Weird clutch issue (1 Viewer)

[4lex]

For a while I've been having some difficulty with the clutch pedal not returning reliably. The clutch assembly itself is only about 20k old and doesn't get worked a lot.

I started by stripping the master out and cleaning up in metho, it felt like it was working fine, then flushed the fluid from the whole system. This worked better, but the fluid is filthy again after just 6k or so - none missing, just absolutely black- and the pedal has been failing to return.

I noticed that I was getting a shorter and shorter time from the clutch before it would stick down, where I could sit at the lights for a couple of minutes, now I only have ten seconds or so.

But here's the really odd part. I set off across a campsite today, first gear 1k rpm for five mins or so, and went I went to find the clutch after, it had sunk all the way to the carpet. The pedal had actually pulled itself down.

What's going on here?
Cheers

 

[4lex]

For a while I've been having some difficulty with the clutch pedal not returning reliably. The clutch assembly itself is only about 20k old and doesn't get worked a lot.

I started by stripping the master out and cleaning up in metho, it felt like it was working fine, then flushed the fluid from the whole system. This worked better, but the fluid is filthy again after just 6k or so - none missing, just absolutely black- and the pedal has been failing to return.

I noticed that I was getting a shorter and shorter time from the clutch before it would stick down, where I could sit at the lights for a couple of minutes, now I only have ten seconds or so.

But here's the really odd part. I set off across a campsite today, first gear 1k rpm for five mins or so, and went I went to find the clutch after, it had sunk all the way to the carpet. The pedal had actually pulled itself down.

What's going on here?
Cheers

I should add also that drive is fine. I wonder if I'm causing a vacuum in the system hooking the pedal up with my toe

 

[LandLocked93]

I should add also that drive is fine. I wonder if I'm causing a vacuum in the system hooking the pedal up with my toe

Just a data point...had a 6sp Volvo S40 and it's clutch pedal did exactly the same thing.
I could press the clutch to the floor, remove my foot and place it on the floor, then put my foot back on the clutch pedal before the pedal came back up from the initial depression.
Volvo dealer had it for 8weeks, pretty much replaced everything inside the case.
I think they ended up discovering (or deciding maybe) it was "tweaked fingers" on the clutch (whatever that means )

 

[4lex]

Thanks for that. Sadly I replaced a perfectly good clutch assembly not long ago due to my misdiagnosis of the pedal/hydraulic problem, so I'm confident the friction hardware is fine.

Problem at this stage is I'm several hours drive from home, going to see if a local workshop can help me out today.

 

[4lex]

No parts available where I am apparently. Had a go of changing the fluid, and while it is clean now, I'm not able to bleed it successfully, it's pulling air in somehow. There's no fluid leakage, so I'm inclined toward a master cylinder diagnosis.

 

[4lex]

Should also note that last time I changed the fluid I had a vacuum bleeder. This time around I'm working with a coke bottle and a foot of tube

 

[LandLocked93]

No parts available where I am apparently. Had a go of changing the fluid, and while it is clean now, I'm not able to bleed it successfully, it's pulling air in somehow. There's no fluid leakage, so I'm inclined toward a master cylinder diagnosis.

Well if you don't know it's history, and you plan on keeping the truck at least till Russia invades a country near to, no harm in replacing it (with OEM of course).
Suggest posting in the diesel forum for possibly much more concise and relevant edit:useful responses.

 

[atomicshawn]

Unless you’ve got fluid in the slave boot, sounds like a bad master cylinder to me.

 

[4lex]

Thanks guys. Had managed to source an overhaul kit in a town a couple of hours away. No there's no fluid in the slave boot. It still beats me how air can get in without fluid getting out!

 

[LandLocked93]

Thanks guys. Had managed to source an overhaul kit in a town a couple of hours away. No there's no fluid in the slave boot. It still beats me how air can get in without fluid getting out!

Air compresses.
Fluid doesn't.

 

[4lex]

Air compresses.
Fluid doesn't.

Accepted, of course. So the pedal actuates the master cylinder piston, which is flooded in dot 3 by way of the reservoir. The pedal end of the piston is open to air. That's how I think it works anyway?
So in actuating said master piston, pressure in the master is increased and any weakness in that seal ought to give rise to a fluid leak past the piston? I suppose it could stand to reason that by hooking my toe under the pedal to pull it up I'm giving rise to a vacuum in the master which pulls air past that seal, no doubt designed to work only one way around, which I then compress into the fluid on the next stroke.

 

[LandLocked93]

Accepted, of course. So the pedal actuates the master cylinder piston, which is flooded in dot 3 by way of the reservoir. The pedal end of the piston is open to air. That's how I think it works anyway?
So in actuating said master piston, pressure in the master is increased and any weakness in that seal ought to give rise to a fluid leak past the piston? I suppose it could stand to reason that by hooking my toe under the pedal to pull it up I'm giving rise to a vacuum in the master which pulls air past that seal, no doubt designed to work only one way around, which I then compress into the fluid on the next stroke.

