Gloyale Posted June 3, 2013 Share Posted June 3, 2013 (edited) I was going to comment on that too... more than once I've been slowing down HARD and stopped the entire drivetrain, engine included. With regards to braking power & such: Your wheel brakes should be able to lock up the tires on dry pavement. Period. If they can't, get them fixed (or, more likely around here, fix them). For an emergency maximum deceleration braking event, you shouldn't bother leaving the engine engaged to the rest of the drivetrain. You're braking so hard that the effect of compression braking is negligible, and stalling out the engine & jolting it back into motion probably isn't terribly good for the engine or transmission. Plus, if you do end up locking the tires and coming to a stop, you now have an engine that's not turning. Not a terribly useful state for an engine to be in. I engine brake constantly, usually with a well executed double clutch (I've been driving a stick just over a year, so it's quite possible to learn "advanced" shifting quickly, you just have to do it). However, if I need to come to a stop in a hurry, I push the clutch in and use the brakes. I have better modulation of the brake pedal, and more control over what's going on. Note that this is for emergency braking (maximum effect, just short of wheels locked) only. -=Russ=- The last thing you want is all 4 wheels locking up. The drivetrain won't be stopped if you properly modulate and don't lock the wheels. (unless we are talking about that last 2mph slowdown on snow or mud that ABS will keep you rolling and make you crash).. But we aren't, we are talking panic braking..... You should not put the clutch in during an emergency manuever. Brake, don't lock up..and steer away......you may need throttle to help maintain control during manuever. Edited June 3, 2013 by Gloyale 1 Link to comment Share on other sites More sharing options...
AKghandi Posted June 3, 2013 Share Posted June 3, 2013 I've always driven a manual, only 3 of the 39 cars I have had were autos, and I hated them. I always downshift, rev match, heel toe, even left foot braking, the whole 9, when I down shift I never slip the clutch so that's a moot point. on snow and ice downshifting is extremely helpful, as the car will slow without locking the wheels. as for engine wear, I have never seen anything to make me think its bad for the motor, and I routinely downshift from 5th to 3rd spiking the revs to 5k plus. the motor is still turning so its still moving oil therefore I don't see it as being an issue. all this is on an ea82t with 250k. I drive it like a rally car, and on the snow, nothing can keep up. I replaced the brakes when I first got it and they are still at 75% 15k miles later. I had to replace the clutch, but that's more to do with launching it in 4x4 and 4x4 low on pavement. and clutch blips at wot to get it to drift on the snow. plus it wasn't a strong clutch when I got it. If you dont downshift thats fine, everyone has their own style, but i do highly recommend at least practicing it for panic stops and bad road conditions Link to comment Share on other sites More sharing options...
kingbobdole Posted June 3, 2013 Share Posted June 3, 2013 Funniest part about this thread is I got to an old Jeff post. Didn't make a damn bit of sense and I wondered how old the thread was. Yup. I downshift because I'm a mechanic and I enjoy the drive not worrying about replacing the bits. I built the car to be driven how I like it, plus its not like I wear out a clutch every year, or ten years even. In ten years my xt6 has gotten three clutches. When I first made it a manual, new clutch. When I made it EZ powered it got a new rs clutch and this year I made it a 6 speed it got a used 6 puck act. Never wore one out. :-p Link to comment Share on other sites More sharing options...
MR_Loyale Posted June 3, 2013 Share Posted June 3, 2013 (edited) Seems like everyone has put in their two cents so I hope folks don't mind me joining in. I have owned the same number of automatics as I have manual vehicles. I prefer a manual for smaller cars and automatics for big things. Shifting a big old truck is not quite a joy as it is in my little Loyale. I live on two long hills I drive up and down every day. I use the compression braking to slow myself down on one long hill that is a mile long. I also use it part way on a steeper hill that is about 1/4 mile long. I tried my brakes alone on this hill (which ends nears the water where you will plunge to if you don't stop) and at the bottom I could almost not stop the car. Also, if anyone has ever been on Mt Walker in Kitap County, then you know the drive down that mountain you will definitely be compression braking as your brakes will be toast. They get real hot real fast- ask me how I know As for the clutch, if you don't do burnouts, then you should be OK with judicious compression braking - at least in my experience. I believe that the standard clutch is rated at about 100K miles or so. Mine made it to 117K and I replaced it on a timing belt/reseal cycle. It was slipping on rapid acceleration(no, I couldn't adjust it), could have still driven it by less aggresive acceleration, but it coincided with a timing belt replacement so I went for it. I expect every other timing belt will be a clutch too and I will pull the engine. When talking about repair costs etc, most of us here do the repairs ourselves, so shop rate isn't really an issue. I don't enjoy replacing clutches but I feel if a part has a stated life expectency, if you get the stated use out of it, you got your value. Edited June 3, 2013 by MR_Loyale Link to comment Share on other sites More sharing options...
