MG4 X Power Vibe/Hum 65 to 75mph

[Bricktop X PWR]

I have a long trip this weekend up the A1 and then back down, so will report back, but on my 15 mile trip home on the M1 from picking up the new car I could hardly detect it at all and I was purposely trying to find it at 65-75. There was a slight feeling in the steering, but no noise, and the feeling was like the tyres were running on a different type of road surface for a while.

Well put m8.
I've said before it's very much like a change of surface in any other car you might have driven.
I can here it in mine though but I do wear deaf aids which amplifies everything ?

Check undertray over rear motor. I bet you it's bulging or hanging down. If it is, and you hit water at speed, it will rip it off. As far as I know, all MG4s have a badly designed and fitted undertray that doesn't fit at all and MG have just screwed it on hoping no one will notice. Don't even bother going to a dealer for a replacement. There is no such thing and they'll only give you lip service.

I really doubt it's the undertrays, but to confirm, I'm taking off the front and rear undertrays over the weekend to rule that out.

 

[JustAnotherMidlifeCrisis]

Here's the YouTube review that mentions this issue. See the discussion at 36:45 onwards:

 

[tsedge]

The belief the front motor doesn't decouple or that current is induced when moving magnets near coils ?

I mean do you know the front motor doesn't decouple for a fact or are you speculating? I haven't seen this published anywhere so I am wondering what the source of this knowledge is (you described it as a 'belief' that is why I am asking).

 

[JonnyG]

I'll try a load of driving combos on my A1 trip to see if any combos make it worse from what I drove home with from pickup (which was Normal / High Regen / 100% battery / LKA off).

 

[Macadoodle]

I mean do you know the front motor doesn't decouple for a fact or are you speculating? I haven't seen this published anywhere so I am wondering what the source of this knowledge is (you described it as a 'belief' that is why I am asking).

Pretty much speculating re motor Can't remember who but someone posted specs of the 3 motor variations MG currently use, 170, 200 and 240 BHP IIRC, I'm assuming uber cost conscious MG just threw the 240 in the rear and the 200 in the front, don't remember one with a decoupling geartrain mentioned but I could be wrong.
If the car still resonates when in 4WD and the front motor is being powered then it can't be back EMF causing it, we'll need a lucky owner to test that.

If it vibes while being juiced then gawd knows. Batch of unbalanced driveshafts, motor shafts, bearings, wheels ??
Shame that it's somewhat tarnishing the driving experience for first owners though

 

[Bricktop X PWR]

"If the car still resonates when in 4WD and the front motor is being powered then it can't be back EMF"
I have, it does.
One of the first things I tried.

 

[Macadoodle]

"If the car still resonates when in 4WD and the front motor is being powered then it can't be back EMF"
I have, it does.
One of the first things I tried.

Ok, so that's that theory blown out the water then can you take a pic of your front drivetrain ? Curious to know what it looks like and if its just the trophy unit with no changes.

 

[Bricktop X PWR]

Well I didn't get as far as taking off the undertray. No need.

I used to be a retail mechanic years and years ago (AutomasterGB Watford)
And an Army mechanic (amongst many other, various and exciting Army things ?) a good while before that.

Anyway I have not seen in all my born days a drive shaft that is not completely in line with the drive unit that it is coming from.

The idea (as far as I am aware) is that once the vehicle is on the ground, the power delivery unit (in our case an electric motor) should be ideally, directly opposite and in line with, the driven wheel.

I was extremely surprised to find the front motor behind the center line of the front wheel, with the corresponding driveshaft going forward to meet it.

I will add a really, very inexcusably rough drawing, to illustrate my point below, as it can't really be seen in the pictures.

All I can say is that I've never seen that before, and it looks odd to me.

The rear motor and driveshafts are very nearly aligned as I would expect.

Any Learned engineering friends amongst us care to comment???

P.S. I am not dissembling the car.
Thought better of it.

 

[Seaton91]

Well I didn't get as far as taking off the undertray. No need.
I used to be a retail mechanic years and years ago (AutomasterGB Watford)
And an Army mechanic (amongst many various and exciting Army things ?) a good while before that.
Anyway I have not seen in all my born days a drive shaft that is not completely in line with the drive unit it is coming from.
The idea (as far as I am aware) is that once the vehicle is on the ground, the power delivery unit (in our case an electric motor) should be ideally, directly opposite and in line with, the driven wheel.
I was extremely surprised to find the front motor behind the center line of the front wheel, with the corresponding driveshaft going forward to meet it.
I will add a really very, inexcusably rough drawing, to illustrate my point below.

All I can say is that I've never seen that before and it looks wrong to me.

The rear motor and driveshafts are very nearly aligned as I would expect.


Any Learned engineering friends amongst us care to comment???

P.S. I am not dissembling the car.
Thought better of it.


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Worst of all @Bricktop1967 they've fitted a bit of Volcano rather than Racing Green on the underside.

