I have a 2000 Outback with a clutch pedal that is soft for about 1" at the top of the stroke and then becomes firm and “regular feeling” for the remainder. I’ve replaced the CMC and CSC with LuK parts and bled the system with fresh DOT3. Any thoughts on how to fix the soft spot at the top of the pedal stroke?
A few notes:
The hydraulic line is original.
No evidence of fluid leak.
I did not bench bleed the CMC, but bled on the car (LuK has a bleeder on the CMC).
Clutch fork squeaks a little when depressed.
The car shifts without any difficulty or grinding.
Appreciate the feedback. One last question - sometimes the clutch pedal gets caught about 3/4 of the way back to it’s original position, then I press it again and it comes back all the way. Could this be a worn out return spring?
It depends on what you mean by “soft” - does it feel different than it previously felt when it was operating normally? Expect maybe an inch of free play before the clutch engages, but I in my cars with hydraulic clutches (BMW, VW) this first part just gives less resistance but doesn’t, for instance, feel “spongy” the way a system containing air would. The catch upon return is something to look into.
To be sure your clutch is releasing fully, starting with the engine running, transmission in neutral, clutch pedal up, it should shift into gear freely while the car is standing still (after depressing the clutch give the input side of the transmission a few seconds to stop spinning before shifting into gear) - any catching, grunts, or other oddities from the transmission or felt in the linkage that are not felt when shifting with the engine not running could indicate the clutch isn’t fully releasing, though it might be only slight - if this is happening the synchros will wear prematurely.
The clutch hanging up might be due to a damaged snout on the transmission case. The hardened steel throw out bearing carrier moves back and forth over the aluminum snout which is a part of the trans case itself. This can also cause premature clutch wear.
Here’s a pic of what it looks like; the upright sleeve on the right. It’s a common problem and some clutch kits come with a new sleeve. Others do not.
For a clutch system, DOT 3 would be a better choice, DOT 3 absorbs less moisture from the air.
Usually not concerned about the higher boiling point that DOT 4 would give
I did not know that. That’s a good reason to choose it. I used to be concerned about water absorption back in the 70s when brake fluid turned dark after one year, was black after two years, and started forming muck at the bottom of the reservoir after three years. Then I bought a new '98 vehicle and year after year the fluid stayed clear. Something has changed, I says to myself.
One thing I knew changed - the master cylinder top used to have a hole in it to let air replace the lowering fluid level, then they came up with a diaphragm to keep it sealed. So now it’s a totally sealed system. That’s what I say. Everyone else on this forum says air infiltrates the seals, but I remain unconvinced.
I had this on a couple cars. It can take some maneuvering, but with each I was able to squirt some TriFlow or lithium grease on the squeaky moving part and the action got smooth and quiet.
Those fluids have significantly larger molecules than air, and the seals can maintain a complete block against fluid leaks. Air molecules and water in air can not only pass by the rubber/metal seal, but may also migrate through the rubber. As an example, a former co-worker ran experiments to see how much moisture passed through solid composite panels. The composite panel was mounted on a flange of a vacuum chamber, and a humidity controlled container was then mounted on the other side of the composite panel. The vacuum chamber was pumped down and sensors measured the increase in moisture that migrated through the composite. If moisture in air can pass though solids, it can certainly migrate past seals.
Science, who needs it when it destroys my perfectly ignorant opinion? If Tom Magliozzi were still around he would back me up.
Well, learn something every day.
I still think there was some major improvement to brake fluid chemistry starting in the 90s that resulted in the fluid staying clear as the years went by. That despite moisture and air contamination.
At any temperature above absolute zero atoms are vibrating and jostling in a solid, shuffling in a liquid, bouncing and scattering in a gas.
Leads to diffusion. More subtle and persistent than pressure.
Rubber molecules aren’t so tightly bound that other atoms can’t work their way through.
Tires lose pressure mostly by air going right through the rubber.
Helium atoms are so “slippery” they can move through glass.
And it’s not only the smallest atoms.
Put some peanut butter in a plastic bag and the smell comes right through.
Caliper and wheel cylinder seals can withstand 1,200 psi, but could they do that for, say, 1000 hours straight without weeping?
Diffusion goes on 24/7.
So which part of the story is correct?
Yesterday you said the clutch catches.
Today you say it does not catch.
Earlier I mentioned a repair sleeve for the trans snout. A clutch pedal should have some free play in it BUT some excessive play can also be caused by a hanging (meaning catches) guide sleeve which is part of the throw out bearing.