Is it safe to down-shift auto-trany??

Brakes are cheaper than transmissions. Question, how much extra gas does downshifting use?

You should only downhift if you are going up or going down a steep grade. Downshifting just to stop under normal driving is a waste and putting extra strain on the tranny and engine.

That's nonsense. Engine braking causes no more strain on the engine then the same amount of load under acceleration. By that I mean if you take the amount of braking "sensation" you can get by the engine and turn that around into an equal acceleration "sensation" the load is the same. Looking at it like that, the engine load under de-cel is equal to a very light foot on the throttle leaving a stop light. Same goes for the transmission. In fact there are provisions in transmissions specifically to accommodate engine braking. Not familiar with internals on Explorer trans, but all older GM trans when run in " drive", run in 1st and 2nd gear through a one way clutch, meaning they free wheel in deceleration (this improves upshift times as no clutch or band has to disconnect to move to the next upward gear. When you manually select 2nd gear a band is applied to give you engine braking. This is all by design. About the only thing that can be said as a neg for downshifting is that each time a gear change occurs a clutch pack or band has to engage or dis-engage. It is this action that causes wear and heat in the clutch or band. Once a band or clutch is applied or released there is no movement of one component relative to another and so no wear occurs. So, if you're increasing the number of times clutches and bands apply and release you are accelerating the wear in these components. Having said that though. transmissions seldom fail from worn out clutches or bands like this. It is primarily internal leakage that results in their failure, seals on the pistons that apply the clutches and bands or someone getting stuck and continually going back and forth between forward and reverse that burns out a clutch pack and/or overheats the trans. Steve

"SizzleMP" wrote in message news: snipped-for-privacy@mb-m11.aol.com...

Safe? If you mean for the tranny, yes. If you mean, is it a safe method of controlling your speed, then my opinion is this: It's better to use the brakes. This is what brakes are designed for, and using tyhe brakes means your foot is already *on* the brake pedal. This can be critical if the idjit in front of you decides to stop faster than your tranny can provide; the extra reaction/foot movement time can be critical.

Overall, the saved wear on the brakes is not going to be noticed, and the tranny doesn't need the extra wear that the clutchpacks will get doing this.

: >I typically down-shift when approaching traffic lights, or when exiting the : >freeway, and thereby use "engine braking" to aid in slowing down. : >

: >Will the transmission be damaged if I regulary down-shift??? : >

: >Thanks, : >Mike : >

: Safe? If you mean for the tranny, yes. : If you mean, is it a safe method of controlling your speed, then my : opinion is this: It's better to use the brakes. : This is what brakes are designed for, and using tyhe brakes means your : foot is already *on* the brake pedal. This can be critical if the : idjit in front of you decides to stop faster than your tranny can : provide; the extra reaction/foot movement time can be critical. : : Overall, the saved wear on the brakes is not going to be noticed, and : the tranny doesn't need the extra wear that the clutchpacks will get : doing this. : : -- : Bill Funk : replace "g" with "a"

Downshifting out of an OD gear is handy when one is descending a steep grade or when one is ascending a grade and helps to keep the tranny from 'hunting' between the OD gear and the next 'lower' gear...

YMMV

Rick

I doubt it will be "damaged" but I suspect it will experience more wear. Will it be enough to matter? I don't know. I do know that I'd much rather replace my brakes then have my transmission rebuilt. Downshifting as you describe seems rather pointless to me but the way I accelerate seems pointless to others so don't take it as a criticism.

-- Elbridge Gerry, of Massachusetts:

"What, sir, is the use of militia? It is to prevent the establishment of a standing army, the bane of liberty. . . Whenever Government means to invade the rights and liberties of the people, they always attempt to destroy the militia, in order to raise a standing army upon its ruins." -- Debate, U.S. House of Representatives, August 17, 1789

I'll echo the school of thought that says brakes are cheaper than transmissions. Also, I would think the rear brakes would be more susceptable to locking up if it were wet or slippery during braking & downshifting.

Mike

At last, somebody agrees with me :-)

Another important factor is you don't display brake lights to the guy behind you when you slow down via downshift. This could be bad for you and your bumpers.

From the OP:"I typically down-shift when approaching traffic lights, or when exiting the freeway, and thereby use "engine braking" to aid in slowing down."

Yes, I take the tranny out of DO sometimes on downgrades; it's a recommended practice. I don't find this necessary on upgrades, though, as neither our 92 Sport nor our 99 Expedition will hunt going uphill. Neither did any of our other OD equipped autos. But that's us.

Well, the force may not be too great, but you have just REVERSED the normal flow of force through the engine and the transmission.

While they are designed to handle that, to a degree, it isn't something you should do on a whim.

Actually, I can't believe we're all taking that original poster seriously! Have you heard of a troll?

Well, Alan, I'm not a troll. I've posted here numerous times in the past, and I've even been able to answer a few questions which have helped those who posted them.

