"Heat Soak" behavior on clutch, spongy-then-stiff pedal...

[fixizin]

{Forget this thread for now: https://www.therangerstation.com/forums/index.php?threads/clutch-master-cylinder-tell-me-about-the-rubber-cup-seal-thaaang.204206 }

So 2 years ago I put in a new Perfection-brand Master+Res+Pressure Line, all good, light duty since then, 6,000 miles, 4,000 of that highway, been working at home all summer, so even LESS use...

... then this week, typical hot AH FL afternoon, 12 miles up the highway, A/C ON, engine off for 5 minutes, re-start, 4 miles of stop-and-go, engine off for 10 minutes, re-start, 1 mile into return 4 mile stop-and-go, out of nowhere, clutch pedal has "reverse" resistance, i.e. light for the first 80% of travel, then ultra-STIFF for the last 1-1/2 inches, then weird on the release...

... I nurse it home, park in the shade, 5 hours later, back to completely normal...?? I know brake fluid is made to get way hotter than under-hood temps, but I'm thinking both water and air will expand a lot (boil?) with the temps the Slave-end of that pressure line gets up to...?

Checked the reservoir, level fine, maybe down 1/8" since new, but a bit dirty... hmmm...

Have driven it 2 shorter trips since then, "gremlins" gone, totally normal again.

Anyway, what say ye, RKIs?

 

[franklin2]

If the fluid is dirty I would take a turkey baster and suck out what I can and put new fluid in it. Brake fluid loves to absorb water.

 

[fixizin]

Yeah, that's the plan... plenty o' humidity and rain down here... actually might bleed from the bottom if I can recruit Camaro-bro to help...

>> Does dirty after only 6k miles mean slave/throw-out bearing is "going"?

Looked in the viewport today (could they route that exhaust pipe ANY friggin' closer?), dry as a bone, NO BOOT visible on original '99 factory Slave--could see the whole length of big spring... sorry, no pics--phone cam couldn't focus that close...

 

[Josh B]

Could you have left the boot out once when you were looking it over?

 

[fixizin]

No, not the rubber PLUG that covers up the viewport (I've got that), but the "bellows" that covers the moving piston of the slave cylinder... newer versions (incl. the one I got from Perfection, but haven't used... yet), have the bellows-boot to keep clutch dust out of the slave cylinder-piston interface... wondering if mine had one from the factory, but it's just disintegrated over 24 years?... in fact, I'm wondering if that's not why my fluid is less-than-clean...?

>> What say ye, RKIs? Did the original factory Mazda slaves have the bellows-boot?

Oh well, I'd rather bleed/refill the fluid every 2 years, than go thru/pay for the tribulation of dropping the trans (and xfer case), and replacing the 12(?) pricey parts that "make it worth" dropping said trans! (I've only got 86k original miles on this mostly-trusty pup!)

 

[franklin2]

Make sure you have the rubber seal on the master and the cap fits tight. These things have a aggravating seal that drops down and covers the complete top of the master reservoir. If it gets stuck to the reservoir when you pull the cap off, it's hard to see and you pour fluid in it, it fills the rubber seal and the fluid doesn't make it to the bottom of the reservoir where it needs to be.

 

[sgtsandman]

The heat shouldn't have made a difference. I've never had an issue. I rarely do a lot of stop and go traffic but I have and the clutch was fine. The same with long highway trips.

The above recommendation of sucking out the reservoir is something I do roughly every three years when I "flushing" the brake lines with new brake fluid. So, that may be why I haven't had an issue. I don't vacuum flush or gravity bleed the clutch line because I'm scared I'll accidentally go to far and suck air into the system.