6MT Centre Differential Rebuild Project

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Re: 6MT Centre Differential Rebuild Project

Postby Brunsy3.0 » Sat Aug 13, 2016 8:45 pm

Geez, what a mess
....THE WHITEWASH....
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Re: 6MT Centre Differential Rebuild Project

Postby BillyCorgi » Sun Aug 14, 2016 12:43 am

Rebuilt a 5MT Centre Differential today.
Miss Sally led the duties with the QA inspection of the Fiction Clutch Discs.

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Re: 6MT Centre Differential Rebuild Project

Postby Pylon 500 » Mon Aug 22, 2016 9:22 pm

May I say that I have never (never, ever, ever) seen a Centre Differential Viscous Coupling like this.

WOW, That is horrendous!!
He must have been driving only on dirt roads, and probably thought they were rougher than they really were!
Watching your work with interest...
Since running with axle height instead of pressure, I'm not getting much binding, although the other day I dragged a box trailer with a 300kg compressor in it for about 40km, and I had a good thumping from underneath by the time I got home.
All good the next day after cooling down, and no trailer.
My MY04 3.0r Bspec 6mt wagon now has 168k on it, so I'm keeping an eye on your site, but I must say I'm not looking forward to doing gearbox work again.
I did a swap and rebuild of the 4eat tranny in my SVX, but it took around three weeks to get done, and really don't want to go there again....
I'll keep reading about pulling the rear of the box off till I feel I can do it in a couple of days, just got so many things on at the moment.
Glad I retired a few years back, damned if I could find time to work now!!
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Re: 6MT Centre Differential Rebuild Project

Postby fedaykin » Tue Aug 23, 2016 5:12 pm

Animal testing is unethical :P
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Re: 6MT Centre Differential Rebuild Project

Postby BMCracer » Mon Jul 03, 2017 5:25 pm

Late to the party as usual, but........... Have you had any experience with 5eat units from a 3 litre Spec B? Description of what mine is doing here

viewtopic.php?f=2&t=34809

Would be interested, and grateful, for your insight Mr BillyCorgi.

Edit - on the plate on the left hand front strut top, the transmission code is TG5C7CVDBA, whatever that means :?
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Re: 6MT Centre Differential Rebuild Project

Postby BillyCorgi » Mon Jul 03, 2017 6:40 pm

BMCracer wrote:Late to the party as usual, but........... Have you had any experience with 5eat units from a 3 litre Spec B? Description of what mine is doing here

viewtopic.php?f=2&t=34809

Would be interested, and grateful, for your insight Mr BillyCorgi.

Edit - on the plate on the left hand front strut top, the transmission code is TG5C7CVDBA, whatever that means :?


Responded to your post in the mentioned thread. Cheers!
Get your Short Shift Adaptor viewtopic.php?f=68&t=30525
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Get your Centre Differential Rebuild viewtopic.php?f=6&t=31089
Want a custom built Brake Cylinder Stopper? viewtopic.php?f=6&t=31321
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Re: 6MT Centre Differential Rebuild Project

Postby Zachius » Sun Jul 15, 2018 9:55 pm

Are you still doing this? My 6MT in my 07 3.0RB needs a rebuilt centre diff.

It has had symptoms for a while (after a highway drive slow turns go clunk clunk).

What cost am I looking at for exchange (with getting the rebuilt one first, will need a couple of weeks to change it over). Am in Newcastle if that makes a difference.

Will probably be needing to do this in the next month or two as something in the gearbox output/diffs has developed a serious whine :-(
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Re: 6MT Centre Differential Rebuild Project

Postby BillyCorgi » Sat Jul 28, 2018 3:06 pm

Zachius wrote:Are you still doing this? My 6MT in my 07 3.0RB needs a rebuilt centre diff.

It has had symptoms for a while (after a highway drive slow turns go clunk clunk).

What cost am I looking at for exchange (with getting the rebuilt one first, will need a couple of weeks to change it over). Am in Newcastle if that makes a difference.

Will probably be needing to do this in the next month or two as something in the gearbox output/diffs has developed a serious whine :-(


PM sent on 18th July.
As yet no response.
Get your Short Shift Adaptor viewtopic.php?f=68&t=30525
Get your Gear Shift Rejuvenation Kit viewtopic.php?f=68&t=31240
Get your Centre Differential Rebuild viewtopic.php?f=6&t=31089
Want a custom built Brake Cylinder Stopper? viewtopic.php?f=6&t=31321
Need to hire a Guard Rolling Machine? viewtopic.php?f=6&t=31899
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Re: 6MT Centre Differential Rebuild Project

Postby BillyCorgi » Fri Sep 21, 2018 5:39 pm

We have not posted for a few months, so here are some updates…….

We have been building 4kg diffs and have also built some higher torque setting differentials.
To do that, higher viscosity siloxane fluid has been sourced from overseas manufacturers, that are used straight or blended with the 4kg fluid to get diff settings between the two extremes.

