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View Full Version : O.T. Two mystery questions...



A.K. Boomer
07-27-2015, 10:07 AM
Just a couple quick questions not related to machining much at all but would like to throw them out to the board for pure curiosity's sake,,, and because we have allot of people who know allot about allot of different things...

Ok - first off --- how come when your cooking something on the stove - and using either water to boil first or heating up cooking oil - how come no smoke or vapor from either till you turn the heat off then all the sudden it comes pouring out of the pan or pot? with my gas stove this is instant... is it just smoking all along and I don't see it cuz the increased air flow from the burner? I don't think so because even in the center of the pot or pan there is nothing when the burner is on... turn it off and wham all kinds of smoke...


Ok second question related to hydraulics of auto's...

just ran across this in a Dodge truck and also my personal car --- and I think I know the answer to this one but just want to see what you guys think,
air trapped in a clutch hydraulic master cylinder and or slave...
clutch goes to the floor after sitting overnight --- let all the way up slow, try again - same results, over and over,,, but rapid pump and the clutch pedal starts to come around to the point of being almost normal --- vehicle can be driven with no problems,,, let sit overnight or for many hours and pedal goes spongy again...

in the case of the Dodge these are brand new components both slave and master and the system is sound - just trapped air and no bleeders on the system...

what has changed when rapid pumping? I will remind everyone that you are not pumping more fluid into the system because after every stroke you are still letting all the way up and uncovering the reservoir port and there is no "check valve" of any sorts,,, so why does this work? and then after it works then why does it go back to being spongy after sitting for along time???

Fasttrack
07-27-2015, 10:44 AM
Just a couple quick questions not related to machining much at all but would like to throw them out to the board for pure curiosity's sake,,, and because we have allot of people who know allot about allot of different things...

Ok - first off --- how come when your cooking something on the stove - and using either water to boil first or heating up cooking oil - how come no smoke or vapor from either till you turn the heat off then all the sudden it comes pouring out of the pan or pot? with my gas stove this is instant... is it just smoking all along and I don't see it cuz the increased air flow from the burner? I don't think so because even in the center of the pot or pan there is nothing when the burner is on... turn it off and wham all kinds of smoke...




I would guess it has to do with the temperature of the surrounding air, not the actual "air flow", so to speak. When the burner is on, you have a good convective current carrying hot air towards the range hood, parallel to the column of hot water vapor/oil vapor. When the burner is turned off, this convective current stops and the cooler air from the kitchen rushes in. Now you have a column of water/oil vapor traveling through much cooler surroundings and it begins to condense. So what you are seeing is not really "smoke", but the condensed vapor.

HWooldridge
07-27-2015, 10:45 AM
Not sure what kind of stove you have but I can see smoke/steam whenever the pan/pot gets hot. Doesn't seem to have anything to do with turning off the heat. Do you have a vent-a-hood that evacuates the air automatically?

My vote on the hydraulic clutch issue is that air is contained in one or a few large bubbles inside the system at high points in the plumbing when the system sits for a period. Pumping breaks up the bubbles and pushes them throughout the system so the fluid offers more resistance - and the system returns to equilibrium after being left alone for a while. However, it's still a bad condition that should be bled out.

Noitoen
07-27-2015, 10:51 AM
There is a check valve on the master cylinder. The piston seal on the master cylinder has tiny holes on the rubber that touches the piston. When the movement is forward the holes are pushed against the piston and seal. When reverse, the holes open up to let oil from the reservoir that is connected behind the piston to flow forward. Rapid pumping allows this action better.

A.K. Boomer
07-27-2015, 10:58 AM
Wow two good immediate answers --- FT that makes allot of sense and HW this is a huge and immediate effect - clear as can be and then turn off the heat and instant

But HW I think you are very close to what's going on with the hydraulic system --- I know I have the same displacement of air inside the system so this means the same for the fluid - so why the different behavior?

I believe after whipping the large air pocket into a frenzy and creating a "froth" of tiny bubble that there can only be one conclusion, given the same overall displacement --- tiny bubbles are harder to compress than large ones,,,

if it's not that then I do not know what else would make as much sense, sure willing to learn though... Thanks for the good reply's guys.

