2021 Ford Bronco Sport: shudder or vibration when accelerating

Filed Oct 26, 2026 · Fuel system, Transmission · OH

The contact owns a 2021 Ford Bronco Sport equipped with an 8F35 automatic transmission. While driving between 25 and 45 MPH under normal acceleration, the vehicle experienced repeated violent hesitation, jerking, and lunging 4 to 5 times in rapid succession, accompanied by rapid RPM fluctuations between 2,000 and 3,000 RPM. The condition mimics an engine misfire or momentary stall and loss of motive power during acceleration, creating an immediate safety hazard and risk of rear-end collision in active traffic. The vehicle was taken to an authorized Ford dealership (Cronin Ford North) on September 30, 2026. The dealership verified and duplicated the complaint on a road test, monitored PIDs, and officially confirmed that the torque converter clutch (TCC) was slipping. Despite confirming mechanical slip, the dealership stated in writing that there were "no relevant articles," overlooking the published Ford Special Service Message SSM 54797 for 8F35 torque converter shudder below 60 MPH. The dealership recommended replacing the torque converter and main control valve body for over $5,200. When the owner declined due to cost, the vehicle was released back into service without answering the owner's written safety inquiry regarding whether the vehicle was safe to operate with verified drivetrain slippage. Additionally, the vehicle has an open safety recall (25S76) for which Ford corporate confirmed no remedy or parts are currently available. The vehicle has not stalled completely, but the severe hesitation and surging persist under normal acceleration. The manufacturer has not provided a resolution.

Filed Oct 3, 2026 · Steering, Transmission · MO

The rear drive unit (RDU) is the suspected culprit for a harsh rubbing sound which occurs during turns at low speed, typically 20mph or less. Safety is a concern because the manufacturer has identified several issues with this year/model and its RDU, and the concern is contaminated lubricants can cause unseen damage leading to the potential loss of motive power or uneven power distribution. I was lucky to have found the problem before it became significantly worse. Ford has acknowledged the issue in at least three service bulletins I was able to find. No warning lamps or messages, but the shudder started around 40-50k miles.

Filed Sep 28, 2026 · Transmission · IN

At around 75,000 miles, we noticed a small, occasional transmission shudder. We were told that these vehicles feel like that sometimes. We brought it up again around 100,000 miles. We were told we needed to change the purge valve assembly. We did. It did not help. We took the vehicle to a transmission shop and were told that the torque converter was slipping, and that the transmission needed rebuilt or replaced. We took it back to Ford to confirm. They quoted us for a rebuild. I have seen many other people online with the same issue. Some happening, luckily (I suppose), while still under warranty. These transmissions are failing and no one is doing anything. I now have a transmission repair on a vehicle with only 120,000 miles on it that is going to cost me almost as much as the vehicle is worth. This could be a safety issue if the transmission were to fail in Chicago traffic, or when merging into traffic.

Filed Jun 16, 2026 · Transmission · FL

The rearend is making a shuddering on tight turns . Vehicle only has 24,700 miles on it. Unknown if oil is low in differential oil or if vent hose is plugged. May be contaminated oil in differential.

Filed Apr 23, 2026 · Transmission · MI

Transmission failed - vehicle completely lost power alternating with shuddering and full stopping without braking at slower speeds. Vehicle revved at very high RPMs at low speed, and struggled to shift. Sometimes, when shifted into reverse, vehicle would unexpectedly roll forward almost an entire car length. Transmission fully failed on freeway doing highway speeds of 75+ MPH. Full transmission failure has been confirmed by Ford dealer.

Filed Dec 10, 2025 · Transmission · GA

The main symptom is chatter/shudder during low speed turning events. This is due to a faulty rear differential unit. The problem has been confirmed by the dealer. No lamps or other warnings present prior to the failure. The manufacturer has issued multiple TSBs, latest being TSB 25 2351.

Filed Nov 24, 2025 · Transmission · HI

For over a year now my car has been making a chatter/shudder noise during low speed turning. The car even shut off completely on me once while turning on a busy highway. There is a recall out (21S02) for my exact car, but built between 10/29/2020-12/11/2020. My build is not within the range however after getting it inspected, I have this exact issue with my axle having lubricant below the minimal fill level. I am worried that I will lose control of my car again and end up in a life-threatening accident.

Filed Nov 20, 2025 · Electrical, Transmission · FL

On or about 1/16/2025 I started to have issues battery would get display on the display screen it said to turn off ignition or draw Cato conserve battery and on the ford a] it said all or some options would be disabled to save battery and also the vehicle would shudder upon slow acceleration going forward straightforward I took it to the for inspection and they said it was OK. On 11/19 -2025

Filed Oct 22, 2025 · Transmission · OH

car is shuddering below 35 mph. The RPM gauge is bouncing. Had the transmission fluid drained and filled. Took it to our local repair shop and there are metal shavings in the transmission fluid.

Filed Oct 2, 2025 · Transmission · KS

RDU (Rear Drive Unit) is beginning to I think fail and I have read on other forums with other people saying there’s failed and can be a safety risk. They are put at risk if the RDU fails while driving resulting in an accident. I haven’t gone to the dealership yet or let anyone else know. I thought doing a simple fluid change would do but it still persist. I’ve done research to understand what’s wrong. There was no warning lights but shuddering or grinding noise would occur and I believe it appeared a few hundred miles ago then go worse overall.

Filed Sep 9, 2025 · Transmission · 75,000 miles · MI

The contact owns a 2021 Ford Bronco Sport. The contact stated that while driving at slow speeds and turning in either direction, there was an abnormal grinding sound coming from the rear of the vehicle. Additionally, while driving at various speeds, the vehicle shuddered and hesitated while accelerating. The vehicle was taken to the local dealer, who diagnosed the vehicle and determined that the rear differential and transmission were faulty and needed to be replaced. The vehicle was not repaired. The manufacturer was not yet contacted. The failure mileage was 75,000.

Filed Aug 26, 2025 · Engine · FL

Transmission shudders at low speeds (around 25-40 mph) when accelerating. This happens when shifting around 2nd gear something’s between 2nd and 3rd. Many online forums report the same issue in similar model vehicles and year when vehicle is just outside of warranty period issue occurred out of nowhere and happens consistently.