My car slows when going downhill ( auto trans )

[Cd]

Why would my car slow down when going down hill and in gear ? The car is a 1993 Civic DX automatic.

I have to constantly give the car gas to remain the speed limit while going down slopes and hills.

When i put the car in neutral and coast ( engine ON ) the car goes from around 42 mph at the crest of the hill, to over 50 at the bottom, so the car does not have dragging brakes.

[Daox]

The engine is being spun (pumping/compressing air) by the momentum of the car. If you put it in neutral the engine just idles and the car can coast.

[Miller88]

Wish I had that problem. My manual transmission focus doesn't hold itself back on hills at all!

[PaleMelanesian]

Exactly what Daox said. I have to do that all the time in the Odyssey. It will gain you a nice chunk of mpg too.

[mcrews]

ditto what Daox said.
THIS is what you want to happen!!!
probably worth 7-10% on a trip.
when I first joined here, I was only doing engine ON neutral coasting on my 2002 Infiniti Q45. (epa 22 hwy) I would consistantly get 27mpg on a 5 hour trip thru 2 diferent mountian ranges.

[dwarfnebula]

Many American made automatics allow you to coast in gear pretty effectively, they use a one way clutch (called a sprag) mostly because it allows for easier synchronization of engagement/disengagement in shifts. The side effect is that you can coast in gear, lots of GM transmissions won't engine brake at all in high gear. This is less the standard now than it used to be, in the early days all of them were like this.

Honda autos of that era are pretty unique. They're configured much like a manual transmission and they always provide engine braking. Other autos may be built to give engine braking, but every other torque converter equipped auto I know of uses planetary gearsets.

Drop it in neutral going down hills unless you're going down some crazy steep hill. And don't shut the motor off to coast with an auto as a general rule. Most don't circulate lubricating oil unless the engine driven oil pump is spinning.

[user removed]

If you are coasting at 50 MPH and your idling engine is consuming .20 gallons per hour, then you are getting 50X5=250 MPG during that coasting period with the engine idling.
I do it all the time, especially on slight downhill grades which are typical around here.
Last 98 mile trip in my Fiesta the gauge was reading 53.9 MPG when I got home (slightly optomistic).

regards
Mech

[Occasionally6]

Originally Posted by dwarfnebula

Many American made automatics allow you to coast in gear pretty effectively, they use a one way clutch (called a sprag) mostly because it allows for easier synchronization of engagement/disengagement in shifts. The side effect is that you can coast in gear, lots of GM transmissions won't engine brake at all in high gear. This is less the standard now than it used to be, in the early days all of them were like this.

Do you mean in the trans. or in the torque convertor?

There is a stator and associated one way clutch in the torque convertor that is used to redirect the fluid velocity from the drive to the driven side of the TC, thus improving the efficiency of the drive across a range of speed difference between the engine and the trans. input shaft. The presence or absence of the stator defines the difference between a simple fluid coupling and a torque convertor.

There is also, almost universally these days, a lock up function where hydraulic pressure is use to clamp a clutch (Torque Convertor Clutch) inside the convertor and provide direct drive when slip is undesirable.

I suspect that what is happening is the TCC is being locked up creating a solid connection between the engine and trans. such as would be the case with a manual trans.. It might be educational to coast down to a speed at which the TCC disengages and feel the drag of the engine go away as the TCC is allowed to slip again.

[dwarfnebula]

Originally Posted by Occasionally6

Do you mean in the trans. or in the torque convertor?

There is a stator and associated one way clutch in the torque convertor that is used to redirect the fluid velocity from the drive to the driven side of the TC, thus improving the efficiency of the drive across a range of speed difference between the engine and the trans. input shaft. The presence or absence of the stator defines the difference between a simple fluid coupling and a torque convertor.

There is also, almost universally these days, a lock up function where hydraulic pressure is use to clamp a clutch (Torque Convertor Clutch) inside the convertor and provide direct drive when slip is undesirable.

I suspect that what is happening is the TCC is being locked up creating a solid connection between the engine and trans. such as would be the case with a manual trans.. It might be educational to coast down to a speed at which the TCC disengages and feel the drag of the engine go away as the TCC is allowed to slip again.

I do mean in the transmission, not in the converter. There is also a sprag for the torque converter stator. The torque converter, even backwards doesn't slip very much, say 10% or so. GM transmissions are big on this arrangement, TH350s, TH400s, 700R4/4L60Es, 4T60E's, 4T80E's, among others all freewheel nicely. You can watch the tach drop when you let off the gas and the thing will just coast like it's in neutral. It's nice sometimes, little hard on brakes in the mountains for your average driver though.

As per Wikipedia (which is of course always accurate)
"A sprag clutch is used in most older automatic transmissions and some newer ones for shifts which require the synchronized engagement of one clutch with the disengagement of another. Using an overrunning clutch instead of a hydraulically actuated one makes this synchronization automatic. The sprag clutch simply "lets go" once the reaction force it provides is no longer needed. In a Simpson gearset, common to many automatics, this happens on the 1-2 shift, and reverses on the 2-1 downshift. The 2-3 shift is done by engaging a single clutch, and nothing is released. Some newer electronically controlled transmissions make "clutch to clutch" shifts, without any sprags.
This can also be used exclusively in first gear (transmission shift lever in D, but auto valve body or management selecting 1st) on some autos. That way it will automatically provide forward drive, but will not provide any engine braking. This is done not so much to avoid engine braking per se, but rather to allow a low throttle opening 2-1 downshift as a car decelerates, to avoid a loud (and potentially abrupt) and unnerving jolt as a result of the downshift. On transmissions so equipped, manual selection of 1st gear typically engages an additional band that grips the same section as the one way clutch would engage, and thus allows for engine braking."

One of the original selling points of the "Hondamatic" transmissions was their strong engine braking. They are meant to do it, torque converter lockup or no.