wanted to know how much hp can the stock diff hold finishing my 1jz
The pinions do break, this is true, but it is caused for the most part because the LSD is 20+ years old and is worn out. I will do my best to explain why the LSD will break due to wear even in a low horsepower situation.
This first image shows the lower clutch member in the LSD casing. It fits very close to the slot in the casing. It is done this way by design. This clutch member is free to move verticaly in the slot only, it cannot rotate.
This next image is of the upper member in the LSD casing. It fits with a gap, this is so the member can rotate slightly when load is applied to the spiders. This is done by design as well, it allows the members to push away from each other under load. Each member has "ramps" that cause a caming action to force the clutch members away from each other. This is what clamps the clutch plates.
The problem with a worn LSD is that the upper clutch member can make contact with the LSD casing. The cause of this is excessive clearance within the LSD due to wear on the thrust washers and clutch plates. By design, the upper clutch member should rotate slightly while "caming" away from the lower clutch member to clamp the clutches. If the clearances are correct within the LSD the upper clutch member will not make contact against the LSD casing. This places the majority of the forces against the clutches, not the clutch member. In a properly clearanced LSD these forces are applied in the center of the clutch member where the thrust washer meets the side gear. In a worn LSD the clutch member has to rotate too far in order to clamp the clutches and causes the clutch member to slam into the side of the slot in the LSD casing. This causes the clutch member to be wedged in the slot while it is trying to move away from the lower clutch member.
So, why does this cause the clutch member or pinion shafts to break? Well, this is the simplest way for me to describe it.
We have all broken a branch or stick by placing something under each end of it then stomping on the stick in the middle with our foot. Snaps pretty easy. The stick represents the upper clutch member in a worn LSD. This is what is happening when the upper clutch member makes contact with the LSD casing. It places the pressure points on each end of the member and in the middle of the member.
The second sketch shows how the pressure points are applied in a rebuilt LSD. The stick representing the clutch member. The pressure is applied directly in the middle of the clutch member, the way it was designed by the brilliant toyota engineer. In this situation it is very hard to break.
I know some people will say this i pure bull, that I am only trying to sell my parts. In reality, this is why they break. Another reason these LSD's will break is due to the pinion gear making contact with the LSD casing. I have seen this many many times with the GTS LSD. Many people think it was the LSD breaking that made contact with the pinion gear but it is exactly the opposite situation. The crush sleeve on the pinion gear fails, letting the pinion gear move in the housing and make contact with the LSD casing.
The design of this LSD is very good in my opinion and when correctly assembled with the right clearances (so the upper member cannot make contact with the LSD casing) it works fine and can handle way more power than people believe. We have rebuilt many GTS LSD's which are the same in design as the Supra LSD's. We have never had a customer call to tell us their LSD broke after we rebuilt it. Many of the GTS LSD's we have rebuilt are being used in drifting, one of these has a supercharged engine.