Even when you shut the hood

[Cursed Bronco]

Yes, that's it!

From this enhanced sound, it sounds mechanical sort of like gears or a motor whirring which leads me to think it might be the starter still spinning, but idk otherwise. Just curious to know some of these things.

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[Mark S.]

This sound was discussed at length in this thread. OP thought it might be related to the parking brake since it seems to come from the rear axle. @Bigridge83 said he narrowed it down to the rear diff. He says the shop manual calls out an electric motor in the rear diff that "disconnects the differential from the driveshaft." That seems incorrect to me. It seems to me there is already a "disconnect" function in the power transfer unit. It makes more sense to me that the two clutches are controlled with an electric motor. In an update, OP said the service techs at his local Ford dealership told him the noise is the fuel pump.

Whatever is making the noise, it appears to be completely normal given that pretty much every 2.0L Bronco Sport makes it.

 

[Bigridge83]

This sound was discussed at length in this thread. OP thought it might be related to the parking brake since it seems to come from the rear axle. @Bigridge83 said he narrowed it down to the rear diff. He says the shop manual calls out an electric motor in the rear diff that "disconnects the differential from the driveshaft." That seems incorrect to me. It seems to me there is already a "disconnect" function in the power transfer unit. It makes more sense to me that the two clutches are controlled with an electric motor.

You are correct, there is a disconnect at the PTU, but that disconnect is a “dog collar” design, similar to a non synchronized manual transmission. The RDU clutch activates first to get the driveshaft spinning, and when the drive shaft is within 30 rpm of the PTU shaft speed, the PTU will connect to the RDU. In the lower trim models like ours, there is only one RDU motor, whereas the badlands with the twin clutch RDU will have 2. I get the reasoning for disconnecting the driveshaft when not needed to cut down on parasitic drag for them MPGs!! It’s just a lot of stuff that can malfunction

 

[Dude]

shop manual calls out an electric motor in the rear diff that "disconnects the differential from the driveshaft."

“That seems incorrect to me. It seems to me there is already a "disconnect" function in the power transfer unit. It makes more sense to me that the two clutches are controlled with an electric motor.”

I may have misunderstood what you meant by “seems incorrect”… isn’t the PTU located towards the front of the vehicle after the transmission so wouldn’t it be reasonable for the electric motor (two electric motors in the Badlands) to be located in the RDU with the twin clutch ?

From Ford’s brochures etc: “Twin-clutch 4x4 rear drive unit with electronically controlled on-demand torque delivery”

 

[gatornek]

More on this thread please.

Coming from back to back to back RWD vehicles, .... I am all ears as to how the PDU and RDU are being engaged.




Also, there is zero chance that the tech was accurate. No way its the fuel pump. I've always that it was either the PDU or RDU. It sounds like gears.

 

[Mark S.]

I may have misunderstood what you meant by “seems incorrect”… isn’t the PTU located towards the front of the vehicle after the transmission so wouldn’t it be reasonable for the electric motor (two electric motors in the Badlands) to be located in the RDU with the twin clutch ?

From Ford’s brochures etc: “Twin-clutch 4x4 rear drive unit with electronically controlled on-demand torque delivery”

See @Bigridge83's post above. It didn't make sense to me to disconnect the driveshaft to the rear axle at the rear diff. It seemed to me that there was already a method to do that with the power transfer unit. As @Bigridge83 notes, however, leaving the rear driveshaft connected to the rear diff would mean the driveshaft would always be turning. Disconnecting it at the rear diff reduces parasitic drag.

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