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-   -   What are the effects of downshifting on the clutch? (https://www.mazda3club.com/1st-gen-323-glc-engine-drivetrain-59/what-effects-downshifting-clutch-6917/)

mazdaspeedwest May-27th-2002 06:34 PM

What are the effects of downshifting on the clutch?
 
I was thinking about this today, and thought there might be a difference in up shifting and downshifting according to the clutch use.

So question is, how does downshifting affect the clutch and engine? and is there a difference is clutch engagement between up and down shifting?.....and i'm talking technical here, not the obvious "engine braking" ;)

all in reference to a 5sp transmission.........

islandpro May-28th-2002 09:44 AM

i think your putting way to much thought into it. :p I see it as the forces that are put to the clutch when upshifting are then reversed when down shifting. insted of the engine providing the power the trany is. heck i dunno. im confused now.. time to take a nap.;)

islandpro May-28th-2002 09:47 AM

IMO i think the clutch goes threw the same. no matter up or downshifting.

zenilder May-28th-2002 12:22 PM

Re: What are the effects of downshifting on the clutch?
 

Originally posted by mazdaspeedwest
I was thinking about this today, and thought there might be a difference in up shifting and downshifting according to the clutch use.

So question is, how does downshifting affect the clutch and engine? and is there a difference is clutch engagement between up and down shifting?.....and i'm talking technical here, not the obvious "engine braking" ;)

all in reference to a 5sp transmission.........

Well, there's not too much to it. Just so long as you rev match when you downshift, things should be okay.

Upshifting, if you're mashing the pedal, and then shift without letting off the gas, you could run the risk of overheating the clutch with one launch. The disc would slip until the engine slowed down to match the tranny, creating heat. Stock disks will start to slip pretty fast, and then you're left to feather the throttle to gain speed.
Letting out the clutch too quickly will give a jolt to the disc, but the stock discs have a spring loaded plate. So that absorbs a lot of the punishment.

Oh. If your clutch does overheat, and it slips too much, you risk glazing your clutch and possibly warping your flywheel.

The same principles apply to downshifting. If you don't rev match, you're just heating up your clutch, and eventually it'll start to slip.
Letting out the clutch too fast with out rev matching, forces one end to match speeds of the other, and in this case, it's usually the engine that has to match the speed of the car/tranny, which isn't good on the engine (and this doesn't apply to engine braking when the engine is forced to slow down to slow the car. I'm talking about sudden need to slow down). Like I said, the springs on the stock disc absorbs a lot of the punishment, but that doesn't mean that nothing else will be affected by harsh use.

islandpro May-28th-2002 12:43 PM

told you i didnt know. but thought i would give it a shot. ;)

Maz94Protege May-28th-2002 01:54 PM

Re: Re: What are the effects of downshifting on the clutch?
 

Originally posted by zenilder


Well, there's not too much to it. Just so long as you rev match when you downshift, things should be okay.



??? REV MATCH....huh??? you dont ( or not supposed to rev to down shift)

if thats what ur refering to,....i think ur shifting wrong.:rolleyes:

mazdaspeedwest May-28th-2002 02:34 PM

Re: Re: What are the effects of downshifting on the clutch?
 

Originally posted by zenilder


Well, there's not too much to it. Just so long as you rev match when you downshift, things should be okay.

Upshifting, if you're mashing the pedal, and then shift without letting off the gas, you could run the risk of overheating the clutch with one launch. The disc would slip until the engine slowed down to match the tranny, creating heat. Stock disks will start to slip pretty fast, and then you're left to feather the throttle to gain speed.
Letting out the clutch to quickly will give a jolt to the disc, but the stock discs have a spring loaded plate. So that absorbs a lot of the punishment.

Oh. If your clutch does overheat, and it slips too much, you risk glazing your clutch and possibly warping your flywheel.

The same principles apply to downshifting. If you don't rev match, you're just heating up your clutch, and eventually it'll start to slip.
Letting out the clutch too fast with out rev matching, forces one end to match speeds of the other, and in this case, it's usually the engine that has to match the speed of the car/tranny, which isn't good on the engine (and this doesn't apply to engine braking when the engine is forced to slow down to slow the car. I'm talking about sudden need to slow down). Like I said, the springs on the stock disc absorbs a lot of the punishment, but that doesn't mean that nothing else will be affected by harsh use.

thanks, i understand, but i don't or haven't much, rev matched when downshifting, i downshift for engine braking...but i am still on the OEM clutch and yes it does slip nicely in 2nd now...but after 12 years, it's been a great clutch.

mazdaspeedwest May-28th-2002 02:39 PM

Re: Re: Re: What are the effects of downshifting on the clutch?
 

