Hard or soft braking

True, stab braking allows the heat to dissipate better and the lower amount of constant contact lowers wear as well.

The amount of energy that needs to be dissipated as heat via the brake components will be exactly the same however harder braking will result in higher temperatures as the heat is applied over a shorter period of time.

The question then becomes whether brakes wear quicker at higher or lower temperatures?

There are also other factors to consider, particularly the pad material and its suitability for the conditions that apply (consistent hard braking from high speeds requires a different material to the conditions encountered in normal city driving).

I agree that is a fundamental question related to the OP's concern. o Do hot brakes/rotors wear down rotors/pads faster than cooler ones?

Me? o I use Silicon Valley finesse when braking - not brute redneck force.

What I do is coast to a stop whenever possible for a variety of reasons.

1. I put the gears in neutral when I can see the red light ahead.
2. Then, I apply the brakes harder at first, so as to scrub momentum.
3. Then I coast, gently, still in neutral, to the stop light.

While this works whether or not it's a manual transmission, I do agree that some people feel shifting an automatic is (somehow?) bad for the automatic, but I've been doing this for decades, and haven't destroyed one yet.

The _advantages_ of this "coast to a stop" method are, IMHO, mainly: A. It saves on gas mileage (as 20% of the time you never need to stop) B. It saves on pad-deposition (since the rotors have a chance to cool down)

As a bit of finesse, I make sure that if, in the 80% of the time I _still_ have to stop, I simply "almost stop" a car length or two behind the stopped car in front of me, where I then expend the last bit of braking heat, and then coast to the final stop and lift the pedal off (if it's flat).

That way I don't get a pad "footprint", which, IMHO, is a major cause of brake-related vibration at highway speeds (which is a topic we've discussed in infinite detail in the past on this newsgroup so I won't belabor it).

I would guess that heat is always the enemy. Do they get cumulatively hotter with hard sporadic braking or soft longer-lasting braking?

In traffic I just take my foot off the gas as soon as possible. Hubby says I don't do it soon enough, but I hate having someone dive in ahead of me because I left enough room for them to do so. In my defense, some assholes haven't a clue about making left turns in heavy traffic -- they stay behind the limit line until the light turns red and then dive through -- requiring everyone behind them to wait through an additional cycle. If done properly TWO cars can go through on each cycle -- maybe three if all three are quick.

Brake pads are cheaper and easier to replace than clutches/transmissions. I'll put the car in 2nd if coming down the mountains trapped behind some jerk who hasn't a clue about mountain driving -- long ago I used my brakes far too much in a similar situation and had serious fade down at the bottom. Some experiences cast long shadows.

Fine in traffic.

I'm mostly concerned with mountain and highway driving, which is what I use my car for most.

As someone stated, we have to expend the same amount of energy in slowing down the car no matter how we brake - almost all of which is heat energy.

Seems to me that the "temperature" is a function of how hard we brake and how fast we stop, where, IMHO, stopping slower "spreads" out that heat, such that the "temperature" has a chance to not rise as much.

Does it work? o Dunno.

I do it mostly for two reasons: a. Save fuel, and, b. Prevent pad footprint deposition.

Hehhehheh... that happens to me all the time.

I can see their point, as they likely feel I'm "slowing them down"; but they also likely don't realize that I'm coasting because I _know_ there's a red light up ahead (or stopped traffic) - where my goal isn't to stop - but to coast right through the light when it finally turns green and the traffic in front of me clears out.

hehhehheh... I often "need" to go through a yellowish-red light, where suddenly, my visor comes down to cover my face from the stoplight cameras, if any. :)

(Hint: They need to correlate the driver with the license plate, I think.)

Yes. Much. o I've heard this all the time.

But that assumes putting the transmission in neutral somehow "damages" the transmission, or, getting it back in gear while coasting damages the transmission.

The question for this ng is whether that's the case, or not. o I don't know the answer - but I've been running the test for a long time!

Are you in a manual or automatic? o I don't feel much engine braking when using an automatic downhills.

