RDU issue

[Ginadf]

I have a 2021 Bronco Sport that has 66,000 miles. I have had it to three different dealers for a shuddering issue in the rear end. At first I was told that it is a vent that they are having to replace on a lot of sports. I had the vent replaced and the shuddering/thumping has gotten worse. THis happens on sharp turns.
I was then told it needed a whole new rear differential unit and it would be $5800, not under warranty. I got one more opinion, and was told to replace RDU at $3900. Both dealers told me they have had to replace this RDU in a lot of sports, but most under warranty.
I would think with what seems to be a common failure, there would be a recall, but no. It is hard to come up with thousands of dollars when you are still making pmts. on your fairly new vehicle. I have read of many others on FB with the same issue.

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[Mark S.]

There's a TSB that directs changing the fluid. If the vent was bad it allowed contaminants in the RDU, so replacing the fluid will flush them out.

 

[V8 Yankee]

There's a TSB that directs changing the fluid. If the vent was bad it allowed contaminants in the RDU, so replacing the fluid will flush them out.

Fortunately I had my RDU replaced under warranty. I will be doing a drain and fill on my new one every 20k or so. A $40 bottle of 75W oil is cheap insurance for the long term. The shudder you have is what myself and many others have had. There is a post where a another BS owner had the same out of warranty issue. He put a bottle of the Ford Friction Modifier in his RDU and the shudder cleared up immediately. It might be worth a try, a lot less expensive than a new RDU.

 

[Cursed Bronco]

Same thing here. It is cropping up a lot lately. Looks like the vent hose is inadequate and allows debris to enter the unit. If not fixed in a timely manner, the issue will damage the RDU. I have been waiting a month on parts since they are on back-order, and I can feel the issue getting worse. Ford will be replacing my RDU in due time. I am pretty much driving it now trying to accelerate the RDU disintegration before I get a new one.

 

[Ginadf]

There's a TSB that directs changing the fluid. If the vent was bad it allowed contaminants in the RDU, so replacing the fluid will flush them out.

I had the fluid changed, and it seems to be worse since the new vent and fluid change.

 

[Ford Motor Company]

I had the fluid changed, and it seems to be worse since the new vent and fluid change.

Good afternoon, Gina. Would you please send over a private message with your VIN and dealer info so I can look into this RDU concern on my end?

 

[NMhunter]

There is a fix on another thread. He changed the oil and added a Motorcraft additive. I don't remember what the additive was, but it cured his problem. I'd sure try that before I replaced it. Do a search for RDU and you'll find it.

 

[cprcubed]

It is XL-3 Friction Modifier. See this thread: Those of you with RDU woes…. | 2021+ Ford Bronco Sport Forum - Broncosportforum.com

 

[V8 Yankee]

My VIN no. is 3FMCR9B64MRA74192
My Bronco is currently at Rountree Ford in Lake City, FL. They are supposed to be contacting Ford to get some help with this cost. The previous dealer wanted $5800, and I would pay half of that plus about $300 more for the new vent.
I paid them for the vent, but took it to the current dealer because they gave me a quote of $3900.

I had my RDU replaced under the Powertrain Warranty a few months ago. It started to shudder at around 25K, at 40K it was to the point that I didn't think I would make it to work. I duplicated the shudder with a Ford dealer mechanic sitting next to me and he agreed it needed replaced. the whole process took two weeks, would have been 10 days but they decided to replace the left side axle which added a few more days. The total cost including a rental was $4000, zero out of pocket. That included the updated vent as well. I had to call Ford direct to get authorization for the rental, they called the dealer to let them know it was a charge back to Ford. I'm not sure why one dealer would charge more than another, Ford has a set reimbursement for warranty work. Sounds like some dealers skim more off the top for both parts and labor. As long as it was covered I don't really care but it seems some dealers really squeeze customers. Good luck on your repair.

 

[Dannyp56]

Does anybody know if this applies to the 2024 model?

 

[Gnomad]

Does anybody know if this applies to the 2024 model?

The bulletin does describe the affected vehicles, and IIRC the vent was modified mid-2022.
We got rid of our 21 BS because of this issue, which rightly should be a recall as it if the RDU fails in traffic it would be a dangerous situation. Apparently Ford forgot that owners might actually take their Sports off road.

 

[redbucky2022]

I made a write up about this a few weeks ago. I had mine serviced at 20k. started chattering at 37k miles. Dealer was on a 4 to 6 week wait so I walked into the parts department, bought the proper RDU fluid and a bottle of Motorcraft XL3 friction modifier. Mixed the friction modifier into the quart of RDU fluid and drained and filled my unit. Mine chattered and the fluid was crystal clear with no contamination. Added the new fluid concoction and the chatter went away immediately. AWD engagement is fantastic, and smooth as can be.

I'm covered until 75k miles but I got sick of driving over an hour away to get into a dealer with a piss poor attitude and wasn't going to make a payment on something collecting dust in the service department lot. $65.00 bucks and 20 mins of my time to save weeks worth of headaches was worth it to me.

 

[Chibi]

I made a write up about this a few weeks ago. I had mine serviced at 20k. started chattering at 37k miles. Dealer was on a 4 to 6 week wait so I walked into the parts department, bought the proper RDU fluid and a bottle of Motorcraft XL3 friction modifier. Mixed the friction modifier into the quart of RDU fluid and drained and filled my unit. Mine chattered and the fluid was crystal clear with no contamination. Added the new fluid concoction and the chatter went away immediately. AWD engagement is fantastic, and smooth as can be.

I'm covered until 75k miles but I got sick of driving over an hour away to get into a dealer with a piss poor attitude and wasn't going to make a payment on something collecting dust in the service department lot. $65.00 bucks and 20 mins of my time to save weeks worth of headaches was worth it to me.

were you having AWD engagement problems before you replaced fluids?

 

[redbucky2022]

I never had any issues with engagement. Just chatter. I used the snot out of the AWD drive last week. Still have zero issues...

 

[RNM]

Update October 2025

I had the work completed last month. The RDU was replaced, in addition I needed to replace the AWD control module. That is not covered under the warranty. So the RDU was covered thankfully. Now that both units have been installed everything is running nice and smoothly. FYI I made it about $25,000 My post my initial relocation kit installation. I wish they would have went ahead and done the RDU when they had it in the shop originally, but we know how that goes they don't want to put that much money into it until they have to.

Update August 25 2025,

RDU is now being completely replaced. Waiting on parts. Apparently the cheap Ford relocation kit was not the fix.

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I have recently had this issue fixed myself. Somewhere around 60k miles i started hearing a clunk under acceleration, notably while turning, then it started to get louder and more prevalent. At first I was thinking it was my spare tire being loose in the storage compartment. Then I thought perhaps it was something underneath that was loose. Eventually I couldn't deny it was the RDU. so I took it in and the techs said that it was the RDU and they would be replacing it. So it sat for a couple of days while they waited for the part to come in. Then when the parts came in they said that they had to wait for another part to move the vent location. Eventually I was told that they did not actually replace the RDU they just serviced it and installed the vent relocation kit. So far no more noises or problems. However, I still wonder what damage actually occurred while the RDU was acting up internally. Seems that they opted to only replace the vent and service the RDU to save money rather than ensure it won't be a problem down the road.

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