possible 4x4 issue?

[resq302]

Lately I've noticed a significant decrease in my mpgs. I had been getting around 17-18 mpgs highway / city and in the last week, its dropped to 16, to 15, and now in the mid 14's for mpgs. My truck is a 2012 Ram 1500 Laramie crew cab and has the eletronic 4x4 selector switch that can be 2wd, 4wd auto, 4 hi, and 4 low, plus the neutral button. A couple times recently, when I gave it a lot of throttle taking off from a stop, I heard a clunking noise coming from the left front area of the truck, almost like the 4x4 was trying to engage.

I went under the truck today with it up on ramps and with the engine running to see if any of the 4x4 system was engaged with the selector being in 2wd. The drive shaft from the transfer case to the front axle was spinning free. The front axles (CV half shafts) were locked and could not be spun, almost as if the 4wd was engaged. Is this normal? I would have imagined that the front axles would be free also and would engage when the selector was changed to either 4wd auto or 4 high or low.

The truck currently has 52,000 miles and I have the extended bumper to bumper warranty good to 100,000 miles but I still have the deductible. If the part or fix is cheap enough, I'll do it myself.

 

[Burla]

I went under the truck today with it up on ramps and with the engine running to see if any of the 4x4 system was engaged with the selector being in 2wd.

Huh, bud there is a saying, the cheap comes out expensive. Let them fix it.

 

[RamminJammin]

I believe the cv joints are always engaged in modern trucks with ifs and the only thing that's engaged during 2wd operation is the driveshaft between the transfer case and front diff.

 

[RamminJammin]

You can also do some minor launches from a stopped position in 2wd and in 4wd to better isolate which one it happens in or both.

 

[Ricks Ram]

Your front axles are always engaged. When you put it in 4×4 it engages the transfer case.

 

[smurfs_of_war]

I believe your front wheels should spin freely and independent when in 2 wheel drive. The clunk you heard was likely the hubs locking. They are vaccuum controlled- I would be suspicious of that. Be it a line, vaccuum box or switch. If you want to do it yourself- you need to test the vaccuum on the lines at the end point. If it does not hold a steady figure- you've got a leak somewhere. Fun stuff. If it does, then it's likely electronic. Either way- I'd pay the deductible.

Sent from my SM-G925W8 using Tapatalk

 

[jwheeler]

I believe your front wheels should spin freely and independent when in 2 wheel drive. The clunk you heard was likely the hubs locking. They are vaccuum controlled- I would be suspicious of that. Be it a line, vaccuum box or switch. If you want to do it yourself- you need to test the vaccuum on the lines at the end point. If it does not hold a steady figure- you've got a leak somewhere. Fun stuff. If it does, then it's likely electronic. Either way- I'd pay the deductible.

Sent from my SM-G925W8 using Tapatalk

This is completely false. There are no hubs to lock on a 2012 1500 and they are not vacuum operated.


Sent from my iPhone using Tapatalk

 

[resq302]

When I was under the truck I was looking for vacuum lines and did not see any. The only thing I saw by the hubs was the wire for the abs.

I did notice a black plastic kind of box just to the left of the front of the front diff case that had a bunch of wires coming from it. It seems like it is electric actuators now instead Imogene vacuum.

 

[smurfs_of_war]

This is completely false. There are no hubs to lock on a 2012 1500 and they are not vacuum operated.


Sent from my iPhone using Tapatalk

My apologies. I assumed they were similar to the F150s. Didn't know they were that much different. Glad you set me straight.

Sent from my SM-G925W8 using Tapatalk

 

[resq302]

Jwheeler,

So what is the correct system set up? Should the front axles always be engaged like its in 4x4 or should they free wheel when its in 2wd for best fuel economy?

I saw some kind of plastic box that had wiring going to it on the left side of the front of the front differential. Almost looked like a long rectangular box like something might slide in there which would engage the front axles.

 

[jwheeler]

My apologies. I assumed they were similar to the F150s. Didn't know they were that much different. Glad you set me straight.

Sent from my SM-G925W8 using Tapatalk

Oh ok. I don't have much experience with fords. Wasn't sure what you were talking about.


Sent from my iPhone using Tapatalk

 

[jwheeler]

Jwheeler,



So what is the correct system set up? Should the front axles always be engaged like its in 4x4 or should they free wheel when its in 2wd for best fuel economy?



I saw some kind of plastic box that had wiring going to it on the left side of the front of the front differential. Almost looked like a long rectangular box like something might slide in there which would engage the front axles.

You are correct. That is the front axle disconnect. That is what is used instead of locking hubs. The axle are always splined to the hub but the right front axle will spin free from the left. When it is 2wd the front driveshaft should spin free from the rear


Sent from my iPhone using Tapatalk

 

[resq302]

Ok, I get it now. So my front drive shaft spins free, but should the front axles also spin free too, or only if the wheels are off the ground?

 

[jwheeler]

Only if the wheels are off the ground.


Sent from my iPhone using Tapatalk

 

[resq302]

Ok, thanks. I'll jack up the front end tomorrow and see if the wheels spin independently.

I'd really like to know why my mpg's dropped so bad (and still dropping).