Toughest clutch?

[Zer0PSI]

But the LOAD on the clutch comes from the ENGINE TORQUE. What one means by that is how much torque the engine places on the flywheel. It's what you measure on a dynamometer. There is no 4000 lb load on that.

How are you going to make that go up with any load?

It's VERY hard to get around this bit of physics unless one goes into dynamic (shock) loads or somehow changes the coefficient of friction.

IT'S CALLED RESISTANCE!!!! Come on this is 8th grade physics. The resistance on the clutch is greater when your towing an object

 

[MAKG]

Dustin, I'm saying that the flywheel will receive the same 170 ft-lbs of torque (or less) from the crankshaft no matter what you do to it. How will you increase that?

Zer0PSI, this is misunderstood high school (not 8th grade) physics. It's been my experience that "common sense" -- ESPECIALLY when dealing with torques and rigid bodies -- is very often wrong. Appealing to common sense very often exposes a worldview that has never been tested.

You're confusing the load with the source. VERY common, but nevertheless wrong in a steady state configuration (including acceleration). There is a torque due to the engine, a torque due to dynamics and a net torque out the axleshafts (which need NOT be zero -- though under the surface I think you're assuming it is). Add all of these up and you get zero. Let me paraphrase -- Newtonianphysics does NOT say that dynamical load = crankshaft load. It says that if they don't, the vehicle will accelerate. And that's all.

If Allan's comment is right, it simply must go beyond the usual simplified Newtonian high school physics form discussed here.

 

[rusty ol ranger]

Doesnt one of newtons laws also state "For every action there is a equal but oppisite reaction"? The more you load the truck, the more your gonna stress shit, including the clutch. Ok, that may of been a bad analogy....but still.

Think of it this way.....what happens to a vehicle with an Automatic when its loaded to the balls and aimed up a steep hill? It sits there with the engine bogged, but the vehicle doesnt moves does it? Thats because while the Motor is turning, the transmission is not, the same thing happens with a Stick Shift, only not as apparant.

On the other hand.....MAKG....arnt you the one that said gravity doesnt exist? :rollseyes:

later,
Dustin

 

[MAKG]

Dustin, Newton's 3rd law is very often misunderstood in that manner. It says that the torque on the flywheel due to the crankshaft is equal and opposite to the torque on the crankshaft due to the flywheel. It does not say all forces or torques are balanced. If it did, we couldn't go anywhere.

An automatic transmission is an entirely different beast because you are actually putting momentum into a rather heavy fluid whenever you stomp the throttle. You aren't doing this to a clutch unless you're throwing it.

That thing about gravity was a joke several years ago, and hardly has anything to do with anything.

 

[AllanD]

Rusty,

You are right that Newton has something to say but you quote the wrong law, this one is more appropriate to the discussion:
"A body at rest will remain at rest unless acted on by an unbalanced force"

Mike you keep saying "Static" when the model you need to be looking at is dymnamic you cannot simply look at the static forces and understand the other factors.

I have a friend who is a physicst and he has a total inability to see a dynamic model in his head....

Remember also that the carrying capacity of a diphram clutch is not constant. as rpm increases centripedial force wis trying to flatten the diaphram spring and at higher rpm a diaphram clutch can be made to release itself completely! (thus the purpose of the weights on a centerforce clutch to counter this force)

Though in pactical situations the clutch simply starts to slip and the driver backs off.
However in some high rpm situations you can manually release
a diaphram clutch at high rpm and it will simply refuse to re-engage until the rpm drops (I've personally see this, though not in a Ranger)

CAREFUL design must be used to prevent this (an example is the clutch used on the SHO taurus)

when the truck is in it's "light" (non towing condition) and power/torque is applied the truck accelerates

when resistance increases the clutch's capacity to transmit the power through the transmission to the wheels is exceeded and clutch starts to slip.
as the clutch heats up gasses are generated from the friction material and the clutch heats up and slips more.

when manuevering a heavy trailer FAR more slipping is required to get off to a smooth start and that extra bit of heat is all it takes to overload the capacity of the stock clutch. heat degrades the clutch friction materials gripping force. rpm degrades the clamping force of the diaphram spring.
ANY subsequent slippage only makes a bad situation worse.


the fact that resistance is a factor is why a worn clutch will slip in the higher gears at first and as the wear continues to increase it will start to slip in lower gears.

In the lower gears there simply isn't enough resistance to make it slip initially.

