Downshifting to use engin brake coming downhill

[hearno]

Been away from a computer and tired of using my phone... This is taken from wiki:

"Petrol (gasoline) engines

The term engine braking usually refers to the braking effect caused by the closed-throttle partial-vacuum in petrol (gasoline) engines when the accelerator pedal is released. While some of the braking force is due to friction in the drive train, this is negligible compared to the effect from the vacuum."



I see it says the word "negligible..." but, clearly the drivetrain is taking more abuse than it would if you didn't downshift. Anyone with a trans fluid temp gauge willing do drive around and report their findings HONESTLY. I would guarantee that the temp level would be above normal if used to assist with slowing the truck down repeatedly. Preferred would be someone without an aftermarket external cooler as that would be "stock." As far as the 5th gens doing this stock, all well and good. Time will tell. For a group of owners committed to taking care of their trucks, I'm surprised so many would risk their trans over saving pads. Sure, in extreme circumstances like pikes peak, you'll have to do what you have to do but for everyday driving around town, why bother? Use your brakes. Should be somewhat telling that Toyota finally incorporated it into their design but hadn't before. Maybe they've added/strengthened something to accommodate the new ability. Well why do they have the ability to shift into the other gears? My guess is to hold them while accelerating and for the times you need to engine brake.

 

[Antman]

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Anyone with a trans fluid temp gauge willing do drive around and report their findings HONESTLY. I would guarantee that the temp level would be above normal if used to assist with slowing the truck down repeatedly. Preferred would be someone without an aftermarket external cooler as that would be "stock."

I can comment on this with certainty.

I tow regularly (every week on average) and keep a constant eye on tranny temps through the Scanguage. When I tow I always use manual mode and rarely use 5th gear. I use engine braking almost every time I come to a stop. 4th to 3rd to 2nd- never back into 1st though since by that time I'm >25mph or so.

Does tranny temp rise while engine braking? Absolutely it does. It also rises every time you accelerate. In both cases the tranny temp returns to "normal" in just a few seconds. Just short spikes when measured at the sensor. I can also assure you that the temp rises much, much higher under heavy acceleration than it ever does under engine braking.

I'm of the opinion that this transmission was designed to provide significant engine braking for this exact purpose (at least this is one example). Therefor that's how I'm going to use it. And- it works great.

 

[hearno]

I'm of the opinion that this transmission was designed to provide significant engine braking for this exact purpose (at least this is one example). Therefor that's how I'm going to use it. And- it works great.

Sure, as stated, your 5th gen was designed and apparently equipped to do so. Not necessarily true of the older models.

 

[Viper45]

Does tranny temp rise while engine braking? Absolutely it does. It also rises every time you accelerate. In both cases the tranny temp returns to "normal" in just a few seconds. Just short spikes when measured at the sensor. I can also assure you that the temp rises much, much higher under heavy acceleration than it ever does under engine braking.

I think you missed this part. Why would Toyota (or any manufacturer) not design our transmissions for the worst case scenario in terms of load being applied to the transmission?

 

[hearno]

I think you missed this part. Why would Toyota (or any manufacturer) not design our transmissions for the worst case scenario in terms of load being applied to the transmission?

I didn't miss it. One could say the same about the braking system but obviously it has its limits. Rapid acceleration only lasts so long. Examples given here are extended periods of braking that have exceeded the braking system's capabilities or additional weight like a trailer. If you push any machine to its limits regularly - something is bound to fail. Usually it will be the weakest point first. My point is - why risk something so expensive without a really good reason as opposed to doing it "because you can." No one is going to convince me otherwise and obviously I'm not going to do so either. Nor am I trying to. I'm offering my point of view to the OP who asked for opinions. I also had first hand experience with a malfunctioning transmission from doing exactly what is being discussed.

 

[Viper45]

Not necessarily trying to convince you one way or another either... In fact I only posted originally to point out the inherent dangers of using only the brakes down a steep incline such as Pikes Peak. But you're basing your entire argument on anecdotal evidence (such as your single experience), in lieu of decades of data that proves otherwise; which is borderline silly. Which is why you received the replies to your comments.

You'll do what your going to do and I could care less; so I'm out. Have a good weekend and happy modding!

