On Clutches,,there's a thing called a Throw-Out bearing.
Just a Glorified ball-bearing,,you probably know what that is.
Clutch throwout bearings do something that bearing were not meant to do.
They SLIDE,,up and down a shaft.
In clutches,,as they slide they bear against a very heavy load.
And the manner in which force is applied to slide them is not necessarily EVEN.
So they tend to COKK on the shaft,,and as they do that,,they dig-in and wear grooves,notches in the shaft.
Lets use a silly example.
Slide a Donut onto a broom handle.
Donut is the Bearing.
Broomhandle is the Shaft.
Spin the Donut.
Thats what Ball Bearings were made to do,,,take rotational loads.
Here's a Pic of a typical Ball Bearing.
Easy to see how it's built to take rotation.
http://pasture.ecn.purdue.edu/~gem/images/bearing-ball.gif
If ya look at it,,there's NOTHING to reccomend a Ball Bearing for sliding along a shaft.
It just as soon be a Solid Piece of metal,,with a hole in the middle.
Or a piece of pipe sliding along the shaft.
Back to the donut--we spun it,,like a ball bearing.
Now take your fingers,,and slide it along the shaft sideways.
If you use 2 fingers, kinda like a fork straddling the shaft,it'll slide pretty evenly.
But while the Donut with the Big Hole in the middle is hanging from the narrow shaft,,,push it SIDEWAYS along the shaft with ONE finger.
What happens?
Does it slide straight,even,smooth?
Or does it Tilt,,cokk,,then slide?
Just pushing sideways,,from one side,,it's GONNA cokk.
On a Throwout bearing,,that makes i it want to "dig into " the shaft if the SideThrust is not PERFECTLY even.
What's perfect?
Right,,,,Nothing is.
So,Now,,lets Cut some Grooves in the mop handle/shaft.
Slide the Donut/Bearing sideways with 2 Fingers Forked,very evenly.
Can You imaging the DoNut Dragging along the shaft's notches,,falling in/out of the grooves as it slides along?
Snagging,etc?
Now imagine doing it with ONE finger,,trying to slide that donut along that grooved notchy shaft while pushing the donut sideways from it's Edge on one side--trying to cokk/tilt .
THAT is gonna be a BUMPY,Grabby,Sticky Slide.
And its gonna take a LOT of extra force than if everything was nice,smooth,and side-thrust was perfectly even.
On Transmissions,,,there's a Sleeve that sticks out the front of them.
THAT sleeve is what the Throwout bearing slides along when you push in the clutch pedal.
On most "old"gearboxes,,that sleeve is cast iron>Hard
On many Late Model cars,,it's Aluminum>VERY soft.
They get grooved & notchy in a short time.
Here's a picture of an OLD gearbox
(THIS particular aspect of manual transmissions is practically Universal---they are ALL "the same")
http://www.cruiseroutfitters.com/content_images/Used4spd.JPG
On the Lefthand side,,you can see the Shaft coming out which has the heavy,wide Splines in it--Thats the actual Transmission Shaft that the Engine/Clutch turns.
The INPUT shaft.
Then you can see that it's coming out of a Straight,Smooth SLEEVE,,then there's the transmission case-the main body.
That SLEEVE is what the Throwout Bearing slides along,,,while the splined-input shaft turns inside the sleeve.
Here a different picture that shows a good Picture of The Sleeve.
It's to the Left of the transmission case,,Item #3.
It has a hole thru the center for Input shaft to come thru.
And it BOLTS to the case.
It doesnt turn,it doesnt "do anything"---except provide a Sleeve for the Throwout Bearing to slide along the Outside of the sleeve.
http://www.drivetrain.com/m21_p1.jpg
BACK to the previous pic of the OLD gearbox.
Look close at the sleeve,,and notice the SHINY "white"ring around it on right/hand end,,near the trans case.
That's WEAR,,friction,rubbing.
