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Clutch Getting Stiff In Hot Weather

I'm beginning to notice some characteristic changes in my clutch pedal in relation to the outside atmospheric temperature. I've noticed in hotter weather above 80F (hence mostly during summer) my clutch pedal becomes really stiff and very hard to press. It progresses to get worser the longer the drive is too on a hot day. It feels like pressing a stage 3 clutch at times. But in colder weather however, it becomes light as a feather again and feels buttery smooth to press down. Is my hydraulics going out? Should I get new master/slave cylinder? What's going here?

Some info on how I drive; I usually modulate and feather my clutch pedal a lot in slow zones, especially like in parking lots. Is it due to this constant pumping action of the clutch that creates the clutch fluid to heat up faster and lose strength to push the cylinder? That's why it feels stiff and bubbly? Like fluid molecules expands and gets thinner when it gets hot so it loses its strength right? Also I notice while feathering the clutch especially on an uphill I can really really really start to feel the stiffness and sponginess even more than on a flat surface.

When is the last time you did a flush of your clutch fluid? It could be that.

I would also check out your slave and master cylinder, as well as all the plumbing involved. May be on the way out.

I noticed similar issues with my clutch in hot weather. I took it to a shop I trust and they checked the hydraulic fluid and said it looked ok. They suspected that the issue was hydraulic line expanding as it absorbs heat from exhaust pipes, etc.

So after that I had them replace the clutch line with the Nismo braided stainless version, which helped. I can still notice a change in clutch feel after driving on a hot day for a while, but it is less drastic and annoying than it had been.

Anyway, I agree: getting the fluid and cylinders checked out is a good place to start. Then, if they seem ok, consider upgrading to braided stainless line. Hope this helps.

Flush the fluid, change out the slave cylinder if its a DE, preventative maintenance. Mine had a similar issue then the pedal would not return after releasing, usually occurs on hot days. After the flush everything was good again.

Thanks for the input guys! I haven't done any clutch fluid flush or anything of the sort yet. The car has kept its same original fluids and everything in there for the past 15 some odd years! :O I guess I'm way beyond overdue.

Seals are old and swollen, same thing happened to mine

Quote:

Originally Posted by 350z_Lam (Post 10977988)

I can tell you with 90% surety that it's hydraulic in nature. Key is "you still have original fluids". Brake fluid is hygroscopic, meaning it absorbs moisture from the air (and 15 years worth of absorbtion, your fluid is useless by now.) Moisture (H20) doesn't compress and when it's in a brake/clutch system, the heated moisture becomes even more of a problem because the moisture is also trapping air (bubbles) at that point. A stiff pedal is a sure sign of this.

You may find that terrasmak is also correct and you'll require new seals and/or other components where you cannot just replace seals, e.g., master or slave. Check system for leakage before the flush using a power bleeder (or someone in the car mashing/holding down the pedals) to pressurize the system and inspect all components. (Or hopefully, the shop will do this without just blindly doing the fluid change.)

And then, after diagnosing quality/condition of the hardware - and hopefully only thing you need to do - is to swap out all of the fluids. Do both clutch and brakes while you're at it. If you don't have or have access to a power bleeder, you might want to consider either buying one (recommend Motive unit) OR having it professionally done (and the shop will take care of the proper disposal of your old fluids). I say this because the Z hydraulic systems are very sensitive to being properly drained and bled. Air gets trapped in the system and without a power bleeder, you're likely going to run into the dreaded "OK, pedal feels good now" then a few miles down the road, "Ummmm, WTF.... pedal feels like shid...."

Good luck.

Hey Mic! Great to see that you are still active on this forum. I always love reading your long and thoughtout responses not only here but in other posts too. You are always the most informative!

P.S. I still havent gotten a chance to bump into you yet in the bay since that last time :P