Description
Unlock Valve
Check Valve / Clutch Delay Valve (CDV) Delete Kit
Symptom: slow clutch engagement in manual transmission models.
Fits these BMW models with manual transmission:
3-series/M3 1999-2006 E46 chassis (all models)
Z4/Z4M 2002-2008 E85 chassis (all models)
X3 2003-2008 (not for models after 2008)
Many owners of the cars listed above have noticed that they will get an excessive amount of clutch slippage and poor clutch engagement feel. This problem is most noticeable in situations calling for hard acceleration or quick shifting.
The cause is an added check valve (BMW calls it a “lock valve”) in the clutch hydraulic circuit that is intended to slow the engagement of the clutch as you release the pedal. This hydraulic restrictor device is intended to smooth out the feel of shifts and potentially reduce the shock load on the drivetrain. The reality is it causes a high rate of wear on the clutch and excessive heat buildup in the flywheel leading to early failure.
A particular example is a “power shift” where the revs hang for a moment before fully engaging.
The two possible locations:
(click for a larger view)
Replacement of the valve with the no-restriction replacement Unlock Valve in these cars results in very crisp and firm shifts. With the lightweight flywheel, the engagement is so positive and quick that passengers are pushed into the seat with greater force than ever before. Installation is as simple as unscrewing the original lock valve from the slave cylinder line, replacing it with the Unlock Valve, and bleeding the slave hydraulics.