A.K. Boomer
07-27-2015, 11:02 AM
There is a check valve on the master cylinder. The piston seal on the master cylinder has tiny holes on the rubber that touches the piston. When the movement is forward the holes are pushed against the piston and seal. When reverse, the holes open up to let oil from the reservoir that is connected behind the piston to flow forward. Rapid pumping allows this action better.

yes but once the pedal is allowed to go back to rest the port to the reservoir is re-opened so any extra fluid that you may have "stacked" is immediately neutralized again, yet work the clutch a few minutes later and it's functioning great as if there's no air in the system - yet we all know there is because let it settle out for a long time and your back to square one...

Dave C
07-27-2015, 11:32 AM
yes but once the pedal is allowed to go back to rest the port to the reservoir is re-opened so any extra fluid that you may have "stacked" is immediately neutralized again, yet work the clutch a few minutes later and it's functioning great as if there's no air in the system - yet we all know there is because let it settle out for a long time and your back to square one...I haven't fooled with a hydraulic clutch since the 70's, and iirc, back then slave cylinders had bleed screws. However, the effects of air in the system is still the same, bleed screw or no, and must be removed. Looks like it will take pressure bleeding from the master end, and cracking the fitting on the slave to get the air out. What a PITA, just so the manufacturer could save a buck.

lakeside53
07-27-2015, 11:33 AM
Theory #78654. The air is compressed into the fluid -like CO2 in Pepsi.. Without any force to keep it there.. it slowly releases and forms bubbles again.

Dave C
07-27-2015, 11:43 AM
Theory #78654. The air is compressed into the fluid -like CO2 in Pepsi.. Without any force to keep it there.. it slowly releases and forms bubbles again.
Exactly why the system should be pressure bled after the system has normalized (bubbles have risen to the highest point in the system), and prior to pumping the pedal again.

A.K. Boomer
07-27-2015, 11:48 AM
I haven't fooled with a hydraulic clutch since the 70's, and iirc, back then slave cylinders had bleed screws. However, the effects of air in the system is still the same, bleed screw or no, and must be removed. Looks like it will take pressure bleeding from the master end, and cracking the fitting on the slave to get the air out. What a PITA, just so the manufacturer could save a buck.


It's a royal pain --- you have to remove the master and bench bleed it - same with the slave,,, then try and connect the fittings without any fluid leaking out of them cuz that means you re-introduced air, and the icing on the cake?
you don't get to "crack a fitting" to remove air - they are press in's with roll pin retainers...
nice...

about as much sense as rear ends without drain plugs... like you say all to cause frustrations and to save a buck...

Dave C
07-27-2015, 11:53 AM
It's a royal pain --- you have to remove the master and bench bleed it - same with the slave,,, then try and connect the fittings without any fluid leaking out of them cuz that means you re-introduced air, and the icing on the cake?
you don't get to "crack a fitting" to remove air - they are press in's with roll pin retainers...
nice...

about as much sense as rear ends without drain plugs... like you say all to cause frustrations and to save a buck...Wow! it's gotten worse than I thought. The guy that decided to become and engineer, and wound up designing that setup, should have gone to law school instead.

CarlByrns
07-27-2015, 12:06 PM
To bleed the air out of the clutch- lightly and quickly tap on the slave cylinder (if it's external) with the cap off of the master cylinder- this will break the stiction holding air bubbles.

Every modern hydraulic clutch I've work on is self-bleeding- add fluid a little at a time slowly and allow the air to escape and then (when the reservoir is full) pump the pedal about 20 times to move out the remainder. This is the only way to fill the coaxial slave cylinder Ford uses.

There are no check valves on a hydraulic clutch to retain pressure.

The OP's problem sounds more like a master cylinder with an internal leak- pressure is being bled off between the piston and bore. Just because the parts are new doesn't mean they are perfect.

A.K. Boomer
07-27-2015, 12:26 PM
CB good thoughts and practices,

but I have ran into this dozens of times before with "good" systems and I say good due to after finally getting all air removed they behaved normally for years...

