Hello blog followers.
Just a quick tally and we think that we have rebuilt around 585 Subaru centre diffs to date, possibly 590 if the ones in the family R&D cars are also counted.
The proess has become pretty routine and the black magic and witchcraft that haunted us in the beginning has been removed from the process.
So, what have we learned in our journey so far?
Here are a few random things, in no particular order.....
(a) The TY86 6MT centre diffs are the best of all the units. The internal components are case hardened and nitrided. The components are extremely robust and do not wear.
The 6MT units have one weakness, and that is the thrust washer behind the side gear. When the centre diffs fail and the viscous fluid expands, the clearance in the differantial gears can close up and when it becomes interfearence, the thrust washer can be chewed out. Bad ju-ju.
(b) The TY75 5MT centre diffs and the TY75 6MT centre diff components are not case hardened and some parts are soft.
The weakness of these centre diffs are the cap can be worn by the differential side gear and score the support diameter on the cap.
A number of these we turn the cap, Loctite on a sleeve and refinish the sleeve to the original condition.
(c) The other weakness of the TY75 5MT centre diff is the stupid spiral circlip Subaru has used on the diffs to retain the end cap.
When the silicone fluid expands and thw centre diffs fail, the high hydraulic forces generated can push the sprial circlip out of its groove. When this happens the circlip can jump into the transfer gears and munt them up big time.
It is good to see that Subaru have stopped using thse stupid spiral circlips on the OEM repalcement part 5MT centre diffs.
CorgiWerx
WILL NOT USE these spiral type circlips and all our centre diffs are built with the "C" type circlip. Good ju-ju.
BAD BAD BAD BAD
GOOD GOOD GOOD GOOD
(d) Threre are a number of failure modes for the centre diff, some occur independantly, and sometimes they occur together.
The most common failure is where the silicone fluid expands when it fails and all the clearances in the gearset close up and become interfearance. In this mode the little pinion gears refuse to turn, binding up the diff.
Another mode is where the poly-dimethyl- siloxane silicone fluid breaks down and the carbon preciptates out of the methyl moleule. When this happens the carbon coats the plates in the clutch pack and the plates do no want to slide past each other, binding up the diff.
The other failure mode is where the silicone fluid is so severty overheated that the fluid begins to vulcanise and just goes thick-as.
(e) We measure each and every diff we receive during the rebuild process.
We meausre the intenal clearance within the centre diff viscous coupling cavity to determine the clearance inside the cavity for the stacked clutch plate pack. The clearance is about 0.80 to 0.90mm within the cavity for the clutch pack.
We also measure the clearance within the differential gearset. We have found that Subaru's own clearance setting has a wide range.
We have seen gear clearances as low as 0.15mm and as wide as 0.9mm.
Our history suggests that the statistical "mode" of the bell curve is about 0.4 to 0.5mm.
If the clearance is on the low end, the centre diff may fail through clearance reduction by fluid expansion earlier than a wider clearance unit.
All CorgiWerx centre diffs are set to a gear clearance of 0.45 to 0.50mm.
Our assembly process ensures that this clearance is individually adjusted and then maintained during assembly and fluid charging, so when the centre diff if finally closed and the cap fitted and sealed, the gearset clearance is maintained per our tight specification.
Maybe more later.
CorgiWerx - The Subaru Centre Differential Subject Matter Experts
by BillyCorgi » Sat Feb 22, 2020 12:16 pm 
great work mateys