I have an old '91 EB with a recently re-built trany and an old habit of down-shifting left over from many years of owning a standard shift 5-speed sport car. Several months after the re-built trany was installed I began to notice a very slight noise coming from the trany as it drops into OD during normal driving. On a hunch, I stopped down shifting, and the noise has slowly faded.

Is this pure coincidence, or is there some connection which I'm un-aware of. This is the reason for my post.

Mike

Everytime auto trannies shift, they wear. Whether the shift is up or down, they wear. Auto makers recommend that you leave a modern auto OD tranny in OD unless the tranny starts to 'hunt', in which case you take it out of OD.

That said, on long downhills, downshifting can save wear on the brakes, while helping you to maintain a safe speed. The single downshift isn't causing much wear, and the engine braking saves wear on the brakes. *In theory*, the other drivers will be able to understand what's going on. In traffic, though, another consideration comes into play; many drivers really aren't paying much attention to what's going on around them, and will actually miss the fact that the vehicle in front of them is slowing down without those bright red lights to bring it to their attention. In this situation, I use the brakes instead of downshifting; it helps the other drivers keep from buying the back of my vehicle. It also reduces the wear on the tranny.

Without actually knowing what's going on in *your* tranny, it gets hard to diagnose it. General rules tend to break down when we attempt to apply them to individual units. (This is one reason why Jim's replies can be rather long; he does a good job of trying to cover all bases.)

I have two thoughts on this subject. First, remember the old saying, "brakes are cheaper to replace than transmissions". Secondly, I too am of the old school and frequently downshift, depending on traffic, while coming to a stop, but only when I am driving a manual transmission. For an auto trans, I usually leave the transmission in 2 while in the city in congested traffic (where speed does not get above 40 mph). This results in two benefits. One, the transmission starts in 2 and never shifts out of 2, resulting in less wear. Two, you get some engine braking, which results in less brake wear. The amount of engine braking (or compression braking) does not seem to be enough so that I am in danger of being rear ended by another driver, but Bill Funk has a point!

The only disadvantage to leaving it in 2 seems to be somewhat of a loss in power or acceleration due to starting in 2 instead of first gear, and also perhaps some increase in fuel use. However my rpm's never get above 2700 while leaving it in 2 in congested traffic, so I think the increased fuel use is minimal.

Steve

Another down side to leaving it in 2nd is increased trans temp. That sluggish feel when starting off in second gear means the torque converter has to do much more of that, convert torque. This is where almost all of the heat in an auto trans is generated. Once the bands are tightened or the clutches applied there is no slippage and thus no heat generated. Heat is the number 1 cause of trans failure. Excessive heat makes the rubber parts brittle, alters the friction co-efficient of the fluid and it's lubricating qualities. If the manufacurer thought he could get away with delivering a vehicle that took off in 2nd gear that's what they would have done. There are 3 or

I guess I'll jump in with another comment. Steve sorta hit close to it. For extended driving in very slow and go traffic (probably 15 minutes with slowest speed 5-10 MPH) I have been leaving the trans in 2 or 3. This gives me better control with the throttle, i.e. not having to go brake/throttle/brake/... for much of my commute. I mean this thing upshifts to third so fast anyway under light load that I figure I might as well leave it there.

That's all true, but the original poster was asking about his alleged habit of manually downshifting it whenever he was coming to a red light, or a stop sign.

Jeez!

Um, yes... That's why I said, "In traffic, though, another consideration comes into play; many drivers really aren't paying much attention to what's going on around them, and will actually miss the fact that the vehicle in front of them is slowing down without those bright red lights to bring it to their attention. In this situation, I use the brakes instead of downshifting; it helps the other drivers keep from buying the back of my vehicle. It also reduces the wear on the tranny."

Too many posts to read them all.... yes, it's 'safe' to use the transmission as a grade retarder providing the road surface isn't going to cause troubles. Depending on load and surface conditions, engine braking could cause the rear wheels to slide rather than roll.

As far as using engine braking to reduce speed in normal driving..... 'forcing' components to apply will accelerate wear. Much wiser is lifing early..... if there's a stop light or some other impediment to traffic flow, better fuel mileage will be realize from lifting early, light brake application and recover less speed than if we start from still.

All things being equal, we may not even notice any extra wear from the forced downshift but there is so little to be gained (real or imagined) that it doesn't make good sense. Though I have performed many manual forced downshifts in my long and illustrious life ( nobody else going to blow my horn), there has rarely been any requirement for it. When in doubt, read the owners manual.....

Probably not.

However, make sure to touch your brakes lightly to show other traffic (behind you) that you are slowing down.

Also, avoid downshifting in slippery conditions......you can always control brake pressure or just lift off the brakes if you start to slide.....but when you downshift to slow down you give up a certain amount of control.