Twin plate clutch - dramas

[spiller]

had an OS twin plate clutch fitted to my JZA70 on friday and am having a few dramas. the friciton point on the pedal is very low...the clutch engages pretty much as soon as the pedal comes off the floor. i adjusted the pedal from behind the firewall but there wasnt much different - just accepted that its a racing clutch and moved on...no problems.

all has been sweet until i took the car for its first spirited run. as soon as things started to heat up i lost all my gears. as if the clutch wouldnt disengage from the flywheel. the only way to select gears was to turn off the engine and put it in gear. then when things cooled down a little i was able to select gears whilst driving as per normal.

dont think its a hydraulic issue because pedal is always firm and bleeding the clutch (again) didnt make any difference.

OS clutches come with an adjustable slave cylinder...the shaft of the slave has an adjustable length and i have a theory that the length is currently too short and when the clutch gets hot and the plates expand, the piston doesnt push the fork far enough to disenage the clutch so it remains engaed to the flywheel (thus unable to select gears).

have pulled off the inspection cover to attempt to adjust this slave but has been to no avail, the piston just spins around when i try to lengthen it. also took it for another drive and the same thing happens. (sorry for the shit description, people who have worked with similar clutches will know what im talking about hopefully).

should be noted that i have changed to new gearbox oil (VMX80) and replaced the shifter bushes (the new seat is much larger than what was in there) so not sure if any of these things could be causing the issues im having? cant see how...

any ideas??

[The Real Roadrunner]

you will need to lenghthen the slave but yes it is a PITA.

try pulling the slave out to do it, may give you some more room to play with it.

cheers
linden

[spiller]

just been slaving (excuse the pun) under the car for a couple of hours with some trial and error. found a way to pull the rod out to adjust the length without pulling the slave out which was good. lengthened it as long as possible and put it back in to find that my thinking was wrong, i needed to shorten it, not lengthen it. so that was a waste of time, anyhow, have worked out how to adjust it now without having to pull anything out so that is good.

what is not good is this...i shortened to rod (to shorter than it was to begin with) but whats got me puzzled is that the end result is the same..i am still unable to grab gears, infact this time it doesnt matter whether the clutch is cold or not, it just wont go into gear. the clutch cannot be fucked, i was thrashing it around today and it held up just fine, plus, fucked clutches DONT engage, the issue here is failure to DISengage.

im am all out of ideas.

process of elminiation...

slave rod too long = unable to get gears
slave rod too short = unable to get gears
slave rod intermediate = unable to get gears after a spirited run

the one thing i havent played with since is the pedal adjustment, this was adjusted by the mechanic when we first got the car running and all was sweet but i hadnt put the car through its paces yet. is it possible that after adjusting the slave rod, the pedal also might need to be adjusted to make things work?

[98SZR]

Yes try adjusting the actual pedal, I'd say your clutch pedal wasn't set correctly in the first place. Some instructions here : http://www.cygnusx1.net/Supra/Librar...Section=CL&P=3

Also try leaving the slave rod at intermediate so you can at least get gears at first.

[takai]

The problem is that with the lever actuation on the clutch a couple of mm on the slave end can translate to 10+mm on the clutch end, so finding that sweet spot is extremely difficult. It is much easier to adjust it via the pedal.

[spiller]

The problem is that with the lever actuation on the clutch a couple of mm on the slave end can translate to 10+mm on the clutch end, so finding that sweet spot is extremely difficult. It is much easier to adjust it via the pedal.

this is what i was thinking, because as i said, ive tried it at 5 or 6 different spots (only differing by a couple of mm in legnth).

thanks for that link 98SZR...ill have a go at it today.

[takai]

You may need to try it every 1/2 or 1 turn, as thats 0.6 to 1.25 mm assuming standard metric thread pitch.
I had similar dramas setting up the clutch in the race car (before it ripped itself apart).

[spiller]

hmm well the way it is at the moment, it is almost back to where it first was (where it would select gears for normal driving but not when driving hard with things hot). although there is still a few mm's difference there so ill give it a shot.

[takai]

It might be just a 1mm change in the sweet spot which makes it all work. Because that 1mm can be 2-3mm on the other side.

[MR 1JZ]

+repped all people in this thread that provided help...becuase in providing spiller help you are also providing me with help I have to provide to him...if that makes sense

[takai]

+repped all people in this thread that provided help...becuase in providing spiller help you are also providing me with help I have to provide to him...if that makes sense

Haha 2nd hand help FTW....

[MR 1JZ]

sorry that was meant to read

"you guys are providing him with help that I no longer have to provide him with"

lazyness ftw

[allencr]

sorry that was meant to read
"you guys are providing him with help that I no longer have to provide him with"
lazyness ftw

I don't think anyone here is "providing him with help" at all!!
I do not know what a JZA70 is, so I'll ASSume there's nothing special about its clutch operating mechanism.
Unless these manual pages referred to at
http://www.cygnusx1.net/Supra/Librar....aspx?S=CL&P=3
are for the wrong type slave & clutch design(besides the 'twin plate'), you've got a bad clutch.

There is NO CLUTCH ADJUSTMENT, only pedal height & free play can be adjusted and this is mostly for driver comfort & feel, and will not affect the clutch operation unless they are WAY, WAY out beyond anything reasonable. Too much free play, 30mm plus, might not let the clutch disengage, but that's about it for adjusting anything that would help your problem

I'd also ASSume that the new adjustable slave cyl. rod is to allow the installer to compensate for the new position of the release bearing due to the increased height of the twin plate.
I think it should be adjusted short enough so that clutch wear will not allow the slave's piston to bottom out.

The pics show that both slaves have an internal spring and that scares me because I can't think of any clutch operating system that has a reason for it, and this might be completely off base.

[takai]

From memory spillers JZA70 is a factory one, which runs an R154 with a pull type clutch. Thats what the springs are for, to compensate and translate the motion. The ratios on a pull clutch are much much higher than a simple lever action push clutch as they are traditionally used for a much higher clamping pressure.

As such adjusting the freeplay on the slave rod by 1mm can translate to up to 6mm at the actuation end. So the 3-4mm of freeplay which he has now could be causing the dramas.

P.s. refer to the 7MGTE diagrams on Cygnus, not the 7MGE ones.

[MR 1JZ]

oi takai...it was a factory pull type crutch

now runs an OS giken twin plate which is push type and runs a pull to push convertor