Front Differential Question: Front axles spin free when in 2WD?

[Jms1]

Could be a remedial question, sorry in advance. I was curious if the Bronco front axles are free (do not spin) when not in 4WD like the F150 does. However, I did not see any vacuum lines so I am guessing not. So does that mean that the front axles free spin while in 2WD? Thank You

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[Bronco cat]

Yes in 2wd the front axles spin free. Switching to 4wd high or low engages the front axles. If you have advanced 4wd system (4A)the front axle will be electronically engaged when slippage at the rear is detected or under hard acceleration. When either 4WD High or 4WD Low is selected, the system provides mechanically locked (50/50 spilit) four-wheel-drive power to both the front and rear axles for use in off-road or slippery conditions, such as deep snow, sand or mud. When 4WD Low is selected, the system provides additional gearing for increased torque multiplication in conditions such as deep sand, steep grades or pulling heavy objects. Additionally, the system is capable of recreational flat towing by putting the transfer case into the Neutral (N) position.

 

[Ducati1098]

Could be a remedial question, sorry in advance. I was curious if the Bronco front axles are free (do not spin) when not in 4WD like the F150 does. However, I did not see any vacuum lines so I am guessing not. So does that mean that the front axles free spin while in 2WD? Thank You

Only the Bronco Raptor uses vacuum operated IWE’s like the F150

 

[RagnarKon]

So… it’s not a super short answer as it depends if your Bronco has the front-axle disconnect or not.

The Bronco does not have locking hubs—they are permanently locked. There is no electromechanical or pneumatic/vacuum system on the Bronco to disconnect the hubs when in 2WD. So the front half-shafts are always spinning regardless.

Some of the Broncos with the ESOF transfer case (part-time 4x4) have a front-axle disconnect system (FAD). On those Broncos the half-shafts are always spinning but the front driveshaft is not. I believe all of the Broncos without locking axles (Base, Big Bend, Outer Banks), come with a FAD… but not 100% sure about that.

Broncos with EMTC transfer case (advance 4x4) do not have a front-axle disconnect system. On those vehicles, both the front half-shafts and the front driveshafts are always spinning. When in 2WD, the driveshaft itself is sitting in neutral in the transfer case, so no power is sent to front even though the front driveshaft is spinning.

This is primarily done for reliability reasons. Vacuum hub locking systems, like what most pickup trucks have, are not super reliable and tend to fail over time when corrosion/water gets involved. Plus on an off-road vehicle you have omni-present risk smashing your vehicle against the rock and breaking a vacuum line or something.

The downside by not having locking hubs is increased wear on the front driveline components and a small fuel economy hit. So I wouldn’t be surprise if we see aftermarket manual locking hubs come to market some day.

 

[sameoldeddie]

So… it’s not a super short answer as it depends if your Bronco has the front-axle disconnect or not.

The Bronco does not have locking hubs—they are permanently locked. There is no electromechanical or pneumatic/vacuum system on the Bronco to disconnect the hubs when in 2WD. So the front half-shafts are always spinning regardless.

Some of the Broncos with the ESOF transfer case (part-time 4x4) have a front-axle disconnect system (FAD). On those Broncos the half-shafts are always spinning but the front driveshaft is not. I believe all of the Broncos without locking axles (Base, Big Bend, Outer Banks), come with a FAD… but not 100% sure about that.

Broncos with EMTC transfer case (advance 4x4) do not have a front-axle disconnect system. On those vehicles, both the front half-shafts and the front driveshafts are always spinning. When in 2WD, the driveshaft itself is sitting in neutral in the transfer case, so no power is sent to front even though the front driveshaft is spinning.

This is primarily done for reliability reasons. Vacuum hub locking systems, like what most pickup trucks have, are not super reliable and tend to fail over time when corrosion/water gets involved. Plus on an off-road vehicle you have omni-present risk smashing your vehicle against the rock and breaking a vacuum line or something.

