Legacy - Centre Diff Problem?
Discussion
I think the centre diff / viscous coupling / whatever 
in my GTB is knackered 
Got the registration documents for it through on Friday, immediately drove it to Anglesey and as I was over there for a trackday anyway put it on track for a couple of sessions to see how it goes
When started from cold or on a short drive everything seems fine, but if the car is driven hard or on the motorway for a period of time then I have problems at low speed with lots of steering lock on. There's a rhythmic thunking noise and the front end of the car hops in time - its like what I'd imagine turning a 4x4 with difflocks on on tarmac would be like, pressure building up from the wheels being unable to turn at different speeds until something slips and the car frees up again. If you're going faster with a lot of lock on then there's a huge vibration from the front end and LOTS of understeer.
I've had a quick read and it seems like there's a common fault with a solenoid in the autoboxes that causes this to happen, but my car is manual. All the CV joints and driveshafts are in good order, so I think that pretty much just leaves the viscous unit in the centre diff? Anything else it could be?
On the whole the car seems overly understeery and the front end wants to wander and follow bumps in the road more than I'd expect too. Had the geometry checked and it was pretty much spot on, think these could be more mild symptoms of the same problem (although it still has JDM tyres on, so that won't be helping...).
Does anyone know a decent Subaru specialist in the NW? Not sure I can be bothered crawling around underneath it trying to split the tailhousing off the gearbox.
in my GTB is knackered Got the registration documents for it through on Friday, immediately drove it to Anglesey and as I was over there for a trackday anyway put it on track for a couple of sessions to see how it goes
When started from cold or on a short drive everything seems fine, but if the car is driven hard or on the motorway for a period of time then I have problems at low speed with lots of steering lock on. There's a rhythmic thunking noise and the front end of the car hops in time - its like what I'd imagine turning a 4x4 with difflocks on on tarmac would be like, pressure building up from the wheels being unable to turn at different speeds until something slips and the car frees up again. If you're going faster with a lot of lock on then there's a huge vibration from the front end and LOTS of understeer.
I've had a quick read and it seems like there's a common fault with a solenoid in the autoboxes that causes this to happen, but my car is manual. All the CV joints and driveshafts are in good order, so I think that pretty much just leaves the viscous unit in the centre diff? Anything else it could be?
On the whole the car seems overly understeery and the front end wants to wander and follow bumps in the road more than I'd expect too. Had the geometry checked and it was pretty much spot on, think these could be more mild symptoms of the same problem (although it still has JDM tyres on, so that won't be helping...).
Does anyone know a decent Subaru specialist in the NW? Not sure I can be bothered crawling around underneath it trying to split the tailhousing off the gearbox.
The symptoms you describe do sound like a centre diff locking up but I'd expect a knackered viscous unit to stay open rather than lock up.
If it only happens after hard or high-speed driving I'd guess its caused somehow by things heating up, could it be the wrong type of viscous fluid in it?
Edited by GravelBen on Thursday 25th December 09:58
Is it a VDC equipped legacy? there's a VDC fuse in the engine bay fusebox?, its also says fwd on the same fuse hole (ignore that for now) Insert fuse & my bet is noise will go away
If there is'nt one in the fusebox you'll find a lone fuse holder up by the brake master cylinder/strut tower also saying FWD, insert a fuse, does that fix the problem (it will however be in fwd mode)
Either way it'll be the drive clutch to the rear wheels, its a little set of clutch packs that need fixing not a difficult fix but a bit of pain.
On VDC cars they still run in 4wd mode it just disables the VDC which can be a good thing as in snow/ice its an utter pain in the ass being massively over sensitive.
If there is'nt one in the fusebox you'll find a lone fuse holder up by the brake master cylinder/strut tower also saying FWD, insert a fuse, does that fix the problem (it will however be in fwd mode)
Either way it'll be the drive clutch to the rear wheels, its a little set of clutch packs that need fixing not a difficult fix but a bit of pain.
On VDC cars they still run in 4wd mode it just disables the VDC which can be a good thing as in snow/ice its an utter pain in the ass being massively over sensitive.
Edited by cptsideways on Saturday 27th December 15:40
GravelBen said:
Pretty sure VDC was only available on autos and he says his is a manual.
Indeed. Just a viscous coupling in the manuals. So I stripped it down this weekend to replace the coupling (symptoms got a lot worse and started making whining noise related to road speed and load too).It's quite an awkward job to do on axle stands - no individual part is particularly hard, but access etc just makes things tricky and getting enough space to swing a hammer effectively isn't easy
Gearbox oil came out a very strange grey colour (apparently a sign that the viscous unit has split and the viscous fluid mixed with the gear oil), so straight away I was pretty sure the coupling was knackered. There was some rather worrying metal on the magnetic sump plug too though.
Anyway, got the tailhousing off the box eventually but the drop gears are shagged too
Explains the metal on the sump plug and much larger chunk of metal I found in the tailhousing though.
There's a lot of play in the viscous coupling. The shaft for one of the gears connects to the coupling so I suppose play there could let / force it to run out of true and mash the teeth. I don't know for sure though.
The viscous coupling is stuck too which is a bit odd - I'm sure it should just pull straight out now.
The viscous coupling is stuck too which is a bit odd - I'm sure it should just pull straight out now.
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