04-18-2012, 12:22 AM   #2
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There might be a couple reasons why a 6 speed wasn't installed initially:
1. cheaper
2. gearing is such that it won't pull the 6th gear except going downhill or with a tailwind.

Might want to check on #2. If that's the reason I'd save my money.
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Old 04-18-2012, 04:10 PM   #3
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Originally Posted by LJB View Post
Has anyone used Suncoast Transmissions 6 speed valve body and TCM to convert an allison 2500 5 speed transmission to a 6 speed? If so, is it working ok? Did it help fuel consumption? Does it have an economy mode?
How do they get another gear with only a valve body/TCM change ???
Are they locking up the convertor in a lower gear and calling it a 6 th gear??
Do these guys have a web page ?
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Old 05-07-2012, 07:58 AM   #4
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From the research I did on this subject, I assume the 5-speed transmission was used to keep down the cost, because the differential has the same gearing as similar models with the same engine and weight. The transmission gearing was also identical except the 6th gear was left out.

I made many phonecalls for info on this subject. First was a technician at Allison. I gave him the vin# and model of transmission and he said it could be done by reprogramming the tcm and gave me the name and number of a certified Allison repair shop. The gentleman at the repair shop said it could not be done on a 2005 model 2500 transmission.

I called Suncoast Transmissions 2 times and the first person I talked to said he didn`t know about that model of transmission. The next gentleman said it could be converted to a 6-speed by "fooling the transmission into acting like a 6-speed and making 5th gear shift twice". They do this by reprogramming and changing the valve body.

I made a few other inquiries through other phonecalls in between these calls. Too many different answers and too many vague answers to take a chance on this motorhome. I had considered buying this 2005 cross country with the 5-speed. I told the DW I would buy a gasser before buying a diesel pusher with a 5-speed transmission because I would get the same mileage with the gasser without all the extra maintenance costs.
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