And I travel a _lot_ of downhills!

Many miles every day in fact.

Where my tires take a beating like you can't believe.

Almost always, I'm in neutral because the road is twisty curvy so you're limited to between 20 and 35 mph almost the entire way downhill (or up).

Me too, as I live in and around the mountains of Silicon Valley.

See details here: o Does the macadem road surface have a great effect on tire wear?

And here: o How would you run a lateral acceleration test in a vehicle on twisty roads at no more than 40mph?

Depends on the transmission. The FWD driving clutch in a typical 3 or 4 speed auto transmission is engaged in all fwd gears. As a consequence, the return spring mechanism in the FWD clutch can be a diaphragm plate spring. Like this;

BW35 and similar transmissions use these. Excessive flexing, such as when you needlessly shift to neutral while stationary in traffic will cause these to fatigue fail. Pulled many of these down to find broken diaphragm springs. Bottom line, there is no need to shift to neutral whilst stationary in traffic. The stall point on the torque converter means that there will be minimal drag on the engine *at idle*.

Then there is the wait whilst people wake up to the fact that the traffic situation has changed and the delay whilst they reselect drive. Annoying for drivers behind, especially so if they miss their turn through a set of lights.

Our City took those out after only a few years. They didn't get a big enough cut of the resulting fines, although they claimed it was because of the increase in rear-enders.

Doing something different puts wear on the thing that's doing something different.

Auto. The Corolla engine-brakes fine, and so did the POS 88 Caddy.

The Corolla rolls really nicely. I think I could easily go over an edge if I left it in neutral.

Highway 330 and 18 to Big Bear. 40-80 depending on where you are and the direction you're going :-)

Maybe. Maybe not. I really do not know, and don't claim to know.

My assumption is that transmissions were meant to be shifted from D to N and back; but that they weren't designed to do that while moving.

Does doing it while moving "hurt" the transmission? o I don't know.

Maybe someone here, like Xeno, knows "how" that can hurt a 2wd front or rwd transmission?

Hi Xeno,

You've helped me a lot in debugging tire wear on the mountain, where I've informed all the neighbors of the problem set.

Speaking on warranties...

One of those neighbors went to Costco and kept taking advantage of the free rotation, but at 7,500 miles, Costco initially _refused_ to rotate the tires because they were _already_ worn with what we've tentatively concluded is "camber scrub" due, not to alignment per se, but to the physics of many daily low-speed tight steep turns.

They talked Costco into rotating that one time by showing recent alignment results, but the _next_ time we expect it to happen again.

I need to ask them what happened since that was a month or two ago I last spoke to them about it (they took all my advice on the rotation & alignment).

As for shifting to neutral, I wonder if you know if there is any damage to my method (described below) for a non-four-wheel-drive, but for both a front-wheel drive and a rear-wheel drive?

Is there?

Here's what I do on both the front-wheel drive & rear-wheel drive: a. Daily, on the downhill, I am in neutral for miles on end, where at the conclusion of the hill, I wait until the car is about 20mph to 30mph and then I match the RPM by feel and slip it into gear without lurch.

b. At every opportunity for a "planned stop" (such as a red light up ahead, or traffic up ahead), I slip it into neutral, slow down harder than I would otherwise to scrub off speed, and then coast to the blockage - where the hope is that I can coast right through it as it clears.

c. When it's time to get back in gear, I slip it from N to D while matching RPM to the road speed, with the goal of eliminating all lurches.

I've been doing that for years.

Dunno if it hurts the transmission or not though, as there's not much value in a study of just one.

Transmissions will do that without complaint. What is at issue is whether it is a good idea to be in neutral whilst on the highway. My viewpoint is that it is not - whether the trans is a manual or an automatic. The issue here is *safety*, not trans damage.

Doing it whilst moving will not, in the short term, damage the transmission.

Must ask one question here.

Why shift to neutral when going down hill? What is the benefit?

Again, why the shift to neutral?

