Background:  1993 JDM WRX transmission/clutch/slave & master cylinders.  No previous problems with shifting or using the clutch.

 

Yesterday I noticed that my clutch fork didn't have its return spring, so I bought one and fabricated a bracket for it to hook onto.  When I went to test the free play after installing the spring, the clutch pedal went straight to the floor and stayed there, as if the master or slave cylinders were shot.

 

I removed the spring and the clutch feels pretty normal again.  Haven't driven the car since this happened yet, so I can't 100% confirm it works OK without the spring, but the pedal doesn't stay on the floor without the spring.

 

The spring tension is so small that I have a hard time believing that it caused this, but here we are.

 

The slave cylinder (30620AA021) was used on USDM cars and I can get a new one no problem.  The master cylinder (37230FC010) however doesn't seem to match up to any Subaru sold in the U.S. and seems pretty hard to locate on a web search.

 

What do you folks think?  Is this a master or a slave problem?  Does the system just need to be bled?  Replace both?  Has anyone converted a JDM clutch hydraulic system to a USDM one?

 

 

Master is NLA but a WRX one should work. Was used JDM/ EDM only

I would say that the spring pulled the slave into an untraveled, dirty area, and it sucked air in the system. That it returned to normal after you took the spring off is super weird... did it leak fluid into the boot?

I've read that the USDM WRX clutch master cylinder is 11/16" where this one is a 5/8", so I hesitate to mix'n'match...

 

I'll have to double check on the fluid, but I didn't notice any on the slave boot.

You have to be careful with return springs on a pull clutch - if you overcome the throwout retainer's spring force (some of them don't even have proper wave-washer springs, while other's do) you will introduce a bunch of free-play to the system and the pedal return spring will snap the pedal to the floor simply because you have moved the fluid from the slave into the master and introduced a bunch free play that has to be taken up before the slave will begin to move the pressure plate.

 

There is likely nothing wrong with it at all. 

 

They don't generally need return springs as gravity naturally drains fluid into the slave taking up the slack in the system. And there is no way to keep the throwout from spinning since its integrally attached to the pressure plate.

 

Some (STI's generally) have assist springs that maintain some pull on the fork and keep tension on the throwout. You didn't mean an assist spring did you? 

 

GD

Edited August 10, 20178 yr by GeneralDisorder