# Rear Diff Haldex Dissection After Diff Was Destroyed



## dpbayly (Mar 16, 2011)

Well after my Haldex unit was wrecked last Thursday night by the re mappers on the rolling road i spent all day Friday sorting it out by collecting a complete replacement and fitting it in the afternoon and today i decided to pull apart the old unit to see what had happened heres some pics:

First drained the Haldex fluid in to a container, believe it or not i only changed the oil and filter last week check out the state of it now it should be a nice gold colour:










I then drained the diff itself and that fluid was fine.

Then i split the Haldex off the diff:










The inside of the diff, nice and clean so will be keep this as a spare.










Splitting the Haldex unit was fairly straight forward:










This is what was inside once split in half:

Prop side:








Diff side:









These are the clutch plates there's 7 sets a set comprises of 1 clutch and one pressure plate they are all sandwiched together so you get clutch, pressure plate, clutch, pressure plate, clutch, pressure plate and so on:










Out of the 7 sets 4 sets were ok and looked like this:










But 3 sets where stuck on the main shaft diff side and stuck together (welded)

Here's what they looked like when i got them apart:










How the unit works is the the pressure plates (smooth ones)have teeth on the inside and they slide over a splined shaft which is fixed to the diff and the clutch plates (patterned ones) have teeth on the out side and slide in side a the case which is fixed to the prop shaft and the prop is constantly spinning and when the Haldex control unit receives the signal to activate the rear diff it pressurizes the pump and pushes all the plates together tight so they all grip together and then that transfers the drive to rear diff then on to the wheels.

With mine what caused the problem is where the Haldex was not deactivated for the rolling road when the pump pressurized and sandwiched the plates because the rear wheels were unable to move the clutch packs were just spinning (slipping) and they got so hot the the metal on the plates fused together so that caused me to have constant 4 wheel drive, so that is how my rear diff got destroyed.


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## Gone (May 5, 2009)

Sorry to hear about your grief mate, sounds like a right nightmare - cheers for posting up the post mortem, it will surely come in handy for other folk down the line. Certainly interesting to see what's inside the magic box!

I presume the remapper is paying for the replacement?

Also, what's the difference between what's above and the blue variant?


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## TTMBTT (Jul 22, 2010)

Informative post, always wondered exactly the haldex was constructed. Explains why
it must be electrically isolated before two wheel rolling road is used. Having said that
you would have thought the the people carrying out the work would have known what
to do also, have they offered to compensate you for their failure. :?


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## techfreak (Aug 13, 2010)

Excellent disection job...as far as i'm aware they did refund him, and apparently they couldn't find the haldex fuse?


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## Hoggy (May 8, 2002)

Hi, Pleased all sorted now, & thanks for the update, bet the remappers won't make that mistake again.
Hoggy.


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## peter-ss (Sep 3, 2008)

Sorry to hear your problems, but pleased that you've taken the time to post the pictures up; it's nice to see how things like this work.

It's a good job that it was strapped down well, otherwise it might have shot off the rollers!


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## dpbayly (Mar 16, 2011)

Thanks guy's

yep the Mappers sorted me out for the damage they offered to have the new diff fitted to but being a mechanic myself i wanted to do it as its always good to know how it all works and goes together...

I'm on good terms with Evolve the company who remapped my car and previous cars, they have had many TT's on there rollers including the Green Monster of a TT from the TT Shop a few times and have never had a problem till mine they couldn't find the Haldex fuse little did they know mine being an early one (99) doesn't have one BUT they know now and wont be making that mistake again, these things happen mistakes get made Diffs get broken  But they were good to there word and sorted me out and there custom stage 1 map is great although i have no reading off the rollers but I'm going back in a few weeks to do a live stage 2 for a VERY GOOD PRICE  on the rolling road with the Haldex controller unplugged at the diff this time....

i was going to rebuild the Haldex unit but the clutch packs seem expensive so i will just keep the Diff as a spare along with the drive shafts, Haldex controls and Haldex pump never know if they may come in handy....


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## tony_rigby_uk (Nov 27, 2008)

Good to see matey... very interesting...

I'll have to dissect my diff now then we have a complete senario of the failure of haldex and diff's for future users


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## pinotattt (Oct 5, 2007)

dpbayly said:


> Thanks guy's
> 
> yep the Mappers sorted me out for the damage they offered to have the new diff fitted to but being a mechanic myself i wanted to do it as its always good to know how it all works and goes together...
> 
> ...


Hi There,

Old post but I wanted to ask you if you changed the whole unit, Haldex and Differential, or just the Haldex unit. If so does the crownwheel of the new Haldex match up with the old differential, no shimming involved or particular adjustments involved :?:


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## jhoneyman (Aug 8, 2012)

Its a shame these pics are no longer visible :roll:


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## SPECSMAN (Oct 11, 2016)

jhoneyman said:


> Its a shame these pics are no longer visible :roll:


+1 Photobucket will never get my business. :x

8)


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## Moonwatcher (Apr 1, 2015)

SPECSMAN said:


> jhoneyman said:
> 
> 
> > Its a shame these pics are no longer visible :roll:
> ...


I agree about Photobucket, they keep emailing that I can upgrade for $399 a year, they're having a :lol: :lol:


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