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-   -   When 'coasting', 8 speed noticeably drags (http://www.ramforumz.com/showthread.php?t=154287)

skytop 09-30-2013 09:54 AM

When 'coasting', 8 speed noticeably drags
 
I notice that when I remove my foot from the accelerator pedal and 'coast' as I approach a turn, the 8 speed transmission (smoothly) goes into a lower gear which noticeably drags speed down. There is no usual coasting as with all other modern automatics I have driven.
Anyone else recognize this 8 speed characteristic as well?

Arth 09-30-2013 10:23 AM

Honestly it sure seems like a way to save brake life. I have seen this on a few other threads.

It is strange for a RWD to do it though. My wife's FWD 13 Malibu does this.

GTyankee 09-30-2013 10:38 AM

I remember reading about all of the things that happen when you take your foot off the Go pedal
In a couple years, i half expect to see all new vehicles coming to a stop, using some sort of accident avoidance system technology.
Like if a driver is unresponsive, the vehicle will try to alert you to do something & if nothing is done at that time, the vehicle will stop

gwilburn 09-30-2013 11:38 AM

Quote:

Originally Posted by skytop (Post 1210920)
I notice that when I remove my foot from the accelerator pedal and 'coast' as I approach a turn, the 8 speed transmission (smoothly) goes into a lower gear which noticeably drags speed down. There is no usual coasting as with all other modern automatics I have driven.
Anyone else recognize this 8 speed characteristic as well?

I have not noticed this yet... I really, really like the way it downshifts on steep hills... mine seems to do this when I let off accel. only when on a downhill... drops another gear or two if truck accelerates on it's own or if I touch the brake.

Droptop87 09-30-2013 03:05 PM

I have noticed this a lil bit too and I think maybe its just where there are more gears closer together it seems like its helping to slow it down more? Now if the gas gauge would slow down...

anothernewb 09-30-2013 04:18 PM

I've noticed this too. To take a total stab in the dark on it. perhaps it's intended design based around maximizing city gas mileage. 1. it helps braking. 2. it is in a lower gear per unit speed and responds to the alternating of gas-brake-gas-brake in stop and go traffic better?

again my .02 from observations. I find my truck doesn't have to downshift back and forth in stop and go. keeping in one or 2 gears to keep the torque up certainly affects acceleration.

JCC11 09-30-2013 04:23 PM

Quote:

Originally Posted by skytop (Post 1210920)
I notice that when I remove my foot from the accelerator pedal and 'coast' as I approach a turn, the 8 speed transmission (smoothly) goes into a lower gear which noticeably drags speed down. There is no usual coasting as with all other modern automatics I have driven.
Anyone else recognize this 8 speed characteristic as well?



Yes, all of the 8 speeds do this and it is absolutely normal. This is a characteristic of a high quality performance oriented trans. You will feel the same thing happen in a modern sports car (think BMW and Porsche, which use this same transmission in some models).

The transmission will not up shift while coasting, which would allow spped to increase without your input, as readily as less sophisticated units. This helps control your speed and allows the transmission to downshift early while you coast to a slower speed (engine compression braking).

If you do not want the feel of the engine compression (or as you described "drag") while coasting, just give an ever so slight pressure on the accelerator. The "drag' of the engine compression will go away, and the trans may even switch to the next sequential gear if you are coasting downhill.

This transmission is one of the greatest features of our RAM. It allows it to work like a truck, but perform like a sports car (in terms of shifting personality).

skytop 09-30-2013 05:27 PM

Quote:

Originally Posted by Arth (Post 1210938)
Honestly it sure seems like a way to save brake life. I have seen this on a few other threads.

It is strange for a RWD to do it though. My wife's FWD 13 Malibu does this.


Not at all. Just coming home from work earlier, I was making a left turn onto the main avenue. I was going about 30 mph and took my foot off the gas to carefully make the turn, I immediately felt the transmission dragging down the speed of the car even though I had no intention of slowing down but rather accelerating once I was onto the main avenue. Gas has nothing to do with it. I think it is a flaw in the transmission firmware.

JCC11: I have a Mercedes with its ZF 7 speed transmission. It is a high quality, hi performance, hi tech transmission and it coasts perfectly when your foot lifts off the gas pedal. There is no drag as the Chrysler tranny exhibits. I find it unpleasant in the Ram.

Gantman 09-30-2013 05:43 PM

Well Skytop, you really have to understand the term, Engine Braking, as this may have an effect along with vehicle speed while coasting. Engine Braking, is caused when the throttle is closed while coasting, which greatly restricts air flow to the intake manifold. Because of this, the engine has to work against the restricted air flow thus causing the brake effect. It does it on the Hemi with the 545/65RFE as well, as I like to use it while coasting downhill. Technology I tell ya, it's too Kewl.

TransEngineer 10-01-2013 07:58 AM

I suspect that what you're noticing is Decel Fuel Shut-Off (DFSO), which cuts all fuel to the engine while you're coasting. I don't know for sure whether the 8-speed uses DFSO, but I would think (since it's aimed at increasing your fuel economy) that it does.

Since the engine needs to be kept turning (even when fuel is shut off, to avoid bumps / jerks / etc. when you step back into the gas), the Torque Converter Clutch (TCC) is kept locked during DFSO. In higher gears, as you slow down, the engine speed would fall below what is needed for a smooth "re-start," so that is why the transmission downshifts as you slow down. It is just keeping the engine speed within a certain range to ensure good response when fueling resumes.

If you don't like the "draggy" feel when coasting (I personally don't like it either), you can shift the trans to Neutral (while coasting), which should give you a "normal" smooth coastdown. As long as the engine remains running (so that the trans has lube pressure), coasting in Neutral should not harm the transmission. But don't coast in Neutral AND turn the engine off; that is NOT a good idea.

Now as noted, I can't say for SURE that this (DFSO) is what's going on, but that would be my bet...


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