Catmando clutch operating instructional manual.

Well we shall see how this works. The age old question. Double clutch or not. Some guys have drove 75 years and never wore out a clutch or transmission because they shift like butter. Well that's debatable and most can not. I'll do my best to explain, while I'm not the best author.

Eaton fuller instructions indicate double clutching is proper shifting technique. CDL requirements require double clutching. But we need to dive deeper into this.

The reasons are much deeper than most see. The process of double clutching provides much more than simply wearing out a clutch. In a non synchronized transmission, you the driver are the one responsible to sync gears. Now imagine a clutch as fuse between a engine and trans, a safety. It is designed to wear out. So here is a few simple issues with floating gears. When you simply slip that out of gear and into gear with out clutch input.

With clutch engagement, the transmission and drive train are underload, regardless of rpm. When you depress pedal and disengage clutch the transmission is not under engine load. Non synchronized transmissions are not designed for shifting under load. So what happens, there is more force applied to all gears, mostly sliding clutches, main shafts, main gears. They have a tendency to bind, grind, rake. Now guys can do this very smooth with practice. I have seldomly seen many people that actually can. Meet alot that claim to. The gears are not built for load while gear change, the are only designed to have load while fully engaged. This accelerates wear on matting gears between gear splines, sliding clutches and main shaft. Extremely possible to twist mainshaft splines during a shift under load. Main shafts are straight cut splines with floating gears. Power flow is from input shaft main drive gear to counter shafts, to selected gear on main shaft. Locking main together creating output to aux. box to output shaft. But we shall go deeper. Torque is a twisting force that results in motion. We design bearings, parts to control torque, eliminate endplay. However must have some endplay to allow operation. Endplay is in engines, wheel ends, differentials, especially transmissions. The main shaft in a eaton fuller trans is floating. When you do not the disengage clutch, there is little to no endplay in shaft during gear change. Bound is the word I would use. When your under throttle heavy load. Every thing is loaded from engine back. When you depress clutch pedal you unload transmission for a gear change. This effects much more than one imagines. In my fleet experience this loss of motion accelerates wear. Engine crank thrust bearing. Modern engine do handle this better. But normally can look at a engine thrust bearing and tell if a driver uses the clutch. Hammers out pilot bearings in flywheel with the movement underload. The shifting underload leads to extended input shaft wear, deep teeth wear patterns on trans input shaft. Which later in life shows up as a clutch engagement issue. A grabby clutch. Now for one that I have zero in print proof but real world witness, I suspect, I see damper springs hammered out of clutch plates. They are experiencing a shock load during gear change. Which end up stuck between plates causing poor engagement. Or just laying in the bottom of flywheel housing.

All cause by a quick change of motion by not properly loading and unloading power to transmission.


On the output side of trans, you have the same issue, it shock load to the complete drivetrains accelerating wear. Could show up in ujoints, differentials.

Everyone is welcome to drive how they want when they own the equipment. But I'll say this, you should know how to double clutch, you will need to someday. For the guys running big power and haul heavy, this multiples x10.

Again. Drive how you want, repair what you choose. The clutch is one of the cheapest parts in a truck. Properly used can save you troubles. Not used properly can be expensive. If everyone is the best gear jammers in the world. We would not have automatics or automatic restrictions on cdl. They are more expensive and not as efficient as a properly shifted manual. But fleets are seeing them as cheaper than improperly shifted manuals.

I typed this before coffee. So don't murder me for any screw ups.

 

Here is a few great videos for guys who wanna learn how they actually function. Very informative.

 

Good post, lots of good information here. But I do have to take exception with the part that I quoted above. I think fleets have gone to automated transmissions for fuel economy purposes first and foremost, that way they can control when the transmission shifts and when it doesn't.

 

I may not have been very clear. My fault. I agree. But so far there is no automatic or automated trans mission that will out preform a properly shifted manual transmission. The autos do outperform a improperly shifted manual transmission. Which is all driver input and fleets like to control driver input.

 

Modern AMT's are programmed to float without the pneumatics double clutching...so the transmission manufacturers program their equipment to shift improperly?

