Engine braking in an automatic???? - JeepForum.com

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post #1 of 25 Old 05-09-2013, 08:28 PM Thread Starter
YellowJeepGuy94
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Engine braking in an automatic????

Ok ok so I know this is a noob question but bare with me. When going down a steep hill you want to brake using the engine because you have more control then just riding a brake pedal. I know in a manual you can engine brake using 4 low and 1 gear. Does the automatic have the same effect if I put my shifter in 1st gear and use 4 lo? Thanks in advance. Happy trails

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post #2 of 25 Old 05-10-2013, 07:59 AM
222Doc
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yes. going to your lowest gear slows you down. the lower your axle gears and the Tcase gears or the Trans gears the slower that 1st gear is.

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post #3 of 25 Old 05-10-2013, 09:15 AM
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You can engine brake with either.

All about that unibody life.
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post #4 of 25 Old 05-10-2013, 05:41 PM
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Is this "steep hill" pavement or dirt trail? For the sake of your drive-train I hope it is on the trail.
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post #5 of 25 Old 05-10-2013, 05:52 PM
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Quote:
Originally Posted by flying2275 View Post
Is this "steep hill" pavement or dirt trail? For the sake of your drive-train I hope it is on the trail.
And why is that? Do you think your driveline is being excessively strained going down steep hills on the engine brake?

Guess what.. It's not

Drivelines are over-engineered to handle the extreme stresses that every day driving puts on your vehicle. Whether it's accelerating to top speed wide open throttle, or crawling up your driveway. Modern vehicles are even equipped with a newer feature called DAC or "Downhill Assist Control", which basically is an automatic only feature. It works by downshifting the transmission a gear when you apply the brakes to aid in downhill braking. This reduces wear and tear on your brakes as well as your foot.

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post #6 of 25 Old 05-10-2013, 11:27 PM
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Quote:
Originally Posted by Xpress View Post
And why is that? Do you think your driveline is being excessively strained going down steep hills on the engine brake?

Guess what.. It's not

Drivelines are over-engineered to handle the extreme stresses that every day driving puts on your vehicle. Whether it's accelerating to top speed wide open throttle, or crawling up your driveway. Modern vehicles are even equipped with a newer feature called DAC or "Downhill Assist Control", which basically is an automatic only feature. It works by downshifting the transmission a gear when you apply the brakes to aid in downhill braking. This reduces wear and tear on your brakes as well as your foot.
You know, lots of people dont know this.

My dad is one for example; saying that you should NEVER use the entire RPM range of a vehicle; that at high RPMs (still below redline) you run the risk of blowing the engine. If the engine was designed to run at 5000RPM; its fine to run at that RPM.

If it wasnt safe, they wouldve lowered the redline below that higher RPM range, right?
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post #7 of 25 Old 05-11-2013, 06:05 AM
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Engine braking will not harm the vehicle beyond a little extra fuel consumption (sometimes). However on a Jeep, only use 4 wheel on loose surfaces, not pavement.

BTW using 4 low in first gear is a much better way to control descent on loose surfaces than using brakes, as it equalizes the loads and makes it very unlikely for 1 wheel to lock up. (Even ABS brakes are not very good at low speed tricky control situations).

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post #8 of 25 Old 05-11-2013, 08:03 AM
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Actually, it won't increase fuel consumption at all. Modern FI engines are designed to cut fuel supply above idle speed with no throttle applied. So in an engine braking situation the engine is only being turned by the momentum of the vehicle.
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post #9 of 25 Old 05-11-2013, 09:07 AM
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Quote:
Originally Posted by Maverickxeo View Post
You know, lots of people dont know this.

My dad is one for example; saying that you should NEVER use the entire RPM range of a vehicle; that at high RPMs (still below redline) you run the risk of blowing the engine. If the engine was designed to run at 5000RPM; its fine to run at that RPM.

