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Clutch pedal get soft when hot
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Old 10-20-2018, 10:02 AM   #1
GC84ever
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Question Clutch pedal get soft when hot

Since my last clutch job, I've noticed my clutch pedal gets very soft with hardly any feed back when it gets warm. Example stop and go traffic on a warm day. But on a cool day the pedal stay nice and heavy with lots of feedback. Also the pedal re-stiffens up after being parked for a bit.

Any thoughts?
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Old 10-21-2018, 12:19 AM   #2
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Sounds like you are driving a subaru.
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Old 10-21-2018, 04:48 AM   #3
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May try different fluid. Maybe a dot 4 to take the heat alittle better. ATE Super Blue, Motul, or what ever flavor floats your boat. You have to watch out for some absorbing water very quickly.
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Old 10-21-2018, 02:55 PM   #4
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Originally Posted by scruff3333 View Post
May try different fluid. Maybe a dot 4 to take the heat alittle better. ATE Super Blue, Motul, or what ever flavor floats your boat. You have to watch out for some absorbing water very quickly.
Fluid should not be responsible for this.
It's a known subaru issue for which recalls have been made and no conclusive answer has been given.
Recently a member has come forward with a theory in a very recent thread, see the troubleshooting section and DAFS.
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Old 10-22-2018, 09:58 AM   #5
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A new clutch master cylinder solved this for me.
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Old 10-22-2018, 01:21 PM   #6
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A new clutch master cylinder solved this for me.
A new slave cylinder solved for me.
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Old 10-22-2018, 08:46 PM   #7
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I replaced both, problem still exists.
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Old 10-22-2018, 10:26 PM   #8
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I was subaru tech for 40 years and found that the hose between the master cylinder and slave cylinder when engine bay is extremely hot collapses internally. I have replaced many hoses along with a new slave cylinder and has worked every time and make sure you bleed the system very well. Good Luck
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Old 10-22-2018, 11:47 PM   #9
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I was subaru tech for 40 years and found that the hose between the master cylinder and slave cylinder when engine bay is extremely hot collapses internally. I have replaced many hoses along with a new slave cylinder and has worked every time and make sure you bleed the system very well. Good Luck
I replaced it along with the master and slave. No Dice.
I still believe the answer is in the post I referenced, once the slave has been allowed to hyperextend the system will be prone to issues.

Interesting to note that basically every part mentioned has had a recall issued for it at one point or another.

Hence "It's what makes a subaru a subaru"
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Old 10-23-2018, 06:43 AM   #10
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The one time this happened to me was actually caused by a tiny leak in the hardline to slave hose that would only leak when it got hot.

My symptom: Clutch got soft after going from driving on the highway to stopped on the highway in traffic. It would eventually come back no problem once I started moving again.

The heat in the line expanded it JUUUUUST enough to cause the leak to happen, and when it got some airflow back through it to cool it off, it went back to sealing and being fine.

Eventually what happened, is that one time it did this, it eventually ran the MC dry and I had no clutch.

Swapped the line, bled it again, and boom never had the problem ever again.

The rubber line is the suspect to me in OPs case.
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