Using AT to engine brake down mountain...will it hurt AT?

[mrdctaylor]

Guys,

My wife and I just got back from a nice trip out west. It look us through parts of Utah and Colorado. When coming down long declines out of a mountain pass, I usually manually kept my automatic transmission in 2 or 3 depending on how fast I was comfortable going. It was never at high or even moderate RPMs. I'd always heard this was safer because if you ride your brakes down a mountain they can overheat and fail.

Anyway, I've had some people tell me that it will wear out my transmission. Obviously, I want to be safe but I'd also rather wear our brakes than a transmission. For those of you that live in mountainous terrain: what is the proper procedure? Should I manually downshift my auto to keep the speed low on a long descent or should I just leave it in D and use the brakes?

Thanks in advance!

PS. This was in my 2012 Highlander. It has a "manual" shift mode where I can control the gear my tapping the gearshift towards the "+" or the "-".

 

[Delta]

You're fine. I have to travel over the mountain everyday and when I take the Camry with the 6 speed auto I'll keep it in 4th up and down. Done this with the old Expedition and Jeep with no issues. I think the problem comes from people constantly (like daily) shifting an auto manually. Keep the vehicle in a lower gear and stab brake. Happy travels!

EDIT: Just remembered my coworker only uses the brakes on his Dodge truck and goes through brakes every 7-8 months. Camry has almost 20K and no sign of excessive brake wear or transmission issues.

 

[mrdctaylor]

Thanks! That's exactly what I did. Never rode the brakes. Just tapped them as needed. My son my be going on a trip out west next summer and I want to give him the proper advice.

 

[fraso]

I regularly use transmission braking to avoid overheating my brakes and to minimize brake wear. My understanding is that any transmission wear occurs in the the clutches when you shift gears, which an automatic transmission normally does all the time.

 

[blupupher]

Every owners manual I have read specifically states to use the transmission for engine braking on downhill driving.

 

[Donald]

Originally Posted By: mrdctaylor
Thanks! That's exactly what I did. Never rode the brakes. Just tapped them as needed. My son my be going on a trip out west next summer and I want to give him the proper advice.


And he will listen?

 

[Astro14]

Leaving it in a lower gear causes no wear.

Downshifting when you're already going fast (causing a high RPM engagement of the lower gear) will cause wear.

Shift early, leave it, you're good.

 

[PimTac]

My Mazda does it automatically which is something I haven’t experienced before with a auto transmission

 

[mrdctaylor]

Originally Posted By: PimTac
My Mazda does it automatically which is something I haven’t experienced before with a auto transmission


Interesting! I've never experienced that either.

 

[E150GT]

That’s what I did when I was in Seattle. There was some big hills and I was following my sister. Going down the hill she rode the brake the whole time. I used the manual shifter and never touched the brake and stayed a comfortable distance from her. After that I told her husband who is car illiterate to make sure he gets his brake fluid changed at least every two years in that kind of driving since they are both going to be riding brakes down hills regularly.

 

[gregk24]

Originally Posted By: mrdctaylor
Originally Posted By: PimTac
My Mazda does it automatically which is something I haven’t experienced before with a auto transmission


Interesting! I've never experienced that either.


Honda does it too. When pressing the brake going down a hill the transmission will downshift to a higher gear.

 

[john_pifer]

Originally Posted By: gregk24
Originally Posted By: mrdctaylor
Originally Posted By: PimTac
My Mazda does it automatically which is something I haven’t experienced before with a auto transmission


Interesting! I've never experienced that either.


Honda does it too. When pressing the brake going down a hill the transmission will downshift to a higher gear.


My Tacoma does it as well. Downshifts when you hit the brake.

 

[JLTD]

You did the right thing.


Originally Posted By: blupupher
Every owners manual I have read specifically states to use the transmission for engine braking on downhill driving.



Originally Posted By: Astro14
Leaving it in a lower gear causes no wear.

Downshifting when you're already going fast (causing a high RPM engagement of the lower gear) will cause wear.

Shift early, leave it, you're good.



^ Exactly. With an automatic it's the shifting that causes wear, not being in a gear.

And Astro14's "Shift early, leave it, you're good" applies going up mountains as well, especially when towing.

 

[chainblu]

My wife's little Mitsubishi has a detent on the shifter for engine (trans) braking. It doesn't get used much here in Florida.

Twenty years ago while visiting Colorado, we drove up Pikes Peak. There was a sign on the way down that there would be a brake check (for temp) at the bottom of the peak. We drove that rental in low all the way down. The Ranger was very surprised how cool the brakes were.

 

[bubbatime]

Just got back from the Smokey Mountains. My 2017 Pacifica down shifted on its own. It has a weird rotary shift dial and I haven't figured out how to manually down shift on my own, if that is even possible.

 

[charbaby]

Originally Posted By: mrdctaylor
Originally Posted By: PimTac
My Mazda does it automatically which is something I haven’t experienced before with a auto transmission


Interesting! I've never experienced that either.


Hmmm, my 95 Accord EX automatic did this. It was a great transmission.

 

[Gimpy1]

Here in Mexico city, to get out of the city there are some serious uphill and downhill grades. In the wife's New Beetle I put the gear selector to manual shift (it's a 6 speed Tiptronic) and use engine braking as much as I can. Every time we go on a road trip (1 -2 times a month to Cuernavaca) I can smell or see other drivers brakes overheating especially tractor trailers. As long as you don't over rev the engine or shift when the engine is at high RPM you should be ok. The only thing I could see happening is an elevated ATF temp which you may have to change more often, but compared to cooked brakes, and not being able to stop its really negligible. I also believe that your owners manual addresses down shifting on steep grades or towing and advises what gear to put it in.

 

[PandaBear]

That's just engine braking. You are fine with the transmission but you may cool down your engine a lot and "burn some oil" because of the vacuum.

I used to drive through the Tejon / grapevine on I5 with a "loose" thermostat, and going downhill I'll see the temperature dip to almost cold. After replacing the stat the temperature remains warm.

You "may" also use some more fuel, depends on whether the engine cut fuel / ignition during cruising or not (i.e. if AC is on or not).

 

[RoadRaceJosh]

The only vehicles I'm aware of which have trouble on down-grades caused by engine braking are diesels with aftermarket engine brakes. The added load with low throttle pressure (low transmission clutch apply pressure) can cause slippage. For the hydraulically controlled Dodge automatics there was a kit to move the throttle pressure lever on the transmission to the full-throttle position when the engine brake was engaged keeping the clutch apply pressure high and preventing burned clutches. This was made obsolete once the OEMs started doing engine brakes.

Automatic down-shifting on grades is commonly called grade shifting. Most late model trucks do it. Even my wife's 2004 Corolla does it.

 

[meep]

the 2.7 ecoboost will be an interesting tow vehicle on downhills. The engine offers negligible engine braking after 2nd gear (10 spd) when empty. Most of the parks we camp at don't have more than a few miles of descents, but it's enough to really be glad to have the extra margin of engine braking. In this case, the trans just spins the engine up and up with little effect.

back OT, like astro said, the only wear is during the downshift process. you can lessen it by anticipating, doing it early, or even a well-timed throttle tap.

-m