2021 Bronco sport Big Bend rear diff speed sensor

[drusiss]

Had a shudder while turning at low speeds in my 2021 Bronco sport big bend, I was also getting a “4wd fault” I scanned it and it was for the rear diff speed sensor . Took it to the dealer for the battery recall, while I was there asked the tech about the shudder. He took it for a ride, came back and said it was the rear diff and showed me the recent service bulletin about this. He told me that before they had the fix (replacing rdu) they were flushing the fluid, adding friction modifier additive with the new gear oil and replacing the stock vent hose with a new hose that points down instead of up and that was working. I asked if he thought the speed sensor was actually bad then or if this was related to the shudder. He said most likely the sensor was bad and said that they book 8hrs of labor to replace the sensor because most of the time it’s frozen in the top of the RDU, they break when attempting to take them out and have to drill them out. I ordered a new sensor, replacement vent hose, 2qts of the specified motorcraft rear diff gear oil and a 4oz bottle of the friction modifier.
Yesterday I replaced the faulty vent hose with the new one and attempted to remove the rdu speed sensor which sits on top of the rdu. Wanted to do the sensor before the fluid flush since I’m sure during removal and replacement of sensor you’ll get some crap in the rdu. The sensor is aprx 1 inch long, is plastic/rubber and has a shaft that drops into the rdu and a wire harness inlet on top. The shaft that drops into the rdu .25 inches down is a o-ring that seals it(Which I believe allows corrosion to get into that space freeze it in place) the sensor is mounted with one bolt that came out easily. However that sensor was seized in place. I tried everything to remove it, sprayed it with blaster and let it sit, pulled it with channel locks, pry’d it with a small pry tool, attempted to turn it back and fourth but it is really frozen in place. I left it and reconnected the wiring harness. Performed the fluid flush of the rdu replaced fluid and added the friction modifier. The flush fixed the shudder and the car is running fine now however still getting the “4wd fault” on the display.
Has anyone successfully replaced this speed sensor without breaking it off and have any tips or tricks???My plan now is to spray the sensor with pb blaster 2x a day for the next week and hopefully get it to free up.
I know the shudder is a common problem, if anyone plans on flushing the rdu to fix it you’ll need a long extension with a 3/8 swivel to get at the fill plug, and you’ll need a fluid pump to add the new fluid since the fill plug is horizontal, I have a cheap one that is a pump you screw on to the gear oil qt with a 12in shot of hose that worked well. The motor craft fluid for the rdu is expensive, 47$ a qt. The tech told me it takes 1.2 qts which it doesn’t, it takes .9qt and with adding 2oz of the friction modifier it takes even less. I have include pics of the gear oil and the new sensor below, I didn’t take a pic of the new vent hose prior to install but it looks like the old hose except it goes up higher in the wheel well and you will have to drill a new anchor point for it up high. It was an easy job except for the speed sensor being frozen in place. If anyone has any advice on how to get it out let me know!!!

 

[RSH]

Unfortunately the vent hose and fluid swap is basically a band aid TSB for an RDU that's on its way out. It may quiet down initially with the fluid change but ultimately the RDU will need to be replaced or repaired. There is a new TSB that is an actual repair. If your vehicle is still under warranty, get Ford to make it right before the warranty runs out.

 

[drusiss]

Unfortunately the vent hose and fluid swap is basically a band aid TSB for an RDU that's on its way out. It may quiet down initially with the fluid change but ultimately the RDU will need to be replaced or repaired. There is a new TSB that is an actual repair. If your vehicle is still under warranty, get Ford to make it right before the warranty runs out.

Not a band aid, and I’ve seen the new tsb as I stated above. The rdu is causing the shudder due to contaminated gear oil, idk why you’d think it’s on its way out? Do you understand how a rear diff works?

 

[RSH]

I do know how the RDU works, and the shuddering isn't a good sign. Others here have had the same issue and ended up with having the RDU replaced even after having the fluid change and updated vent tube installed.
The latest TSB supplies a parts kit to basically rebuild the RDU rather than replace it.
Maybe you'll get lucky with the fluid change and vent tube.

 

[ShawnK80]

Had a shudder while turning at low speeds in my 2021 Bronco sport big bend, I was also getting a “4wd fault” I scanned it and it was for the rear diff speed sensor . Took it to the dealer for the battery recall, while I was there asked the tech about the shudder. He took it for a ride, came back and said it was the rear diff and showed me the recent service bulletin about this. He told me that before they had the fix (replacing rdu) they were flushing the fluid, adding friction modifier additive with the new gear oil and replacing the stock vent hose with a new hose that points down instead of up and that was working. I asked if he thought the speed sensor was actually bad then or if this was related to the shudder. He said most likely the sensor was bad and said that they book 8hrs of labor to replace the sensor because most of the time it’s frozen in the top of the RDU, they break when attempting to take them out and have to drill them out. I ordered a new sensor, replacement vent hose, 2qts of the specified motorcraft rear diff gear oil and a 4oz bottle of the friction modifier.
Yesterday I replaced the faulty vent hose with the new one and attempted to remove the rdu speed sensor which sits on top of the rdu. Wanted to do the sensor before the fluid flush since I’m sure during removal and replacement of sensor you’ll get some crap in the rdu. The sensor is aprx 1 inch long, is plastic/rubber and has a shaft that drops into the rdu and a wire harness inlet on top. The shaft that drops into the rdu .25 inches down is a o-ring that seals it(Which I believe allows corrosion to get into that space freeze it in place) the sensor is mounted with one bolt that came out easily. However that sensor was seized in place. I tried everything to remove it, sprayed it with blaster and let it sit, pulled it with channel locks, pry’d it with a small pry tool, attempted to turn it back and fourth but it is really frozen in place. I left it and reconnected the wiring harness. Performed the fluid flush of the rdu replaced fluid and added the friction modifier. The flush fixed the shudder and the car is running fine now however still getting the “4wd fault” on the display.
Has anyone successfully replaced this speed sensor without breaking it off and have any tips or tricks???My plan now is to spray the sensor with pb blaster 2x a day for the next week and hopefully get it to free up.
I know the shudder is a common problem, if anyone plans on flushing the rdu to fix it you’ll need a long extension with a 3/8 swivel to get at the fill plug, and you’ll need a fluid pump to add the new fluid since the fill plug is horizontal, I have a cheap one that is a pump you screw on to the gear oil qt with a 12in shot of hose that worked well. The motor craft fluid for the rdu is expensive, 47$ a qt. The tech told me it takes 1.2 qts which it doesn’t, it takes .9qt and with adding 2oz of the friction modifier it takes even less. I have include pics of the gear oil and the new sensor below, I didn’t take a pic of the new vent hose prior to install but it looks like the old hose except it goes up higher in the wheel well and you will have to drill a new anchor point for it up high. It was an easy job except for the speed sensor being frozen in place. If anyone has any advice on how to get it out let me know!!!

The dealership replaced my RDU. It was doing the same thing with the same potential remedies. The new RDU I've not had any problems.