Transmission/Differential/VC Viscous Coupling Problem Research/Info Thread

[jdmvip]

I found this thread really interesting and useful.
http://www.subaruforester.org/vbulle...ce-them-46979/

Basically there are two types of center differentials according to that thread:

Phase 1: 1991-1998 Subaru 5 Speeds (I'm not sure when JDM models changed to Phase 2 though)
Phase 2: 1999+ Subaru 5 Speeds

Copied from the Forester Forum:


I am quite sure that my car 1993 JDM Impreza WRX RA must use a P1/Phase 1 differential as would most early JDMs.

The center diff is serviceable by replacing the VC (Viscous Coupling Unit) and can be done with the transmission on the car (although you have to remove the driveshafts and exhaust still). I'll leave the rest of the details to the link above.

In automatic Subaru's this is called the MPT (Multi Plate Transfer Clutch).

Symptoms of center diff/Viscous Coupling Problems/Failure

1.) When the car is hot and you make tight turns you should hear clunking and banging.

[MatchstiK]

Great to know! I never would have guessed that the center diff could be serviced without removing the tranny in phase 1 setups.

[raceready68]

That would make it really easy to make it rwd for summer

[jdmvip]

MatchstiK apparently that's what Subaru doesn't know or has always wanted everyone to believe. The other thing is that it's true that the viscous fluid if gone bad/broken down can't really/practically be serviced but everyone except that smart person on the Forester forum seems to have forgotten that the Viscous unit itself is replaceable.

I'd like to post more info here about how to identify different transmission problems including more symptoms of bad VC and other issues especially rear diff issues.

[king_cobra]

Great to know! I never would have guessed that the center diff could be serviced without removing the tranny in phase 1 setups.

Yea, same here! Great post vip!

[Kilroy]

The driveshaft can be removed in about 10 minutes once you know what you are doing. It's really a very simple matter of removing a few bolts while trying not to get your face smashed when it finally drops.

[Kingsoup]

Now what we need to find is a mechanical that allows 70/30 rear split we can replace the stock viscous with!

[jdmvip]

Just bumping this as it's said that the BE5/BH5 Legacy's 5MT VC unit is very prone to failure.

[jjm]

How prone is the auto vc for failing ?

[jdmvip]

I believe the auto doesn't use a VC but the equivalent is called an MPT (multi plate transfer clutch) and apparently doesn't have any issues.