legacy center differential

[Guest beargrease]

hi fellas, my friend has a94 legacy wagon awd .He had tranny replaced 30,000 ago ,now there is a whinning noise in center of the car at all speeds that gets louder the faster you go.Goes away when put in neutral. GUY told him it was center diff,where is it and how hard is it to fix.speedometer no longer works also.car has 185000on it . Thanks for your time

[Guest Setright]

If it's a manual transmission the center diff is inside the gearbox casing. It's a viscous oil/plate system with no cogwheels inside. How would that start to whine?

 

Auto trans use a hydraulic clutch to send power to the rear wheels, on demand, and in my opinion this isn't really a differential. I don't know for sure, but expect the clutch system is also integral with the transmission. How would that start to whine?

 

Basically, a pain to get to, cause you need to take the gearbox out, which means that front drive axles and exhaust have to come off too...

 

Is it manual or auto? Does the noise disappear when coasting in neutral, or only when stationary? Clutch engaged or disengaged?

 

There are plenty of bearings in the system that can start whining, but you need to be sure of where its coming from.

[Guest Frag]

Center diff or viscous coupling on a man trans is an independent unit bolted to the rear of the trans that can be removed without moving the trans. It's a sealed unit.

I dont know about auto trans but I would suspect it's also an independent unit.

Just an idea : since the speedo stopped to work at about the same time, could the noise come from where the speedo cable connects to the trans ?

[Guest beargrease]

Its a auto and only makes noise when moving but goes awaywhen slipped into neutral. thanks

[Guest gotsubarus]

On the automatic trans you have to remove the tranny. It is the front part of the tranny. Is it Front wheel drive or All wheel drive? If it is All wheel you will have to match the ratio with the rear differential 4:11 or 3:90 ... look at the sticker on the back of the rear end.

[Guest beargrease]

its awd and the whinnig and growling sounds like its comeing from the back of the tranny,any idea why the sound goes away when slipped into neutral. thanks also whereis speedo cabel hooked to tranny.

[Guest Suzam]

The first thing I'd try would be installing a fuse into the FWD fuse holder in the engine compartment (I think the MY94 had them?). If the noise goes away then I'd suspect the center diff not the trans. If that fails to stop the noise then I'd suspect the transmission.

 

I would also want to know it the noise is present in all the shift lever positions i.e.: 1st, 2nd etc. when you start from a stop.

 

You say it's gone in neutral, how about when down shifting from D to the lower gears, is it different?

 

Also is it in reverse too?

 

Also noise at all speeds or does it start after a specific speed say 10MPH or higher?

 

It's hard to diagnose a problem without being there. The more info we get the more we can guess some possible causes of the sound.

[Guest beargrease]

noise is there in all gears and at all speeds faster you go whine increases slip it in neutral it goes away

[Guest Setright]

Could be the bearings holding the rear drive axle. Haynes calls these universal joint bearings. Under power they whine, but in the less stressed neutral position they quit making noises.

 

FRAG: The viscous diff on my manual 4WD is inside the main transmission casing. I know, I have replaced the main bearings

[Guest Frag]

Not so on my 96. What MY is your car ?

And is it clear we are talking about the center diff and not the front diff.

[Guest Setright]

Ahh, the age could explain things, mine was built in February 1990 - coinciding with a delivery of duff main bearings that all the cars produced around that time have suffered from around 125K miles.

 

Yes, I do mean the central diff

 

Glad to hear that they had the sense to move it out of the main casing on later models.

[Guest Setright]

Built in Japan, by the way.

[Guest Legacy777]

The center diff on the 5spds has not changed over the years. It's still inside the transmission.

 

I think some of the confusion is coming from various people's definition of what's considered "inside" or not.

[Guest Setright]

Thanks Josh

[Guest beargrease]

I think the part im looking for is the transfer clutch, housed in the tail section of the auto trans. Has any body changed this,how long,how much,and where do you get the parts. thank you...

[Guest Frag]

I dont want to make this into a debate ont the definition of inside and outside but what I meant is the viscous coupling is a sealed unit with it's own fluid and - if i'm not mistaken - housed in the rear portion of the trans (thus one can say it's "in" the trans), this portion having its own case and being bolted to the rear of the rest of the transmission (thus one could say it's "outside" the trans.

Am I right in tinking that if you unbolted this rear portion (rather short compared to the rest of the trans) the entire viscous coupling would then be removed, and the trans itself would still be operationnal (FWD) if you found a way to keep the trans oil inside. Moreover, if you removed this rear portion (having it's own case) and replaced it with a new one, the result would be a trans with a new viscoup coupling.

At leas that's the way i've always understood the mechanical relation between the coupling and the trans.

Please correct me if i'm wrong.

[nv1z]

I have a 1990 Subaru Legacy that appears to have some center differential issues. It is an AWD model, but when both front wheels OR both rear wheels are on a low-traction surface, one of the wheels on that axle spins and torque is not shifted to the other axle. In other words, both axles get torque at different times, but no shifting of torque between axles happens when it is supposed to.

[Fairtax4me]

It's not supposed to "shift power". That car was made long before electronic traction and stability control systems. The diffs are either "open" or "limited slip".

 

An open diff means there is no resistance from one side to the other. One wheel can spin freely while the other hardly moves or sits completely still.

 

With a limited slip diff the action of the diff will be different based on which type of LSD it is. Viscous, clutch type, helical gear type, etc. But the basic gist is that when one wheel spins the other wheel will spin with it, but there is still some room for independent slip so the car can go around corners without binding.

[CNY_Dave]

I have a 1990 Subaru Legacy that appears to have some center differential issues. It is an AWD model, but when both front wheels OR both rear wheels are on a low-traction surface, one of the wheels on that axle spins and torque is not shifted to the other axle. In other words, both axles get torque at different times, but no shifting of torque between axles happens when it is supposed to.

 

 

Manual or auto?

 

Dave