Jump to content
LegacyGT.com

Viscous Centre Diff To Open Centre Diff


Recommended Posts

Hi,

 

I have bad torque bind on my 2005 GT Legacy 5 speed manual.

 

Replacement viscous couplings are so expensive not to mention the labour on top to fit it.

 

As I have just spent loads on an engine rebuild, replacement gearbox, new clutch and new flywheel etc. I feel rather aggrieved at the thought of having to spend a load more cash on a new centre viscous coupling (part number 38913AA102).

 

If the diff had completely failed (broken / stripped teeth) I guess I wouldn't feel quite so bad but the fact is that the differential is essentially fine; it's 'just' the viscous coupling that is binding. Hence I feel aggrieved at the thought of having to buy a completely new centre differential and viscous coupling assembly.

 

If the viscous couplings failed to an 'open' differential rather than failing to a 'locked' differential then probably 99% of owners would never realise anything had gone wrong!

 

 

 

Question:

  • Not all Legacy's have a viscous centre coupling; i.e. lower powered non-turbo versions have 'open' centre differentials I beleive. Do these cars have an equivalent centre differential but without the viscous coupling part? If so could one of these 'open' differentials be swapped for a viscous centre differential?

I still have my 'old' gearbox which has the same viscous coupling in as the one which is binding in my recently replaced gearbox. My old gearbox has done 100k miles and my recently replaced gearbox has done about 50k miles.

 

 

 

Question:

  • Is it possible to take these viscous couplings apart and drain the silicone fluid and put back together to effectively have an 'open' differential? I know there are some downsides such as less traction but it still going to be better than a 2 wheel drive car and 99% of the time I probably wouldn't even notice the difference?

If this is possible I could save myself a lot of money!

 

Any thoughts welcome!

 

Telephonewire.

Edited by Telephonewire
Link to comment
Share on other sites

I'm pretty sure you're not really sure what you're talking about. If your car is a manual you have a viscus coupling. Every manual 5 speed has it. Automatics have transfer clutches. No you can't do what you're saying. An open diff doesn't mean there isn't a viscus transfering power to the rear. An open diff just meands there isn't an LSD in the front diff.
Link to comment
Share on other sites

Hi,

 

I have bad torque bind on my 2005 GT Legacy 5 speed manual.

 

Replacement viscous couplings are so expensive not to mention the labour on top to fit it.

 

a new center diff is around $520+labor. not that bad considering aftermarket units are 2-4 times that.

 

 

 

 

 

Question:

  • Not all Legacy's have a viscous centre coupling; i.e. lower powered non-turbo versions have 'open' centre differentials I beleive. Do these cars have an equivalent centre differential but without the viscous coupling part? If so could one of these 'open' differentials be swapped for a viscous centre differential?

 

All late model 5mt subaru's use a VLSD in the center including the non-turbo ones.

 

I still have my 'old' gearbox which has the same viscous coupling in as the one which is binding in my recently replaced gearbox. My old gearbox has done 100k miles and my recently replaced gearbox has done about 50k miles.

 

 

 

Question:

  • Is it possible to take these viscous couplings apart and drain the silicone fluid and put back together to effectively have an 'open' differential? I know there are some downsides such as less traction but it still going to be better than a 2 wheel drive car and 99% of the time I probably wouldn't even notice the difference?

 

The VLSD diffs are sealed units. you can not "drain the fluid out." you can swap in the full diff in your "old trans" in your the one that is binding if its still good.

 

 

If this is possible I could save myself a lot of money!

 

Any thoughts welcome!

 

Telephonewire.

 

I'm a little skeptical of the fact that your center diff has gone bad. If you haven't had someone verify that it is your center diff, you should get a second opinion. Could just be a bad axle. If it is in fact your center diff, then it must be replaced. No getting around it. you could get one of the fatermarket ones, but of course they are alot more $$$$.

Link to comment
Share on other sites

Question:

  • Is it possible to take these viscous couplings apart and drain the silicone fluid and put back together to effectively have an 'open' differential? I know there are some downsides such as less traction but it still going to be better than a 2 wheel drive car and 99% of the time I probably wouldn't even notice the difference?

If this is possible I could save myself a lot of money!

 

Actually, it would be a completely FWD car. The center differential allows the front and rear axles to rotate at different rates. An open differential simply lets them spin at different rates, but does not provide any power transfer. An open center diff = FWD.

 

You could probably hack the car to FWD by removing the rear drive shaft and sealing the coupler. I think someone on the first or second gen forums did this mod.

Link to comment
Share on other sites

^wrong.

 

An open center diff is not FWD. its AWD with no limited slip TQ transfer. with an open center, power would just be sent to the path of least resistance, but it would still be either the front or the rear. if you were to remove the drive shaft on a true open center diff, the car would not move.

Link to comment
Share on other sites

^wrong.

 

An open center diff is not FWD. its AWD with no limited slip TQ transfer. with an open center, power would just be sent to the path of least resistance, but it would still be either the front or the rear. if you were to remove the drive shaft on a true open center diff, the car would not move.

 

Ah, right. I stand corrected. In fact it would be worse than a FWD car, you could get stuck by having either the front or back tires on ice.

Link to comment
Share on other sites

All late model 5mt subaru's use a VLSD in the center including the non-turbo ones.

 

Ok - so there isn't a swappable 'open differential' alternative available.

 

The VLSD diffs are sealed units. you can not "drain the fluid out." you can swap in the full diff in your "old trans" in your the one that is binding if its still good.

 

Ok - so that option isn't avavilable either!

