Clutch disengagement point moves when hot :S

[Stefan]

In my GA65, I have this problem where I have the clutch pedal adjusted such that, cold, the shifter is at it's least notchy when pushed to the floor (pretty much end of clutch master adjustment). But often after driving up to temperature, parking car for a short period then driving again, it becomes quite hard to shift when pushed to the floor. The point where it is easy to disengage actually moves up when hot, and pushing beyond this point makes it hard to shift again. The portion of pedal travel during which you can shift is very narrow.

Any ideas? It really seems to be a heat soak issue - would boiling fluid give these symptoms?

History:

• First I thought this was lack of gearbox oil, so I changed that, problem remained.
• Then I noticed the clutch master was just starting to leak at the top of the pedal, so replaced that. (Slave is already new). Problem remained.
• Assumed that I was cooking the master - dump pipe is right near it - so made up some heat shielding. This seemed completely fine for a few days, but today after driving during the day without the heater on the clutch point has moved when hot again - even though the master reservoir doesn't seem as hot.

I am running a sprung centre rebuild ceramic puck clutch & aftermarket light flywheel. Car used to have a W55 but is now running a W58 with new slave to suit, and the W55 clutch slave --> clutch fork actuator rod. I've ordered a turbo beanie to see if reduced underbonnet temps will fix, but it hasn't arrived yet.

[dogeatdog01]

it sounds like your getting clutch fade dude.
how close to your exhaust manifold is your lines / clutch master cylinder?

alot of cars take about 2 - 3 mins to warm up the gearbox (become less 'notchy')
its good practice to let your car warm up in neutral (with the clutch out) when u start it in the morning.

this will warm up the thicker oils within the GB and allow synchos to align quicker etc.

i get the impression that the clutch fluid is heating up in the line, and becoming more viscous..therefore having more compression, which means your foot has to travel further (and often further than the floor allows) to move the clutch the same distance away from the flywheel)..
perhaps try insulating your clutch line..
or bleed your clutch.

tell us how that goes..
anyone with any other ideas?

[Stefan]

alot of cars take about 2 - 3 mins to warm up the gearbox (become less 'notchy')
its good practice to let your car warm up in neutral (with the clutch out) when u start it in the morning.

This is a good point, I do let it warm up but possibly haven't set the travel when warmed up.

i get the impression that the clutch fluid is heating up in the line, and becoming more viscous..therefore having more compression, which means your foot has to travel further (and often further than the floor allows) to move the clutch the same distance away from the flywheel)..
perhaps try insulating your clutch line..
or bleed your clutch.

The weird thing is, when hot, the disengagement point is higher and my foot has to travel *less* distance. Travelling further then this - i.e. to the floor - disengages the clutch *less*. The clutch has been bled, but I will try insulating the clutch line.

It just seems strange to me that there is such a narrow window for disengagement before further travel engages it again :S

[Matt-AE86]

Flush clutch fluid, replace fluid, bleed.

Even though you have a heat shield I would say its still cooking it. If you cant have your dump redone to stay as far away as possible possibly have it ceramic coated then wraped aswell plus heat shield, also maybe go for a braided line with heat protection ?

[Stefan]

Flush clutch fluid, replace fluid, bleed.

Even though you have a heat shield I would say its still cooking it. If you cant have your dump redone to stay as far away as possible possibly have it ceramic coated then wraped aswell plus heat shield, also maybe go for a braided line with heat protection ?

Did that when I replaced the master. Dump is wrapped, and all the clutch fluid lines are hard lines. I'll try taping the hard lines anyway, and also wrapping the exhaust manifold. I think a turbo beanie should make a big difference to the heat near there...

[Stefan]

I'd say that the shift point moves about an inch once the engine is hot, but the clutch master reservoir really isn't warm now that it is shielded.

Will try insulating the clutch lines next.

[dogeatdog01]

the other thought, which im not sure if i mentioned is the clutch master might be getting hot and having a different effect.

obviously its some sort of heat issue which is having effects...and i guess you got to isolate the heat source from the clutch system(s).

the only other thought, if its not that - is the fact that:
- clutch oil is old / wrong type?
- master is fading
- slave is buggered
- master is getting hot from frictional usage (not external usages)

try a snail wrap on ure turbo..then maybe exhaust wrap..
that will b a good mod anyway.

tell us how u go.
T

[Stefan]

Thanks again. Clutch fluid should be correct, and both the master and slave are new now.

I find it pretty strange that when you push past the point of disengagement, it starts to engage again :S

I will post what happens once the turbo beanie arrives.

[allencr]

What happens when fluid boils??? Your formerly incompressible fluid then has load of bubbles and will cause the pedal to have almost no resistance when pushed to the floor.

... sprung centre rebuild ceramic puck clutch...

Clutches/pressure plates can change a little with heat but shouldn't and clutch disks can warp & change a great deal, dragging or not dragging and possibly giving the impression of changing their engagement point.

I don't have a clue about what your 'shifter is at it's least notchy' description means.

[vinno]

if you replaced the master before you installed the heat shielding to keep it cool is it possible that you have fried the new master?

As far as the change in disengagement goes, your case is wierd. as mentioned above, warped clutch is the only thing that sounds like it could be causing this but even that sounds strange. How hot is your gearbox when it is playing up?

[Stefan]

What happens when fluid boils??? Your formerly incompressible fluid then has load of bubbles and will cause the pedal to have almost no resistance when pushed to the floor.

Pedal has proper resistance even when hot, does not feel like needs bleeding at all so I guess I can assume the fluid isn't boiling...

I don't have a clue about what your 'shifter is at it's least notchy' description means.

As in, set the threaded pedal/master point such that, when foot to floor, gearbox shifting is at it's least notchy/most butterlike (i.e, fully disengaged). It is possible to shift before (and after) this point, but more difficult.

[mic*]

Firstly if you havent; Check carefully that the pedal assembly itself does not have stress fractures or cracks anywhere. Ive known a few toyota owners who've scratched heads for a while blaming clutches and hydraulics when this was the prob. Hot cold may just be coincidental.

In my head you've covered your bases with the hydraulics if you've carefully bled after checking the lines & replacing the master and slave - but the problem persists before and after doing all that. Ill doubt the fluid is boiling from what you've described. Bite the bullet and pull the clutch out...

You can always get it hot, ie when its being weird, jack it up and watch the slave piston while someone pushes the pedal...

[Stefan]

Good ideas, will do, thanks

One thing that might be relevant - I used to have a W55 in this car and swapped to a W58 (slave other side) along with new slave to suit. Am still using the W55's rod that goes from slave piston to fork... I would assume this is the same, but maybe it isn't.

[mic*]

Good ideas, will do, thanks

One thing that might be relevant - I used to have a W55 in this car and swapped to a W58 (slave other side) along with new slave to suit. Am still using the W55's rod that goes from slave piston to fork... I would assume this is the same, but maybe it isn't.

Shouldn cause your prob. If they were a bit different in length would just move engagement point and you'd adjust pedal/master to compensate.

[allencr]

rod that goes from slave piston to fork... I would assume this is the same, but maybe it isn't.

IF the slave & clutch fork aren't designed with a spring and an adjustable stop, then the length of the rod doesn't not matter at all. It won't change anything but the sliding position, deep or shallow, of the piston in the cylinder. It only has to be short enough so that the clutch can fully engaged with no pressure on the throwout/release/thrust bearing with enough room for future wear, or it has to be long enough to prevent the piston from coming out of the slave cylinder past the dust boot, nothing else - no engagement point.