Please do not teach a new young learner driver to follow that practice.

The correct *slang* term for selecting neutral when coasting downhill is

*Angel's Gear*. And you may well join the angels if you continually practice the habit.

If you think you are saving fuel, you are wrong. In the days of carburettors, yes, fuel continued to flow through the engine, even at the higher RPMs encountered. However, with the throttle plate closed, even that fuel use was at a minimum since the main jets were deactivated. With fuel injection, it's a different story. On coast (overrun) the ECU will cut fuel injection until the engine RPM drops to a specified minimum. Typically this is reasonably well above idle and around 1400-1600 RPM. That means all you need to do to save fuel is leave the trans in Drive and keep the RPM above the point where the injectors will cut back in. And you will have engine braking as a bonus. If you engage neutral and let the engine idle whilst coasting, you are

*still* using fuel.

What you don't have when coasting in neutral is engine braking so you run the risk of getting brakes hotter than necessary.

If the situation changes suddenly, you have no possibly of accelerating out of trouble *until* you re-engage Drive. That seemingly miniscule amount of time may be the difference between avoiding an accident.

While the engine is being overrun by the transmission, the power steering pump is still being operated. If, however, your engine stalls out for any reason whilst in neutral, your engine RPMs will instantly drop to zero and your power steering pump is now not pumping. That means, on most modern vehicles, especially FWD, very heavy steering. Here's a little scenario for you to cogitate on.

You are coasting downhill in *Angel's Gear* and, for no apparent reason, your engine stalls. You realise this has happened because the steering has become very heavy, the dash lights up, tach drops to zero, etc. In these situations, *Murphy's Law* dictates that there will be a sharp corner coming up with a rush. You slip the selector back to D for Drive. Nothing. You select other Fwd gears, nothing. Your transmission has become a *bag of neutrals*. You then hit the key/button and restart the engine - except it doesn't start because - D for Drive. You realise this, select neutral (hopefully not park), hit the key, start the engine, then back into D for Drive. Did you get around the corner? It's more than likely you wouldn't since, with no power steering, zippy movements of the steering are damn difficult and it took you more time than you realised On your seat to come to grips with what was happening.

Why did you have no selectable gears when the engine stalled out? The answer is simple. The transmission needs oil under pressure to operate the various servos. No oil pressure, no servos operate therefore no clutches or bands can operate. The trans oil pump, though located in the transmission, is actually driven by the *engine*. If the engine stops, the pump stops, the pressure drops and the clutches and bands all release. All neutrals.

Some people will try to tell you that the trans has another pump - no it hasn't, they are clueless. The 2nd trans pump, which was typically driven by the trans output shaft, disappeared in the interests of

*efficiency* some 50-60 years ago, nor was it particularly ubiquitous. The old 2 speed Ford transmission had one - How far back were they?

You can try the above exercise for yourself. Please do select a straight stretch of downhill empty road to experiment on.

I might note, selecting neutral and coasting downhills is *illegal* in Australia. The reasoning being that you are *not in control* of the vehicle. If something jumps out in front of you, reaction times dictates that you may not have sufficient time to re-engage Drive and take evasive action. In fact, the most likely scenario is that you will hit the accelerator or brake first, then try to evade the situation by accelerating. You will have momentarily forgotten you are in *Angel's Gear* and it might well be fatal. Sudden panic does that to your memory.

There is no value in selecting neutral and coasting down hills but a lot of risk.

There is no value in selecting neutral when stopped at traffic lights.

Hi Xeno, I very much appreciate your technical acumen.

I would like to ask that we ignore the "danger" factor to humans, as that isn't my technical question in the least.

You've made your point on the "danger factor" so that _others_ will be scared enough to have second thoughts - but the "danger factor" isn't even on my list of the least of my worries (I've explained why in the other post).

My key _technical_ question I would love to know the answer of is this: Q: *Does constant daily prolonged engine braking cause transmission wear*?

Hi Xeno,

What I need help in understanding is the simple answer to the question: Q: *Does constant daily prolonged engine braking cause transmission wear*?

