Manually downshifting a Toyota automatic transmission harmful?

[supton]

Why - unless there is a situation that warrants it let the transmission do what it's programmed to do with respect to upshifts and down shifts.

In areas with "real" hills it often can be advantageous if not outright necessary to force engine braking while descending. While the need may be slowly on the wane, what with automakers adding yet more smart programming, it still applies to a good deal of vehicles that are still on the road, years after manufacturer--and not getting updates to their original transmission programming.

Plus, some people like to think ahead and would like a bit more input to the car operation than others. If I step on the gas, get into an intersection, let off and make a turn, then need to get on it... there's no need for the transmission to upshift, only to have to downshift. This happened a lot on my commute, in one spot, and it kinda bugged me. The transmission does not have eyes, much less can read my mind. It does not know that, if I were driving a manual transmission, that I'd never upshift in this spot, as I will need to be on it in a moment.

And some cars are really awful with their lag, making up their minds, figuring out what gear to be in. Some are faster, some are smarter, and some should be in the junkyard.

 

[D60]

On a forum of "gearheads" I'm simply shocked by how many here think it's bad to manually shift an automatic.

I've been in the Colorado mountains all my life and not only is it considered best practice, it's mandatory if you want to be a safe driver.

I've downshifted every automatic I've ever owned as I saw fit.....although that was mostly domestic trucks.

Some OEMs even simply updated programming so the same trans would downshift to hold speed in cruise like the 4R70. TTBOMK bubble bodies did not down shift but beginning around '04 to '05 with the new body style they did. I don't think any hard parts changed specifically to accommodate the new programming but perhaps @clinebarger would be kind enough to clarify

The 4R70 in my '07 F150 downshifts with cruise to hold speed descending and it's got 231k and counting.

People may consider brakes inexpensive but once they start smoking, they stop working. Compression braking is a useful tool, not an evil thing.

 

[WylieCoyote]

It's pretty much the same situation as downshifting a manual to slow down, versus using your brakes. Every time there's a downshift, clutches have to slip. This is wear. Not excessive wear, but every clutch, be it in an automatic or manual, has a certain number of slips in it before it's worn out. Every time the transmission shifts, you're using a slip. Think of it that way. I wouldn't advise downshifting to stop in everyday situations, but I would advise downshifting when appropriate when you're in a hilly area just to keep the transmission from "hunting" and keep from burning your brakes. Your transmission reacts to what's going on right now, whereas you can see down the road and anticipate what you're going to need. Nothing wrong with helping it out a little bit.

 

[Greasymechtech]

Most want to shift their automatics to play speedracer, like they have a clue.

Many are too incompetent as drivers and shouldn't be given anything more to do when driving. Leave it in drive.

Yes, on a higher mileage transmission that has already shifted several million times, I would not be a wannabe manual driver. Every shift is wear. And eventually, you'll just blame the transmission failure on age/mileage and not on driver shenanigans.

Since the OP didn't mention much about mountains, his locations, condition of transmission, maintenance history, traffic patterns,.... I WOULD JUST LEAVE IT IN DRIVE. The car in most situations is more than capable and usually smarter than most drivers out there.

For those that come down mountains and have experience with their vehicle, do as you want. Most of my automatics were pretty smart and held gears, and even downshifted and declines.

 

[Rmay635703]

Automatics tend to only downshift near the floor. Which also throws you into AFR enrichment and likely into open loop.

Those saying wear, etc apparently overlook that downshifting at full load is likely the worst for wear.

If your going to need full power soon downshift then hammer, ought to shave a second off also.

Many times if you downshift early you don’t need to hammer and can stay out of AFR enrichment which nets better economy.

 

[bobdoo]

"
like they have a clue.

Many are too incompetent "

I'm shocked that you deign to even read our words... I'd think you'd be afraid it would decrease your IQ...

 

[andrew_j]

Drive it how you please . Who knows if downshifting will make a difference if the transmission is ready to fall over the cliff or far from it.

I think you already realize a transmission repair is few thousand dollars as opposed to brakes which run well under $1000 if not $500.

 

[Greasymechtech]

"
like they have a clue.

Many are too incompetent "

I'm shocked that you deign to even read our words... I'd think you'd be afraid it would decrease your IQ...

Quit being a troll

 

[slybunda]

Leave it in D. Use the brakes, unless transmissions are cheaper than brake pads where you are.

 

[Rmay635703]

Leave it in D. Use the brakes, unless transmissions are cheaper than brake pads where you are.

Photos of what happens any time an automatic transmission downshifts

It’s amazing anyone makes it to the end of their block with an automatic transmission

It’s why tractors don’t have automatics

 

[PontiacHO]

Using the engine to slow the vehicle creates additional wear. I’ve never liked my engine(s) attempting to “breathe” through the crankcase with the throttle plates closed or close to being closed. Think about there is still an intake stroke…

 

[supton]

Using the engine to slow the vehicle creates additional wear.

So we should avoid both deceleration and acceleration, since both are causes of wear?

