Was in a conversation with someone recently regarding pros and cons of standard braking vs. engine braking. (I am generally against the latter.) When you brake using brake pedal, wear occurs on the brake pads. Where (or to what) does the wear associated with engine braking occur? I assume it’s somewhere like the valve train, cylinder heads, pistons, rings or crankshaft? Or not…
Interesting question. I’m not sure of the answer. Maybe the torque converter and/or clutch? Maybe just the other side of gears’ teeth?
Everything in the drive train. Motor, transmission and differential are all stressed during engine braking, especially going downhill. 
That’s even when going uphill though
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18 wheelers use engine braking all the time to save wear on brake components.
Main problem I can see with engine braking for a passenger vehicle is if you do it all the time, violently. I.e. dropping down to 2nd gear at 75MPH is going to introduce whiplash in addition to straining the drivetrain while dropping to 4th in the same situation will be markedly less dramatic and is a more appropriate scenario.
Drivetrain components are pretty durable. So long as you’re going for deceleration (planned bleeding off speed) rather than braking (oh sh-t I need to stop) it’s fine. Easier to pull off with a manual transmission than an automatic, although I suppose modern automatics with paddle-shifters can approximate the trick.
Said components are also routinely stressed during acceleration.
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Especially when I hit the NOX bottle. Pistons take a beating. 
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Yes, but once you’ve seen a few trucks and cars combust on the way down from the Eisenhower Tunnel on I70, you realize that just using your brakes is probably not the best life decision.
Friend posted this a few days ago… a Camper and 2 jeeps… hope they packed marshmallows, chocolate, and graham crackers 
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Or when the turbo spools up.
Bottom line, don’t do it. That’s why there are brakes. The brake pads are made for it and pads are cheaper than drivetrain parts.
As an intellectual exercise though, the transmission takes the biggest beating with engine braking.
This was my argument to the other guy. As well as being easier to fix/replace as well. He thought he was saving wear and tear on the pads, thereby braking (i.e. getting mechanical work) for free.
That said, you could put everything I know about auto mechanics into a thimble and still have room left for a shot of Ripple.
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Engine Braking is mainly used on Tractor Trailers and is typically referred to Jake Brakes web page shows demos of how it works. It was developed to mainly to prevent brakes from overheating. The FAQ tab is interesting in that some companies like Ford have asked they not develop products for engines. They also note that “Jake Brakes” are designed primarily for engines >10 l /600 ci.
FAQ3:
Can you tell me more about the history of the Jake Brake® compression release engine brake?
ANSWER:
Clessie L. Cummins, founder of the Cummins Engine Company, drove across the United States to demonstrate the viability of diesel engines in 1931. While descending Cajon pass in California, the foundation brakes on his vehicle faded and he and the crew of his truck were nearly killed. Shortly after this experience Clessie first conceived the idea of using the engine to slow a vehicle going down hill. Clessie developed the first concept of a compression release engine brake in 1954, after leaving the company that he founded. Despite repeated rejections from major engine manufacturers, Clessie continued to pursue his idea.
Goes on to tell how company released first product in 1961.
Also how they are trying to develop them for gasoline engines to replace “butterflys” in the intake system as part of the Air/Fuel system.
The FAQ page I thought refreshing in it tells both the advantages and disadvantages of the system on the engine and drive train.
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I suspect that unless you’re transiting mountain passes in a heavily laden vehicle daily or routinely inducing whiplash deceleration, the practice is likely amount to a rounding error on the lifespan of your drivetrain since there are few other routine opportunities to use it.
I do it occasionally on road trips, always when going down a long steep descent (I’d rather not experience brake fade on a steep slope), and rarely coming up to a stoplight from a ways off with light traffic. The drivetrain routinely deals with harder acceleration, so it can handle that kind of deceleration. Otherwise, there are friction brakes for a reason.
EDIT: the transmission in the vehicle is going to dictate appropriateness.
- A strong majority of the vehicles I’ve driven have had manual transmissions, meaning that there is both the control and granularity to allow it at any speed
- The semi-standard 4-speed automatic in passenger cars often won’t allow for it at highway speeds since most seem to have “1”, “2” and “D” positions - you’ll either have to just let your foot off the throttle and let the engine resistance at idle throttle do the trick or avoid the practice since dropping to “2” is not a good plan
- More recent “autostick” 4-speed transmissions or DSG transmissions can pull off the trick, but will require attention on the part of the driver to ensure that the transmission doesn’t default to normal operation assuming the driver forgot to upshift
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[quote=“ESmith, post:12, topic:23957”]
The drivetrain routinely deals with harder acceleration, so it can handle that kind of deceleration.[/quote]
Drivetrains are designed for acceleration not for deceleration. I spend a lot of time fly fishing in Colorado, thus driving those steep hills. Brakes are the only way to go. I suppose if you shift down at low speeds like an automatic normally does, it might be ok, but then why?