Is it so hard to grasp that adding additional resistance (a trailer)
would change the point at which the clutch would slip?

Even presuming the clutch is gripping at it's designed capacity there is some point at which it can be made to slip.
the problem is that the stock clutch on a 2.9 is NOT designed for the engine
it is fitted to, it's what the factory used but it's STILL wrong.

a 3.0 only makes 10ft/lb less torque (160ft/lb Vs 170ft/lb)
than a 2.9, but has to spin faster so instead of torque you have rpm and rpm acting on the diapham spring is just as bad as total torque, and once the slipping stops it's a cascade failure in action...

Wit the 3.0's lower peak torque and it's higher torque peak rpm you have to slip it even more to keep from stalling or "lugging" the engine and that only makes an awful situation worse.

The simple fact is that EITHER more engine torque OR more RESISTANCE against that torque would cause a clutch to slip if the clutch doesn't have sufficient reserve gripping force, and simple reality is that the stock 8-7/8" clutch is inadequate for anything with more torque than a 2.3Lima engine.

If you slip the clutch just a little the degradation of grip from even a small ammount of additional heat results in failure.

It's like having a radiator that can keep an engine cool in normal light operation but pull one steep hill and you get a thermal runaway that can only be corrected by stopping and keeping the engine at 2000rpm in neutral for 10minutes to cool it back down.

Think of torque like a bolt of lightning inthat it follows the path of least resistance.

Either it accelerates the truck, it spins the tires OR it slips the clutch.

If the truck is too heavy to accelerate EASILY and the tires have traction the Engine SHOULD stall, if it doesn't the clutch is slipping. PERIOD!!

I could demponstrate with a new but broken in 2.9 clutch that you could slip it just a bit more than was proper to get started plant my foot into the throttle sidestep the clutch
and with my foot completely of the pedal the clutch WILL continue to slip until you bounce the engine off the rev limiter

that just ain't right.

I can do this in a supercab with 4.10 gears

Once the clutch STARTS to slip all it will do until it cools off completely is get progressively hotter and slip more and more. and it is WAY TOO EASY to get the stock clutch to that point.

Infact if you get it hot enough the clutch will NEVER grip correctly again and that also is WAY too easy to accomplish with the stock crap.

Just a tiny ammount of "extra" heat and it falls flat on it's face.

Stock clutch: "I've fallen and I can't get up!"


that all being aid if you are FORCED to stay with the small diameter clutch, either the 8-7/8" or the slightly later (94-ish)
9-1/4" clutches then I strongly recommend an aftermarket clutch.

The prime benefit of the aftermarket clutch not being the stiffer diaphram spring or the weights that centerforce adds to it's CF-2 and it's Dual-Friction clutches, but rather use of a more heat resistant friction compound OR though a stiffer diaphram and centrifugal assist weights...

Simply put, the stock clutch is NOT "adequate".

I LIKE the stock (LuK) 4.0 clutch.
Ford did THAT correctly.



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[Aragorn]

so what's the best clutch to put in a 3.0 again? I must have missed it.

 

[jv982]

Rusty,

the fact that resistance is a factor is why a worn clutch will slip in the higher gears at first and as the wear continues to increase it will start to slip in lower gears.

In the lower gears there simply isn't enough resistance to make it slip initially.

Is it so hard to grasp that adding additional resistance (a trailer)
would change the point at which the clutch would slip?

That is a great example I think.

 

[michowski]

aragorn I recommend zoom http://store.summitracing.com/partd...924677+4294839534+4294865886+115&autoview=sku. That is the kit for your year and motor.

 

[AllanD]

My personal recommendation is for the Centerforce 2 clutch.

should run you just a bit over $200, though they may not list one for
your (3.0?) application the clutch input spline and the pressure plate bolt pattern is the same on ALL RBV's except the 4.0.

So worst case is you order a CF-2 for an '88-92 2.9 and bolt it onto your 3.0
(though a 3.0 later than 1993 will require you to discard the release bearing supplied with the clutch kit as the '93 up slave cylinder uses a different bearing.)

The later 3.0's (94-ish) came with a slightly different "adjustable" pressure plate
and used a 9-1/4 or 9-1/8" clutch disc if Centerforce lists one for that use it.
Again the pressure plate bolt pattern to the flywheel is the same so this larger clutch
(if it actually exsists) could be retrofitted to 2.3 and 2.9's with the reverse situation of the supplied release bearing.

Though on a 2.9 I strongly recommend the heavier (23#) 4.0 flywheel
and the 10" clutch.

