4.8is - cracked open front diff

[centurion]

This is second time front diff failed on me with two of 4.8is's i have had within last 3 years in a first week of ownership... believe it or not!

Now i'm going to really start thinking about whether lighting really strikes twice...? long and short of it it will be fixed at the end of the day but i'm really keen to know why these items fail on 4.8's - too much power, too much torque, big wheels... what could it be.

FYI - this one cracked as the guy was taking it over a brake test bit (don't know the name sorry) when going for an MOT.

Any thoughts would help? Thx

[X5Sport]

What tyres?

[centurion]

Really std setup on 4.8is's - 20" wheels with Bridgestone's all around (@ ~30% wear).

[X5Sport]

I thought these things had to be done on a 4WD rolling road (two rollers) to avoid transmission wind up?  Might not have been the cause, but it could have been.  Kkx5 will know more being our guru on these things 

[centurion]

thanks... FYI - the MOT guy was just going over them in a car to check the lights etc. first before testing the brakes and it cracked at that point. It could have been me in the car at a time but i just asked him to take it through... and bang (the rest is history).

I will get some pics next week... but there is a massive crack and i'm really curios what caused it (for the 2nd time in 3 years).

[Upex]

Did the first fail in same manor, ie during mot test at that garage, if so perhaps x5sport theory has a lot of legs!

[IanP]

So it cracked as he drove forward over the brake testing rollers?

[centurion]

[quote="IanP"]
So it cracked as he drove forward over the brake testing rollers?
[/quote]

Yup...


Sent from my iPhone using Tapatalk

[kkx5]

Well...That video will telll you all...
https://www.youtube.com/watch?v=-L5PzR6apg4

Testing the service brakes on all BMW X-drive 4x4 vehicles

As a precaution, treat all BMW 4x4 vehicles as X-drive vehicles. To test the service brakes on a roller brake machine (which must have 4WD mode), carry out the following procedure:

1.Make sure HDC (Hill Descent Control) is switched off (the HDC light will be off).
2.Put the vehicle into Neutral.
3.DO NOT touch the accelerator pedal and DO NOT select a gear while the rollers are turning to avoid
damaging the vehicle or rollers.
4.Carry out brake test as usual using the roller brake machine’s 4WD mode.
5.When the rollers have stopped turning, lock the rollers, select a gear and drive forward slowly.

[centurion]

Get it fully... he wasn't testing the brakes. Literally went over it to get it on a canal to show me worn suspension arms. It cracked as he was going over the rollers hence the curiosity on "why" it went pops?


Sent from my iPhone using Tapatalk

[henrym3]

Forgive my ignorance but when you say "cracked" do you mean the casing cracked and dumped the oil  or it cracked as when something breaks inside.

[centurion]

[quote="henrym3"]
Forgive my ignorance but when you say "cracked" do you mean the casing cracked and dumped the oil  or it cracked as when something breaks inside.
[/quote]

No worries... casing cracked and it dumped the oil.



Sent from my iPhone using Tapatalk

[kkx5]

[quote="centurion"]
Get it fully... he wasn't testing the brakes. Literally went over it to get it on a canal to show me worn suspension arms. It cracked as he was going over the rollers hence the curiosity on "why" it went pops?


Sent from my iPhone using Tapatalk
[/quote]

Well, for me is straightforward, whatever he did or did not , your car broke on rollers...

[Glen]

Hi kkx5 do you reckon it'll be better to have a MOT at a bmw center

[Steamyrotter]

Theorising or Hypothisising...(even if i cant spell any of them!!)

When driving forward to the pit the wheels drop into the rollers.
Assumption here that the rollers were not locked???
in which case the front wheels will spin up due to less effective grip.

Regardless of the TC cutting in he revs to push out the pit and front wheels hit the slope off of the rollers.
Potentially one wheel first
Sudden torque demand at the front causes any backlash in the diff to be taken up with a thud and forces dispersed ineffectively to the weaker casing elements.

end result  Puddle of oil on floor and a rather upset owner!!