Every diff that we obtain is stripped and cleaned, and then after cleaning is dry assembled to measure the key parameters of the differential.
From this statistic, we have established what is the “normal” factory clearances for the gearset and what is the “normal” factory clearances for the viscous clutch plates.
All centre diffs are individually “adjusted” or “tuned” to these key measurements when reassembled.
When required, some components will be machined to set the internal clutch plate clearances back to the statistical “sweet-spot”.
All units have the thrust washers adjusted to produce the desired clearances within the differential gearset.

Our processes have been refined to achieve a smooth reassembly that guarantees a consistent and repeatable outcome.
The measurements taken and the adjustments made allows us to know that the centre diff will reassemble correctly.
During reassembly, special tooling is employed to ensure that the differential gearset clearances are maintained.

During reassembly, the diffs can suffer from what we refer to as "hydraulic-lock" where the viscous fluid is prevented from escaping when sealing the lid and the hydraulic forces cause the side gear to close up the clearances in the differential gearset. We have perfected the assembly of the viscous clutch plates to mitigate the action of "hydraulic-lock" during seal-up, to ensure correct gearset clearances are maintained.

When completed, the centre differential should turn with a firm, but smoooth buttery feel, without any kick-back from the meshing of the diferential gears.

CorgiWerx - The Subaru Centre Differential Subject Matter Experts
Last edited by BillyCorgi on Sat Sep 22, 2018 10:04 pm, edited 2 times in total.
Get your Short Shift Adaptor viewtopic.php?f=68&t=30525
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Get your Centre Differential Rebuild viewtopic.php?f=6&t=31089
Want a custom built Brake Cylinder Stopper? viewtopic.php?f=6&t=31321
Need to hire a Guard Rolling Machine? viewtopic.php?f=6&t=31899
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Re: 6MT Centre Differential Rebuild Project

Postby tom_kauf » Fri Sep 21, 2018 7:28 pm

Sounds great Billy - better than ever 8)
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Re: 6MT Centre Differential Rebuild Project

Postby BillyCorgi » Sat Sep 22, 2018 10:00 pm

So, what causes a Viscous Coupling Centre Diff failure? (or you may ask)

The straight answer is that the viscous silicone fluid goes bad. It goes from a Taupe colour to a foul smelling black tar.
The fluid shows signs of burning and break down of the siloxane polymer chain.

The basic failure is the fluid can start to separate into a black deposit that forms on the clutch plates causing the plates to bind when the fuild gets hot,

The second and related failure mechancs are a permanent expansion of the silicone fluid which causes an hydraulic lock.
The building fluid pressure pushes the side gears together absorbing any differential gear clearance causing the gears set to bind and the diff to lock-up.
On 5MT centre diff model, the ones that use the spiral circlip, can have the circlip dislodge due to the increasing hydraulic pressure, Tthe dislodging circlip then pops out and jumps into the transfer gear set, destroying them in the process.
The 6MT models and those with the single C-Type circlip, have a more robust circlip not prone to popping out. They will just bind up and lock, but will save teh transfer gears from self destruction.

The basic silicone fluid has a very stable coefficient of thermal expansion, however appears to suffer from permanent expansion once the fluid comences to fail.

CorgiWerx maintain a Unit History Card with every Centre Diff rebuild.
We record the internal clutch plate clearances, the initial Thrust Washer clearances and confirm the setting of the gearset clearance during reassembly.

CorgiWerx - The Subaru Centre Differential Subject Matter Experts
Get your Short Shift Adaptor viewtopic.php?f=68&t=30525
Get your Gear Shift Rejuvenation Kit viewtopic.php?f=68&t=31240
Get your Centre Differential Rebuild viewtopic.php?f=6&t=31089
Want a custom built Brake Cylinder Stopper? viewtopic.php?f=6&t=31321
Need to hire a Guard Rolling Machine? viewtopic.php?f=6&t=31899
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Re: 6MT Centre Differential Rebuild Project

Postby bigBADbenny » Sun Sep 23, 2018 4:26 am

What’s your impression of the C-D failure mode?
Eg, gradual or event linked (flat tyre etc), related to just overheated fluid or maybe compounded by a compromised or worn seal?

Have you considered testing a sample of burnt diff silicone for eg oil contamination?

Could a thermocouple be placed on or near the diff in order to monitor the casing temperature?
Or would a gearbox oil temperature sensor and or cooler be sufficient to monitor or control C-D temperature?

I had a quick read of the vw-kern visco-blog: very interesting.
It appears that these diffs feature a pressure relief valve, allowing this rebuilder to vacuum purge the rebuilt diffs and refill with CO2, adding to the service life of the diff.
https://vw-kern.at/blog/en/2016/06/17/n ... c02-visco/

My memory was also jogged regarding a dead end query on this forum, a member wanted to develop a torsen C-D replacement. I have a spare STi 6mt torsen front diff in the stash if you’re interested to borrow it for appraisal.
I’d happily cover the postage for the sake of research.
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