I am no engineer but your explanation and illustration add up to potential imbalance, added load and mechanical wear. Hope I'm being alarmist and happy to be corrected!

 

[Macadoodle]

Yup, inner and outer CV joints will be constantly working, and despite their name I'm not sure thats a good design decision.
You may well have identified the cause, only trouble is there's not much that can be done barring a clean sheet redesign

 

[Bricktop X PWR]

Yup, inner and outer CV joints will be constantly working, and despite their name I'm not sure thats a good design decision.
You may well have identified the cause, only trouble is there's not much that can be done barring a clean sheet redesign

You see on the other hand I hope I'm wrong.
They will have encountered this during testing, surely? No doubt about it, seeing as all XPWRS in owners hands have it so far.
yet some engineer, signs it off as OK?
You would really, really hope not wouldn't you?

 

[Macadoodle]

Demonstrates how the ball cage has to slide when in motion to accommodate any angle off dead straight.
Maybe 65 to 75 is the wobble frequency that sets it on the vibe ?

Hopefully more simple though as you say

 

[seamust1000]

Mine feels like I'm driving over a cattle grid at speed, I get a hum and vibration in the steering wheel. I did a mainly motorway journey on Wed but had to stick at 69mph...anymore than that, the car would vibrate. I've emailed my dealer and I've also emailed MG direct [email protected].

 

[Bricktop X PWR]

Mine feels like I'm driving over a cattle grid at speed, I get a hum and vibration in the steering wheel. I did a mainly motorway journey on Wed but had to stick at 69mph...anymore than that, the car would vibrate. I've emailed my dealer and I've also emailed MG direct [email protected].

Good Grief M8!
Sounds much worse for you! Sounds like somethings not bolted up right?
Mine is much less dramatic.
I did say somewhere that this will feel differently for all of us.
I'm not considering rejection (yet!) but feel disappointed that some engineer in MG somewhere said "that will do.......
They might not notice!"
Have you pointed them to this thread?

 

[JustAnotherMidlifeCrisis]

If this is a serious issue it is disastrous for MG.

 

[DougC]

Well I didn't get as far as taking off the undertray. No need.
I used to be a retail mechanic years and years ago (AutomasterGB Watford)
And an Army mechanic (amongst many other, various and exciting Army things ?) a good while before that.
Anyway I have not seen in all my born days a drive shaft that is not completely in line with the drive unit that it is coming from.
The idea (as far as I am aware) is that once the vehicle is on the ground, the power delivery unit (in our case an electric motor) should be ideally, directly opposite and in line with, the driven wheel.
I was extremely surprised to find the front motor behind the center line of the front wheel, with the corresponding driveshaft going forward to meet it.
I will add a really, very inexcusably rough drawing, to illustrate my point below, as it can't really be seen in the pictures.

All I can say is that I've never seen that before and it looks wrong to me.

The rear motor and driveshafts are very nearly aligned as I would expect.


Any Learned engineering friends amongst us care to comment???

P.S. I am not dissembling the car.
Thought better of it.


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Yes, that's an odd design. Off road high travel suspension vehicles often travel with a large angle on the driveshafts, angled downwards in anticipation of the upward suspension travel after landing a massive jump. Looks like MG were unable to place the motor in line due to their front chassis design, and it was too expensive to make an mg4 X power specific item that would allow good alignment. A bit of vibration/hum/ excess wear in an extreme off road vehicle would hardly be noticed, possibly.

 

[Alb]

I used to have a pair of ramps like this. They saw many years service over a number of different vehicles but I eventually scrapped them because they didn't work with the low ground clearance cars I was then driving. As I was getting rid anyway, I thought I'd test the strength of the welds using a hammer blow test. Nearly all of the welds fractured on the first blow!
Be very careful using these with a heavy car like an EV.

 

[JustAnotherMidlifeCrisis]

You see on the other hand I hope I'm wrong.
They will have encountered this during testing, surely? No doubt about it, seeing as all xpowers in owners hands have it so far.
yet some engineer, signs it off as OK?
You would really, really hope not wouldn't you?

Very interesting diagnosis. If that is it, I think the question is whether the problem is just a bit of noise/vibration - annoying but perhaps not fatal - or instead that the design affects the structural integrity of the vehicle.

 

[Bricktop X PWR]

View attachment 20618

I used to have a pair of ramps like this. They saw many years service over a number of different vehicles but I eventually scrapped them because they didn't work with the low ground clearance cars I was then driving. As I was getting rid anyway, I thought I'd test the strength of the welds using a hammer blow test. Nearly all of the welds fractured on the first blow!
Be very careful using these with a heavy car like an EV.

Thanks Alb.
My 2.5 ton Audi was last up them with no issues.
10 years old and live outside.
Bit of surface rust is all.?

 

[JustAnotherMidlifeCrisis]

A quick search confirms use of CV joints is very common in cars, particularly FWD ones. So if that’s what MG have done I see no problem in principle.