nobangmycar Posted June 3, 2013 Share Posted June 3, 2013 Are you guys serious?! LOL. What a wierd thread. It doesn't matter either way, and you should be double clutching anyway. If you are double clutching it saves the synchros in the 'box and there is no clutch slippage or wear anyway. Solves both arguements really. If you are really ace you could up and downshift with no clutch operation at all if you were being clever. I don't see how in the big picture of driving, your theory would make a considerable differrence to anything. If your trans is clunking you have another issue my friend... Link to comment Share on other sites More sharing options...
mikaleda Posted June 3, 2013 Share Posted June 3, 2013 (edited) I just had to post seeing some of the myths in here, compression braking doesn't affect milage, evn though your engine is spinning at higher than an idle the fuel/air flow is the same as at an idle. it doesn't hurt your clutch other that you at shifting a little more often and if you know how to rpm shift this isn't a problem. As for wearing stuff out quicker compression braking save ALOT of wear on your brakes, I tend to use a mixture of brakes and compression to slow me down it works well as a happy medium. Compression braking is not bad for your engine as long as you are sensible about it and not revving the engine way up when your slowing down. Just my $0.02 Edited June 3, 2013 by mikaleda 1 Link to comment Share on other sites More sharing options...
WoodsWagon Posted June 4, 2013 Share Posted June 4, 2013 With most fuel injected engines from the mid 80's on, an engine doing compression braking uses NO fuel, vs the baseline fueling needed to keep it idling. Under engine braking the computer does a full fuel cut until the clutch switch, neutral switch, or vehicle speed sensor warns it to go back to fueling the engine to keep it idling. Compression braking causes no harm to the engine and transmission, and if done right should not cause any more clutch wear than a normal shifting event does. Which is to say, no wear. Almost all the wear on a clutch is from getting the car moving from a standstill. I would not recommend compression braking for panic stops or slippery situations. Use the service brakes to get things back under control, then use compression braking to maintain the lower speed. Trying to row through the gears while controlling wheel slip and skid angle to dodge whatever you are trying not to hit is stupid. It adds confusion, takes a hand off the wheel, and doesn't add any braking force beyond what the service brakes can offer. Plus it's less controllable, if you lock up a wheel it takes longer to sense it and get it to release with the engine doing the braking vs easing up on the brake pedal a bit. Comp braking is great for going down long grades. The engine can slow/hold your speed all the way down with no damage or overheating, while you could get the brakes hot enough to fade if you used them alone. It's great for slow changes in speed like rolling up to the next traffic light. Downshift through a few gears, then use the brakes to finish the stop. It should be a part of normal driving, but not emergency or panic maneuvers. 1 Link to comment Share on other sites More sharing options...
JEBalles Posted June 4, 2013 Share Posted June 4, 2013 This thread needs to be renamed. You cannot effectively "compression brake" with any gas engine. You can however "engine brake" There is a huge difference. Compression braking is a mechanical method of slowing a diesel engine by releasing the compression on the up stroke. This generates a vacuum on the down stroke, slowing things down. It is required due to diesel engines not having a throttle plate. Actually on a gas engine it has little to do with combustion, and much more to do with the throttle plate, An engine is nothing more than an air pump. Keep turning the crank with a cork stuck in the intake (throttle plate shut) and you will create resistance in the form of a vacuum. This slows you down. Point a vehicle downhill with the engine off and your foot off the throttle and it may or may not move. Apply the throttle and it will start rolling. Correct me if I'm wrong, but I always thought it mostly had to do with the internal friction of the engine. This is why when you park the car and you put it in gear, it won't move (or takes more force than the gravity pulling the car down the hill). If it was only due to the engine pulling a vacuum, the car would have to roll some amount of distance until the engine pulled enough vacuum to stop the car. Since the static coefficient of friction (such as when a car is parked in gear) is greater than the kinetic coefficient of friction (such as when the engine is turning), however, vacuum would play more of a role during moving engine braking. You are correct when you say that compression braking is not the right term. During engine braking in a gasoline engine, the pistons are merely "bouncing" off the compression, not consuming any energy. Link to comment Share on other sites More sharing options...