I appreciate your advice as you know transmissions better than I do. o The main point is to minimize _wear_ on the transmission - with finesse.

Nothing else matters to me as I've _already_ taken it all into account. o The _only_ real unknown is whether I'm saving wear on the transmission.

That's where I need your technical advice most: a. Does _not_ engine braking (for miles and miles every single day) save wear on the transmission?

As for brake-system braking, I fully understand your question, where we have to remember the fact there is absolutely zero chance of not braking at every curve. Zero. With or without engine braking.

So you're gonna brake like hell, no matter what.

The second point is that an automatic doesn't do all that much engine braking, so, you're _still_ gonna brake "about as much" with or without engine braking (although certainly you'll be braking a bit more).

Third point is that engine braking itself, "may" contribute to transmission wear, whereas traveling in neutral "might not", as long as we assume that the transmission isn't spinning and if it is, then it's getting the oil it needs (e.g., when towing, I believe that's an issue, is it not?).

Fourth point is that the gas mileage will be better (slightly) without the engine braking, which, since it raises RPM, raises fuel consumption (only slightly, of course). [EDIT: I just saw your fuel injection info below.]

The fifth point is that eventually, at the bottom of the hill, miles later, you do have to match the RPM when you finally put it in gear, which "can" perhaps damage the transmission over time.

Add all five points up, and I don't see how engine braking "helps" protect wear on brakes, where replacing brakes is trivial compared to replacing transmissions, so as long as coasting down a hill does not damage a transmission, then coasting down a hill saves on gas mileage and transmission wear (all things added up).

The key question in that calculation, of course, is whether or not there is damage to the transmission from these key factors: o Coasting for miles at low speeds (~20 to 25mph) in neutral o Engine braking damage to the transmission by _not_ coasting in neutral o Shifting into N at the start & then into D at matched RPM at the bottom

The potential benefits are clearly obvious - if admittedly rather slight. o The key question is whether any "damage" occurs to the transmission.

Is there?

As explained above, it's a logically inspired tradeoff by the "theory" that it's better to shift wear from the transmission (due to constant engine braking) to the brakes.

It's also (admittedly slight) an improvement in gasoline efficiency. o And, in fact, truth be told, it's kind of fun to use "potential energy".

The math works out wonderfully, if admittedly slight, only if there's no additional damage to the transmission incurred by coasting for miles in neutral on a steep downslope at low speeds.

I'd even turn the engine off, if I could, but of course, then there's be no power brakes or power steering, so the engine must idle the entire way while we're otherwise on 100% potential energy the entire fun trip!

I teach the kids "finesse", e.g., to slow down well before a stop, so that they don't leave a pad imprint on the rotor (which can build up over time and cause DTV (disc thickness variation) vibrations).

I also teach the kids "finesse" in turn signaling (it's not for the cars you see - but for the cars you don't see); and I teach them finesse in shifting in a manual (revs into the power band are your friend); and I teach them finesse in turning (always take the lane nearest you so that the car you don't see has room to get around you); etc.

I teach them finesse such as understanding how US Interstate road signs work (i.e., in a single mile in any Interstate in the USA, you can tell both what direction you're going and how far it is to your exit and how far to the end of the road in one direction, and what other Interstate the Interstate you're on connects to, etc.).

I teach them emergency actions, such as interpretation of the slanted yellow and black signs (almost nobody knows which "direction" they go but I teach the kids the proper direction); and I teach them how to pump the brakes in an emergency (although admittedly, some of the cars I'm teaching them on have ABS).

Remember, this is a road where, on a Sunday, for example, no cars will go up or down for an entire day (I've hiked the entire road many times, miles and miles, and there were no cars).

The fact is that you'll _never_ need to hit the gas. You just won't.

We're not talking a divided highway with other traffic, both ways, and turnoffs.

This is a windy mountain road that has almost zero traffic on it, where the ONLY thing you'll EVER need to do, is brake.