Of course the ultimate deceleration technique for rapid braking is throw it into reverse! 
The “wear and tear” is minimal; no more than running the engine at the same RPM in steady state or acceleration (and as noted, arguably less). The majority of the energy is converted to heat, and is easily dissipated via the cooling system, as is the design.
There is a solid argument for clutches being designed for one-way power transmission, but this is largely negligible as well, as vehicles have, for the last 90-or-so years, been designed to allow engine braking (as long as we’ve had to negotiate cargo down mountain passes).
As for saving wear and tear on the brakes, in modern cars (i.e. since the advent of disc brakes in ca. 1950’s) there is nothing to be gained there. In cars with 4-wheel drums, however, you’ve got a race. Service brakes are designed for short bursts of heavy heat dissipation, unlike engines, which are designed for long-term small bursts of heat dissipation. When the braking situation calls for long-term but reduced magnitude conversion of kinetic energy to heat energy (such as trundling down the far side of the Rockies) the engine is better. But in daily use, in Texas, especially Dallas, there’s no point.
The better point, though, is that there is no point arguing. If you enjoy engine braking, have at it. If you don’t, don’t do it. Hardly matters…
~an engine braking advocate
PS: JakeBrakes are a different animal, but the same principles of heat dissipation applies. The major difference is that Jake Brakes dissipate more heat through the exhaust owing to the double-pumping evacuation of the combustion chamber thereto.
PPS: even though modern automobiles are capable, in general, of not overheating their brakes on mountain passes, as @Ian_Jaeger showed, sometimes they still do; thus, among other reasons I advocate strongly the engine braking technique for long/steep downhills.
PPPS: @Owen_Soccer22’s reverse thing is a total myth, unless you have regen…
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[quote=“Owen_Soccer22, post:13, topic:23957”]
Drivetrains are designed for acceleration not for deceleration.[/quote]
This is true, but you’re not trying to push on a rope when you engine brake - there’s a lot of high-strength steel in the drivetrain and the engine that has to manage varying loads under normal operation. The entire drivetrain from the transmission to the wheels has to work both directions anyway.
[quote=“Owen_Soccer22, post:13, topic:23957”]
I spend a lot of time fly fishing in Colorado, thus driving those steep hills. Brakes are the only way to go.[/quote]
I hope you always start out those trips with brake pads with a lot of life left. I also sincerely hope that you never experience brake fade induced by the heat of your brakes boiling off your brake fluid.
I keep harping on the difference between deceleration and braking because the former is the appropriate use of engine braking - for gradual-ish planned deceleration where you have many seconds - ideally tens of - to execute. A steep descent is the epitome of this situation - crest the hill then downshift at the right moment before you pick up any significant speed, let the engine’s resistance regulate your speed as you go down the slope. In a vehicle with a manual transmission this often means just keeping it in 4th gear since you may have been in the gear the entire climb anyway.
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If I’m towing a trailer I would downshift and let that help control speeds going downhill… but my new F250 will downshift itself if the cruise control is on to try and maintain speed. I thought that was pretty cool.
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I find myself doing it perhaps once a week in the late afternoon or evening: there are a few lights I can see from a quarter-plus mile away that I know I’m going to miss. Too far out to actually need to brake, but close enough that just coasting will mean I just need to brake in a few seconds. So I downshift a gear and do some modest engine braking - most of the time it changes before I have to brake and I have momentum to immediately start going again, often passing vehicles that passed me opting to brake late.
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Oh yeah. I do that frequently, but it’s not to save wear and tear, nor because I necessarily think it is more efficient (though there’s an argument it is), but because it’s how I roll. Your (generic “your”) arguments be damned, that’s what I do because it is what feels right for me on my vehicle. Happy to let you (generic you) do as you wish… Except two-foot driving automatics where the brake lights stay on as they zoom away from the stop; can’t abide that. But engine braking or service braking: have it your way…
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he he…pretty punny!
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I lived in Colorado for nearly two decades. Engine braking is part of driver education there for a reason. Brakes alone cannot cope with long and steep descends. The engine can easily and safely handle the task.
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