man on the moon Posted June 9, 2013 Share Posted June 9, 2013 If there were that much friction in the motor, you would never be able to start it. When the engine is off, the valves don't move, and at least some (if not all) are in the closed position. The air pressure/vaccuum (depending on where in the cycle a given piston is) is sufficient to keep the pistons from moving, even with the weight of the car resting on it. The CLUTCH has enough friction to prevent slippage, but you have to use the clutch pedal when you want to shift. There is not clutch pedal for the cylinders, though! Link to comment Share on other sites More sharing options...
Idasho Posted June 10, 2013 Share Posted June 10, 2013 Correct me if I'm wrong, but I always thought it mostly had to do with the internal friction of the engine. This is why when you park the car and you put it in gear, it won't move (or takes more force than the gravity pulling the car down the hill). If it was only due to the engine pulling a vacuum, the car would have to roll some amount of distance until the engine pulled enough vacuum to stop the car. Since the static coefficient of friction (such as when a car is parked in gear) is greater than the kinetic coefficient of friction (such as when the engine is turning), however, vacuum would play more of a role during moving engine braking. You are correct when you say that compression braking is not the right term. During engine braking in a gasoline engine, the pistons are merely "bouncing" off the compression, not consuming any energy. You are correct in that I was partially incorrect I mistyped a bit. So long as you replace "friction" with compression, you would be more correct. And correct, the analogy I provided would be better suited when coasting, engine off. You are correct that the initial energy needed to turn the motor must overcome is compression. Link to comment Share on other sites More sharing options...
Twitch de la Brat Posted June 10, 2013 Share Posted June 10, 2013 I'm amused nobody has mentioned the effect of reverse force on the clutch itself. When you're rowing through gears normally that slight slip as you engage gears is pulling the clutch one way, and one way only. Well, to maintain a well scuffed surface (for maximum friction) you have to reverse the rotational force to prevent polishing of the surface. So in essence, engine braking scuffs the clutch disc and technically extends its life. Or so says my logic. Twitch 1 Link to comment Share on other sites More sharing options...
Godsmulligan Posted June 10, 2013 Share Posted June 10, 2013 Keep your foot to the floor, grab a gear and piss off your girlfriend. Link to comment Share on other sites More sharing options...
CarpeNoctem Posted June 10, 2013 Share Posted June 10, 2013 many of the above points are valid but I wanted to add the line I use on people I see doing it. "Which is cheaper and easier to replace Clutch or brakes?" they of course answer brakes. Then why beat on your clutch when you can hold it in and slow with the brakes that are meant to do that job, then select the needed gear when you can take off again. As a mechanic the only time I see warped, and burned flywheels and torn up clutches is with new drives (or new to manuals) and people who downshift. There is no purpose except a few occasions on icy or loose surfaces. Link to comment Share on other sites More sharing options...
ecky Posted June 11, 2013 Share Posted June 11, 2013 I double clutch to slow and stop all of my cars. I notice no clutch wear except for after Iet my niece drive. My 2wd Toyota PU basically has no rear brakes so down shifting greatly shortens my stopping distances. Link to comment Share on other sites More sharing options...
