Downhill in lower gear with automatict ransmission

tqh

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I have a Toyota Camry with an automatic transmission with a shift knob to force the maximum gear, i.e. if I move it to 3rd, it'll only choose among gears 1, 2, 3, but not 4 or 5. When going downhill I can shift to one of the lower gears to slow down the car without using the brakes. Is it bad for the transmission - as long as I keep the rpm within a reasonable range (< 3000 rpm)
 

JHZR2

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If you're in hilly terrain, it's useful, but other wise penny wise, pound foolish. Brakes are meant to be worn and replaced... As data points, doing this regularly in hilly terrain makes Camry ATs fail around 80k miles and honda ATs fail around 30k, both from firsthand experience.
 
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You are doing exactly what is recommended for good driving. Disengaging overdrive and going in 3rd gear or even 2nd gear for extreme downhill travel allows your engine to partake in some of the braking, which helps prevent your brakes from overheating and glossing over. In turn, when going uphill, it is good to disengaged overdrive, which allows the transmissions to stay in third, without creating excessive wear of having to jump from higher to lower gears every time you accelerate. Keep doing what you are doing.
 

jaj

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My wife's BMW automatically shifts into a lower gear going down a hill on a mountain highway. So, "yes" it's safe and "yes" you should do it. The risk of brake overheating is small, but it's there, particularly if you don't change the fluid very often (or ever).
 

MolaKule

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Quote:
tqh: Is it bad for the transmission - as long as I keep the rpm within a reasonable range (< 3000 rpm)
Consider this, high temperature in a transmission degrades the fluid through oxidation, and increases wear in the clutch packs, etc. Using a transmission in a lower gear to do your braking raises internal transmission temperatures. Brakes jobs cost much less than a tranny replacement. I think a better approach is to anticipate the hill and slow at the top so your descent speed will be slower as well.
 
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Unless you need to control downhill speed on a long downhill or you are in terrain that makes the transmission shift up and down constantly, you don't need to touch the gearshift. To put it another way, if you are going to heat the brakes hot enough to not do their job or if the transmission is trying to wear itself out, then you need to downshift.
 
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My dad blew a transmission in his 05 matrix driving around hilly Vermont in lower gears. The rebuilt transmission had an updated valve body/linkage/programming that apparently went into the newer versions of that trans. Long story short, it freewheels a lot more now. LOL
 
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Ive never noticed excessive heat coasting down a hill in a lower gear, in fact usually the temperature would drop slightly since I usually bomb hills at 75mph in third with the TC locking and unlocking. But, YMMV.
 
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To those who are worried about overheating the transmission. I used to live in Colorado and did a lot of mountain driving. Sometimes you just have to use the added braking power of lower gears. When brakes outgas you get a total failure. You can literally stand on the pedal and there is no perceptible braking. Better to get ahead of the game slow the car with the transmission and know you always have a bit of reserve in the pads. So better to add wear and tear to a transmission than wreck your car or risk your life or injury.
 
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Originally Posted By: JHZR2
If you're in hilly terrain, it's useful, but other wise penny wise, pound foolish. Brakes are meant to be worn and replaced... As data points, doing this regularly in hilly terrain makes Camry ATs fail around 80k miles and honda ATs fail around 30k, both from firsthand experience.
+1 I try to anticipate the hill and slow down at the top of it and pump the brakes as I accelerate. Using D instead of OD, or 4 instead of 5 in a 5 speed AT is OK. Going lower than a final drive gear builds up a lot of heat and can eventually cause transmission problems. This information came from a very knowledgeable transmission re-builder, and other people I highly respect in the industry.
 
