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Old 06-26-2004, 10:50 AM   #1
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better gear ratio cheap

I've been discussing the topic of changing the final drive ratio of the skoolie on another site. There are some good options that were mentioned, but they were not cheap.
Two of the best ideas:
Install a manual transmission with double overdrive
or
Install a 2 speed rear end with a 4:10 final drive

Neither of these options are cheap.
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Old 06-26-2004, 10:54 AM   #2
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Last nite while i was laying in bed, i came up with a cheap idea......

Why not install a standard transmission backwards behind my existing allison automatic?

If the "new" trans was a 4 speed, placing the trans in 3rd gear would significantly lower the engine rpm's at any given speed.

In the unfortunate event that the skoolie engine could not handle the new gear ratio, the aux trans could always be put back into high gear which would give a 1:1 gear ratio and act as if there were no modification at all.


What are YOUR thoughts on this project??

I found a 4 speed manual trans from a big truck for $100 at the bone yard.
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Old 06-26-2004, 10:31 PM   #3
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Connecting your driveshaft to the input shaft of the second transmission will interesting. I've them do things like this on junkyard wars but never on a real passenger vehicle.
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Old 06-27-2004, 02:39 AM   #4
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I really don't believe that the input shaft ( now the output shaft ) is supported nearly enough to take the load, it is a very short shaft with inadequate bearing to take the torque you are going to throw at it .
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Old 06-28-2004, 05:30 PM   #5
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What are you trying to do, get better go faster or get better mpg? Even my 72 international with only 182 hp can do 70 on the interstate.
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Old 06-29-2004, 01:11 PM   #6
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"what are you trying to do? go faster or get better fuel economy?"

The answer is YES.

My primary focus is to increase ground speed. I have plenty of engine, but not enough gear ratio to reach decend highway speeds. The bus cruises between 57-61 mph on flat ground fighting the rpm govenor all the time. On the x-pressway, big trucks run you over at that speed!There's the possibility of better fuel economy if i were to keep the bus at 55-60 mph, that would be a nice bonus, but that's not the main motivation behind the change in gear ratio.

After talking to a few mechanics, and reading quite a few posts, I think the inverted transmission idea is not a no go. Perhaps i'll start diligently searching for a 2 speed rear axle with a 4.10 final drive. If I find one at the junk yard, i can probably bring it home for $100 bucks. The problem is finding what i'm looking for. Most of the axles i've looked at are not clearly marked with the ratio. That requires jacking up one set of duals, and counting the number of revs of the drive shaft it takes to turn the wheels one complete revolution (then multiplying the number by 2) It sound easy, but most axles are on really big trucks that are on dirt or mud in the middle of the bone yard which makes jacking quite difficult.
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Old 06-29-2004, 08:57 PM   #7
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My '91 with the 7.8L diesel and 5-speed can get up to 65+ without much difficulty. I don't like to run that fast just because it seems like the engine is turning at a pretty high RPM for my taste.

Anyway, are you sure you are hitting the RPM limiter, or a speed governor? The buses I drove for Laidlaw all had speed governors on them and were set between 55-60 mph. Which made it nice on the highway, just peg the throttle and the bus would keep it at the speed limit. Granted they are all newer than my bus and automatics....
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Old 06-30-2004, 12:43 AM   #8
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I'm not certian if there is a speed govenor on my bus....but it seems unlikely. The getleman i spoke with at the transmission shop today believed that the bus was running against the govenor. He sais the bus engine speed is set far below redline and could be "bumped up" without any detriment to the engine. To which i replied: "my bus already has over 265 thousand miles, i would prefer not to do anything that would significantly reduce what's left of my engine life"

I drive my bus with the accelerator all the way to the floor. I really only need two throttle positions: idle and full speed. I've joked about putting a brick on the gas pedal when i'm going down the expressway.
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Old 06-30-2004, 12:53 AM   #9
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I made a new friend today. I took my bus to the transmission shop to talk about options for increased highway speed. The owner of the shop really liked my bus. We talked about a standard transmission with double OD.....way to pricy! Also talked about replacing the axle with a 2 speed. He thinks that a 3.83?:1 gear ratio would be an ideal final ratio with a 2 speed rear end.