Remember with the same clamping force and the same friction material a larger diameter disc will have more leverage against the shaft it is trying to turn simply because of it's larger radius. Just like with brakes the larger radius the better because the larger the radius the less clamping force you need to accomplish the intended goal. (real simple physics)

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[MAKG]

Allan, the bit about extra heat makes a lot of sense. There is no reason at all to expect friction coefficients to be temperature independent, especially if something starts warping or outgassing.

Your observation about clutches always slipping in higher gears first doesn't match my experience. I've worn out three clutches on three different vehicles (one was a 2.9L powered Bronco II), and all slipped at full throttle in any gear (a common experience when you drive mountains constantly) except first (only because the vehicle accelerates too quickly to stay in first for more than a second or two at full throttle, even on steep hills). They also had some trouble "catching" -- in any gear -- if I got too close to peak torque while still slipping. I suspect this is the heat issue you're after, though it is also explainable by the difference between static and slipping friction (static is always higher). Note that I have more trouble slipping the clutch uphill in top gear near home, because it's only 50 MPH and the engine isn't very close to peak torque for any of my engines except the Chevy. But the Chevy has a massive 12 inch leg-building clutch that I haven't put anywhere near enough miles on to wear out.

Static forces do not mean the vehicle is stationary or at constant speed. I'm not sure you got that, though I think you did. They mean that the situation is steady state -- you aren't in the process of twisting up a driveshaft or changing compression in the clutch springs and so on.

The standing-stop issue is certainly important because it will certainly generate more heat than the same gear would unloaded. But the other half is, can you make a cool clutch (say, after 30 minutes on the highway) slip due to the load?

 

[Aragorn]

aragorn I recommend zoom http://store.summitracing.com/partd...924677+4294839534+4294865886+115&autoview=sku. That is the kit for your year and motor.

haha. thanks. i was just going for reminding them what the thread topic is. I actually have a 2.9 and will probably go with allan's recommendation of a 4.0 clutch next time it needs doing.

 

[rickcdewitt]

from my understanding you have to apply more of the engines torque to get moving in a heavier truck.the max load you can apply is max torque of the engine of course,but with more weight you want more ability to absorb the extra slippage and heat.i have a 10" explorer clutch in my 2.9l truck and it won't slip taking off fast uphill on pavement like it did with the small clutch.

 

[4x4junkie]

My experience with a worn clutch matches AllanD's.
The vehicle (engine) accelerates faster in lower gears than higher, so it doesn't put quite as much load on the clutch as when you're flooring it to maintain speed up a steep grade (or as originally pointed out when towing a trailer).

Something that hasn't been brought up about the little stock clutches yet... Pedal feel.

I did the 4.0L clutch swap on m 2.9, and I can't even begin to say how much easier it is to modulate the clutch now. Even if the stock clutch had adequate grip, it's STILL worth the upgrade just for this reason alone.

I've been driving a stick all my life and I still on occasion stalled out the motor (or revved it up higher than needed) when starting out because it had such a short throw on the pedal.

 

[AllanD]

The great factor is that slippage is progressive and proportional to heat buildup

In lower gears you may be expending more power and fuel but you generally get past the torque peak and the clutch re-locks quickly enough to prevent much heat buildup

In higher gears you are running the engine at or near it's torque peak

It's all about tradeoffs... it's dynamic and synergistic, thus my comment
that your static model is flawed

The comment that a worn clutch will slip more in the higher gears
is a subjective statement. It is simply FAR easier to observe a clutch slipping
in the higher (taller) gears because it is easier to bear down against the greater resistance.

In the lower gears it is easier for the force that is transmitted by
a slipping clutch to move the vehicle.

so technically you are right, but subjective is how most people see
things so it's more efficient to talk in subjective terms and save yourself from some of the explanation that is required to make someone understand...

AllanD

 

[rusty ol ranger]

Let me put it simple.....

What happens to a ratchet when you overload it? Lets say trying to break a bolt on a 20 year old Ranger with a 3\8 drive, an 3 ft braker bar, and a 250lb dude? It slips.

Same concept. The Bolt represents the load, The person represents the Engine, and the Ratchet represents the drivetrain, and the gear inside the ratchet (which is responsible for transfering torque, just like a clutch) is the clutch.

Said guy, PUshes on bar with all his strength, the ratchet slips, because it simply cant handle that much torque, he busts his knuckles, and swears. Same concept with a clutch.

later,
Dustin