Clutch system: can this happen withOUT master/slave cylinder failing?

[d00df00d]

2012 Mazda5, 2.5L MZR L5-VE engine, 6-speed manual. 177k miles. Clutch disc, pressure plate, throwout bearing, and pilot bearing are all basically new; hydraulics are all original AFAIK.

Background first, then question.

After a few fast shifts yesterday – not clutch dumps or anything; just getting on/off the clutch pedal quickly – the clutch pedal suddenly started feeling like there was air in the hydraulic system. It has been a bit inconsistent – the more I use the pedal in a short span of time, the more normal it feels – but for the most part the engagement point was near the floor, and there was little to no feedback except spring pressure for the first ~3/4 of pedal travel.

Question: Is there any way this might happen WITHOUT either the master cylinder or slave cylinder having failed? I do intend to bleed the system and see what happens, but if it's more likely that something has failed, I might just preemptively replace a thing or two while I'm under there, just to cut down on total time spent.

Really hoping it's not the master cylinder. That job looks like it kind of sucks...

 

[97prizm]

Throwout bearing?

 

[Nukeman7]

It could be a failing slave or master cylinder, so try bleeding the hydraulics first. Worse case, you might have broken a finger spring on the pressure plate. That would entail pulling the transmission...essentially redoing 80% of the clutch job!

 

[Cujet]

That sounds like air. Try bleeding it from the bottom up. The clue being it gets better with repeated use.

I've had air enter a clutch system in remarkable ways. Remember, the fluid sloshes farthest during hard braking and air can be sucked in during downshifting. This is why many race cars have tall fluid reservoirs, sometimes with a rubber air bladder up top.

 

[KrisZ]

Sudden change like that, check around for a leak. How does the brake fluid level look like? I presume the clutch uses the brake reservoir?

 

[JohnnyG]

Sudden change like that, check around for a leak. How does the brake fluid level look like? I presume the clutch uses the brake reservoir?

I hope NOT!

 

[Chris142]

I hope NOT!

Many cars did.

If it's getting air suddenly it's got a bad pàrt. Ofteñ they are sold as a pre bled ready to install set.

 

[nwjones18]

I hope NOT!

It does on my 07 Mazda 3.

 

[JohnnyG]

I would not have expected, or wanted that!

 

[drtyler]

I hope NOT!

BMW's use the top portion of the brake reservoir for the clutch hydraulic system.

Failed clutch line would not drain it.

 

[kschachn]

It is a shared reservoir on my ECHO as well.

 

[JohnnyG]

BMW's use the top portion of the brake reservoir for the clutch hydraulic system.

Failed clutch line would not drain it.

THIS makes much more sense.
So, the OP could be a little low on brake fluid.

 

[d00df00d]

Throwout bearing?

Worse case, you might have broken a finger spring on the pressure plate. That would entail pulling the transmission...essentially redoing 80% of the clutch job!

If either of these were the case, wouldn't there be noises? And wouldn't the behavior be much more consistent? I verified this again on the drive I just completed: if I use the clutch a lot or just pump it a few times, it firms up and engages higher; if I let it sit for several minutes, it loses pressure.

I've had air enter a clutch system in remarkable ways. Remember, the fluid sloshes farthest during hard braking and air can be sucked in during downshifting. This is why many race cars have tall fluid reservoirs, sometimes with a rubber air bladder up top.

Makes sense. I suspected this kind of thing was possible but I'm a noob.

Was very much hoping to encounter some technical hypothesizing like this. Thanks for posting.

Sudden change like that, check around for a leak. How does the brake fluid level look like? I presume the clutch uses the brake reservoir?

Yes, shared reservoir with the brakes.

Fluid level looks to be unchanged. No super obvious leaks but I haven't checked too thoroughly; will likely check soonish.

 

[KrisZ]

Yes, shared reservoir with the brakes.

Fluid level looks to be unchanged. No super obvious leaks but I haven't checked too thoroughly; will likely check soonish.

Since you can still operate the clutch, the leak may be very small. I had a much bigger one on an 07 Focus and the clutch would just go to the floor. It turned out to be the line between the master and slave cylinders connection was leaking.

https://bobistheoilguy.com/forums/threads/2007-focus-clutch-goes-to-the-floor.302200/#post-4992322

 

[someonesomewhere]

It does on my 07 Mazda 3.

Same here. And it's quite tall (or deep, depending on how you look at it).

 

[d00df00d]

Thanks again, everyone. Bled the clutch last night and put some miles on it today, and it seems fine. Pedal feels normal and consistent. Fingers crossed this was a one-off issue!

 

[Number_35]

Thanks again, everyone. Bled the clutch last night and put some miles on it today, and it seems fine. Pedal feels normal and consistent. Fingers crossed this was a one-off issue!

I first encountered this problem perhaps five or six years ago. Bleeding the clutch's slave cylinder worked at the time, and it was good until recently.

The symptoms came back a couple of days ago. I bled the clutch again, but I can see leakage now on the inside of the firewall, where the clutch master cylinder interfaces with the clutch pedal lever. (Sorry, awkward wording, but I hope you get what I mean.)

Anyway, I plan to change the MC when winter's done.

Edit: 2009 Mazda5 MT c. 214000 km

 

[DriveHard]

It is common to get very similar conditions in a C5 corvette...to the point there are tons of threads about it. I got it on my car. Common solution is to thoroughly flush the system, as the consensus is that it is caused by debris in the system (tiny black chunks). I have done the flush this winter, but waiting for spring before I know if it worked or not.

 

[Number_35]

@d00df00d, I recommend checking the clutch master cylinder from inside - when mine failed, it leaked into the passenger compartment. You'll see where the push rod contacts the clutch pedal; feel along the push rod toward the clutch MC. If it's wet with brake fluid, there's your leak.