Seems to me, we each have differing levels of what is acceptable causes of wear.

 

[Shel_B]

The only reason to downshift is for descending long hills that would overheat the brakes, or brake fluid. This is the "saving the brakes" you hear about.

My dad had a 2005-ish Matrix AWD wagon. It ate a transmission by his using manual 2nd gear to descend, and properly control his car, down a 25 mph hill he lived on in Vermont. This is a known weakness of that particular transmission.

Downshifting a camry on interstate off-ramps is boy-racer stupidity.

Or when driving in hilly, mountainous country one might downshift to avoid lugging the engine. If you let the engine choose the shift points, all too often the trans will shift in and out of gears, which causes more wear than, for example, downshifting into 3rd or 4th and leaving it there. I've driven my Camry through the mountains for thousands of miles, and using the shifter in that way is a smart and good option.

Toyota included the sport mode in their setup for people to use in an appropriate manner. Remember, there's really little, if any, difference to the trans if the driver chooses the shift point or the trans makes the choice.

 

[clinebarger]

Some OEMs even simply updated programming so the same trans would downshift to hold speed in cruise like the 4R70. TTBOMK bubble bodies did not down shift but beginning around '04 to '05 with the new body style they did. I don't think any hard parts changed specifically to accommodate the new programming but perhaps @clinebarger would be kind enough to clarify

The 4R70 in my '07 F150 downshifts with cruise to hold speed descending and it's got 231k and counting.

A Input Speed Sensor was added, That way the PCM could reliably-in real time detect clutch slippage & increase Line Pressure accordingly.

As an example.....47RH, 47RE, And early 48RE units put behind Cummins engine in Dodge Truck used a Throttle Valve Cable to control Line Pressure & therefore could not be used with a Exhaust Brake unless you added a Servo/Motor to mechanically actuate the TV Lever when the exhaust brake was activated. Dodge was denying transmission warranty on auto trucks with brakes.
Later 48RE's used a Electric Servo to control the TV Lever.

GM 700R4 & 200-4R units also used Throttle Valves, To get around the lack of Line Pressure when downshifted to L2 or L1, A second Boost Valve was employed to bump Line in L1, L2 & Reverse.

Basically.....Nothing wrong with downshifting, Long as there's adequate line pressure to keep the frictions from slipping.

 

[2strokeNorthstar]

My CX-5 will *automatically* downshift when going down hills, and exceeding the cruise control set speed.
I'm sure Mazda knows a hell of a lot more than internet forum posters.

I had a Ford Flex rental and it did that. I thought something was wrong the first time. It's an odd strategy

 

[PimTac]

Automatics tend to only downshift near the floor. Which also throws you into AFR enrichment and likely into open loop.

Those saying wear, etc apparently overlook that downshifting at full load is likely the worst for wear.

If your going to need full power soon downshift then hammer, ought to shave a second off also.

Many times if you downshift early you don’t need to hammer and can stay out of AFR enrichment which nets better economy.

A modern computerized automatic will adjust for the conditions. It will know how steep the hill is that you are on as an example.

I like how the SkyActiv automatic downshifts even when approaching a stop. I don’t get that dead reaction that I would on older vehicles and have to mash the accelerator to get a response.

It holds lower gears longer on hills and I get engine braking on declines.

 

[PontiacHO]

So we should avoid both deceleration and acceleration, since both are causes of wear?

Seems to me, we each have differing levels of what is acceptable causes of wear.

Some here really do not understand the principles and design of a four stroke engine. How does the engine collect an intake charge via the intake stroke while throttle plates are closed or relatively closed during engine braking on a downshift? The intake stroke happens EVERY revolution of the crankshaft. It will pull as much as possible past the piston rings and through the crankcase. That’s not how modern engines should be operated.

 

[supton]

Some here really do not understand the principles and design of a four stroke engine. How does the engine collect an intake charge via the intake stroke while throttle plates are closed or relatively closed during engine braking on a downshift? The intake stroke happens EVERY revolution of the crankshaft. It will pull as much as possible past the piston rings and through the crankcase. That’s not how modern engines should be operated.

So you are against engine braking, and advocate coasting down hills in neutral, so as to avoid super high vacuum conditions?

What do you consider is “too high” for vacuum? anything over that is seen at an idle condition?

 

[PontiacHO]

So you are against engine braking, and advocate coasting down hills in neutral, so as to avoid super high vacuum conditions?

What do you consider is “too high” for vacuum? anything over that is seen at an idle condition?

No. Didn’t say that. Engine braking is necessary in a situations like down a mountain. My opinion is downshifting using the trans/engine for slowing just because you can isn’t wise.

 

[demarpaint]

To hold the car back going downhill using the transmission to engine brake along with the brakes imo is a good idea. Downshifting an automatic transmission under normal conditions to slow a car down is a waste of time, and over a long period of time might cause additional wear and possible damage to an automtaic transmission. I see zero upside, and possible downside. JMO