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Discussion Starter #1
Would like to say hello again, been away for quite a while. My new interest is in getting better mileage, all time best of 30.75mpg.

Anyway, I have the 3.89 gears already and i went cheap with used tires and have 215/60/16's so now my cruising rpm's are a bit high and really limit my mileage conquest. 2100rpm at 60.

QUESTION: Can the two sprockets at the rear of the transmission be transposed so the larger one is on the output shaft and the smaller one is on the diff. shaft?

Thanks.
 

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I am going to guess that the answer to that question is no. However, that particular gearset can be swapped out with the gearset out of a base model 300m which has a gear ratio of 3.66 instead of the 3.86 gears that are currently in your car.
 

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if you want lower RPMs at 60mph you should put in the 3:66 gearset that come in 3.2L and 3.5L cars (non 300m special)
This is your answer. 3.89 is what comes with 300M Special's and 2.7L LH vehicle's, it's the go-too for torque and speed. Only other options would be Prowler gears and Prowler Pro Gears. But performance options.

If you run some numbers and know your math and find it will be in more of your favor swapping output shaft and differential shaft gears; then it is an option. Providing both gears are not identical in tooth count (excuse me if I never counted them LOL).

Pretty easy procedure, more so with the transmission OUT of the car.

- Raise the vehicle. Level is recommended since you likely don't want to be showered in extra transmission fluid. But consider this a good time for a new gasket and filter.

- Put in a jack to support the transmission, if you secure it under the oil pan, I suggest a wood block across the entire pan to ensure nothing gets dented.

- Remove the six bolts on each side of the support beam, which connects to the body and engine cradle. CAREFUL, they will shear as they tend to corrode, suggest putting anti-seize on everything you put together that is steel-on-steel.

- Remove the four or six bolts securing to the transmission. CAREFUL, they will shear if they are built up with oxidization.

- Remove the gear cover.

To remove gears, just rotate the fancy clip until it lines up with the gear splines and pulls off. Gears slide off very easily.

You'll need to visit Dodge and get some ATV transmission sealant for the cover when sealing it back up.

Expect to loose 2-4 liters of fluid as well. Use ATF-4 ONLY. If you reuse your old fluid via catching it by a container, I SERIOUSLY recommend a paint strainer in the funnel with a magnet. This way all dirt and debris is caught.


That said, I get 30-35 MPG with my Police 3.5 with ported heads, new injectors, 3.89 gearing and shift kit, on autostick. Mind you I'm driving terribly, well - by the books and it feels slow and awful.

In the famous words of Jeremy Clarkson... POOOWWWEEEERRR!
 

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Ahh. OK. Learned something. I see in the sketches of the chain area with the cover off in the FSM a "chain oiler" referenced.
 

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There's no fluid in the area of the chain and sprockets is there?
Yeah - I didn't think it was in the ATF sump either but it is.

You can easily loose 1-3L of fluid from the back cover alone.

I put in seven liters of fluid when I dropped the pan for a filter and the gear swap.
 

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Discussion Starter #10
This is your answer. 3.89 is what comes with 300M Special's and 2.7L LH vehicle's, it's the go-too for torque and speed. Only other options would be Prowler gears and Prowler Pro Gears. But performance options.

If you run some numbers and know your math and find it will be in more of your favor swapping output shaft and differential shaft gears; then it is an option. Providing both gears are not identical in tooth count (excuse me if I never counted them LOL).

Pretty easy procedure, more so with the transmission OUT of the car.

- Raise the vehicle. Level is recommended since you likely don't want to be showered in extra transmission fluid. But consider this a good time for a new gasket and filter.

- Put in a jack to support the transmission, if you secure it under the oil pan, I suggest a wood block across the entire pan to ensure nothing gets dented.

- Remove the six bolts on each side of the support beam, which connects to the body and engine cradle. CAREFUL, they will shear as they tend to corrode, suggest putting anti-seize on everything you put together that is steel-on-steel.

- Remove the four or six bolts securing to the transmission. CAREFUL, they will shear if they are built up with oxidization.

- Remove the gear cover.

To remove gears, just rotate the fancy clip until it lines up with the gear splines and pulls off. Gears slide off very easily.

You'll need to visit Dodge and get some ATV transmission sealant for the cover when sealing it back up.

Expect to loose 2-4 liters of fluid as well. Use ATF-4 ONLY. If you reuse your old fluid via catching it by a container, I SERIOUSLY recommend a paint strainer in the funnel with a magnet. This way all dirt and debris is caught.