So - back to the smaller air bubbles VS large, domes and spheres are stronger the smaller they are meaning for the same reinforcements they become harder to crush, would not the same apply to a fluid trying to compress them whilst the pneumatic structure on the opposite side try's to resist? Hmmmmm

Mike Amick
07-27-2015, 01:32 PM
I've had some embarrassingly long battles with bleeding hydraulics. What finally did the trick was taking a big ass
hypodermic needle and pushing the fluid from the slave ..or ... brake cyclinder up into the master. Air bubbles
in the line really hate traveling "down" to the bleeding nipple. They "love" traveling "up" to the master.
Works every time. No pumping involved.

duckman
07-27-2015, 01:42 PM
With no bleeders what I've done is to pump up what ever is not working right then block or hold the pedal in the down position for at least hour, then let the pedal up rapidly, waiting the half hour lets the bubbles float up to the high point, then the rapid release lets the servo cylinder push the bubble up to the reservoir.

A.K. Boomer
07-27-2015, 02:23 PM
Duckman with no bleeders that's makes really good sense,

also - figuring out the angle of the master and slave for that matter and parking on a big angle to get the air in the right side of the units for purging as some trap just by angle... might have to do them separately starting with slave...

kendall
07-27-2015, 02:26 PM
With no bleeders what I've done is to pump up what ever is not working right then block or hold the pedal in the down position for at least hour, then let the pedal up rapidly, waiting the half hour lets the bubbles float up to the high point, then the rapid release lets the servo cylinder push the bubble up to the reservoir.

Used to have a length of 2x4, press pedal down, then move seat forward to keep pressure on it. Worked great. My kid had a ball with a small noise maker/vibrator deal in it that made it bounce around when you rolled it. Dog got it one day, so I took the guts out, ended up using that as a 'bleed assist' Zip tie it snug to the cylinder and turn it on while the clutch was depressed.
I learned the absolute easiest way on the ranger clutches (with bleeder) was to roll back the carpet and drill a 1/2 inch hole above the bleeder. Reach through with a wrench, crack the bleeder, then press a finger over the tip and slowly pump the clutch. When done, close the bleeder and seal the hole with a plastic push cap. I only did it the 'recommended' way once before looking for a better way.

A.K. Boomer
07-27-2015, 02:36 PM
I use a spring loaded adjustable shower rod to solo-bleed brakes and clutches - ones with bleeders that is. :-)

wierdscience
07-27-2015, 02:37 PM
Last time I did a Ford hydraulic clutch the method described in the book was to fill the reservoir,depress and hold the pedal for 20 seconds and repeat as needed.Took three cycles and it was done.That was on a new master though,no idea if an old one would take longer.

The cookstove,I've seen the same thing on my gas stove,but not on the electric I currently have.I chalk it up to the hot combustion products heading towards the ceiling.

flylo
07-27-2015, 03:05 PM
Rotax 582 ultralifgt engines will air lock like that & I've had to almost turn them upside down to let the bubble out. With brakes we used to leave the cap loose overnight & sometimes the air would rise out by morning.

kf2qd
07-27-2015, 03:24 PM
Try the method I have used bleeding Disc Brakes.

Leave the slave cylinder loose and gently pump it up all the way. Then fully depress the slave to force all the oil and air out. Let it sit a couple minutes and repeat. This moves a a large volume of oil back and forth and that volume of oil will force the air to the tank. Waiting a few minutes let the air rise as high as it can in the system. Works on motorcycles and cars.

J Tiers
07-27-2015, 04:03 PM
I have a 2000 S10, and a few years ago right after the clutch was replaced, it started to fail intermittently. Did it the next day, on a highway trip. Worked fine and suddenly it would go to the floor with no resistance. I had some real "fun" driving that.

It WOULD usually work if pumped like crazy..... for a while, long enough to get home. Then it worked on and off..... while I tried to get a shop to find it.

The shop had convinced me to have a new "donut" style slave put in at the same time as the clutch, because it was at 100k+ and it costs the same to do the work all over to replace a bad slave as for a clutch. Sounded good, didn't save me a dime.

NOBODY could find it. It would never fail for a mechanic, but it would do it for me intermittently

Finally, the dealer asked if the mechanic could drive it home and back to see if it would happen. It did, I can only imagine what he said, because he had about 20 miles to go, and the last time it had failed for me, I drove it 25 miles in 2nd gear because I could not get it into any other gear even pumping hard.

Had to replace the NEW slave. Dunno what was wrong with it that was partly fixed by pumping the crap out of it, but ever since the slave was replaced , it has been fine. I have the bad slave, but have not looked into it.

It sure wasn't bleeding it, it was bled about 12 times by different people.