NickNakorn Posted June 11, 2013 Share Posted June 11, 2013 An interesting thread, I found myself agreeing with everyone; it all depends what you're trying to achieve. When I was young I drove like a maniac and used every ounce of braking and acceleration available to me and changed my brakes twice a year, my clutch once a year and my tyres - well, I don't even want to think about it. Now, 40 years later, I find I'm still harsh on tyres (change them about every three years - about 25k miles) but I hardly ever need to change my brake pads or shoes - and even then it's usually for reasons other than wear. Clutches? I haven't worn out a clutch in 20 years but change them if I have the engine out anyway but that's not very often. And I have always double-declutched, used engine-braking and heeled and toed. In other words, if you drive gently and with expertise, everything lasts for ages and now I find I can drive as fast as I ever did (when law allows) without trashing components. Here in the UK, petrol prices have always been very high and so we're used to having to be economical. But, when there was a tanker-driver's strike, we had to be really, freally frugal because fuel wasn't available. I tried different techniques and got about 75mpg out of my 1988 Honda Civic - lots of coasting in neutral, low revs (limited myself to 2500), no engine braking and lots of thinking ahead, anticipation and very gentle driving. Using the same techniques in my Subaru L-series (loyale/leone) I can get about 55mpg but I prefer to drive a lot more briskly and tend to get 40mpg very easily on a run and 30mpg around town without banning myself from engine braking . But very occassionally, for the hell of it, I'll use the car in, lets say, a sporting manner and and fuel consumption drops to 15mpg if I'm lucky. By the way, I agree too that many countries have laws banning coasting in neutral for historical reasons; brakes were very unreliable 50 years ago. But some cars - early Saabs for example - actually had a freewheel device as standard. My conclusion? We're all right! 1 Link to comment Share on other sites More sharing options...
CarpeNoctem Posted June 11, 2013 Share Posted June 11, 2013 that's not a defense. bad brakes should be taken care of. using one system to make up for another is just robbing peter to pay paul. And the idea that leaving a load on your drivetrain that is trying to drive it FORWARD is helping yo BRAKE is completely against physics. the less load your car has trying to propel it forward the more efficient the brakes are because they don't have to fight the energy you are allowing to fight against their purpose. this is why a manual trans always has a shorter braking distance than an auto and why their brakes last longer. because less force is needed to stop the momentum. an automatic is ALWAYS trying to push the car forward when it is in drive. just as an engaged clutch is. You cannot possibly have a shorter braking distance that way. IF to set of braking systems are equal in every way and have the same force being applied to them, with the only difference being that one has a mechanical load trying to drive it forward, the one with the load will ALWAYS take longer to stop because it has to fight more forces than the momentum of the vehicle. it also has to fight the force the driveline is putting on it. Engine braking DOES increase clutch wear. ANY time the engine is running and you engage or disengage the clutch it get some wear, engine braking means you do those things more often. Your science is way flawed man. The only reason to downshift while slowing is in a situation where it helps regain traction. (mostly on ice but a few other loose conditions apply) Link to comment Share on other sites More sharing options...
mikaleda Posted June 12, 2013 Share Posted June 12, 2013 that's not a defense. bad brakes should be taken care of. using one system to make up for another is just robbing peter to pay paul. And the idea that leaving a load on your drivetrain that is trying to drive it FORWARD is helping yo BRAKE is completely against physics. the less load your car has trying to propel it forward the more efficient the brakes are because they don't have to fight the energy you are allowing to fight against their purpose. this is why a manual trans always has a shorter braking distance than an auto and why their brakes last longer. because less force is needed to stop the momentum. an automatic is ALWAYS trying to push the car forward when it is in drive. just as an engaged clutch is. You cannot possibly have a shorter braking distance that way. IF to set of braking systems are equal in every way and have the same force being applied to them, with the only difference being that one has a mechanical load trying to drive it forward, the one with the load will ALWAYS take longer to stop because it has to fight more forces than the momentum of the vehicle. it also has to fight the force the driveline is putting on it. Engine braking DOES increase clutch wear. ANY time the engine is running and you engage or disengage the clutch it get some wear, engine braking means you do those things more often. Your science is way flawed man. The only reason to downshift while slowing is in a situation where it helps regain traction. (mostly on ice but a few other loose conditions apply) No, just stop man. You're science is flawed, when you let off the gas in gear the engine is not trying to propel you foreword or compression braking wouldn't work, excluding doing 10 mph in 4th gear the emine is holding you back with the foot off the throttle (And yes I am exagerting on the numbers above I'm sorry I don't have all the numbers in front of me. 1 Link to comment Share on other sites More sharing options...