I asked him about the backwards transmission idea.....He said it's been done before. The only thing it requires is a bearing on what is now the output shaft. He said it would work, but there's a lot of labor and fabrication involved in making it work properly. Then he mentioned that they make auxilliary transmissions that would work perfectly with no modification and they can be install it backwards to get my desired effect. Even better, he found a scrap guy that had an old Ford with the same size driveshafts as my bus that has such a trans already installed. It's an old grain truck, and was on it's way to be crushed as soon as the fields dry out. (apparently it's stuck in the mud in some farmers field)

He's sais gonna get back with me soon, but it sounds like this is my ticket....and should even be in my price range WE talked about "bus stuff" for more than an hour.
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Old 07-20-2004, 01:55 AM   #10
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just outta curiosity... what size engine do you have in your skoolie ??
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Old 07-20-2004, 09:27 AM   #11
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the approximate size of my skoolie engine: too small!

it's a 6.6 liter brazialian made ford diesel......inline 6 cylinder turbo rated at 180 hp. will it have enough power to drive the bus faster than 60 mph?? I don't really know.

The beauty of the auxilliary transmission is that if i do all the work and find the bus can't handle an 18% incerease in the gear ratio.....i can just leave the aux trans in 4th gear permenantly. If it was a ring and pinion change...it would cost me hundreds of dollars to return the bus to it's original gearing.

I am planning ot visit the transmission shop again today and see how the project is coming along.
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Old 10-07-2004, 11:06 AM   #12
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I just found out what my gear ratios are, this is probably why I really out accelerated you last month Jason!

2 Speed Diff Carr GR: 6.33-8.81
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Old 11-26-2004, 08:15 PM   #13
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Cheaper option

I considered this on my bus
My bus has 22.5 tires in the rear
I thought of haveing 24.5 put on it this would increase the distance traveled per revolution and allow a higher cruising speed. My only problem is the 8.2L detroit is a pooch going up hills but has huge torque under 10 mph. Im thinking of adding the 24.5 tires and installing propane injection for the long hills. Propane is said to decrease cylinder temps and of coures add power.
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Old 11-26-2004, 08:18 PM   #14
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Gear splitter

I have installed a few gear splitters in some 1 ton trucks at work and those have been a great option. I looked for days for one to go behind my allison AT545 auto and had no luck.
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Old 11-26-2004, 11:48 PM   #15
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Mr. Lapeer, You have got me a little nervous about the Brazillian 6.6
The bus I would like to puchase is a 1998 Ford with the 6.6 I just got rid of a large transit bus because of top speed 55 MP/H.

I would like to have a cruising speed of 70 MP/H.
Having said that, I have not gone to see what this bus will do. It is a 72 Passenger bus.

Am I wasting my time going to see it??

Cheers!
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Old 11-27-2004, 11:28 AM   #16
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The 6.6 New Holland is a good engine--I've even seen them push 25-ton 10-wheelers to 65MPH (eventually).

However, the AT545 emasculates ANY engine it's behind. Essentially ANY other tranny would be a better choice. The 545 is a true "slushbox", in that it never locks up. It's also Allison's weakest tranny, the converter stalls too high, & it runs tremendously hot.

Lapeer: what tranmny do you have? If it's a 545, you're basically out of luck.
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Old 11-30-2004, 10:26 PM   #17
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I have the 545.. it's the 2nd trans in this bus. The first one went about 150,000 miles. The bus now has just over 276,000 miles.


thanks for the input.

This was one of my crazy ideas that i've since decided was a bit too crazy to put into practice.
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Old 12-01-2004, 03:27 AM   #18
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Quote:
Originally Posted by lapeer20m
This was one of my crazy ideas that i've since decided was a bit too crazy to put into practice.
Till next summer when it is warm out again and you are looking for something to do
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Old 12-01-2004, 06:18 PM   #19
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i believe that swapping the allison auto for the eaton 13 speed is a viable solution. I'm just not sure if the advantages are worth the effort.

swapping an auto for a manual trans might be way more difficult than i realize.

I still have access to an eaton 13 speed and the rear axle from a big truck for cheap..... $250.00

I also have a clutch pedal that is hydrolic actuated. That would make life a lot easier than trying to install the linkage.

Winter has set in here in the great white north. Any project on that scale would have to wait until warmer weather.
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Old 05-18-2006, 05:11 AM   #20
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slow as a snail

I have a 1975 Ford B600 with an unknown gas engine. I suspect a 361. I has a 4+2 which gives me plenty of torque but with the original goverened holly double pumper, 60 sounded like I was ripping the engine loose.

On one trip last year we discovered that it was flooding onto the maniforld so this year we've purchased a brand new Edelbrock Performer economy carb that is a bolt on replacement. The only problem is it won't accept a governor. So I'm going to have to govern it manually somehow. Probably just by keeping a VERY close eye on the new tach.
I have 8.25x20's on the rear right now and 10(.5?) x 22.5 G159's on the front. The rear is bias and the front is radial. I'm hoping that by changing to radial 22.5's all the way around I'll increase my speed without worrying about damaging my engine.
Any thoughts?
If I remember right the block code on the engine is D3TE-1
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