Look Close in the Middle of the sleeve.
You can see another Rubbed spot,,it's short & just a spot,,AND it's at an Angle,,like a / .
It's very faint,,looks like a Light Smudge.
That Angle is some indication of Tilting,Cocking happening as the bearing slides across it.
Immediately to Left of THAT,,notice another Faint Rubbing mark.
It is a Bright Reflective spot on the photo,,at bottom edge of shaft.
If it's Bright enough to flare the Camera,,where's the "Ring" around the Shaft THERE?
There's none,,all the wear is on one side,,where it's shiny and reflective---there's no even wear ring all around the sleeve---like there is on far right/hand side.
Now look at far Left/hand end of the sleeve.
Look CLOSE,,and notice it's apparent "texture" of the wear ring.
It's grainy looking,,splotchy.
Compare to the more smooth,uniform look of wear ring mark on opposite end of sleeve.
That texture is cuz the Throwout bearing is Really Digging In and "gouging " the sleeve,,hi/heavy wear.
THAT is equivalent of the Grooves on our silly Broom Handle example..
If You could SEE that,,and feel it in Real Life...
You would NOT think much of it.
It's rarely more than "FAINT" barely perceptible.
I have NEVER seen one that looked BAD,,Terrible,,all tore up.
But I have seen some about equal to the condition in that picture,,or a LITTLE worse,,,that I couldn't hardly push the clutch in.
There is NOTHING about a Clutch that can even come close to the Noise and Effort,,the Gritty,Crunchy,creaky,snap/crakle/pop,jerky pedal feel & noise that little bit of wear we saw in that picture will cause.
Aluminum Sleeve gear boxes wear Much faster,and much worse.
Yours CHANGES with TEMP???
What is it about a CABLE,,or PEDAL ,,that changes with Temps??
Nothing.Not really
Aluminum Expands/Contracts at a dramatically different Rate than Steel does.
STEEL,,hardened,Heat-Treated,Stabilized Steel Throwout Bearing,,,,sliding along a Soft,Aluminum Shaft,,,tilting/cocking,,and digging in,,"biting" the shaft as it slides along
How does Warming Up change it??
The Shaft SWELLS.
Clutches get HOT,,Extremely Hot,,and are hanging off back of a 200*F+ Engine.
When the Shaft SWELLS and the Bearing Doesn't,,,,
The Clearance between the 2 Closes Up.
The Bearing is then "more Centered",,cannot TILT as much and dig into the shaft.
Cold,,shrunk Sleeve = lottsa clearance,,Lottsa TILT of the bearing
Warm,Expanded Sleeve= Tighter Clearance,Better supported bearing,,Less Tilt,,less Sliding friction.
Is Clutch kinda "Grabby" when you release it??
Or silky smooth?
I mean the actual clutch engagement,,not just the pedal feel.
"Sticky-ness" of the throw-out bearing along that sleeve Feels the Same to the CLUTCH as it does to your pedal foot.
Jerky,Crunchy,Creaky,,,and as ThrowOut bearing chatters it's way back along the sleeve,,
Clutch engagement action will Often mimic that jerkiness.
TUFF to get a smooth,slick release of the pedal and engagement.
Trans must be removed,,and that Sleeve replaced.
Greasing it and polishing the sleeve will offer ONLY temporary releif.
If You wanna Crawl under it,,theres probably some access to see the throwout bearing.
Have somebody "pump" the clutch pedal while you spray some WD40 at that area.
Watch what happens soon as ya get a little in the right spot.
Nothing about pedal,cable,linkage,or high clutchplate spring pressure will cause the symptoms you've described.
"Sticky" throwout bearing grating along that sleeve,,,
thats a Classic cause of those symptoms.
Certainly,,I could be wrong.
But there just ain't that much to a clutch.
Good Luck with it.
2006-11-02 19:36:56
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answer #6
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answered by Anonymous
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