 

[Canazes9]

I didn't miss it. One could say the same about the braking system but obviously it has its limits. Rapid acceleration only lasts so long. Examples given here are extended periods of braking that have exceeded the braking system's capabilities or additional weight like a trailer. If you push any machine to its limits regularly - something is bound to fail. Usually it will be the weakest point first. My point is - why risk something so expensive without a really good reason as opposed to doing it "because you can." No one is going to convince me otherwise and obviously I'm not going to do so either. Nor am I trying to. I'm offering my point of view to the OP who asked for opinions. I also had first hand experience with a malfunctioning transmission from doing exactly what is being discussed.

With all due respect

<iframe src="//www.youtube.com/embed/xVTpCViyUwM" allowfullscreen="" frameborder="0" height="315" width="560"></iframe>

you are mistaken on this issue. I don't know the circumstances or why the Toyota dealership told you what they did with your previous car, but engine braking is required to maintain safe, controlled descents on steep downhill grades and when towing heavy loads - the brakes may not be able to handle the load on their own. Overheated brakes result in far worse catastrophic failures than a transmission failure....


David

 

[Flahart]

Been away from a computer and tired of using my phone... This is taken from wiki:

"Petrol (gasoline) engines

The term engine braking usually refers to the braking effect caused by the closed-throttle partial-vacuum in petrol (gasoline) engines when the accelerator pedal is released. While some of the braking force is due to friction in the drive train, this is negligible compared to the effect from the vacuum."



I see it says the word "negligible..." but, clearly the drivetrain is taking more abuse than it would if you didn't downshift. Anyone with a trans fluid temp gauge willing do drive around and report their findings HONESTLY. I would guarantee that the temp level would be above normal if used to assist with slowing the truck down repeatedly. Preferred would be someone without an aftermarket external cooler as that would be "stock." As far as the 5th gens doing this stock, all well and good. Time will tell. For a group of owners committed to taking care of their trucks, I'm surprised so many would risk their trans over saving pads. Sure, in extreme circumstances like pikes peak, you'll have to do what you have to do but for everyday driving around town, why bother? Use your brakes. Should be somewhat telling that Toyota finally incorporated it into their design but hadn't before. Maybe they've added/strengthened something to accommodate the new ability. Well why do they have the ability to shift into the other gears? My guess is to hold them while accelerating and for the times you need to engine brake.

I descended Pikes Peak in my 5th gen roughly 6 weeks ago and using the Android app Torque saw that my trans temps were LOWER than normal driving when descending using 1st gear and minimal brakes in the corners to descend safely. When I reached the first ranger station on the way down the ranger laughed at how cool my front brakes were. I was loaded for a weekend camp trip with the Wife and I.

You need to buy a manual trans vehicle and drive in the mountains for a few years. You'll learn that no harm is done when engine braking, I do it daily in my 1st Gen Tacoma.

 

[JB.]

Rapid acceleration only lasts so long. Examples given here are extended periods of braking....

Since engine braking is the reverse of forward drive force, consistent logic dictates you should keep forward acceleration rates and durations below those of any deceleration rates and durations you perceive as damaging.

 

[ajwalks]

Doesn't the 2011 have a button above the rear view mirror for down hill control? I think it is labeled DAC.

Yes, it does, so does my 2010 LE. I've asked once or twice on here how to optimally use the DAC on downhills, but nobody seems to respond?

 

[cbreze]

I think the DAC is for when your in lo range and need some extra help going slow down some really steep hill. Makes a hell of a racket when you engage it.
Edit: after reading the manual I tried to engage it in 2 wheel high and it wouldn't work. 4 wheel high also, no go. Lo range it works. As was posted here previously, somewhere it does make a lot of disturbing noises when engaged. Sounds like you've done something wrong. I turned it off and doubted be using it much. 4x4 in low and 1st gear is enough for me.

 

[Ol'Baditude]

I think the DAC is for when your in lo range and need some extra help going slow down some really steep hill. Makes a hell of a racket when you engage it.

That's correct, it's for very low speed(<15mph as per Toyota) controlled descent on perceived steeper than normal and adverse(rocky, bumpy, icy, etc) terrain, and to be applied in Low/Low. As such I'm not sure it fits as a solution or alternative for the conditions being described in this thread, but as someone who has tried it for its intended purpose, it actually works very well. And yeah, the ABS makes a hell of a racket; much like when ATRAC engages.

PS: [MENTION=49728]ajwalks[/MENTION] for info on DAC, you need look no further than YouTube.