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Author Topic: GEAR RATIO, REAR END ?  (Read 6695 times)
lostagain
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« Reply #45 on: April 12, 2010, 08:50:48 AM »

 At Brewster's in the '70s, some of the MC5As went that fast. They had the 8V71 and 4 speed manual. Most of them only went 65 to 70 mph. I had one the summer of '75 that was like Ed's, I was scared to find out how fast...

JC
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
rv_safetyman
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Jim Shepherd


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« Reply #46 on: April 12, 2010, 08:57:50 AM »

Clifford, I had posted somewhere that I had a great gear manufacturer who was willing to work with me (at least at the time) to cut the gears to make an overdrive for the drop box. 

The issue I always struggled with were gear centers.  I did not want to get into modifying the housing to change gear locations.  At the time, I asked if anyone was willing to "lend" us a drop box to do an engineering study.  Didn't get any offers, so I dropped the project.

If the box manufacturer did the design work, and if the center locations are the same, it would be real interesting to get one and see what it would take to replicate the parts.

Jim
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Jim Shepherd
Evergreen, CO
85 Eagle 10/Series 60/Eaton AutoShift 10 speed transmission
Somewhere between a tin tent and a finished product
Bus Project details: http://beltguy.com/Bus_Project/busproject.htm
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Ed Hackenbruch
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« Reply #47 on: April 12, 2010, 03:58:19 PM »

Clifford, i think that i will just keep it no matter what it is.   Smiley  Bus races anyone? for pink slips? Grin
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1968 MCI 5A with 8V71 and Allison MT644 transmission.  Western USA
Tom Y
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80 5C With Cummins L10 in Progress




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« Reply #48 on: April 12, 2010, 04:30:51 PM »

Jim, The only way to change ratios is to change centers. Or are the gears different sizes? I think the input and output are the same size?

Clifford, Do the trucks run the same input gear as the busses?      Thanks Tom Y
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Tom Yaegle
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« Reply #49 on: April 12, 2010, 05:54:35 PM »

Tom, there are three gears (input/idler/output).  At first, I thought you might be able to change the number of teeth on the input and output gears and compensate with the idler gear.  That would not make any sense if you consider the input would have to have more teeth (smaller idler gear) and that would not match with a smaller output gear.  My next thought is that a person could look at other gear profiles that might make the gear centers work out, but I thought more about that today and it does not seem logical.  Thus, a change in gear center would be required.

We have a person in the Eagle International Chapter that said he made an overdrive drop box.  I will try to see what he did when I get some spare time. 

I talked to Wayne ("Rusty") today and he has a spare drop box that we could play with.  However, I don't have the time and it looks like an uphill battle.

The main reason for an overdrive gear box is probably to properly gear a bus when a four stroke conversion is done.  However, that conversion suggests that a 35% plus overdrive is ideal for most applications.  Thus a .93 does not do much.  It is probably OK for a four stroke that wants a bit more speed.  When I first started thinking about the overdrive concept, it was several years ago and both AutoShifts and World transmissions were priced sky high.

So, it looks like a whole drop box design would be required.  Probably way too costly for our limited market.

BTW, I looked at the .93 gearing and that still does not explain Ed's speed capability if he has a 3.73 and 2100 RPM speed limit (~~ 77 MPH).  If he had a 3.36 and .93, he could probably do 86.  If he just had a 3.36 he could do about 80.  All of this are rough calculations based on tires that have about 500 rev per mile.

Jim
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Jim Shepherd
Evergreen, CO
85 Eagle 10/Series 60/Eaton AutoShift 10 speed transmission
Somewhere between a tin tent and a finished product
Bus Project details: http://beltguy.com/Bus_Project/busproject.htm
Blog:  http://rvsafetyman.blogspot.com/
Tom Y
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« Reply #50 on: April 12, 2010, 06:51:41 PM »

Jim, I agree with your thinking. But with my setup the .93 may be just right. I to looked at the world tranny at the time. Way to pricey, now I would do it as the price has really come down. I have a good 740 so the .93 sounds good.   Tom Y
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Tom Yaegle
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