When floating, you find the point where you're not accelerating or decelerating, so there is no load on the gears so it 'floats' out of one gear and into the other with very little effort. I normally shift with 2 fingers on the stick. I learned on an old Mack 5 speed where you couldn't force it in gear no matter how hard you tried, unlike these modern transmissions where drivers jam it from one gear to the other. Back then you had to learn to synchronize the engine and transmission in order to get it to shift, clutch or no clutch. The last truck I drove for that company had 3.2m miles on the cab and chassis. It was on it's 3rd engine, 2nd transmission and the rear diffs had been rebuilt twice (standard equipment, not heavy duty, and we pulled chickens from the farms to the processing plant and regularly grossed in the upper 80's to low 90k lb range). All these modern AMTs are doing what us old school drivers have been doing all along. And every AMT I have had the displeasure of driving were nowhere near as smooth as I am on a bad day. The secret to smooth floating is in your right foot.

 

ATM-s while I'm not very experienced with. The Ultra shifts do use the clutch for shifting and in my lack of proper knowledge on them. They incorporate input and output speed sensors to calculate shifts and uses the clutch.

 

Broken damper springs can be caused by shock load.
As well as lugging
Slipping the clutch or pulling out in high gear
As well as misalignment and hanging the trans off disc both which it seems are non driver related. So let’s touch on this. How many mechanics realize to stab a trans it has to be straight and push up flush easily. How many various forms of ho #### have you heard about cause some ########## couldn’t get it straight. We also know that putting it on the input shaft of trans and rolling the motor is not the correct way though many do it. Some with success others with claimed success.


It’s also fair to say clutch or no shock load can happen either way due to improper technique. Any thing taught must be practiced and honed to skill. Now you gotta give a #### to have the want to to do so.


For the record I’ve never claimed to be a smooth operator or good or anything like that. I suck at driving the truck. I mean I barely pass that class. But the class I have straight A’s in is making it do its job and correctly. 9 out of 10 gear specialist are butchers that cannot properly set preload on a carrier. So they set depth or back lash whichever you prefer to call it and I can show you it’s loose. Why because they are lazy. Lazy is why I don’t double clutch. I am not saying it wears a clutch. Lazy and using to high a gear wears a clutch. Jack ##### that don’t know to set the brake to throw out bearing distance to 1/2 inch first then set free travel by putting a feeler gauge between brake and throw out bearing and it should stay clamped depressed and fall out at I believe 3/4 of an inch pedal movement. I’d have to look been 20 years since I read that. So all that to say you posted flow charts and supporting evidence but made no case. I get it you can’t put your thoughts or knowledge to paper I do understand that. I understand that Eaton the manufacturer says so. I will also say till you have worked on my truck transmission or any other part do not make assumptions. They can be a hard uncomfortable pill to swallow

 

The Freightliner ATM floats and the mDrive I drove for 3 years did as well.

 

You also touch on an important point thrust bearing and tell if they use the clutch. You betcha as in hold it down at lights, needs adjustment and the forks are pulling on the thrust bearing causing excess wear on the crank and thrust bearing. Riding the clutch will cause this too. Your beloved Cummins will #### the thrust washers right in the pan because of it. Every time you push that clutch you pull the crank backwards or to the non load side with 1 bearing face usually. The transmission side being the load side has 2 top and bottom and whether you use the clutch or not the load I’d going to push on the flywheel. How you depress the throttle will decide if it’s an even push or a snap. Also pushing the clutch guarantees full slack movement every time of thrust bearing. Whether it’s .025 or.010. Every time let that sink in your crankshaft is going clunk forward then clunk backwards rather hard. Why you think floating is done under gear load idk but I promise you that won’t work. And again I’m not saying that double clutching is the death of your thrust bearing…..I’m just saying give your proof as I just have mine

 

Wore, I have no axe to grind with you or anyone. I was asked for my opinion. I'm providing it. I find you very knowledgeable and informative. One of the best on here.

I'm not seeing your proof. Other than your experience like myself. Am I reading this correct that you claim your loading a crankshaft by disengaging the clutch at a stoplight? A push type clutch will. A pull type clutch would release load from crank shaft. Shifting without clutch hammers the crank back and forth. Again, maybe I'm miss understanding your point. For that I apologize, and yes I do struggle putting thought to print. This is my opinion and experience. I enjoy and appreciate anyone addition. Doent mean I'll agree. But it's welcome.