I can't even imagine a situation where you'll need to accelerate.

Hmmmm..... this is GOOD information. o All these vehicles are fuel injected.

Hmmmmm... that's double idle speed. o I don't see how the _engine_ braking won't control the RPM

Each RPM has an injection cycle into the intake manifold, doesn't it?

I don't understand. o Doesn't each RPM have its own fuel injection cycle into the manifold?

I equate RPM with gasoline used (even if the throttle plate is closed). o Is that wrong?

But engine braking "may" also translate to "wear" on the transmission. o All that force has to go somewhere.

Of course. o But you're at 700 RPM with zero load on the engine.

While this is "technical" and fundamentally true, I doubt it matters. o There's absolutely zero chance you're not braking under all condistions.

You're just braking less while engine braking. o Where you're trading, I assume, transmission wear for brake wear.

Given _that_ tradeoff, I'll take brake wear any day over transmission wear. o Hence, the entire argument boils down, fundamentally, to one question:

Fundamental technical question: Q: *Does engine braking cause wear on the transmission, or not*?

Not gonna happen. o Not on these roads.

I can't say there's zero chance, but, I can't even _imagine_ a situation on these roads where you'll need to accelerate out of a problem.

I guess, thinking hard, a tree could be falling in front of you where you decide it's better to accelerate past it (and crash on the other side of the curve instead of being crushed by the tree) but, in reality, the chance of needing to accelerate on these untraveled roads, is nearly zero.

I don't want you to think I'm dismissing out of hand your concern, where I'm well aware it's illegal to ever be in neutral for _that_ reason; but it's like owning a chainsaw or working on brakes - you have to be able to assess the risk where that risk I dismiss out of hand on these roads.

The only reason _not_ to do this would be if there's some other disadvantage, such as if it's actually _causing_ wear to the transmission instead of the goal, which is to _prevent_ wear to the transmission.

I'm not worried about loss of power steering, Xeno. o I may as well worry that my tires are gonna blow up in my face when I mount them.

Sure, it "can" happen; but to worry that much about something so remote that is easily recovered from, I'm just not gonna worry about that.

If that's the _only_ reason to not do it, then there's no good reason not to do it.

The main concern I have, which is a _technical_ concern, is whether or not I'm saving damage to the transmission by not using it for engine braking.

With all due respect on your technical acumen, _that_ is where I need your advice most.

Yup. Just like using a chainsaw is dangerous but effective, I am not in the least worried about the law in this case. I understand the law.

What I need help in understanding is the simple answer to the question: Q: Is constant daily prolonged engine braking causing transmission wear?

I've assessed the risk; what I need to know is the "technical" stuff. Q: Does constant daily prolonged engine braking cause transmission wear?

The technical question is whether or not wear occurs due to constant incessant repeated daily prolonged ever-present engine braking?

It's illegal in many US states for the same reason.

Short answer; no.

Xeno

There is value in _not_ imprinting the pad footprint on a hot rotor. o How you go about _not_ depositing the footprint is what we can debate.

Then that makes the decision rather easy. o Daily incessant constant slow-speed engine braking for miles on end; o ... or ... Daily incessant brake-system braking for miles on end.

There's no danger either way given acceleration on this road is almost impossible to fathom (as you'd run off the road if you accelerated).

You're going to be constantly "braking" either way given the facts:

The trans is better able to dissipate heat than the brakes under low speed decel.

Also, on your road, I wouldn't be on the brakes much at all. I would just manually select an appropriate lower gear. I like to preserve the brakes as much as possible and the trans is designed with ablative technologies in mind.

As far as gear wear is concerned, in the overrun you are using the coast (back) side of the gear teeth so the relatively *unworn* part. As well, one single full throttle acceleration would apply the wear of a thousand engine braking instances. Under acceleration, you are applying the *full power* of the engine. Under engine braking you are only applying friction and engine pumping losses. If you are concerned about transmission wear, it's not engine braking you should be concerned about as most wear occurs under acceleration.

That works until shit happens.

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