The downside by not having locking hubs is increased wear on the front driveline components and a small fuel economy hit. So I wouldn’t be surprise if we see aftermarket manual locking hubs come to market some day.

Thanks for taking the time to write all this out, super informative

 

[RHeinz]

So… it’s not a super short answer as it depends if your Bronco has the front-axle disconnect or not.

The Bronco does not have locking hubs—they are permanently locked. There is no electromechanical or pneumatic/vacuum system on the Bronco to disconnect the hubs when in 2WD. So the front half-shafts are always spinning regardless.

Some of the Broncos with the ESOF transfer case (part-time 4x4) have a front-axle disconnect system (FAD). On those Broncos the half-shafts are always spinning but the front driveshaft is not. I believe all of the Broncos without locking axles (Base, Big Bend, Outer Banks), come with a FAD… but not 100% sure about that.

Broncos with EMTC transfer case (advance 4x4) do not have a front-axle disconnect system. On those vehicles, both the front half-shafts and the front driveshafts are always spinning. When in 2WD, the driveshaft itself is sitting in neutral in the transfer case, so no power is sent to front even though the front driveshaft is spinning.

This is primarily done for reliability reasons. Vacuum hub locking systems, like what most pickup trucks have, are not super reliable and tend to fail over time when corrosion/water gets involved. Plus on an off-road vehicle you have omni-present risk smashing your vehicle against the rock and breaking a vacuum line or something.

The downside by not having locking hubs is increased wear on the front driveline components and a small fuel economy hit. So I wouldn’t be surprise if we see aftermarket manual locking hubs come to market some day.

….and I believe correct…

One question, on the vehicles with the Front Axle Disconnect, does the disconnect function via a dashboard switch, or is it controlled by the 4H or 4L selector?

If I understand how it functions correctly, it “breaks” one of the axles where it enters the differential. The opposite axle is still one piece and as such is still spinning (when the vehicle is in motion) and the spider gears stop the ring and pinion motion. Is this correct?

 

[Dream_Solventless]

….and I believe correct…

One question, on the vehicles with the Front Axle Disconnect, does the disconnect function via a dashboard switch, or is it controlled by the 4H or 4L selector?

If I understand how it functions correctly, it “breaks” one of the axles where it enters the differential. The opposite axle is still one piece and as such is still spinning (when the vehicle is in motion) and the spider gears stop the ring and pinion motion. Is this correct?

Im curious about this myself, but I believe because it is an “open” diff when lockers are unlocked so when the FAD disconnects (it disconnects the passenger axle from the intermediate shaft) neither axle spins anymore.

I currently have an issue in my front differential, a pretty aggressive bind/grinding noise that only happens when the front axle disconnect engages. Conveniently, ford does engage the Front Axle Disconnect below 32 degrees even if the vehicle is not in 4 Hi or 4 Lo and it automatically engages when you select 4 hi/lo as well

 

[RagnarKon]

….and I believe correct…

One question, on the vehicles with the Front Axle Disconnect, does the disconnect function via a dashboard switch, or is it controlled by the 4H or 4L selector?

If I understand how it functions correctly, it “breaks” one of the axles where it enters the differential. The opposite axle is still one piece and as such is still spinning (when the vehicle is in motion) and the spider gears stop the ring and pinion motion. Is this correct?

It gets connected/disconnected automatically with the transfer case is put in 4-High or 4-Low. And you are correct, the FAD is connected to the right-hand halfshaft on the Bronco.

---

Which brings up a good point that I should have brought up, cause this can be confusing concept for those who aren't used to FADs and how differentials work. The FAD does not disconnect the driveshaft from the differential. ( I guess you could make a FAD that does that, but... also... why?) The FAD works by breaking the front axle (or in the case of the Bronco, one of the half-shafts) in two, which in effect disconnects the differential's ring gear from front axle. As a result the only gears inside the differential that still spinning are the smaller spider gears. Overall this results in less movement inside of the differential, which means there is less friction, which means better fuel economy and less component wear.

