Unusual clutch problem. R154 Jzx100

[joey]

Hey guys,
Need some opinions on the shit of a clutch on my chaser. Ok explanation goes:
- Driving normally the clutch is fine, acts proper, feels meaty... no problems.
- However as soon as the engine is revved over 4k rpm the clutch pedal feels light and sticks down most of the time.
- You can change when the pedal is stuck down but it feels like it isn't fully engaged and hard to get into gear.
- I am able to slide my foot underneath the pedal and bring it back up to which it acts normally again until i go over 4k rpm.

Now the clutch is an original toyota organic plate and feels meaty still, no slipping ect. It has a braided line to the slave.

Solution:
- Suspected air in the system, bled and tried agan.... same problem. Bled the whole system with new dot3... didnt make a difference.
- Suspected bow or pitting in the master cylinder, buy new cylinder kit and get it rebuilt by a mechanic, which will check the bore aswell. The bore seemed fine, no pitting and no bow, cylinder kit is put in anyway and problem is solved... for 2 day and it has come back!
- Taken to a clutch specialist today who charged me $44 to drive the car around the block, and tell me he thinks its a hydraulic issue, maybe try getting a new slave cylinder.

Now before i go any further i though i would consult you guys on here if anyone has had anything like this happen before. It ONLY happens when going over 4k rpm and the pedal mechanism moves freely and freshly lubed up. I'm stumped as to what the problem might be.... anyone have any theories?

Cheers, Joe

[WDE_BDY]

Any issues around wastegate maybe? If its revs dependent it is unlikely to be hydraulic, boiling fluid etc won't suddnely cool just because revs drop off. Trace along the clutch line and look for anything that could be moving that is dependent on revs and see if there are any likely suspects particularly around the slave cylinder and clutch fork. Does the pedal drop as soon as revs hit 4,000 or does it just not come back after after first use of the clutch over 4,000? That may indicate it is an issue inside the bellhousing.

Callum

[joey]

Sorry, i edited my original post a bit to make it more clearer, it is the clutch pedal that sticks down, not the accelerator so its not free revving and wouldnt have anything to do with the wastegate i would think.
The only thing that moves dependant on revs i think would be friction plate/flywheel. Pedal doesn;t drop when those revs are reached, it is only when pushed down. The next step i think will be to take off the bellhousing and have a good look but i thought i would try here first before i go undertaking a reasonably big job like that.

Cheers, Joe

[forey]

i had to put reflective tape over the clutch lines and a turbo beanie to keep the heat away (gt35 and dump pipe right under MC)
what happend with mine it was anything over 15psi boost the clutch would go in without any pressure and couldnt change gears unless you backed off. after the beanie was put on the issue went away
cheers

[joey]

Hmmmm interesting forey. I have the standard turbo with a custom dump but both utilise the standard heat shielding. Possibly the stainless steel dump is letting off much more heat than the standard cast one boiling the fluid, master cylinder is right above the dump. Might be something to investigate...
I have some of that heat resistant silver tape at home, might try that on the clutch lines and get one of those beanie things that look like a sweat band to put over the master.

[renxun]

hey i have this problem too... r154.. mine happen right after i change my clutch to hks gd pro twin plate. mine happen exactly same with the thread starter description but the only differance is mine happen on 7k rpm hard pull. havent solve it yet. did all the above mentioned too except changing the slave's seal.

[lexsmaz]

Tis a strange one, i was thinking how is your slave cylinder piston positioned in the slave bore ? could it be that when you hit 4,000 i pressume its under boost & pulling hard, could the slave piston be pushed down the bore further under the acceleration force creating a bigger gap between the pushrod & the clutch fork or the slave cylinder piston ? which then creates the low m/cyl pedal etc when you go to use the clutch ... whats it like if say you hit 4,000 plus but dont use the clutch & back off steady & slowly, is the pedal normal ? . If its normal it might be something else, but you will need to slow down gradually so you dont push the slave piston foward under deceleration forces ..

Personally i would suggest that you need to get under the car & check if you can push the slave cylinder piston down the bore of the slave cylinder, ie; making a bigger clearance between the pushrod & the fork ... Obviously make sure no one has their foot on the m/cyl pedal & there is sufficient clearance at the m/cyl to pedal ..

Rob ..

[allencr]

R154 clutch pedal issue Started on 12-5-09
http://www.toymods.net/forums/showthread.php?t=48487

What could be causing this? T50 slave cylinder issue. started on 27-5-09
http://www.toymods.net/forums/showthread.php?t=49009


I don't see what's wrong with this repeat posting or the other one, just one common denominator because the MC can't hold down its push rod unless the the frame/body/moncoque twist significantly, and because that T50's fork clip just doesn't do all that much.

[joey]

This is 2 different issues on two completely different cars. The celica has a push type clutch as has since been ficed with a new fork which has the locating tab on it. The jzx100 is a pull type clutch, has completely different symptoms and and if it was the same problem then it would happen all the time, not just over 4k rpm....

Anyway further progress on this is that i took the slave off today and popped the piston out, it had pretty severe scoring around the piston and one of the o-rings looked a bit perished, hopefully im on to something here. Since i couldnt get a kit for it i've had to buy a new one which will be in tomorrow morning. Will see how it goes.
Cheers, joe

[big wad]

i dont suppose its one of them flash super light clutch flywheel combo,s is it . i had one in my bus doing much the same thing, turns out tas driveline found the fly wheel to be flexing and got worse as the revs climbed. cheers bigwad

[joey]

Nah, had a look through the inspection plate today at is a big meaty mother of a flywheel so i presume its a stock one.

[joey]

Took the slave cylinder off and inspected it, there was a fairly large amount of scoring around the piston and one of the seals was on its last legs. Since i couldnt get a kit for it i just bought a brand new unit. Just finished putting it all back together and took it for a drive.... seems a little better but its still there Clutch stuck down after 5k rpm a couple of times.
I guess i might just have to bite the bullit and take the bell housing off :\

[joey]

After talking to another clutch shop the assured me it would be the master cylinder that has been causing the problem so i sent it off to go get sleeved. $160 later i installed it today and the problem is still there. I'm just about ready to call it quits.
Has anyone heard of a friction plate being sucked to the flywheel under high rpm?
Cheers, Joe