Gloyale Posted June 12, 2013 Share Posted June 12, 2013 Engine braking affects the balance and fore/aft pitch of the car in a different way than simply braking. driving aggressive into a corner.....if you ride the brakes into the corner and then try let off and power out the weight transfers more abruptly.....not to mention the risk of the inside rear tire lifting and then locking up....espescially in wet conditions....not what you want when you are hanging on to the road with every ounce of grip the tires have. This is not how race drivers do it. On the other hand, braking lightly, while downshifting (heel n' toe) before the corner....then letting the engine braking do the rest of the slowdown as you enter the corner, then throttle on as you exit shifts the balance of the car smoothly, without ever risking ANY wheel lockup. This is how the pros rock. There is a reason that professional drivers of all types use engine braking for MANY situations. There are some cases where it's not nessecary of course. But there are lots more in my opinion where maximum control of the vehichle means Rev matching, downshifting, and engine braking.....in combination with the brakes. I don't really care about clutch wear vs. brake wear......meaningless compared to control and safety. 2 Link to comment Share on other sites More sharing options...
mikaleda Posted June 12, 2013 Share Posted June 12, 2013 Engine braking affects the balance and fore/aft pitch of the car in a different way than simply braking. driving aggressive into a corner.....if you ride the brakes into the corner and then try let off and power out the weight transfers more abruptly.....not to mention the risk of the inside rear tire lifting and then locking up....espescially in wet conditions....not what you want when you are hanging on to the road with every ounce of grip the tires have. This is not how race drivers do it. On the other hand, braking lightly, while downshifting (heel n' toe) before the corner....then letting the engine braking do the rest of the slowdown as you enter the corner, then throttle on as you exit shifts the balance of the car smoothly, without ever risking ANY wheel lockup. This is how the pros rock. There is a reason that professional drivers of all types use engine braking for MANY situations. There are some cases where it's not nessecary of course. But there are lots more in my opinion where maximum control of the vehichle means Rev matching, downshifting, and engine braking.....in combination with the brakes. I don't really care about clutch wear vs. brake wear......meaningless compared to control and safety. Exactly, I have driven a stick since I learned how to drive and I've always used compression braking and brakes together to have maximum control 1 Link to comment Share on other sites More sharing options...
MilesFox Posted June 12, 2013 Share Posted June 12, 2013 Downshifting shouldn't wear the clutch if you match rpms, double clutch, etc. Bad driving habits ruin brakes and clutches, not the mechanical operation of the running parts. This thread is flawed science if there is no control amongst varying driving habits and experience levels to use scientific method in this theory. It reads more like politics 2 Link to comment Share on other sites More sharing options...
CarpeNoctem Posted June 13, 2013 Share Posted June 13, 2013 Mikaleda that is because you are giving the car less power than needed to maintain current momentum. Any time the engine is running and the clutch is engaged it is attempting to move you foreward. Its just that current momentum higher than what power is being supplied because ypu are off throttle and have changed the gear ratio. Rruckers and likewise racecars have eeasons they downshift. Truckers carry loads so heavy they would blow through pads weekly if they used them all the time. Same reason they only clutcg 1st and sometimes 2nd gear but rpm match otherwise. To prevent wear on components. Track racers do it because they use them so often and so hard that they do it to mitigate brake fade due to gas out. And pros get a new clutch every race. If they used brakes every corner they'd have their pads fading a few laps in. I'm talking real world cars not extreme usage. Link to comment Share on other sites More sharing options...
CarpeNoctem Posted June 13, 2013 Share Posted June 13, 2013 Mikaleda that is because you are giving the car less power than needed to maintain current momentum. Any time the engine is running and the clutch is engaged it is attempting to move you foreward. Its just that current momentum higher than what power is being supplied because ypu are off throttle and have changed the gear ratio. Rruckers and likewise racecars have eeasons they downshift. Truckers carry loads so heavy they would blow through pads weekly if they used them all the time. Same reason they only clutcg 1st and sometimes 2nd gear but rpm match otherwise. To prevent wear on components. Track racers do it because they use them so often and so hard that they do it to mitigate brake fade due to gas out. And pros get a new clutch every race. If they used brakes every corner they'd have their pads fading a few laps in. I'm talking real world cars not extreme usage. Link to comment Share on other sites More sharing options...