I think most Wranglers have a FAD system, and one of the most common aftermarket upgrades is to delete the FAD system and replace it with manual locking hubs. There isn't anything wrong with FAD systems, they are just less robust than having an entirely solid front axle. As an added bonus... if you have a manual locking hub then nothing inside the differential spins when the hubs are disconnected, providing the most wear protection and best fuel economy. The obvious downside is you have to get out of your vehicle to lock in the hubs, and if it's snowy/muddy/rainy outside... not particularly fun.

 

[Jms1]

So ideally it would be great to have the manual hub option. In the summer, highway cruising or just running around you could not engage the hubs. Technically this would save wear and tear. In the winter months or off-road conditions engage the hubs. Does anyone believe a hub will be made for the bronco? Thank you all for the explanations, it has cleared this issue up.

 

[dgorsett]

So… it’s not a super short answer as it depends if your Bronco has the front-axle disconnect or not.

The Bronco does not have locking hubs—they are permanently locked. There is no electromechanical or pneumatic/vacuum system on the Bronco to disconnect the hubs when in 2WD. So the front half-shafts are always spinning regardless.

Some of the Broncos with the ESOF transfer case (part-time 4x4) have a front-axle disconnect system (FAD). On those Broncos the half-shafts are always spinning but the front driveshaft is not. I believe all of the Broncos without locking axles (Base, Big Bend, Outer Banks), come with a FAD… but not 100% sure about that.

Broncos with EMTC transfer case (advance 4x4) do not have a front-axle disconnect system. On those vehicles, both the front half-shafts and the front driveshafts are always spinning. When in 2WD, the driveshaft itself is sitting in neutral in the transfer case, so no power is sent to front even though the front driveshaft is spinning.

This is primarily done for reliability reasons. Vacuum hub locking systems, like what most pickup trucks have, are not super reliable and tend to fail over time when corrosion/water gets involved. Plus on an off-road vehicle you have omni-present risk smashing your vehicle against the rock and breaking a vacuum line or something.

The downside by not having locking hubs is increased wear on the front driveline components and a small fuel economy hit. So I wouldn’t be surprise if we see aftermarket manual locking hubs come to market some day.

THIS

Also:
Some of the Broncos with the ESOF transfer case (part-time 4x4) have a front-axle disconnect system (FAD). On those Broncos the half-shafts are always spinning but the front driveshaft is not. I believe all of the Broncos without locking axles (Base, Big Bend, Outer Banks), come with a FAD… but not 100% sure about that.

Those Big Bend and OBX Broncos with 4.27 gears (rear locking only) do not have FAD for some reason, which I'm good with.

 

[HoosierDaddy]

@RagnarKon
@Dream_Solventless
Wow , excellent posts. I had no idea any of this FAD stuff was going on!

 

[HoosierDaddy]

@618TRVLWILD can probably confirm that your front axles do not ALWAYS freespin

 

[JT58Bronc]

Any Bronco with the Advanced 4WD system- the front half shafts, differential and driveshaft always spin and it's only disconnected in the transfer case as already stated. I have a Base Sasquatch and it has the advanced 4WD system. When I reserved it I had hoped it was the other system that only the half shafts spin and the front differential and driveshaft are disengaged and do not. But it is the advanced system. I already had a driveshaft failure at 1200 miles and had to have it replaced. It was due to the CV boot making noise. It is a recall for some Broncos and my Bronco was outside of the recall but it still had the issue.

I would much prefer front locking hubs. Some aftermarket manufacturer might eventually offer them although I bet it will be very pricey. I had a 97 TJ Wrangler previous to the Bronco and the front axle, differential and driveshaft also spin and is disconnected only at the transfer case, same as the Bronco advanced. A locking hub system is offered although it is super expensive. I did the math for fuel savings and the payback was not there so it was not worth it.

 

[RHeinz]

My Bronco Badlands SAS has the 4A transfer case. Both front axles and the front driveshaft spin all the time. This allows the driver to shift into 4A at any speed.

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