Originally posted by Maz94Protege


??? REV MATCH....huh??? you dont ( or not supposed to rev to down shift)

if thats what ur refering to,....i think ur shifting wrong.:rolleyes:

rev matching is more of a racing technique. also refered to as heel-toe.

when you enter a corner under braking (heel on the brake pedal) you rev (toe on the gas pedal) the engine to match the downshifted gear's RPM, this way you'll be in the power band when exiting the corner and the car will not slow down due to engine braking, but rather spit you out of the corner faster.

very dificult to do correctly i might add, takes alot of practice.

Maz94Protege May-29th-2002 05:39 PM

Re: Re: Re: Re: What are the effects of downshifting on the clutch?
 

Originally posted by mazdaspeedwest


rev matching is more of a racing technique. also refered to as heel-toe.

when you enter a corner under braking (heel on the brake pedal) you rev (toe on the gas pedal) the engine to match the downshifted gear's RPM, this way you'll be in the power band when exiting the corner and the car will not slow down due to engine braking, but rather spit you out of the corner faster.

very dificult to do correctly i might add, takes alot of practice.

oooo aight gotcha...thanks for the clearing up!:D

Sir Nuke May-29th-2002 07:40 PM

I really don't see where there is a problem with this at all....can't see where it does any harm.... I have over 135K on my little truck...and the clutch don't slip a bit...and I use the engine to break ALL the time....its how I drive.

zenilder May-30th-2002 11:11 AM


Originally posted by Sir Nuke
I really don't see where there is a problem with this at all....can't see where it does any harm.... I have over 135K on my little truck...and the clutch don't slip a bit...and I use the engine to break ALL the time....its how I drive.
I'm not saying that any of this does any harm. At the worst, the springs on the clutch disc will wear out, glaze the clutch and possibly warp the flywheel. I certainly don't mean any of this will be the result of light engine breaking while going to the market to pick up a six pack of Henry Weinhards Root Beer with some chips & dip to watch a movie at home. I'm say you might see these problems if you tend to do it often enough to see your clutch slipping after a couple of launches or a few dozen turns. The springs on the clutch should be fine unless you really punish them by letting the clutch out quickly ( and I don't mean doing it on stoplight drags or anything. I mean when you're driving on the street, you're in 2nd, you're about to shift up to 3rd, rev is about 3500, you shift to 3rd, but you don't let the revs drop much at all, and when you let the clutch out real quick *JERK*). I don't like doing that, and I try to stay away from doing it. Especially in my truck, considering that it has monster torque, and doing that will eventually break something in the drivetrain.

So don't stress it if you do your normal daily driving. If you push your car hard everyday, then you might worry about it.

mazdaspeedwest May-30th-2002 09:20 PM

Re: Re: Re: Re: Re: What are the effects of downshifting on the clutch?
 

Originally posted by Maz94Protege


oooo aight gotcha...thanks for the clearing up!:D

no problemo :)

turboge June-7th-2002 04:52 PM

Re: Re: Re: Re: What are the effects of downshifting on the clutch?
 

Originally posted by mazdaspeedwest


rev matching is more of a racing technique. also refered to as heel-toe.

when you enter a corner under braking (heel on the brake pedal) you rev (toe on the gas pedal) the engine to match the downshifted gear's RPM, this way you'll be in the power band when exiting the corner and the car will not slow down due to engine braking, but rather spit you out of the corner faster.

very dificult to do correctly i might add, takes alot of practice.

Hmm... I usually use my toe portion on the brake pedal and stab the bottom of the gas pedal with my heal. I couldn't see my feet turning the other way to put the toe on the gas pedal, and the heel on the brakes.. contortion!?

Brubeck June-7th-2002 09:45 PM


Originally posted by Sir Nuke
...and I use the engine to break ALL the time....its how to drive.
Yes, and I do the same. I put 125k on my Toyota pick-up... engine break as much as possible and never replaced a break pad... never had a clutch problem.

If you doubt that engine breaking works, make a point to get close to an 18-wheeler in traffic. When things start slowing down and you hear rhhhhhaaaaaaaaarrrrrrr gaaaaaa gaaagg ggaaa gaa ga gaaahhhhhhh..... you'll realize that people who drive all goddamn day long know that engine breaking is a fact of life.

mazdaspeedwest June-8th-2002 12:04 AM

Re: Re: Re: Re: Re: What are the effects of downshifting on the clutch?
 

