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Veteran
 
Location: Houston, Texas | Hello forum, need input with my future 90 model 6BT Cummins transplant, the seller gave me the
adapter plate for the 727 Torque Flite, is it possible to change rear end gears to keep my original
transmission and the keep RPMs low enough ? is it worth it ?
would it be more economical to get a 47RH ?
would the 727 provide decent millage ?
the seller mentioned that the engine was from a 1990 Dodge Truck, 727 and 3.73 gears,
and would get around 20 mpg. (I know it was not as heavy as our FMC)
Thank You
Rico Gomez
Houston, Texas |
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Expert
Location: Cottage Grove, OR | My personal opinion is that with the narrower torque band of a 6BT you need more than three gears to get adequate driving performance from a diesel. Also, the 727 does not have torque converter lockup and if doing all the work to do the conversion I would definately require lockup as a feature. If you go with a 5 speed Allison 1000, you will have more gears to get up to speed and up a hill, torque converter lockup and an overdrive which wiil probably eliminate the need for rear end changes. |
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Expert
Location: Cottage Grove, OR | Additionally, have you visited any of the online forums that are dedicated to the Cummins engines? The people on those forums transplant 4 &6BT engines into all sorts of things. There are some FMCs with Cummins in them, but all of those that I am aware of use an Allison transmisson. Due to a shift/change in weight, you should also look at doing additional things to support the engine. |
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Extreme Veteran
Location: Ignacio Colorado | Even with the 47RH you would need a higher gear ratio rear end. Higher ratio means lower number! The 47RH and stock rear end would have you spinning the engine around 2400 rpm at 65 mph in overdrive. You want that engine turning just under 2,000 rpm at cruising speed. The Cumming peak torque is at 1,750 rpm. The coaches running the Cummins have changed to a different differential. Actually they machined a different differential to fit the FMC to get the right ratio. The axle tubes are cut off and the housing machined to accept the stub axles. Being a pusher and having such a short drive shaft between the transmission and differential makes it a tougher job to find ways to fit longer power plants.
I am getting ready to install an overdrive transmission in #902. I am sticking with the big block 440 for the first run. I will be using a very low lift cam to get the peak torque down where the engine and overdrive work together. To accomplish this I have taken the internal geartrain from a 47RH (Cummins or V-10) into the 46RH case. The 46RH fits behind the small block 318-360 v-8. An adapter is required to fit it to the 440. I am using the 4 wheel drive truck 46RH as the 2 wheel drive transmission is way to long for the FMC. this required threading the tail shaft and having a yoke built from the original 727 park brake drum. Maybe Lou will post some pictures of his machine work to make this project possible. The end result is a transmission/adapter that is just under 2" longer than the stock 727. No park break yet but have seen a kit that bolts to the Rockwell with a disc brake for park. Ran out of time, Daughter needs ride to school. Hope to have this in the coach by the mega rally. Come see how it fits. Bill Sitton.
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Veteran
Location: Houston, Texas | I found an 1999 Allison 5 speed with drum brake from a chevy 454 engine,
would this work without computer ?
without changing the rear end gears ?
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Expert
Location: Cottage Grove, OR | ricogomez - 2014-02-19 8:56 AM I found an 1999 Allison 5 speed with drum brake from a chevy 454 engine, would this work without computer ? without changing the rear end gears ? Yes, it will work without a computerized engine. It needs the Transmission Control Module (TMC) and wireing harness which should come with the transmission. You would then need to get an aftermarket throttle position sensor and then it will work. A five speed will give you a 0.71:1 top gear and a six speed Allison will give you a 0.61:1 top gear. You can do the math and see if it is what will work for you. The six speed would be best to get to the rpm range that Bill suggests and not have to mess with the rear end or wheel size. That is what I am using in my Duramax conversion to get to the rpm that I want. You can look at the photo album on this site titled "The dieselfication of 1046" to follow my project. |
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Veteran
Location: Houston, Texas | does anybody makes parts for our FMC rear ends ? |
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Expert
Location: Cottage Grove, OR | Yes.
The differential is a Rockwell and they make the parts for the differential used in FMC coaches. Get the model number and serial number of your differential from the ID plate on the differential and then contact Rockwell. There are other ratios other then the stock 4.625:1 ratio, but I don't know what they are. One other coach owner that I know of has changed his differential to a different model Rockwell, but that is increasing the scope of your project. |
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Veteran
Location: Houston, Texas | Thank You, the 6 speed allison seems to go for about 3 times the price of a 5 speed with the drum brake already on it,
maybe if a go with the 5 speed I won't need a transmission computer ?
maybe shorter too? |
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Expert
Location: Cottage Grove, OR | ricogomez - 2014-02-21 5:15 PM Thank You, the 6 speed allison seems to go for about 3 times the price of a 5 speed with the drum brake already on it, maybe if a go with the 5 speed I won't need a transmission computer ? maybe shorter too? Both of them require the TCM and are the same size as they are the same transmission with some internal changes. The TCM is not expensive and should come with any transmission you are buying. If it is not included with harness, do not buy it. The six speed is more because it is the newer version with some internal strengthening and is in demand because of that sixth gear. |
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6BT future transplant
