99 OBS cyclic clunk

[poolskaterpt]

Getting a cyclic clunk at parking lot speeds while turning, happens in both directions and only once warmed up/ been driving for at least 10 miles at highway speeds.

 

EJ22 with 5MT

 

Tranny oil is fresh, fresh new CVs (was doing this before CVs changed), front end clear of interference points, u-joints are good.

 

Thinking possibly torque bind?

- what are the torque bind symptoms?

- does torque bind only occur in autos?

 

Not being too lazy to search, just not finding info specific to this application

Edited March 30, 2014 by poolskaterpt

[Suzam]

Sorry I missed the 5MT in the original post.

 

I did copy the words "torque bind symptoms" from your post, pasted into the search and got some good hits in the first 5 or 6 for definition including the MT viscous coupler.

 

Edited March 31, 2014 by Suzam

[poolskaterpt]

Not trying to be lazy but when I searched "torque bind" I found a bunch of threads about people's problems that were not torque bind.

[Fairtax4me]

Torque bind can be found in both auto and manual transmissions. The causes are similar in nature, but the parts affected work very differently and exhibit different symptoms.

The general symptom is the car lurches or jerks when trying to make tight turns on asphalt, and you generally have to use more throttle to overcome the forces causing the bind and complete the turn. Manual transmissions generally have to be warm for this to occur, such as after driving for several minutes on the highway.

 

In the manual transmissions the viscous coupling unit in the center differential overheats and locks up. This forces the front and rear driveshafts to turn at the same speed when they need to turn at slightly different speeds.

Normally these differences in speed between the front and rear axles will be absorbed by the center diff. But when the diff locks it forces those differences to be absorbed by the tires, which they do by slipping on the road surface. On dirt or gravel its not noticeable, but because asphalt has a higher friction co-efficient the tires grip and cause the drivetrain (axles, driveshaft) to soak up the difference until it binds.

 

Early stages could be described as a clunk feeling, or you may even hear a clunk if you have any worn out suspension parts like ball-joints or tie-rod ends.

 

The primary cause is uneven tire wear, and mismatching tires front to rear. I.E. 2 New tires in the front, 2 old worn tires on the back. Or buying 1 new tire because of a blowout, and the other three are 50% worn. This causes the front and rear driveshaft speeds to differ ALL of the time, which causes the viscous coupler to have to work ALL of the time, and leads to overheating of the fluid in the unit. A difference in axle speeds causes the viscous fluid to heat up, which is what makes the unit work, but when the difference is too great it causes the fluid to overheat, which will make the unit lock up entirely.

 

Fixing this first requires making sure all 4 tires match in size, brand, and wear within 1/4" of circumference from least worn to greatest worn.

Sometimes just getting new tires will alleviate the difference in speed between front and rear axles and prevent overheating of the fluid in the unit, which will keep it from locking. This will only happen if caught at a very early stage of torque bind.

 

The next step is to replace the center differential unit. The viscous coupler is not serviceable by itself, though the unit can be replaced. It's just much easier to pull the center diff and put a whole new center diff back. These don't go bad often so used is a good option. New units are in the $400+ range last I checked.

[poolskaterpt]

Thanks Fairtax, was hoping you'd chime in. Yeah that's what I thought a torque bid would feel like: like turning a 4WD with a Locke diff on pavement.

 

I've had the tail section off this tranny before when I had a center diff support bearing fail/explode in there. Should be pretty simple to swap.

 

Any tips on OEM vs after market for replacement?

[Fairtax4me]

I'm not aware of any aftermarket source for the VC unit or center diff.

 

99 was a transition year. I do know you can get the VC from a dealer and replace just that part on the older transmissions, up to 98. In 99 they changed the design so you couldn't replace just the VC IIRC. Some 99 cars had the new trans and some still had the old style, and I'm not sure the VC can be replaced without replacing the whole center diff. But like I said, these don't go bad very often, so you can get a good used center diff and pop it right in. Post in the classified here, I'm sure someone has one. I have one but its from a 97 trans.

Edited March 31, 2014 by Fairtax4me

[poolskaterpt]

Hey Fairtax, what kind of mechanical damage to other components am I looking at if I drive it until if fails completely?

 

I have some thoughts on the potential consequences but want to hear what you say and see how they match up. This is my first Subie so the AWD system is a new animal for me but I wrench on lots of stuff so I'm not a hack by any means. Just trying to reason my way through this thing to make sense of it.

[poolskaterpt]

WOW, $737.50 from the stealership

 

Found one from an 09 WRX (stage 2 5MT), will that work for this application?

 

It's my understanding the center diff is the same for all the stage 2 5MT and the ratio should be no different in the center diff even though the tranny gear ratios are different.?.? Correct me if I'm wrong please.

 

If above is not correct- Compatible models? (link, chart etc?)

[Fairtax4me]

It puts more stress on pretty much everything. Axles, front and rear diffs, suspension bushings, ball joints, tie rods.

If the center diff fails it can fill the trans with metal or even crack open the case.

 

I'm not 100% sure on compatibility for the phase 2 trans. What's the build date on your car?

[poolskaterpt]

Thanks fairtax, that's exactly what I was thinking was coming my way too. 

 

no idea the build date, 6th VIN digit is a "4", keep on getting asked that one by parts suppliers. 

Part # i'm looking for is Subaru part # 38913AA100

 

From what I can gather I can grab one out of any 02-14 WRX 5 speed. 

 

Just want to get this right so my OBS can rip its way up the mountain this weekend and gets my girls and I snowboarding. 

 

Thanks man.

[upnorthguy]

Build date should be on a little plate on the driver door edge or door jam (I can't remember which).  For instance, '95 wagon had a build date of "09/94" (or something like that later in '94).