Engine braking bad for automatic transmission?

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2,129
Location
WA
I call hogwash.

the amount of resistance an engine puts on the driveline during engine braking is paltry compared to what it can do under load. The max psi /against/ the cylinders will be 1 atm (15psi), as a vacuum, whereas under power is somewhere between 600 to 2000 psi. That directly correlates to driveline force at the TC and everywhere else.

the only moment I cringe is if you implement a poorly timed downshift where the clutches have to raise the engine rpm from no-load cruise (say 1000) to braking (say 3000 or more). If I’m manually forcing the downshift, I might blip the throttle to rev-match.

TC fluid shearing and heat load I think would be very inconsequential. The greater risk I would consider is unloaded piston forces at upper rpms at the tops of their travel.

m

You mentioned rev-matching. Were you talking about manual transmission or auto?
Sometimes when I'm in 5th with TC locked, I give it a little gas and TC unlocks and rpm goes up a little and then I downshift to 4th. I'm sure with the small delta rpm (from 5th to 4th) this is not necessary or may not even be advisable. I do it more often when down shifting from 4th and Locked to 3rd. I used to drive manual trans forever but had no choice with the new truck and maybe old habits.

Anyway, curious how you do your "blip the throttle to rev-match." since you can't go to neutral and then downshift like you can with manual trans.
 
Messages
278
Location
MN
I call hogwash as well...

There's a few here too obsessed with transmission temps while descending a hill.... Well... how did you get up that hill? I guarantee more heat was generated and rejected climbing that elevation change yet we don't think twice about doing that.

Also another newsflash, your vehicle was tested by the manufacturer to keep all fluids within safe limits while getting hammered on in death valley when its 115+ degrees out. Also, these days the torque converter is locked as much as possible
 
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4,705
Location
Southeast
So, in an auto it would be like if I were to shift from D to L, knowing it’s going to go from 3rd to 2nd, or 4th to 3rd. or in the f150, which has almost no authority engine braking, dropping to 3rd to 2nd manually. I’ll anticipate the lag it takes to do it and try to time the rev blip about before it’s going to grab. I used to drive manuals so it’s similar to thinking of a manual downshift too, just with the added unknown delay of the auto trans. I don’t always get it right, and sometimes it starts that marriage-building game we call, “what are you doing?”
 
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5,406
Location
Fort Worth, Texas
I call BS.....They even mentioned plastic Thrust Washers, Yes....Many units use plastic thrust washers, But NEVER on components that see ANY thrust loads. They are used on components that "Float" & the washers only purpose is to prevent metal to metal contact.

I have seen units with Overrun/Brake Frictions/Bands burnt up from aggressive use....Very rare though.
 
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4,868
Location
OK
What if you descend while shifting through the gears in an auto? I once was in a pack of cars going down a mountain and each driver in the pack had their idea of what speed was appropriate, so despite everyone going in the same direction with the help of gravity, there was still a need to shift around.
 
Messages
2,129
Location
WA
So, in an auto it would be like if I were to shift from D to L, knowing it’s going to go from 3rd to 2nd, or 4th to 3rd. or in the f150, which has almost no authority engine braking, dropping to 3rd to 2nd manually. I’ll anticipate the lag it takes to do it and try to time the rev blip about before it’s going to grab. I used to drive manuals so it’s similar to thinking of a manual downshift too, just with the added unknown delay of the auto trans. I don’t always get it right, and sometimes it starts that marriage-building game we call, “what are you doing?”

You gave me new ideas! lol
I may do a few experiments just for fun. there is some delay between gear changes. See if I can time it right.
 
Messages
142
Location
California, United States
I spotted an argument in another forum over the merits of engine braking going down grades.

Most were supportive of it, but a few had the position that engine braking somehow hurts the transmission and they would rather torch their brakes than an expensive transmission. One post in support of that stated:

"IDK if I am following how holding the car in a given gear is going to wear out a trans?"

"It's not the gear selection.
You have a torque converter in the equation. Its a fluid coupling device.
The fluid is being heavily sheared between the pump (engine half) and turbine (trans half).
This continuous heavy shearing of oil will raise temps drastically, and can play havoc on plastic thrust washers within the gear box and other sensitive components......
A trans oil cooler would help if you perform this maneuver often.
Towing has the same effect on the oil. "

Is there any truth to the idea that engine braking or holding gears without a load on the transmission is bad for it?
Sooo heres what my 2006 lexus is350 does when going down a more steep hill where you can gain some good speed, I am at around 50-55 and I hit the brakes to slow down on the slight curve ahead and the tranny which is a 6 speed and is in the 6th gear around 50 drops 1 gear and is now in 5th without me doing anything and im revving at 3k while still pressing the brakes. Go ask lexus if they think this is good or bad, personally I think its a safety step more than anything and I am fine with that.
 
Messages
35,475
Location
NY
The only real way to tell if you're doing harm is if you can monitor automatic transmission fluid temperature. Having said that I take the vehicle out of OD and the use the brakes as needed. I haven't lost an automatic transmission in well over 40 years of driving, and the brakes do just fine.
 
Messages
1,648
Location
VA
Your final question is theoretical, but it's hard to answer without thinking about engine braking in practical terms. I shift down on steep grades mainly to control my speed, but also to avoid overheating the brakes. That's where safety outweighs any actual or imagined damage to a transmission.

