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Old 06-22-2009, 09:12 AM   #1
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Transmission, NEED MORE SPEED

My bus is a 1992 Ford B700 with a Brazillian 6.6l engine coupled to the allison 4 speed tranny... not sure what model of tranny it is.

What I am curious about is wether or not these transmissions contained the 5 and 6th gear like the larger allison transmissions found in the city buses or coaches. If so, can you just swap the valve body in them or do you need to get a wholed new tranny? Has anyone had success with swapping the gearing in the rear end? If so, what gears did you use for what result? I can hit about 110km an hour max but she is screaming!

Any help would be appreciated.

Thanks
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Old 06-22-2009, 09:34 AM   #2
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Re: Transmission, NEED MORE SPEED

we need more informtion, specifically what transmission and what axle and ratio is in your bus.
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Old 06-22-2009, 04:59 PM   #3
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Re: Transmission, NEED MORE SPEED

if you are happy with gaining 5-10 mph top end speed for free you can simply turn up the govenor, and with the whimpy 6.6 liter ford might as well turn up the fuel delivery at the same time. Best two mods you will ever do to your bus!

I think a 4:44 rear end or even slightly more conservative (highway) is usually a good choice in a bus. You do loose hill climbing ability and the bus takes off slower from a stop. Theoretically with an mt643 and a 4.44 rear end you should be able to do well over 70 mph, if you engine has the power to push the bus through the wind that fast. I'm not sure how fast the brazillian ford can spin compared to the cummins 5.9.
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Old 06-22-2009, 07:50 PM   #4
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Re: Transmission, NEED MORE SPEED

Quote:
Originally Posted by BrutalBus83
My bus is a 1992 Ford B700 with a Brazillian 6.6l engine coupled to the allison 4 speed tranny... not sure what model of tranny it is.

What I am curious about is wether or not these transmissions contained the 5 and 6th gear like the larger allison transmissions found in the city buses or coaches. If so, can you just swap the valve body in them or do you need to get a wholed new tranny? Has anyone had success with swapping the gearing in the rear end? If so, what gears did you use for what result? I can hit about 110km an hour max but she is screaming!

Any help would be appreciated.

Thanks
You most likely have an Allison AT545. It is a 4 speed transmission and there are no other hidden gears because they would require another planetary set ($$$) within the gear train. Jason makes a good suggestion at bumping the governor and the fuel delivery a little if that is what you desire. Otherwise you will be looking at swapping rear end gears or going to a different transmission. Of course I have to ask why. 110 kph is nearly 70 mph (I drive a Canadian truck here in Minnesota so I have these pretty well memorized). That's moving in a bus! Most of us would kill to be able to cruise at those speeds which exceed most speed limits in my state and many others. How fast are you looking to go? My 6.6 powered bus with an AT545 and 4.56 gears rolling 10.00R20 (~42 inch diameter) rubber will only do about 100 kph on flat land and with a good run up.
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Old 08-25-2009, 01:43 PM   #5
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Re: Transmission, NEED MORE SPEED

If you're talking non electronic allisons, the AT's and MT's, the 5 speed won't help, anyway. The additional gear is a creeper, with a little over 8 to 1 gear reduction. the top gear, whether it is 4 th or 5 th, is 1 to 1. One advantage of the mt series is the lockup torque converter, which would boost the top speed very slightly by eliminating the torque converter slippage. The MT is also a much beefier trans, good for up to about 74000 gvw. the AT545 is near it's max weight in a bus.
The lower first gear would allow you to regear the axle for more speed and retain the ability to accelerate from a stop on a hill. The low first gear is accessed only by manually selecting it- it won't go into the low gear while in 'D'.
I bought an MT653, and plan to do just that. The ring and pinion for my international is only a little over $400, and available in many ratios.
Learn about them before deciding, there are many variations. They come with different torque converters, shift points, methods of determining engine load, accessories, etc. For example, if you get a trans from behind a DT466, and plan on using it with your GM 366 gas, you'll need to make a lot of changes, or might have undriveable junk.
Allison can look up trans details based on the serial number. Lots of manuals on ebay to learn from, too. I'm low budget, but have probably $300 in manuals for bus, engine, and trans. labor is $100 per hour these days.
Also, the AT545 is just under 300 lb, the MT653 is just over 600 lb- a floor jack and muscle don't really cut it with this swap.
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Old 08-28-2009, 09:49 PM   #6
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Re: Transmission, NEED MORE SPEED

The trans should have a tag on the side with the model info. It'll be an AT545, or an MT643 or 653. At that point, go with the gear swap, and/or gov spring mod for more rpm.....but that has already been mentioned. If you're looking for a whole trans to swap, the best one (for an Allison)to use in an older rig is the MD3060. They can have up to 6 forward gears(double overdrive).
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Old 09-14-2009, 12:03 AM   #7
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Re: Transmission, NEED MORE SPEED

I had the differential carrier rebuilt in my 95 Ford Cummins 5.9L /545. I changed the 4.88 RAR to a 4.11. It got me 70 MPH with the acc. pegged on a slight down grade which is plenty. The acceleration is decent and pulls the slight grades here in MI just fine. It basically got me 8 mph faster at the same RPM than I had with the 4.88. I would go much faster than that. It was a hell of a job too. I suggest using a transmission jack with some straps. I did it with a 3 ton floor jack....
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Old 09-14-2009, 05:53 PM   #8
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Re: Transmission, NEED MORE SPEED

I have been a diesel mechanic for long time 20 plus years and people alway wanted there engine turn up. The frist thing I would ask is how long do you want your engine to last....10 or 15% is fine but any more than that your asking for it.....Also you can turn up the HP a little but at a point the more the HP goes up the torque will go down.. I have seen tractor that just dumping the clutch the motor would fall on it,s face...but would 400Hp....I will get off my soap box now.....
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