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Old 05-14-2011
hayduke.klr07's Avatar
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Engine Braking with an Automatic

I recently purchased a 2006 Fx4 level ii, 4.0litre automatic. 28.5K miles on it. got a good deal and like the truck except for this one thing...
When i put it in first gear to decend a hill why does the gear not hold me back? It almost seems like it is in neutral. I would think that it is a mechanical defect but my work truck, an '05 4.0 auto does the same thing.
I have been driving a '93 4.0 5speed forever. You could drop that thing into low four without locking in hubs and idle up or down most anything. sold it now i am in this truck. 99% of the time it is no big deal but that 1% can be important.

Here is the example: Just on the Moki dugway in southeastern Utah: http://www.google.com/search?q=moki+...w=1252&bih=589

Put it in 1st to hold us back and it would roll pretty freely down the hill and it seemed that the rpms wouldn't really react as well. It wasn't scary with just the truck, but if i were pulling a small trailer it would scare the crap out of me. I have tried putting it in 4low to see how it would react and it still rolled pretty freely down a hill. needing 4wheel in the woods and riding my brakes seems pretty silly to me.

any thoughts out there?

Last edited by hayduke.klr07; 05-14-2011 at 03:38 PM.
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Old 05-14-2011
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I didn't watch the video, but if you're going too fast and throw it into 1st, it's not gonna shift into 1st. The RPMs need to be in a certain zone in order for it to shift into 1st.
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Old 05-14-2011
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and you need to be under a certain speed
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Old 05-15-2011
hayduke.klr07's Avatar
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I thought about that too. I have tried it at a stop as well.

Again if you let out the clutch on a manual the RPMs climb. Not so with this transmission? I have used the OD buttom to bring up the rpms as well dropping into 2nd at higher speeds and the RPMs climb. Low just doesn't seem like a true low.
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Old 05-15-2011
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Manual trans = mechanical / hard coupling
Auto trans = fluid / soft coupling
An auto transmission is connected to the engine with what is basicly a fluid connection. When in gear they do not have a solid mechanical connection to the rest of the drivetrain that a manual does.
Hence , little or no engine braking capacity .
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Old 05-15-2011
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OTRtech, don't forget the torque converter clutch. When it locks, there is a solid link through the transmission to the rest of the drivetrain. Power flows from the crankshaft, to the flexplate flywheel, to the torque converter, then to the input shaft and trans pump. With the trans locked into a gear via a clutch pack or band, it's a fairly solid link.

This is why when the TCC fails in the engaged position, the engine will stall if you stop the vehicle.
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Old 05-15-2011
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My truck does the same thing OP, if I switch down into first while descending a hill, say at 40 mph, it won't automatically go down into first gear. It will first switch over drive off, then the rpms will climb and the truck will slow a little. When it slows down enough it will then automatically switch into 4, then the rpms climb again and the process continues until it finally reaches first gear. However, usually it won't ever get to first gear by its own "dynamic motor braking". With the addition of using the brakes as well as shifting/coasting to lower speeds, it will eventually switch in to first.

Another note, it seems to NEVER switch down into first gear above about 30mph, where at that point the rpms would be around 4400k. This is a safety feature so the motor doesn't get damaged by incorrectly downshifting. Its built into the computer to alleviate any excesssive motor/tranny damage.

Long story short, its normal lol.
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