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Old 07-14-2011, 12:33 PM   #1
Join Date: May 2010
Location: San Diego, CA
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Year: 1984
Coachwork: Bluebird
Engine: 8.2L Detroit Diesel
Has any body installed an auxiliary overdrive?

I just bought a Spicer 7231D. Sometimes called a brownie box, it is an auxiliary transmission which provides 1:1 direct drive, 0.83 overdrive and a 2.1 underdrive. I know that they were used a lot in industrial equipment such as cranes. I am planning to use this on the highway to reduce my engine speed, reduce the amount of noise inside the bus, and save some fuel. I am also planning to change my rear end from a 5.29 so something more highway friendly. At the moment I run 70mph on the governor at about 3200 rpm

Has anybody every installed one of these into a school bus? If so any tips would be welcome.


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Old 07-14-2011, 01:14 PM   #2
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Re: Has any body installed an auxiliary overdrive?

I havent but when you do you will have to take in account your speed and odometer will be off unless you find out how to get that corrected to.
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Old 07-31-2011, 11:50 AM   #3
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Re: Has any body installed an auxiliary overdrive?

The overdrive seems to have an output for a speedometer hookup. I haven't torn the whole thing apart yet, so I am not 100% sure on that. I ordered a rebuild kit for it, and it only came in a few days ago, so I was waiting before getting into it. I also thought about installing a GPS and forgetting about the existing speedometer. It gets stuck at 65 any way.

I will also have to splice it into the drive line, so at least one new drive shaft will be necessary. I went out to see a drive shaft specialist last week, and he should be able to take care of that.


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Old 07-18-2019, 06:47 PM   #4
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Wondering if there's any more to this story. I'm seriously considering the same thing.
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Old 07-19-2019, 08:42 AM   #5
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Not sure if the OP ever got it done. But I know a few who have.

Famousinternetjesus did on his bus. He was originally automatic, then added the brownie. He ran that for a while and then swapped the at545 for a manual which is how those are supposed to be ran.

There is a guy on youtube that did the same thing. His username was txstreetman and he also had an at545 with an auxiliary transmission.

I haven't seen any updates in a while on either of them so who knows how they're working.

I have a spicer 7041 sitting on the floor. Not sure what I'm going to do with it.

Your auxiliary transmission will have a spot for a speedometer, all you'd have to do is select the right gear for it internally and then adapt it to the bus.
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Old 07-19-2019, 11:20 AM   #6
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I have a spicer 5831 in my truck that I installed. The overdrive allows for both lower highway rpms, and spliting gears. Not sure on yours but they are normally non syncho, so no idea how it would do with an automatic. Even with a manual you need to double clutch or be good at rpm's and shift timing to have it work well.

Would not change the rearend until you have the brownie in and try it.
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