For example, I spent a couple of summers driving my '01 Silverado up and down a 10% grade once or twice per week. With 3.42 gears and a 4L60E, I went down most of the hill in 2nd and still had to brake going into a lot of the curves. I shifted to D on the last few long stretches, and would immediately coast past the speed limit. That's about the point where the signs said something like "Truckers, you're not down yet" and you could smell the hot brakes on minivans with Minnesota plates.
 
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7,320
Location
California
I’d rather put a little more wear on the engine and use engine braking on a lower gear than have my brakes fail on a long decent. Almost happened to a friend in his Subaru. He now shifts it into 3rd on hilly descents.

in the cars I’ve shifted down to engine brake, almost all of them locked up the TC as soon as you shifted out of the “overdrive” gears. A TC that’s not locked, but “slipping” creates a lot of heat. Where it gets interesting is on a Toyota-based hybrid. You have a B mode for “brake”. What that does is one of the motor/generators now spins the gas engine and whatever electricity is above what the battery can take is wasted. It’s a complicated simulation of engine braking.
 

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Messages
45,363
Location
Ontario, Canada
My silverado has towing pkg and i have used it a lot. I don't believe it hurts anything. descending a grade the trans downshifts and the TC Clutch locks up and the engine does the braking just like a diesel rig. The TC is locked so no heat generation there and no monstrous shearing. Other than that what wear there is is just opposite of accelerating loads through drive-train. ....My guess is they are old school analog guys, the new trans is computer controlled and designed for real usages. Let them torch their brakes.

I'm thinking the same. The ZF 8spd in both my vehicles engine brakes as you decelerate and it's quite noticeable. When I had the cruise set coming back from the cottage with the bigger boat (>5,000lbs) coming down a pretty good sized hill coming out of Omeemee the truck dropped three gears(!!!) by itself and was engine braking surprisingly well to keep the speed in check. IIRC, that put me in 4th, as it locks out 8th when you are in tow/haul. Now of course with 5K pushing, it was not going to be able to keep that speed in check, so I applied the brakes but it required very little in the way of application to rear things in at which point the trans jumped back to 6th, I hit resume on the cruise and then after it settled, hopped into 7th.
 
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1,616
I had a rental 2020 Tacoma TRD 4x4 last month when I did a camping trip in the Colorado Rockies last month. Pressing on the brakes hard when descending down a steep hill would immediately cause the transmission to downshift and keep the RPM high for engine braking. It was very effective.
 
Messages
2,129
Location
WA
That’s running an Aisin tranny, right? I would guess that I have the same behavior with my Toyota Fortuner, which is running an Aisin AC60F. Just got back from the mountains, so I had to use engine braking for a 30km descent from 4300 meters down to 1400 meters.

I read somewhere that Tundra has the Aisin transmission which Toyota is a major shareholder but not %100 sure. It is supposed to be a very solid trans. I haven't heard or read much about one failing.
 
Messages
17,514
Location
NH
Toyota seems to use Aisin for transmissions, not sure if across the board, but certainly in the Tundra's. The 4.6's and 5.7's use different transmissions, oddly, the 4.6 has a deeper first/second/third but then 4-6 are the same ratios (I guess to make up for lack of power?). But very similar operation.

I've used 3rd for engine braking at times. It will impart quite a bit of engine drag, the engine spools up quite nicely. It'd probably be better if the TC locked up, but it still does something. Not worried about fluid temps, mine has a good sized transmission cooler (part of the towing package) (mine might be a lo-po 4.6 but it came with the optional tow package) and I don't remember if I've seen fluid temps rise during engine braking... nothing like when it climbs a hill with the TC unlocked.
 
Messages
954
Location
Alberta
Sooo heres what my 2006 lexus is350 does when going down a more steep hill where you can gain some good speed, I am at around 50-55 and I hit the brakes to slow down on the slight curve ahead and the tranny which is a 6 speed and is in the 6th gear around 50 drops 1 gear and is now in 5th without me doing anything and im revving at 3k while still pressing the brakes. Go ask lexus if they think this is good or bad, personally I think its a safety step more than anything and I am fine with that.

My 2005 Sienna does this.▲

In Tow/Haul mode, my 2016 F150 Max Tow (11700lb rated) truck AGGRESSIVELY downshifts as soon as you touch your brakes. up to 5000+rpm if necessary. This is so aggressive that I refuse to us that mode even towing our 7000lb RV trailer through the mountains. I'd rather manually lock out the required gears. This is on a 6R80 transmission (originally based on a ZF unit) that is known to be quite robust.
 
Messages
16,525
Location
...
Toyota seems to use Aisin for transmissions, not sure if across the board, but certainly in the Tundra's. The 4.6's and 5.7's use different transmissions, oddly, the 4.6 has a deeper first/second/third but then 4-6 are the same ratios (I guess to make up for lack of power?). But very similar operation.

I've used 3rd for engine braking at times. It will impart quite a bit of engine drag, the engine spools up quite nicely. It'd probably be better if the TC locked up, but it still does something. Not worried about fluid temps, mine has a good sized transmission cooler (part of the towing package) (mine might be a lo-po 4.6 but it came with the optional tow package) and I don't remember if I've seen fluid temps rise during engine braking... nothing like when it climbs a hill with the TC unlocked.


Toyota owns Aisin.
 
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