 

My old transmission has done 100k and having read various articles about them the viscous couplings often only last about this long so I am slightly reluctant to swap it as I may have the same problem again in a very short time!

 

I'm a little skeptical of the fact that your center diff has gone bad. If you haven't had someone verify that it is your center diff, you should get a second opinion. Could just be a bad axle. If it is in fact your center diff, then it must be replaced. No getting around it. you could get one of the fatermarket ones, but of course they are alot more $$$$.

 

Fairly certain it is the centre viscous coupling:

 

Test 1

Turning the stering wheel, whilst manoeuvring at low speeds, feels like gently applying the brakes; i.e. the transmission is binding.

 

Test 2

Front weels off the ground (rear wheels on the ground), with the transmission in nutral, I can't rotate both front wheels in the same direction at the same time.

 

Thanks for your advice "whitetiger" - looks like I will just have to 'bite the bullet!'

 

Thinking about why it may have failed - I did get a puncture about 3 or 4 months ago where I had to put the 'space saver' spare wheel on and drive ~30 miles. As the space saver is a smaller diameter this will have caused the outputs of the centre diff to be spinning at different rates and heat up the fluid which ultimately could have cause the failure I now have.

 

If this is the case why do Subaru put space saving wheels in their cars? ...because if they are ever used they are likely to result in centre viscous coupling failure! Do they warn about this in the owners manual (unfortunately I don't have an owners manual to check).

Link to comment
Share on other sites

Center diffs typically fail from owner abuse and neglect. Poor tire pressures, doughnuts, hard launches, high mileage fluid changes, etc. The bottom line is: overheating and aggressive fluid breakdown lead to increased wear on the components.

 

Which axle did you put the spare on? If it was one of the rears, that very well could have caused serious issues as you mentioned.

 

From my recollection, with the car in the air and in netural, the front wheels will spin opposite directions. You shouldn't be able to move the front with the rear wheels on the ground. I'd double check this, but I believe this is a correct statement.

 

Best test is to take a highway drive for about 20 minutes to get the fluid to temperature, then go into a parking lot and drive in figure 8s at low speed, near full-lock. If the wheels hop/drag or the car is very difficult to turn, you have a bad center diff.

 

The braking sensation may actually be your brakes. Check if one of your calipers is sticking.

 

I'd recommend replacing the center diff with the factory unit. A brand new one can be had for around $450 from Heuberger (a forum vendor/sponsor). If you are mechanically inclined, you can do this in your driveway/garage with one set of ramps and some basic tools. It does not require a transmission removal. Here is a link of photos to help you determine if this is something worth doing.

Edited by compsurge
Link to comment
Share on other sites

I can also help you out with a new OEM unit and can send you a digital copy of the section of the manual that covers replacement.

 

+1 to what Whitetiger and compsurge have said. I suspect a different failure mechanism though, since the typical failure mode - "worn out" fluid - causes the diff to act open rather than lock-up.

Link to comment
Share on other sites

Maybe this is just in the 5EAT, but isn't there an AWD fuse you're supposed to pull when you put on the spare tire (switching the vehicle to FWD only)?

 

If this is true for the 5MT, I think it would be a good temporary solution. Maybe I'm thinking of a different vehicle though.

 

No

Link to comment
Share on other sites

Maybe this is just in the 5EAT, but isn't there an AWD fuse you're supposed to pull when you put on the spare tire (switching the vehicle to FWD only)?

 

If this is true for the 5MT, I think it would be a good temporary solution. Maybe I'm thinking of a different vehicle though.

 

Its not in the 5EAT either. The FWD fuse is only found in the 4EAT, which is the 2.5i.

 

For 4th gen Legacies its best to put the donut on a front tire, as the open differential will help reduce the rate difference seen by the center diff.

Link to comment
Share on other sites

Test 2

Front weels off the ground (rear wheels on the ground), with the transmission in nutral, I can't rotate both front wheels in the same direction at the same time.

 

 

This is normal behavior. If you were able to rotate both front tires in the same direction, it would mean that the center differential was acting as an open differential.

 

Spinning both front wheels in the same direction would rotate the propshaft between the center differential and front differential. Because the center differential is preventing the front prop shaft from rotating independently, the front wheels can't both be rotated in the same direction.

Link to comment
Share on other sites

Hi,am having a similar problem.I drive a 5MT Legacy.Recently the car has been binding when taking slow turns and going forward especially after driving for a while.I managed to change the center diff but the problem is still there.I have pulled out propeller shaft and the binding is not any more could it be the rear diff?
Link to comment
Share on other sites

  • 7 years later...

I have a Subaru Legacy 2010

I drove around 230000. Right now I have one problem.

When you turn right or turn left then I am hearing a sound “tuk tuk tuk” sound.

But when I took my car in the morning there was no sound after a few minutes of drive the sound appears.

Please let me know what is the cause of the problem

 

Thanks

 

 

Sent from my iPhone using Tapatalk

Link to comment
Share on other sites

I have a Subaru Legacy 2010

I drove around 230000. Right now I have one problem.

When you turn right or turn left then I am hearing a sound “tuk tuk tuk” sound.

But when I took my car in the morning there was no sound after a few minutes of drive the sound appears.

Please let me know what is the cause of the problem

 

Thanks

 

 

Sent from my iPhone using Tapatalk

 

 

Sounds like a cv joint but try the 2010 forums or take it to a mechanic for diagnosis.

 

 

Sent from my iPhone using Tapatalk

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


×
×
  • Create New...

Important Information

Terms of Use