Reply to "Adjustable release bearing"

4N, the advantages of a concentric throw-out are;
1)- all the friction-inducing linkage inside the bellhousing is eliminated; a stock clutch then becomes easy to push in using a stock clutch master cylinder.
2)- the throwout's travel from a concentric bearing is further for a given pedal movement, resulting in more clutch disengagement and resulting longer life for your expensive and difficult to replace ZF synchronizers. It acts like a long-throw slave cylinder.
3)- about 6 lbs of weight and complication is eliminated from the engine, and the need to lubricate the two needle bearings at both sides of the bellhousing on the ends of the cross-shaft is unnecessary (most have NEVER been lubed!) The assembly has a remote air bleed that exits the bellhousing thru the now-unused left side cross shaft hole, while the pressure line from the master cylinder enters the bellhousing thru the right side hole. No drilling needed.
The disadvantages are:
A)- you MUST follow the directions EXACTLY in adjusting the assembly, The quad-ring that keeps the hydraulic fluid inside is designed only for linear motion and will not tolerate any rotary motion. NOT setting the free play exatly per instructions means that when things heat up and expand, the throwout piston will bottom in the housing, and will begin spinning with the throwout bearing. 50 miles of this is enough to destroy the quad ring and the assembly will leak.
B)- the assemblies are expensive relative to a stock unit.
C)- being installed around the ZF input shaft just like a throwout bearing, to replace the assembly, the ZF must be removed (or at least slid back enough to access the clutch and throwout assembly). Rebuild parts are available quite reasonably priced but again, this is a precision assembly and needs care and cleanliness when working on it. A leaking assembly may also waste the clutch disc, so given the trouble and expense to redo things, it pays to follow directions!