If it wasnt safe, they wouldve lowered the redline below that higher RPM range, right?
Yes again. Worst case. A "run away". on paved roads IF you are going down a hill that is so steep or the load so heavy. That even in the lowest gear it starts to "run away". You are in deep *****. Brakes will fail in time and now you are in a death run. Most highways have escape areas to run away into they are filled with deep loose gravel.

Off road is not the same. going down a steep perhaps lose trail. You will break tracking before the motor over revs. BUT in jeep if this happens the issue is the rear of Jeep will try to pass the front. If you let this happen you will roll. So if you start to feel the a$$ pass me feeling you need to give it gas enought to keep it going straight. this can be a bit of butt pucker time.

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post #10 of 25 Old 05-11-2013, 09:39 AM
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If you have an automatic transmission with overdrive (OD), simply change the transmission gear selector out of OD, or press your OD OFF switch. Presto, you have engine braking using 2wd or 4x4, for on pavement or off-road. Selecting a lower gear off-road will give you more compression braking.

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post #11 of 25 Old 05-11-2013, 10:15 AM Thread Starter
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Quote:
Originally Posted by flying2275
Is this "steep hill" pavement or dirt trail? For the sake of your drive-train I hope it is on the trail.
Definitely trail
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post #12 of 25 Old 05-11-2013, 06:54 PM
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Quote:
Originally Posted by Xpress View Post
And why is that? Do you think your driveline is being excessively strained going down steep hills on the engine brake?

Guess what.. It's not

Drivelines are over-engineered to handle the extreme stresses that every day driving puts on your vehicle. Whether it's accelerating to top speed wide open throttle, or crawling up your driveway. Modern vehicles are even equipped with a newer feature called DAC or "Downhill Assist Control", which basically is an automatic only feature. It works by downshifting the transmission a gear when you apply the brakes to aid in downhill braking. This reduces wear and tear on your brakes as well as your foot.

I do think his drive-train will be excessively strained if he is shifting into 4L and 1st and while on pavement going downhill. This is why I posed the question if he was doing this while on pavement or on the trail.

I do agree with you than on the trail nothing will happen as long as he keeps an eye on his RPM's.
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post #13 of 25 Old 05-12-2013, 07:55 AM
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my question is why? is it really that out of control during descents?
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post #14 of 25 Old 05-12-2013, 08:41 AM
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Quote:
Originally Posted by flying2275 View Post
I do think his drive-train will be excessively strained if he is shifting into 4L and 1st and while on pavement going downhill......
Shifting into 4lo from 4hi or 2wd requires stopping the Jeep almost completely. Thus, your concerns are unfounded.

Modern computer controlled transmission will remain in a higher gear if the driver is attempting to downshift, and the road speed is too great for a lower gear.

Off-road you should use lower gears to utilize the extra control and traction available with engine braking.

On pavement, engine braking is only called for on highways with steep mountain passes and when towing heavy loads.

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Last edited by CJ7-Tim; 05-12-2013 at 10:51 AM. Reason: added "almost" for the nit pickers
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post #15 of 25 Old 05-12-2013, 09:28 AM
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Quote:
Originally Posted by CJ7-Tim View Post
Shifting into 4lo from 4hi or 2wd requires stopping the Jeep completely. Thus, your concerns are unfounded.
No.

Quote:
4H to 4L or 4L to 4H
With the vehicle rolling at 2 to 3 mph (3 to 5 km/h), shift an automatic transmission to N (Neutral) or depress the clutch pedal on a manual transmission. While the vehicle is coasting at 2 to 3 mph (3 to 5 km/h), shift the transfer case lever firmly to the desired position. Do not pause in transfer case N (Neutral).
On the topic: Engine braking with an automatic transmission is fine. Note that engine braking with the 42RLE automatic with heavy loads puts the transmission fluid way into over heating. A transmission cooler is required in those cases.

Quote:
Originally Posted by Ironhead View Post
my question is why? is it really that out of control during descents?
Brake pads and rotors covered in slippery mud tend to make it much harder to stop efficiently with the brakes.
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