Clutch grabbing

[County3.9]

My clutch is intermittently grabbing on release and I'm hoping someone out there can help!


Symptoms- As I let the clutch pedal out, after about 1 inch of travel the clutch will suddenly grab as if my foot has slipped off the pedal. This occurs about 2-3 times each time I drive it, it seems to do it mainly when cold but still happens very occasionally when warm (although less violently). Sometimes it will feel like a gentle bump and other times will throw my head back or chirp the tyres and stall the engine. The is no noise or different feel to the pedal when it occurs. When pushing the pedal in the clutch works perfectly and is smooth and has a good feel. This problem has been occurring for many years but has been rather soft, now it is a problem. Over the years I've had new clutches and the symptom still occurred, although it only happened once every few months and felt like slack taking up in the drive train.


Things changed- Originally I changed the master cylinder and the symptoms improved. Then I changed the slave but nothing changed. I then replaced the MC again for another reason and the symptoms went away for 6-12 months. Next I changed the flexible hose...no change, so I put another MC in and the symptom stopped. 12 months later and the problems back so in went another MC but this time it hasn't fixed it. I've checked the adjusting linkage and have adjusted the pedal to the correct height.


Vehicle- 86 County, 4 speed LT95, 4BD1 turbo.


This I'm convinced that the problem is hydraulic rather than mechanical as the symptoms change when I play with the hydraulics. But maybe I'm wrong.



Any ideas?

[Bearman]

Sounds like MC problems to me. What were the replacement ones you put in, new or used ones and what quality. The fact that it improved things most times you changed it suggests it may be the problem. Was there any fluid loss at all.

[County3.9]

G'day Brian
No fluid loss
All components are new, not second hand.
I've tried Delphi from MR AUTO(~$100) and a generic brand from the local clutch and brake place ($33). Same result. It makes sense to me that it is master cylinder related but I can't see any problems with the one I just pulled out. My next step was to get the Delphi MC stainless steel sleeved and see how it goes... But since this last MC didn't make a difference I've lost confidence that the MC is the problem.

[Bearman]

The other possibility is that it is the pressure plate diaphragm sticking then letting go. When you say you have changed clutches do you mean both pressure and driven plates or just the driven plate.

[County3.9]

Both plates and fly wheel machined.
If it was the plates then I wouldn't have thought that changing hydraulics would have made any difference.
So frustrating.
The only consistent parts are the hydraulic steel pipes, flywheel, input shaft, clutch rod/ arm and spacer on bearing ( Isuzu requires larger spacer)

[Bearman]

Both plates and fly wheel machined.
If it was the plates then I wouldn't have thought that changing hydraulics would have made any difference.
So frustrating.
The only consistent parts are the hydraulic steel pipes, flywheel, input shaft, clutch rod/ arm and spacer on bearing ( Isuzu requires larger spacer)

Frustrating all right! Well I guess that rules out any problem with the pressure plate. The other bits you mentioned wont be the problem. Back to the MC I would say. Maybe the ones you have bought have been new (old) stock and the rubbers are a bit suspect and bypassing occasionally. That's about all I can suggest:(.

[Blknight.aus]

contamination on the slide for the throw out bearing, failing flex line, contamination in the pipe or the slave cylinder has some crap in it,

Start by pulling the slave and giving it a clean and then removing and inspecting the hyd lines

[yt110]

I'd go with Blknight.aus . contamination on the slide for the throw out bearing,and/or plastic bush on clutch fork pivot.
Is the plastic clip that holds the push rod into the clutch fork still intact?

Jim.

[County3.9]

Update
The symptoms have changed since fitting the MC, now it will only grab when cold. After driving for 10 mins I can't get the clutch to grab, which is frustrating when trying to show a mechanic what's going on! Just after start however, the grab is quite violent and chirps the tyres. Also, it seems worse when the landy is pointing up hill. There is a hill near me that I have to stop at when driving to work and the clutch grabs violently every time (when cold, doesn't when engine warmed up). So, since it has changed again since fitting the MC I'm back to thing it's hydraulic related.

[County3.9]

contamination on the slide for the throw out bearing, failing flex line, contamination in the pipe or the slave cylinder has some crap in it,

Start by pulling the slave and giving it a clean and then removing and inspecting the hyd lines

Hey mate, you back?

Changed the flex line, twice.
We changed the slave remember, didn't change.
I'm thinking of getting the Delphi MC stainless sleeved and fitting that.

[County3.9]

I'd go with Blknight.aus . contamination on the slide for the throw out bearing,and/or plastic bush on clutch fork pivot.
Is the plastic clip that holds the push rod into the clutch fork still intact?

Jim.

I'll have to check
I would have thought that if it was a problem with the fork, slide, or bearing then it wouldn't matter what I replaced in the hydraulic system the symptoms wouldn't change.

[Bearman]

After thinking about your symptoms I suspect that you may have a sticking piston in either the master or slave. I know it's a pita but I would change them both out at the same time and see what happens. Make sure you check the new ones out before fitting to ensure the pistons slide easily.

[schuy1]

Engine/gearbox mounts good?

[County3.9]

Engine/gearbox mounts good?

Actually.... I am having issues with the engine/ gearbox mounts. Why would the mounts have an influence.

[schuy1]

To be honest Im not 100% sure why bad mounts affect clutch operation, but I suspect it has to do with torque influencing release. You let clutch out,plate start to engage flywheel, broken/soft engine mounts allow motor to twist in an uncontrolled manner causing plate to grab flywheel due to movement. Remember we are not dealing with large clearances here its in the order of mm's/thous. I have always been told to check mounts when dealing with clutch shudder, never really had it explained to me though.

Cheers Scott

[Yorkshire_Jon]

To be honest Im not 100% sure why bad mounts affect clutch operation, but I suspect it has to do with torque influencing release. You let clutch out,plate start to engage flywheel, broken/soft engine mounts allow motor to twist in an uncontrolled manner causing plate to grab flywheel due to movement. Remember we are not dealing with large clearances here its in the order of mm's/thous. I have always been told to check mounts when dealing with clutch shudder, never really had it explained to me though.

Cheers Scott

Correct. Torque is inducing movements in a component that shouldn't spin!

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