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Originally Posted By: MolaKule
Quote:
tqh: Is it bad for the transmission - as long as I keep the rpm within a reasonable range (< 3000 rpm)
Consider this, high temperature in a transmission degrades the fluid through oxidation, and increases wear in the clutch packs, etc. Using a transmission in a lower gear to do your braking raises internal transmission temperatures. Brakes jobs cost much less than a tranny replacement. I think a better approach is to anticipate the hill and slow at the top so your descent speed will be slower as well.
I think it comes down to frequency, duration, grade, and the ability of your transmission and its cooling system (if any) to keep everything working within its normal parameters. I would not downshift for a 30 second downhill coast where one or two moderate applications of the brakes would suffice. But I did keep the GP in 3rd for most of a 15+ mile downgrade coming down a mountain in 50F weather and kept an eye on the tranny fluid temp (one of the readout options on the digital dash info system) to make sure it did not get too hot. With the engine at about 2,000-2,500 rpm with very little load and moving at 55-65 mph, the cooling system had no problems keeping tranny fluid temps in check (making the uphill trip in 3rd was a completely different story!). If you do use engine braking regularly and it does (or you suspect it does) increase tranny fluid temps, I would definitely keep a closer eye on the ATF and change more frequently, perhaps following the severe service interval. Edit: And as dermapaint said, I would not drop more than one gear, unless I had to crawl down a hill due to slower vehicles in front of me at a speed that would otherwise require constant brake application to maintain a safe following distance. Additionally, my father used to (don't know if he still does as I do not drive much with him anymore) use engine braking nearly every time he would exit the freeway and never experienced any tranny issues in his Toyota, Nissan, Kia, or GM vehicles that were kept for more than 100k miles each before being totalled or sold to one of us kids (who never experienced any issues, AFAIK). Before finding BITOG, I did not realize transmissions or engines could/do give people so many problems or require rebuilds/replacements before 200k miles!
 
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^ "Anticipating" the hill of course depends on the altitude difference and grade of the drive. I lived on top of the ridge of the San Bernardino Mountains for a year. Headed down towards Los Angeles was a 20 minute drive during which we would descend 6,000 feet. Your vehicle is going to accelerate regardless. In this circumstance, engine braking is recommended, where the retarding forces within the engine will help to slow the car. Engine braking can only occur in 3rd gear, and requires disengaging the overdrive.
 
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I would only do that if you are driving in the mountains and want to prevent the brakes from cooking. Unnecessarily putting wear and tear on a transmission is stupid. A transmission repair is expensive. Brakes are relatively cheap.
 
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Maybe you are going too fast through the mountains? Brakes are certainly cheaper than a transmission.
 
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Originally Posted By: dparm
I would only do that if you are driving in the mountains and want to prevent the brakes from cooking. Unnecessarily putting wear and tear on a transmission is stupid. A transmission repair is expensive. Brakes are relatively cheap.
Exactly, which is why it is important to put this in context. Using the compression stroke of your engine to slow down during mountain descents is far safer than heavy braking. Ultimately, downhill descents require a mixture of both braking and downshifting, but this is to be determined by the severity of the grade and speed of descent.
 
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If you have ever decended parts of the rockies, you HAVE to engine brake or you will melt your rotors into molten chunks. Even with engine braking in 3rd, I still had to pull off into a cool down chute to let my brakes cool down and stop stinking. When i finally got to the bottom an RV was off the side of the road with flaming front wheels. It had markings of a rental so i hope they got the insurance.
 

01rangerxl

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From my truck's owner's manual... Drive (O/D OFF) provides more engine braking than Overdrive and is useful whenever driving conditions (i.e., city traffic, hilly terrain, etc.) cause the transmission to excessively shift between Overdrive and other gears. Deactivate (Overdrive) when: • driving with a heavy load. • towing a trailer up or down steep hills. • additional engine braking is desired. It seems to imply that excessive shifting, especially with a load, is more of a concern than engine braking raising temps. I monitor temps with a Scangauge and with my truck they are about the same whether OD is on or off. I have turned OD off many times in the truck's life, sometimes for extended periods (hundreds of miles while towing), and it shifts like new at 150K miles.
 
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