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Old 08-23-2011, 11:57 AM   #11
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Location: Central Tennessee
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Re: High RPMs?

Thank you all for the replying to this post.

I do indeed have a placard on the dash. It says 6.8 gear ratio.




I am fairly sure that the rear end gears have been changed. The only way that I will know is to do the spin the tire and driveshaft method of calculating.

My computer died but magically came to life again after two days. Weird. I sure hope it continues to work. I love coming to this site. Gonna go look at the tranny today. Hopefully I will find the tag with the data on it.
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Old 08-23-2011, 05:16 PM   #12
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Re: High RPMs?

I went under the bus today and found the tag on the transmission. It is an Allison made by Detroit Diesel Company. The model is MT 640.

Anyone know much about them?
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Old 08-23-2011, 06:06 PM   #13
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Re: High RPMs?

The mt is a great and durable trans. You should get a nice, long, trouble free life from it.
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Old 08-27-2011, 06:17 PM   #14
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Re: High RPMs?

Quote:
Originally Posted by nevrenufhp
I was only saying it was the calculation, not the actual gears. I'd be more inclined to say 5.13s or 5.29s too. With at best of 210hp & no turbo, it would have a real hard time with 4.10 gears. If it had more power, 4.10s would be great.
Yes, going 60 will also help fuel economy too.
I have 4.10's and only 200HP...it works beautifully!
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Old 08-27-2011, 06:19 PM   #15
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Re: High RPMs?

Quote:
Originally Posted by Accordion
I went under the bus today and found the tag on the transmission. It is an Allison made by Detroit Diesel Company. The model is MT 640.

Anyone know much about them?
As neverenuf said, great trans...same as in my Genesis. It's running at about 1/3 of its rated weight in a skoolie, so it will go just about forever. That's the same trans used in the 50,000+lb trash truck my brother drove.
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Old 08-28-2011, 01:29 AM   #16
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Re: High RPMs?

Jarlaxle, that DT 466 has way more torque than my 8 cylinder. I wish I had that motor. Many people claim that it is the BEST motor.
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Old 08-28-2011, 07:33 AM   #17
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Re: High RPMs?

It is!

But at the power peak, torque kind of doesn't matter. The powerBAND matters (If your power peak is 2800, you will not be climbing hills at 1900RPM; at least, not very well.), but not really the torque peak.
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Old 10-09-2011, 02:34 PM   #18
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Re: High RPMs?

I have an 8.2L Detroit in front of an MT643 Transmission and a 5.29 rear end. It will go 68 on the governor, but it judging by the noise it must be set remarkably high. My bus seems happy at about 58mph on the highway. I would like to be able to drive at about 65 with 20% fewer revs, so so I am installing an auxiliary overdrive. I bought it used, and am about half way through the rebuild. It is a Spicer 7231D. It has a 2.14:1 under drive, and a 1:1 and a 0.86:1 overdrive. I am hoping that this will allow my bus to get better fuel economy on the flats.

Has anyone else installed an overdrive in a bus? Any tips for what might go wrong.

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