[Flarpswitch]

Diagnosing something like this from a distance is a challenge. One thing that I notice with the Torsen LSD on the BRZ/86 is that it is pretty aggressive. It feels like it treats even the slightest difference in rotational speed as a loss of traction. If what I understand so far is this: only on right hand turns the problem occurs, left turns are OK. Rear drive train components appear to be sound. When you say the left rear wheel loses grip, you mean it spins up trying to burn rubber? Or, does do you feel any wheel hopping; that is the wheel is more in sync with the right wheel and it drags and hops. If you found an open space where you can drive in tight circles left and right, what do you experience? You can try this at faster speeds, but don't get into trouble. Getting both rear wheels in the air, you can try turning each wheel one at a time forward and reverse with the driveshaft locked. Feel for any differences in movement. Note the direction of wheel spin on the opposite side if any. Next, with the drive shaft free to turn, turn the wheels manually again. If the opposite wheel turns, have someone restrain it and note any movement in the drive shaft. Any limited slip differential will behave differently from an open differential. There are many types of LSD and the Torsen is just one of them. Differential failures are not the most common thing at low mileage. In my experience, the most common failure is a pinion bearing, often accompanying the failure of the rear drive shaft u-joint. One time I had a differential that lost a ring gear bolt that floated around in the housing. The first thing it did was get in the spider gears and mess with the differential action. After it did damage there and fell out into the case, everything seemed to be ok for about a week or so until at high speed on the highway, the bolt got swept up in the oil flow and wedged between the ring gear and the differential housing casting blowing a gaping hole in it. Sounded like a gun shot. Layers of plastic bags and tape got it back to the garage. I once loaned out a car and later discovered that it had taken a turn too tight and the right rear wheel hopped a curb. It was later that week at 2AM and 10 degrees F I was stopped at a light. When the light changed I let out the clutch and BANG! The engine raced as if I was in neutral. The short drive shaft had broken right at the spline where is goes into the carrier. It was an easy fix since it was independent rear suspension and I could replace the right shaft without having to remove the differential from the frame. That did not change the fact that I was royally pissed at my buddy. Don't loan your car out to a Hoon. Has this car seen some serious drifting?

My suspecting the differential is sort of grabbing at straws. My two BRZ cars are the only Torsen diffs that I have any experience with and I have never had one apart on the work bench. I have read up and watched videos a dozen times and I can't completely grasp why it works the way it does. It is one of those things that I would have to take apart to see. When the car is driving straight, equal amounts of torque are applied to each wheel. There is a threshold where the tire loses traction and it slips. There is a certain amount of torque bias that the differential will allow and then it starts locking (or not). If something is whacked internally, could left wheel or right wheel bias be different accounting for only right turns affected?

I have sympathy for the mechanics who can't figure this out. When I twisted wrenches for money, I always got the stuff no one else could figure out or knew before hand that they would loose their lunch money on the job. I would tell the boss to take me off flat rate hours for the job and pay me hourly. I have found stuff that came out of the factory that because you assume they did it 'right' you would not think to go down that road. Some highlights are clutch disks installed backwards at the factory, overhead camshafts installed with the valve timing retarded and a crankshaft that did not have oil passages drilled from the mains to the connecting rod journals. The crowning jewel was when I got into a shouting match with the factory man from Rolls Royce after I repaired the charging system and I told him that it was an easy fix pointing to an MG-B in the next stall: They are all the same, there is the front, there is the back, it has four wheels and a motor... what else is there to know? Well, the one mechanic who was certified was on 'Holiday' and I was the only one that was not scared shitless to touch the Rolls. I did borrow the car for the weekend for a quality control road test. Lovely automobile, so I can sort of understand why the factory guy got huffy. That does not change the fact that he was a butthole.

I just have to know what is up with this BRZ. Probably nothing I thought of.