IncoDisco
Member Since: 17 Oct 2024
Location: England
Posts: 1
  
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| Strange thuds on acceleration. Cant find the problem |
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Hello all
I hope I'm posting this in the right sub-forum.
I've been experiencing a strange issue with my Discovery 4, which briefly worsened the other day before settling back down.
When the car is stopped (say, at the lights) and I accelerate from stop I can feel a few (normally two-three) thuds which feel like they're coming from the front/front-left of the vehicle. When three thuds happen the first two feel stronger. I'm not sure if it has to do with the speed of the vehicle getting greater, but the time between the second and third thud is shorter than the time between the first and second indicating it's probably to do with the rotations (of whatever is doing it) increasing. The time between thuds is less than a second at most, indicating it's something rotating more frequently than the wheels.
The thuds don't always happen when accelerating, sometimes I set off without any noise/thud. Accelerating more sharply/faster from stop makes it more likely or even certain the thuds will happen. Accelerating from stop uphill also makes them far more likely to happen (and be more intense). Thuds don't happen when the car accelerates naturally, for example when rolling downhill. Additionally, after a sharp acceleration that leads to intense thuds, it is likely that the next few accelerations from stop are also going to have some loudish thuds before it all settles back down. Lastly, the thuds don't seem to happen when the car is already in motion, even after flooring it (though, it would be hard to hear or feel them with the engine's noise).
A second symptom, which may be another issue entirely, is that when accelerating from stop with the wheel locked one way (or most of the way) in either direction, there's a chance that the vehicle will briefly 'jump' forward and perhaps a little to the opposite direction before it begins to turn the intended way. This is only a short distance but it's quite noticeable and a problem when navigating tight spaces. This happens when accelerating with the wheel turned over 2/3 of the way right or left but never does when turning in motion (even slow) or while accelerating from stop on less steep turns.
The other day, I accelerated from a side street onto the main road while turning (somewhat sharply) and felt a much stronger/louder than usual thud that made the front of the car jump. Subsequently, for the following few sets of lights, the thuds became a hundred times worse, basically making the front of the car 'dip' forward each time one happened, with the steering wheel vibrating in tune. Thuds were strong and happening continuously bellow 15mph no matter how little the acceleration, but would go away completely in higher speeds. Like before, letting the car roll immediately made the thuds stop even below 15mph.
On that day, this kept happening until I got to the garage. They managed to replicate the symptoms, but after a few test drives, came back saying the problem was no longer present! It seems the car returned itself to its prior state (that is, only two-three light thuds and slipping when turned).
What baffles me is that there are no DT codes, lights on the dash, oil leaks, loose components, or anything visually wrong...
The diff oils were changed recently and looked quite clean for age and mileage. Also had the gearbox serviced and the oil there wasn't too bad either, and free of metal chips. An LR specialist checked everything they could under the car (propshafts & ujoins, halfshafts & ujoins, diff, wishbones, transfer case, ...) without dismantling, and it all looked solid without any play/looseness. They also run the car with wheels off the ground and nothing appeared to move unexpectedly (or make the thud or noise). They suggested it could be an out-of-round bearing in the connection between prop and diff but that won't be known without disassembly.
I'm wondering if anyone's had this before, or if you have any suggestions as to what it might be?
Thanks for any help
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 20th Oct 2024 9:09 pm |
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