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  #1  
Old 01-26-2013, 10:45 AM
duncanmb duncanmb is offline
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Default Front diff. question

I have 32k on my 09, and have already changed rear diff. fluid. I'm getting ready to change the front, but was wondering, does the front diff. actually turn when not in 4x4? I was under the impression that there were electronic axle disconnects in the front serving (if you will) as locking hubs, and of course the transfer case on the other side. My service man said it's turning all the time, but it seems hard to believe my gas mileage if i'm spinning a front diff. when not in 4x4. I still will be changing the front diff. fluid out, but is it really seeing that much wear if I occasionally use 4x4?
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Old 01-28-2013, 09:08 AM
seanbeckaroo seanbeckaroo is offline
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Quote:
Originally Posted by duncanmb View Post
I have 32k on my 09, and have already changed rear diff. fluid. I'm getting ready to change the front, but was wondering, does the front diff. actually turn when not in 4x4? I was under the impression that there were electronic axle disconnects in the front serving (if you will) as locking hubs, and of course the transfer case on the other side. My service man said it's turning all the time, but it seems hard to believe my gas mileage if i'm spinning a front diff. when not in 4x4. I still will be changing the front diff. fluid out, but is it really seeing that much wear if I occasionally use 4x4?
Each wheel in a car is bolted to a hub. Part-time four-wheel-drive trucks usually have locking hubs on the front wheels. When four-wheel drive is not engaged, the locking hubs are used to disconnect the front wheels from the front differential, half-shafts (the shafts that connect the differential to the hub) and driveshaft. This allows the differential, half-shafts and driveshaft to stop spinning when the car is in two-wheel drive, saving wear and tear on those parts and improving fuel-economy.

Hope this helps!
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Old 01-29-2013, 07:34 PM
duncanmb duncanmb is offline
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Yes, I wound up changing the gear lube in the front diff. and was surprised to see the amount of fine metal on the bottom just from occasional use. Thanks
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Old 01-29-2013, 11:46 PM
storeboy storeboy is offline
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Quote:
Originally Posted by seanbeckaroo View Post
Each wheel in a car is bolted to a hub. Part-time four-wheel-drive trucks usually have locking hubs on the front wheels. When four-wheel drive is not engaged, the locking hubs are used to disconnect the front wheels from the front differential, half-shafts (the shafts that connect the differential to the hub) and driveshaft. This allows the differential, half-shafts and driveshaft to stop spinning when the car is in two-wheel drive, saving wear and tear on those parts and improving fuel-economy.

Hope this helps!
Normally this is correct, but on the 4th gen Rams it is not (I cannot speak from experience on the 3rd gen Rams). Your service tech is right in that there is no disconnect in the front hub and your front diff and driveshaft is turning all the time. The transfer case is disconnected.

Why they went back to this design I have no idea. I believe in the '13 Rams they went back to an electronic disconnect in the front hub assembly to save on wear of the front drive line and improve fuel mileage. I guess better late than never.
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Old 01-30-2013, 10:55 PM
duncanmb duncanmb is offline
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Quote:
Originally Posted by storeboy View Post
Normally this is correct, but on the 4th gen Rams it is not (I cannot speak from experience on the 3rd gen Rams). Your service tech is right in that there is no disconnect in the front hub and your front diff and driveshaft is turning all the time. The transfer case is disconnected.

Why they went back to this design I have no idea. I believe in the '13 Rams they went back to an electronic disconnect in the front hub assembly to save on wear of the front drive line and improve fuel mileage. I guess better late than never.
Now i'm really confused, because when i finally changed my front diff. gear lube I had the front end jacked up, and I thought I would answer my own ques. by turning the front wheels. When I did this the drive shaft going back to the transfer case didn't turn. I took this as proof that the half shafts were disconnected from the front diff. in non 4x4 mode.
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Old 02-02-2013, 03:00 PM
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That big block with the plastic cover on the passenger side of the front axle is the axle disconnect, There's a electronic actuator on the back side of the axle tube that moves a collar when you select 4wd. This locks the right side axle shaft to the rest of the axle making it a "live" axle. The right side axle shaft splines directly into the side gears so whenever the truck is moving the side gears are spinning, which also spin the intermediate shaft, but in 2wd the intermediate shaft is not connected to the right side axle shaft via the collar. It the axle disconnect was not there you would back feed power into the transfer case causing tons of wear and tear on the front axle and transfer case, plus reduced gas mileage. Hope that clears it up for you a little.
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Old 02-02-2013, 05:20 PM
duncanmb duncanmb is offline
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Yes this does help. If I have this right, the gears in the diff do move via the left half shaft, but with the right side half shaft disconnected and the right wheel free wheeling there is no torque created thru the diff.to turn the drive shaft going back to the tc. Bottom-line is very little friction/wear on front diff. when not in 4x4. Thanks

Last edited by duncanmb; 02-02-2013 at 05:23 PM.
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Old 02-02-2013, 05:36 PM
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That is exactly correct
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Old 02-02-2013, 11:29 PM
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Quote:
Originally Posted by frickenbored View Post
That big block with the plastic cover on the passenger side of the front axle is the axle disconnect, There's a electronic actuator on the back side of the axle tube that moves a collar when you select 4wd. This locks the right side axle shaft to the rest of the axle making it a "live" axle. The right side axle shaft splines directly into the side gears so whenever the truck is moving the side gears are spinning, which also spin the intermediate shaft, but in 2wd the intermediate shaft is not connected to the right side axle shaft via the collar. It the axle disconnect was not there you would back feed power into the transfer case causing tons of wear and tear on the front axle and transfer case, plus reduced gas mileage. Hope that clears it up for you a little.
Thanks frickenbored, I had always been told that it was left connected. That makes me feel better because I have wanted to put manual hubs on just to reduce the wear.
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Old 02-03-2013, 08:25 AM
Yellow Jacket Yellow Jacket is offline
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Sounds like a better design than my '01 Pathfinder, which uses drive flanges on the wheel hubs, so in 2WD both front drive axles are turning, and are disconnected INSIDE the front differerential. This causes a lot of wear on the CV joints, not to mention the decreased mgp from all that rotating mass, as well as the differential gears spinning (albeit freely) constantly. I got manual locking (and unlocking) hubs to avoid this wear and tear.
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