Originally posted by turboge


Hmm... I usually use my toe portion on the brake pedal and stab the bottom of the gas pedal with my heal. I couldn't see my feet turning the other way to put the toe on the gas pedal, and the heel on the brakes.. contortion!?

i guess it's just natural for me, and you get more pressure on the brake with your heel than your toe :D

mazdaspeedwest June-8th-2002 12:05 AM

How does that go now?


Originally posted by Brubeck
you hear rhhhhhaaaaaaaaarrrrrrr gaaaaaa gaaagg ggaaa gaa ga gaaahhhhhhh.....
aaaaahhhhhh, ok i get it....:D :D :D :D

oregano June-27th-2002 10:52 AM

your toe is more sensative, and you can use that sensitivity to keep your tires from locking up. the gas does not require this sensitivity, only proper timing. my problem is that my heel gets stuck on the side of the centre console:p

mazdaspeedwest June-28th-2002 10:01 PM

ya thats more like what i do too, i've been practicing in our lovely Cali traffic..... aftermarket pedals help too, as the gas pedal will have a tab on the brake pedal side. This helps me perfectly, since when i come home at night the system is at FULL VOLUME (stress relief) and the RPMs will dip at a dead stop. So i have my foot half on each pedal and can keep the RPMs at 1000 to keep from dipping....ya i know, time for a bigger alternator, but eh, won't make me go faster so it's not a priority :D :D :D :D

It's kind of a roll over effect too, hard to explain, but hey do what ever works for you.

Eddiewould August-13th-2002 03:07 AM

Umm is it just me or is the point being missed in this thread?

Well its my belief that engine breaking doesn't really do anything to the clutch

the only thing engine breaking will really affect are the syncho's in the gearbox. And this wont happen unless you're doing some heniously different revs from one gear to another.

my $0.02

JJB August-13th-2002 07:10 AM

Re: Re: Re: Re: Re: What are the effects of downshifting on the clutch?
 

Originally posted by turboge


Hmm... I usually use my toe portion on the brake pedal and stab the bottom of the gas pedal with my heal. I couldn't see my feet turning the other way to put the toe on the gas pedal, and the heel on the brakes.. contortion!?

the way that it is taught at performance driving schools is to use the ball of your foot on the brake (this still provides a good amount of force should you need it) and then you use the heel of your foot to blip the accelerator.

Here's a good on-line article on it.

David August-13th-2002 07:34 AM

That's a nice site.

turboge August-13th-2002 06:56 PM

I should have a couple video's with a little heel/toe shifting up on the web shortly. I just pulled them off my camera along with a quick little run through the mountains in the Spec V.

August-13th-2002 08:56 PM

Clearing up a few things here.

Engine braking does so little that it's not very useful for slowing a car. It was done in the past because brakes were not very good (rear mechanical drums, hand-lever operated), engines were huge and full of friction. Nowadays, brakes on cars are so good that downshifting to slow a car is pointless.

Also, most of the braking is from friction, not compression. And what isn't friction is actually vacuum braking, as the pistons try to pull air past the closed throttle plate.

Now, downshifting for performance driving, or when entering a corner, is something different. Here, it's done so that you are in the correct gear when you exit a corner.

The point of heel-toe downshifting, or rev-matching downshifts, is that it reduces the upset to the car (don't believe me, try downshifting a RWD car without rev-matching and watch the lightly loaded rear wheels lock up. It will also reduce wear on the synchros.

And, diesels engines produce almost no compression/vacuum braking, because they have no throttle plate. That noise you hear diesels making is from a device called a Jake Brake (generically). This acts on the valves to produce nearly 100% of the engine's output in braking force (A typical 400hp diesel engine might have 350-400hp of braking with a Jake Brake). Diesel pickups often use an aftermarket exhaust brake (a valve in the exhaust system that can be closed off) to perform a similar function. Semis also use things like hydraulic retarders to slow them down, but these generate enormous amounts of heat.

mazdaspeedwest August-14th-2002 06:45 AM

Diesels also use an exhaust brake, or is that the Jake Brake your refering to?

August-14th-2002 07:42 PM


Originally posted by mazdaspeedwest
Diesels also use an exhaust brake, or is that the Jake Brake your refering to?
Big rigs use an exhaust brake, but it is intregrated into the head (controlling the exhaust valves) rather than on the exhaust pipe itself, as is fitted to pickup diesels.

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