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Old 03-01-2017, 07:44 AM   #1
Mini-Skoolie
 
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Cummins 5.9 W Alison Tranny

My question is more tranny related. my 1995 BB FE Cummins has a Alison 545??? I think. I have been told some of these had the top gear removed electronically from operation. This over drive gear (if I have it) would be very helpful to reach highway speeds without turning up power too much on the 5.9 12 valve. So if the engine is computerless 12Valve is the matching tranny electronic on mechanical? If it is electronic has anyone figured out how to an a switch/signal to allow the missing overdrive to be engaged?
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Old 03-01-2017, 08:00 AM   #2
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Originally Posted by EZBUZZSAW View Post
My question is more tranny related. my 1995 BB FE Cummins has a Alison 545??? I think. I have been told some of these had the top gear removed electronically from operation. This over drive gear (if I have it) would be very helpful to reach highway speeds without turning up power too much on the 5.9 12 valve. So if the engine is computerless 12Valve is the matching tranny electronic on mechanical? If it is electronic has anyone figured out how to an a switch/signal to allow the missing overdrive to be engaged?
545 is a four speed with no OD.
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Old 03-01-2017, 08:20 AM   #3
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Sorry mate, if its a 545, Eastcoast is correct, Its a 4 speed- No Overdrive. I believe you are thinking of the 3000 series Allisons. They have an electronic control that can be reprogrammed to open up 6th gear.
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Old 03-01-2017, 08:28 AM   #4
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the 4 in 545 means 4 speed
same for the 643, the most common swap you see with the 545. the 643 is stouter than the 545, it can take more hp than the 545.

changing the rear end and big tires would get you more speed. you want a 4.10 rear gear.
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Old 03-01-2017, 12:09 PM   #5
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BB Gear change

I got a 95 BB CSFE with 5.9 12 valve and a 545 behind it. Got 4.78 gear in the rear. 22.5 rear tires. I love the gear I have. I was unhappy with it when I first converted my bus but after driving to west coast twice I am happy with it. I can go 70 on flat ground at 10 MPG (awesome!) and when I got to the Rockies I was able to go 35 MPH up the steepest grades. If I had a taller gear to improve highway speeds I would have been going 10 MPH up those hills. Just think about it before you switch it. Bluebird knows what they are doing when they built these things.
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Old 03-01-2017, 08:34 PM   #6
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&) mph

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Originally Posted by Paulkeenan View Post
I got a 95 BB CSFE with 5.9 12 valve and a 545 behind it. Got 4.78 gear in the rear. 22.5 rear tires. I love the gear I have. I was unhappy with it when I first converted my bus but after driving to west coast twice I am happy with it. I can go 70 on flat ground at 10 MPG (awesome!) and when I got to the Rockies I was able to go 35 MPH up the steepest grades. If I had a taller gear to improve highway speeds I would have been going 10 MPH up those hills. Just think about it before you switch it. Bluebird knows what they are doing when they built these things.
I can hardly hit 70 going down hill. I have the same gears as you do, have you turned up your throttle screw? I am at 2550 RPM at 63.5 MPH and only get 8.9 MPH. Maybe I better start checking things on the engine, like fuel pressure or maybe she is just not broke in yet....3880 confirmed miles.

Thanks for all the feed back yall!
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Old 03-03-2017, 11:36 AM   #7
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It's broken in. That's all just fanboy crap about an engine not being broken in at 100k miles.

What size tires do you have? That's just as important as the gear ratio.
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