That said, I get 30-35 MPG with my Police 3.5 with ported heads, new injectors, 3.89 gearing and shift kit, on autostick. Mind you I'm driving terribly, well - by the books and it feels slow and awful.

In the famous words of Jeremy Clarkson... POOOWWWEEEERRR!

I understand all the gear options. You say you have done the gear swap so here is a more specific question. Are the two individual gears in the transmission similar enough they could physically be installed "backwards". Call me crazy, but this is actually my goal.

Just curious, do you hand calculate your mileage or is it by the overhead display? I find my display to be anywhere from 15-25% optimistic.
 

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When I just had a set of gears in hand that I sold something seamed different between them besides the size. It might have been the hole size or number of splines.... just cant remember.

Here is a pic of them,



From this pic it does seam possible if the splines are the same number

 

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I understand all the gear options. You say you have done the gear swap so here is a more specific question. Are the two individual gears in the transmission similar enough they could physically be installed "backwards". Call me crazy, but this is actually my goal...
This doesn't answer your question, but this will give you an indication of the results if you do it (of course, whether you can do it or not I guess depends on if the shaft diameter and keying are the same and if there's room for the 33- or 34-tooth sprocket inside the trans. output side of the case):
 

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Peva - Where did you find that chart?

It leads me to believe you can swap the gear locations but with some slow take-off
 

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Discussion Starter #15
thank you all for the info, chances for this working seem high enough, ill prolly give this a try soon. Also, instrumentation is no concern, i use the torque app so i can either correct the data coming from the computer or just use gps speed.

I'm not too concerned about "off the line" acceleration, it's not exactly stellar anyway.
 

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I do believe the gears can be interchangeable, but everything will be off speed wise and your low end would be so terrible, but supposedly MPGs will increase.
Peva - Where did you find that chart?

It leads me to believe you can swap the gear locations but with some slow take-off
:) I created the spreadsheet just for this discussion.

I don't know what ksa's goal is. Is it to compensate for the smaller tire size so his speedometer and odometer readings will be correct (which would also put acceleration and mileage back to the original), or is he wanting to intentionally over-compensate and go for mpg at the expense of acceleration? Since I didn't know, I gave him all the information so he could pick among the available operating points (assuming you can swap the input and output gears).

Not sure how close to perfect swapping the gears he has would put it. That would up his actual speed 6.35% from what it is now for a given speedometer reading. I haven't checked to see what the difference in tire diameters are. My guess is not that much.

EDIT: Difference between 225/60-16 and 215/60-16 is less than 2% (1.77%).
 

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I believe he is going for MPGs and not correcting.

Also hypothetical is there a possible way to combine different gears from the 3.66 and the 3.89 to make an even more fuel efficient combo? Or the other extreme, better off the line with worse mpgs, with the sacrifice of a correct speedo?
 

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I believe he is going for MPGs and not correcting.

Also hypothetical is there a possible way to combine different gears from the 3.66 and the 3.89 to make an even more fuel efficient combo? Or the other extreme, better off the line with worse mpgs, with the sacrifice of a correct speedo?
Keep in mind that the same chain is used with either sprocket set. You go mixing and matching the sprockets from the two sets and you would have to change the chain length. Not sure how easy that would be.

Having said that, if you look at the number of teeth on the 4 sprockets, you'll notice that the two sprockets in the 2.7/Special set are the highest (34) and lowest (31) - the the extremes on both ends of the mileage/performance tradeoffs woud be had using just those two sprockets.

You could add the Prowler Pro gears into the mix for some more options and more extremes.
 

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Keep in mind that the same chain is used with either sprocket set. You go mixing and matching the sprockets from the two sets and you would have to change the chain length. Not sure how easy that would be.

Having said that, if you look at the number of teeth on the 4 sprockets, you'll notice that the two sprockets in the 2.7/Special set are the highest (34) and lowest (31) - the the extremes on both ends of the mileage/performance tradeoffs woud be had using just those two sprockets.

You could add the Prowler Pro gears into the mix for some more options and more extremes.
True true, I guess if you wanted a combination of a little performance gain and little mpg loss a combination would work. Interesting.
 

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there's nothing saying that the performance choice isn't the mpg choice.
these are a high revving motor.
a little higher rev and lighter load just may be conducive to more mpg's.
 
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