Went for a 300 mile round trip drive yesterday first 1hr long drive went I got to my exit the clutch would be very soft almost to half way but was still able to engage So i kept going hr an half later got my last exit same thing stopped at mobil station got a bottle of brake fluid came back out fluid was fine no leak anywhere and when I got back in clutch was stiff again. did everything I had to do driving around to a couple of towns and then headed back to the highway long drive and it did it over again it only happens if im in one gear for a long period of driving for awhile. leading me to believe it might be a vacuum leak. is the clutch a closed hydraulic system or is it the same as the brake master cylinder and have a vacuum hook up to it? Like I said after I stop for a bit pressure comes back idk what to think.

 

How long has it been since you've replaced the fluid? How old and what kind of clutch?

 

check the floor carpet by your clutch pedal and see if it is wet. It is possible that your master is leaking and that's why you feel the softness over time. if you do notice its leaking there is your problem. otherwise check your slave to see if there its leaking. if all of those are fine you might want to bleed your system again.

 

Dont know the what the clutch is. I said tho that when I got fluid their was none missing its still full today. it is pretty nasty looking tho. so yes a fluid change would be good for it. why would it be soft and then go back to being good again tho? is there a vacuum hook up for the clutch system?

 

Brakes get stiff. Clutches don't. I gotta be honest and this isn't meant to be personal but I think you're imagining it if the clutch pedal is able to engage and disengage the clutch disk to allow you to be able to shift properly.

However, if you're simply speaking incorrectly and the pedal, when you think it's "soft", isn't allowing the clutch disk to allow you to shift then you could have air in the system and you would need to bleed the system, or you could have a failing clutch master cylinder. This assumes that there are times when the clutch disk isn't disengaging.

 

I've had it happen before on my old clutch, so I know what he's talking about. Does your engagement point change? Mine was kind of opposite, but on my old clutch if the car sat for a couple days and then I drove it, the clutch engagement would be nearly at the floor and then after a bit of driving it would return to normal. Sometimes after driving on the freeway the clutch engagement would be almost at the top though too.

My first guess honestly would be the clutch going. As you drive on the freeway the heat builds up in the pressure plate and clutch disc and is possibly changing the pedal feel (ie maybe the fingers get softer on the pressure plate). However, the cheap thing to do first is flush your fluid a couple times to clean it up. It's also possible you just have a bunch of junk and moisture in there and the changing temperature is affecting the hydraulics. To answer your question, no, there is no vacuum boost like there is for the brakes; the clutch line is a sealed system.