Anything can happen.

 

[atomicshawn]

Something I’d throw out there, that I doubt applies to you (my money is on a bad master cyl), but might help the next guy, is the mechanical side… the pressure plate (which I understand you replaced), and also the clutch fork.

I spent quality time in the garage this weekend with my little 01 Taco. Clutch wasn’t disengaging properly, weird and squishy. Adjusted the clutch pedal. Helped for a minute, but problem returned. Over 200k miles so figured I’d throw a master and slave at it. Didn’t fix it! Still had a sloppy, inconsistent clutch! Then clutch stopped disengaging all together. Then I found this

 

[atomicshawn]

…figure it must’ve been cracking, bending back and forth, then snapped.

 

[BILT4ME]

For a while I've been having some difficulty with the clutch pedal not returning reliably. The clutch assembly itself is only about 20k old and doesn't get worked a lot.

I started by stripping the master out and cleaning up in metho, it felt like it was working fine, then flushed the fluid from the whole system. This worked better, but the fluid is filthy again after just 6k or so - none missing, just absolutely black- and the pedal has been failing to return.

I noticed that I was getting a shorter and shorter time from the clutch before it would stick down, where I could sit at the lights for a couple of minutes, now I only have ten seconds or so.

But here's the really odd part. I set off across a campsite today, first gear 1k rpm for five mins or so, and went I went to find the clutch after, it had sunk all the way to the carpet. The pedal had actually pulled itself down.

What's going on here?
Cheers

I don't have experience with Toyota hydraulic clutches, so this is about ideas.

1) Does the clutch pedal have a return spring to pull it back into position?
2) If you have replaced the fluid and bled it, then in a short time it's black again, then the seals are breaking down and/or you're getting water and air into it.
3) Is there fluid on the boot side of the pedal rod (not the slave boot)?
4) The ones I have used had a spring behind the piston on the master to push the piston back to the rest position and push up the pedal.
5) If you use your toe to pull the pedal up, it creates a vacuum on the back ot the piston and will push the fluid from the boot area back into the opposite side of the piston.

Some of the older hydraulic clutch systems I have worked on had a fixed rod to the master cylinder piston. If the piston would leak, it would fill the boot with fluid and the weight of the clutch pedal would push it down until it bottomed out. All the fluid was on the rod and boot side instead of inside the master.

Basically, the seals on the master piston are shot and you need to rebuild it or replace it. I would replace both the master and the slave and the hose so that all rubber parts are replaced at the same time.

 

[4lex]

Thanks for that. I've been able to acquire an overhaul kit for the master, I just hope the bore's in good enough shape for this to work. I do agree with your sentiment about replacing the lot while I'm at it, but I'm on the road and a long way from my shed - and have strictly limited facilities and tools at my disposal, never mind parts.

I'm on the lookout for a how-to guide on this now, I'm happy I can figure it out on the way through, but forewarned is forearmed and all that. I think I recall seeing a write up over on lcool if youtube doesn't provide, but if anyone has a link it'd be welcome.

Cheers

 

[4lex]

Something I’d throw out there, that I doubt applies to you (my money is on a bad master cyl), but might help the next guy, is the mechanical side… the pressure plate (which I understand you replaced), and also the clutch fork.

I spent quality time in the garage this weekend with my little 01 Taco. Clutch wasn’t disengaging properly, weird and squishy. Adjusted the clutch pedal. Helped for a minute, but problem returned. Over 200k miles so figured I’d throw a master and slave at it. Didn’t fix it! Still had a sloppy, inconsistent clutch! Then clutch stopped disengaging all together. Then I found this

View attachment 2946294

I've had one of these too. Can't remember what vehicle, but the diagnosis was a tough one

 

[4lex]

And here's a how to

 

[atomicshawn]

@4lex

Well? Did the rebuild take care of it?

 

[4lex]

Well kinda. So I pulled out the master and stripped it with the assistance of some circlip pliers scrounged from a better prepared camper. The piston seals looked a bit average (that's Australian for 's***') and the spring was about 10mm shorter than the replacement part. Swapped them over, filled the master as best I could with fluid, and refitted.
Tried to bleed the assembly, not entirely successfully I feel. Having bled the pressure from the master off at the slave, one has to then pull the pedal back up, which I suspect is likely to damage the seals, so i did so very gently and slowly. Now the pedal does return at its own behest to about 80% of the upward travel, and we have sufficient clutch engagement - probably all of it in fairness as it's holding whatever torque the FT motor is making at 1.5bar of boost with a brand new pump and injectors.
Pedal still feels a bit squashy. I noted while I was contorted under the dash that there is, oddly, a spring that pulls the pedal down, so I think I'll disconnect that next.
Today, in an effort to resolve the bleeding question I gravity bled (just open the slave bleed nipple and kept filling the res) another 200ml of fluid through the system and saw zero bubbles, so maybe I was successful on the first bleed.
In any event, it's much easier to drive now, and manouevre the 3.5t trailer, so that's a plus.