Gloyale Posted June 13, 2013 Share Posted June 13, 2013 Mikaleda that is because you are giving the car less power than needed to maintain current momentum. Any time the engine is running and the clutch is engaged it is attempting to move you foreward. This isn't true. Engine is not ALWAYS trying to move you forward. Give the engine no Gas.....it does nothing but act as resistance to the rolling momentum. An engine with no gas being fed to it, or a completely closed throttle plate is acting as a braking force.....period. The on;y time your statement would apply is at too low a speed for a given gear.....i.e. letting off throttle and coasting to 10mph in 5th gear.....at that point the engine RPMS would be below 400-500, and the ECU will try to keep the enigne running so will give it a bit of fuel and the enigne will fight the car trying to slow. But c'mon......you are the one who said this is about "real world" situations. Obviously knowing what gear you need to be in is required. Maximum control is the issue.....not wear on either brakes or clutch.....both are wear items and meant to be replaced eventually. Slipping clutches kills them.....riding brakes kills them........Using either in the proper manner.......they will last as long as they were meant....... I engine brake/downshift into almost every corner.(in addition to brakes)....it affects the way the car pitches fore/aft and the way the tires grip the road in a different way than brakeing alone. I don't go through clutches or brakes more so than anyone else.....in fact I think both my brakes and clutch last longer than most peoples because I don't slip the clutch, I don't power into the clutch until it's released fully, and I don't ride my brakes hard into every corner. I've been driving like this for 20 years. The only clutches I ever have to replace seem to be on my wheelers.....not my road cars. And by the way......Truckers use their clutches. It's stupid not to espescially when you consider the price of big rig trans repair. You'd get fired if the company that owns the truck caught you doing that. Many truck trans don't even have synchros, That's why they rev match during the DOUBLE CLUTCH......not no clutching at all. 1 Link to comment Share on other sites More sharing options...
CarpeNoctem Posted June 13, 2013 Share Posted June 13, 2013 (edited) Nevermind ill just stay out of this Edited June 13, 2013 by CarpeNoctem Link to comment Share on other sites More sharing options...
Tsuru Posted June 13, 2013 Share Posted June 13, 2013 Ok, I'll play this silly little game... There are many forces acting upon a vehicle in motion, but let's just concentrate on Acceleration and Drag (forward and not so much forward) With the engine running, and in first gear, in idle on level ground it is wanting to go forward. Everyone still with me here...good...there's more... if there is a slight incline down (relative to the vehicle) the engine is still trying to drive the vehicle forward, BUT, the engine will only turn so fast at idle. THUS (and this is the fiddly bit) The engine cannot drive forward as fast as the vehicle wants to go... AND The engine will only "DRIVE" the vehicle up to a certain speed. THEREFORE Drag is induced, maintaining some semblance of control over the acceleration of the vehicle. (not considering other factors, this is a simplified illustration) Think of it like this... You take your dog for a walk, if you do not have one it's okay, this is a thought experiment, you can just make one up. You put it on a leash because you are a conscientious pet owner, and do not want a repeat of the Poodle/Greyhound (the 5:45 for salt Lake city) incident from 1985. You and your dog are walking at 5 miles per hour, there is no acceleration felt by you (remember all things are relative...except your goofy aunt, no one claims her after last July and the potato salad incident, who knew a bikini could hold so much potato sala-oops, sorry) then you stop. the dog wants to go on. Lets say you have a poodle. (lets say you need a better dog...but you can upgrade later) the resistance felt as the dog tries to go on are the combined forces of drag/acceleration. you are stopped (or stopping) and the dog is attempting to go on... Is the dog "Accelerating"? Depends...remember it is relative. Lets use the ground as a reference, it's there and it's free for our illustrative purposes. If the dog manages to move relative to the ground, it is under acceleration. with you holding it back it's under drag, the resistance factor that keeps it in check. if you "throttle up" and run after the dog, you are "releasing the brake" and away the dog goes...straight for the Greyhound terminal and onto that damned 5:45 outbound for Salt Lake. Ok its a basic illustration, but I didn't see a consistent frame of reference in the arguments presented. And the argument that it wears out clutches faster,.I have no evidence that this is so. I've just pulled the engine out of my Ranger (1991 XLT 5 speed) It has had exactly one