Clutch not working when hot

[Helirich]

Anybody have their clutch not work when hot? Today I drove the car for over an hour. Everything was fine. Parked the car in the full sun (for an hour) and it wouldn’t go in reverse. The clutch felt OK, but the gear shift would just grind. It went into first gear reluctantly. In the other forward gears I think it wasn’t working good, but it went better because I matched the rpms while shifting. I checked the fluid level and it’s full.

[82DMC12]

Been there done that. First make sure you've replaced the original plastic clutch line with a SS braided line. If you did that already and you don't see any leaks , flush and bleed the clutch. I have the DPI remote clutch bleeder which makes it so much easier. If you keep having to bleed it out , you probably have air getting in at either the master or slave cylinders. Check for fluid leaking into the foot well where the clutch master is bolted to the firewall.

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[Ron]

+1

And if you can find no leaks, suspect a seal bypassing internally...

[Helirich]

Been there done that. First make sure you've replaced the original plastic clutch line with a SS braided line. If you did that already and you don't see any leaks , flush and bleed the clutch. I have the DPI remote clutch bleeder which makes it so much easier. If you keep having to bleed it out , you probably have air getting in at either the master or slave cylinders. Check for fluid leaking into the foot well where the clutch master is bolted to the firewall.

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Mine has the SS lines. I’ll check for leaks. Wouldn’t the fluid go down?

[82DMC12]

Mine has the SS lines. I’ll check for leaks. Wouldn’t the fluid go down?

Doesn't take much of a leak at all to draw air into the line. The piston barely moves anyway, and air compresses; fluid does not.

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[Helirich]

So I checked for leaks in the floor. It’s all dry there. I noticed that the pedal will go down an inch before it actually does anything. Seems like I brought this up before when it wasn’t as bad. I think my master is about a year old. Maybe it’s no good. I could extend the linkage to take up the play, but I’m wondering if that will just make the pedal bottom out sooner. Does the spring ever ware out in the master? Maybe poor machining catches the piston?

[82DMC12]

It's almost certainly air in the clutch line. The master is pushing in, the air is compressing, and once the air is compressed, the fluid finally moves and makes the slave work. That's why the pedal moves so far before the slave starts to work.

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[Rich]

Does the problem disappear after the car cools down, as if the master and slave are both OK? Only happens when you hot-soak it, parked after a long drive on a hot day, especially at low speeds around town before parking?

Then the clutch fluid is probably boiling inside the SS line back there above the drivetrain.

1. Check the routing of the SS clutch line. Be sure none of it got coiled too close to the exhaust crossover pipe.

2. Be sure there are still 2 complete heat shields bolted onto the crossover, Items 10-11 in this schematic.

I assume you aren't running headers (no crossover in that case).

[Helirich]

It's almost certainly air in the clutch line. The master is pushing in, the air is compressing, and once the air is compressed, the fluid finally moves and makes the slave work. That's why the pedal moves so far before the slave starts to work.

I believe the rod is not hitting anything during the inch of pedal travel. If it was air, I think it would have some resistance and than get harder when it moves fluid. I realize squeezing air is not much, but the piston and seal have to move. (Or should move) I’m thinking the piston/seal is stuck down a bit.

Does the problem disappear after the car cools down, as if the master and slave are both OK? Only happens when you hot-soak it, parked after a long drive on a hot day, especially at low speeds around town before parking?

Then the clutch fluid is probably boiling inside the SS line back there above the drivetrain.

1. Check the routing of the SS clutch line. Be sure none of it got coiled too close to the exhaust crossover pipe.

2. Be sure there are still 2 complete heat shields bolted onto the crossover, Items 10-11 in this schematic.

I assume you aren't running headers (no crossover in that case).

I’m not sure if it will disappear this time, but it has in the past. In the past, I needed to push every last bit to work the clutch. This time, I pulled the carpet clear and pushed till I got to the floor and still it would not disengage. I have headers. Not sure if the line can get hot on something else. I’ll look in to it.

[DMC-Ron]

It's almost certainly air in the clutch line. The master is pushing in, the air is compressing, and once the air is compressed, the fluid finally moves and makes the slave work. That's why the pedal moves so far before the slave starts to work.

Agreed. Air in the clutch line would seem the most likely suspect. If the air is trapped where it gets heated, it expands in volume, pushing clutch(brake) fluid back to the reservoir. So, when it's hot, the area ratio of air to liquid increases. The result is more air compression and less actual slave piston movement with a given clutch peddle displacement.

Ron