Clutch Bleed Issues - Pedal Falls to Floor, Magically Returns

[jarey]

Hi all, I’m in the process of bleeding by clutch fluid (saw that it was dark and dirty in the reservoir, everything worked fine before otherwise). I’m doing everything per the service manual guidelines, with the help of an assistant.

 

The clutch pedal is pumped and then pressed to the floor, at which point I crack the bleed screw on the slave cylinder and some fluid shoots out, with minimal bubbles (if any). I then re-tighten the screw and lo and behold, the pedal is stuck to the floor. 
 

The pedal will spring back up from the return spring if pulled a little bit, but snaps back to the floor when pressed. No amount of pumping seems to rebuild pressure in the system. Oddly enough, after 5 minutes of letting the cad sit with the pedal up, pressure has magically returned to the pedal. The level of fluid in the master cylinder reservoir does not move when pumping the limp pedal but does slowly get sucked into the system over time.

 

This sounds like a non issue, but it makes me suspicious whether or not the pedal is as stiff as it should be, or if there is impending clutch doom on my horizon when something gives. Perhaps a clogged line or issue with the slave cylinder? Thanks for any advice!

[jarey]

Another note, just squeezed the fork+slave cylinder (as pictured), and the fluid level shot up in the master cylinder reservoir. It however did not shoot back down when I released the slave cylinder, and the pedal is limp again. Looks like somehow fluid is either not easily flowing to the slave cylinder, or the slave cylinder is worn in some way that prevents it from returning after the piston is compressed. Still stumped

 

Edited February 11, 2023 by jarey

[jarey]

Update: picked up a pressure bleeder to pull fluid via vacuum on the bleed screws (both on slave and master cylinder), to no success. Luckily just resetting everything and then letting the car sit seems to fix everything. Was even able to drive normally, though the pedal isn't the stiffest.

I have a running theory, will test this out tomorrow. I'm thinking that the clutch master cylinder piston is not retracting far enough to allow fluid from the reservoir to flow into the rest of the system, hence why the level doesn't change initially upon bleeding, and why the pedal goes limp (since the missing transfer of fluid means there is a vacuum in the post-master line and slave cylinder, I think).

The fix I have in mind is to adjust the clevis on the clutch pedal to make the pushrod a little shorter, thus pulling the master cylinder piston back far enough to allow reservoir fluid in. Found a couple threads on different forms with the same issue as me, this seemed the most promising: https://forums.anandtech.com/threads/im-screwed-bleeding-my-subarus-clutch.2112814/

Can't find the original post though lol. Will report on my findings!

[rhino6303]

I'd recommend following the FSM clutch pedal adjustment procedure.

[m sprank]

You need to bench bleed the master cylinder. This is notmal with Subies. Bad design. Bleed is low instead of high.  Its a pain in the arse.  You let the fluid level drop just a hair too low and I mean a hair. They are that finicky. 

[jarey]

8 minutes ago, m sprank said:

You need to bench bleed the master cylinder. This is notmal with Subies. Bad design. Bleed is low instead of high.  Its a pain in the arse.  You let the fluid level drop just a hair too low and I mean a hair. They are that finicky. 

Fingers crossed adjusting the pedal solves my woes, I kept the fluid level topped up save for when I initially sucked the old fluid out of the reservoir with a turkey baster. Guess that could’ve done it  

[jarey]

Update: doesn't seem like there's anything to adjust with the pedal, had trouble actually getting at the clevis on the master cylinder pushrod. Opted to instead detach the master cylinder from the firewall and pull on it, while my assistant held the clutch pedal, in an attempt to see if there was any more travel in the piston (did not seem like there was). Tried bleeding again to no avail, but the pedal is fine somehow. Looks like that bench bleed is in order

[cheeseenlo]

@jareyYou'll want to remove the slave. Here's a quick video tutorial of what has worked in the past for me.