clutch replacement in it's lifetime, and that was at 300,000 miles, I know because I did it. Did it NEED it? no, the throwout bearing was screaming, and needed replaced, so the whole assembly got uprated bits. By the way, the engine let a headgasket go at 400,098 miles...so do NOT LECTURE ME about how it WEARS OUT AND ENGINE AND CLUTCH...it just does not if you use the clutch as intended, and do not slip it all the time. I have however, seen them blow up, Guys going downgrade in a fullsize Chevy 4X4, Manual tranny in first, Transfer Case in low range 4X4, they hit 15mph and decide to give the engine a rest and push in the clutch...suddenly their braking force from the engine is gone...and the compound gearing spins the clutch beyond its ability to - well - spin. Makes a real mess of things, If you are lucky its only vehicle parts to replace, and not human body bits. As far as shifting... I've been a Professional driver for over 20 years. (and a lot of hands on vehicle drivers training on top of that) So any discussion on any particular techniques I take with a grain of salt. Having said that, Here is what I have done for pretty much all my driving life. (I learned to drive stick in a 1957 Triumph TR3A so I started out with the good stuff) When up shifting I pull the tranny out of gear without using the clutch, by easing up slightly on the throttle. If I am familiar with the vehicle (as in only with my own equipment) I then feather the throttle down and put light pressure on the stick for the next highest gear, you do NOT want to push firmly on the stick until it is ready to go into gear. you just want to "feel the grease between the cogs" it will tell you when it is ready to shift. you can run the gears all the way up that way, easier of course if you have a tachometer. (shift points for your personal vehicle, learn them, it makes a difference!) Downshifting is similar in technique, ease up on the throttle (just like you are going to push the clutch in, only don't push the clutch in) then slip it out of gear into neutral... At this point you CAN go ahead and push the clutch in and complete the down shift, it is the SAME THING as double clutching only with one less motion. OR, you can feather the throttle up to match engine to road speed while putting LIGHT pressure on the gear shift lever. Remember, you are "feeling the grease..." In anyone elses vehicle I shift the standard way, clutch in, shift, clutch out. (it isn't mine to do as I please even though I have proven on countless vehicles that its easier on the drive and engine) The clutch should only be "slipped" when starting to move from a stop. Otherwise treat it like an On-Off switch. ESPECIALLY if you have a ceramic clutch! those do not just wear out when abused, they BREAK! (it is a very expensive sound to hear a clutch go out) Engine braking, either with a Jake or not, has saved my life on many occasions, There are times where I have nearly gotten into trouble with it too! Icy or slick conditions, you want ALL FOUR (or as many as you have) wheels providing a balanced slowing force, if its just the drive wheels (front or rear) and you are using engine braking, you run the risk of them breaking loose, In an 18 wheeler that means jackknife in no time flat because your drive wheels are right in the middle of what's going on and when they break free of their earthly bonds they want to get out in front and see what all the fuss is about. Rear wheel drive vehicles means a spin. Remember, a skidding or sliding wheel will want to overtake, thats why drift cars can corner the way they do, the rear wheels slide out with more acceleration and tuck back in line with slightly less throttle. You can do it on a motorcycle too, its fun! Since I'm flying my credentials here I'll add that I have also had many hours of Emergency Vehicle Advanced Driving Education (EVADE), I'm qualified to drive everything from fire trucks to ambulances and Enforcement vehicles (Includes armored trucks, dump trucks, straight trucks, bus' and 18 wheelers). at one time I could outdrive 95% of the general population, but age and caution has brought that number way down I am sure. I have to sit back usually when these discussions come up, quite entertaining. I am NOT pointing fingers or casting blame here, but it is fun to watch some bring up "experiences" that they have had and banner it as gospel for all to obey. "Thou Shalt" doesn't usually work for me without consideration of the source. I try and follow this basic philosophy when it comes to vehicles: "Use the best parts you can afford, drive as efficiently as you can, help others as often as possible whether it be with wrenching, troubleshooting, or just plain listening." And in my personal existence: "Go Placidly amidst the noise and haste and remember what peace there may be in silence..." to that sweet silence I now return... Peacefully, Timothy 2 Link to comment Share on other sites More sharing options...
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