In the Clutches of My Clutch: A Scion tC Story Part II

Hey Everybody,

My '07 Scion tC clutch pedal hangs in the depressed mode about once every ten strokes.  Neither the master nor the slave are weeping.  The pedal return spring is intact and connected at both ends.  When shifting, the clutch engages fully without detectable slip, even with the pedal hanging.  After consulting the four-volume, 2,000-page manual, I notice there are bushes around one end of the return spring, the master cylinder pushrod, and the pedal pivot.  Then the pedal assembly has to come out for the spring bush (not sure about the pedal pivot or pushrod bushes yet).  If the pedal assembly has to come out, that requires most of the dash to be removed, according to the book.

Has anyone else experienced this issue, especially with the clutch being fully engaged with the pedal still on/near the mat?  The shifting action still feels as nice as it did after last year's clutch job otherwise.  I really don't want to haul out the top half of the dash with a bunch of airbags and stuff.  Any/all logical/harebrained theories/fixes welcomed.

Thanks in advance,

Jerry

More:

I checked the clutch master rod bushing and everything looks good.  The master rod clevis hole does not appear to be worn oblong.  However, with the master rod and helper spring detached, the pedal itself displays quite a bit of waggle from side to side in an arc.  Maybe a good half-inch measured down at the pedal pad.

I'm self-zombie-ing this thread because the problem is no longer occasional.  It seems to happen mostly when I push the pedal all the way to the floor.  It mostly happens when I am driving the car after sitting for awhile.  if I push the clutch to the floor, the engine will sometimes load up because the clutch hasn't released.  The hydraulic system has the usual master/slave/hardline with a replaceable hose section (like a brake caliper).  The master shares a reservoir with the brake master.  There is fluid in the reservoir, which is filled about halfway, based on brake wear.  I don't see any evidence of leaking from either the master or the slave. 

My theory is the hose section may have deteriorated internally and is blocking return flow.  However, the clutch remains engaged and the car drives.  After driving it awhile, I can get the clutch released to shift if I don't depress it to the floor.  The car has 191,000 miles on it with original hydraulics.  The clutch was replaced in 2021.  

I'm trying really hard not to fire the parts cannon on this one unless absolutely necessary.  The pattern of failure is still a little scattershot so I'm hoping someone in our universe has had the same issues.

Jerry

Douse everything under the dash with PB Blaster, and cycle???

In reply to wheelsmithy (Joe-with-an-L) :

I'm kinda off the under-dash stuff.  If the springs or the bushings were binding, the clutch would remain disengaged until I could free the pedal.  That's not the case here.

New working theory:  Both the clutch master and slave have springs inside them.  One of those springs could be broken.  The Toyota manual lists them as non-reusable in a rebuild situation.

Rock auto shows a clutch master cylinder for 28.79 (LUK) and a clutch slave for 17.73 (LUK).

If you didn't want to use the parts cannon, bleed it and see if it changes.  Or in ultimate cheapness get a spring from the hardware store to pull the pedal back up.

In reply to Noddaz :

I already own the Aisin master cylinder for the application.  They literally built the car around this thing so I don't want to dig it out if I don't have to.  Aisin also makes the slave for this application.  Rock Auto has them both.  They cost a little more than the LUK parts but are exactly the same as the Toyota parts.  I will try a bleed session and see how that goes.

Ironically, this car has a way of knowing when I'm going to work on it because it will stop doing whatever I'm trying to stop it from doing on its own.  So of course the thing drives perfectly fine all day.  However, I did bleed the hydraulics carefully with a MightyVac and made it better.  For the moment, the clutch works as it should.  If it deteriorates again, I will know for sure the problem is hydraulic in nature and will start installing goodies.

I never have a problem spending money for good parts.  My issue is spending money for unneeded parts.

Thanks to Noddaz for the tip.  Sometimes we forget the easy stuff.

For some inexplicable reason, I feel it necessary to provide closure on this issue.  A couple of days ago, I did replace the clutch primary (master) cylinder.  The shop manual calls for removing the brake booster but the job can be accomplished without doing so.  I did loosen the brake master and move that out of the way (there's enough slack in the brake lines).  I used a MightyVac to empty the brake/clutch reservoir so I could remove the clutch supply line from the reservoir.  The shared reservoir apportions a relatively small area to the clutch hydraulics.  However, the supply hose is at least 13 mm in diameter and almost a foot long.  The hose itself serves as the real reservoir for the clutch.

The rest of the disassembly included the wiper arms, cowl, wiper motor assembly, airbox, and an access undertray.  There's just enough clearance to sneak a 10 mm flare nut wrench in there to loosen the hard line flare.  After loosening, a 10 mm open-end finishes the job.

I took the driver's seat out to make it easier on my back while undoing the mounting nuts in the footwell.  I never actually saw the nuts so the whole job was by feel (let the double entendre fly).  Yanking the old one out and placing the new one in was easier than I originally thought.  Replacing the mounting nuts went easier than expected as well.  After that, it was refit the supply and hard line, then refit parts until nothing was left.  After a careful bleed, the car shifts great.  Let's see if she holds.  The last bleed lasted about six days.

A side-by-side comparo of the offending article and the new part (right).  The old unit has "Aisin" and "Toyota" cast into it.  The new one has "Aisin" both cast and printed.  The original also has the usual "TAG" in a circle cast in while the new one has that mark ground off at the factory.  You can still see a little remaining bit.

You can see our new little friend hiding in the corner.  I did loosen the booster just in case but  there was no need to remove it.  I did remove the driver's side kick panel for ease of wrench swinging.  That wasn't in the manual.  The cowl void above the brake master is the access tray location.  The wiper motor assembly blocks access to the access tray so out it came along with the cowl and wiper assemblies.  Removing the airbox made it easier to use socket extensions on the brake master and pull it forward off its mounting studs.