Engine braking bad for automatic transmission?

Messages
2,569
Location
Kentucky
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?
 
Messages
1,052
Location
Caldwell Idaho
The torque converter is what generated the most heat in an auto trans but these days the converters lock up so who can really say ? Brakes are much cheaper to replace.
 
Messages
1,004
Location
Arizona
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.
 
Messages
1,258
Location
Sask, Canada
Hmmm neat debate. I was taught as a kid to drop gears, even in an auto. I do it extensively in all my vehicles. Nothing has fell apart yet.

My gasser trailblazer has 255,000km and the original front pads and rotors are still on it with some meat to spare.

My 3500 is a bit different with the but I rarely use the service brakes. Its all downshifting and exhaust brake.
 
Messages
8,790
Location
Virginia
I have a manual option in my car with a CVT... I drove down from Lover's Leap at 3,300 feet down to 1,500 feet east on Rte 58. I used the manual mode and barely touched the brakes. And there are part of that road where the grade is 9 percent... And I drove on the Green mts in Vermont and did the same. Drove up to near the top of Mt Mansfield highest mountain in Vermont with a elevation gain of 2,400. Going from 1,400 feet to 3,800 feet. Hardly used the brakes going back down the toll road. And it was very steep in places.
 
Messages
1,840
Location
WA
Speaking of auto trans:

Moderation could be the key!
Also depends on the situation e.g. towing a heavy load going downhill all brakes is not a good idea.

just remember heat has to go somewhere. Brakes or engine (higher rpm) & transmission (most likely unlocked Torque Converter) or the combination of both (brake & engine brake).

Every situation is different. For example coming to a stop sign under normal conditions (with auto trans with no load), doing mostly engine brake may not be the best idea.
 
Messages
6,760
Location
Katy, Republic of Texas
Engine braking with an automatic increases transmission fluid temps, which is a bad thing over time. An engine cooler or vehicles designed with this in mind (as noted above, many vehicles have a downhill assist feature) it really is not a huge issue. Just change your ATF on a regular basis and you should not have any transmission issues.

Riding the brakes down a grade will overheat the brakes, creating fade, which will reduce your chance of stopping in a timely manner, which can cause much more issues than overheated transmission fluid.
 
Messages
513
Location
South Wales, UK
Most modern automatic boxes lock up pretty much as soon as you get moving. Certainly the AW71-SC's that were in my Volvo's would lock up as soon as it shifted into 2nd. My ZF 8HP, I don't quite understand yet, with the BMW being a mild hybrid it does all sorts of weird and wonderful things I don't quite understand as well as I'd like.
 
Messages
485
Location
Daytona Beach
If it would damage transmissions, a whole bunch of car makers just screwed up installing paddle shifters on a whole bunch of cars. Including my Mercedes.
The GM engineer that used to be here was a proponent of the WOT maneuver to unstick rings in a Northstar engine. This process did not involve downshifting from speed, but locking the trans in second and running up to near redline then letting go of the throttle pedal.
Naturally this was NOT to be done daily, just on occasion. It worked for me actually, reducing oil consumption over time in my '99 STS.
Don't forget though, the Northstar was quite a different design at the time and was meant to be driven "aggressively" shall we say.
Curiously, the direct injection turbo 4 in the Merc is almost useless when downshifted providing almost no additional braking.

Counter to all of that, my dad used to tell me "they put brakes on this car for a reason!"
 
Messages
1,840
Location
WA
....My guess is they are old school analog guys ...

analog guys listen to AM and you may find couple of transistors or even vacuum tubes in their glove box. :alien:

Op,
My truck only locks in 4th, 5th and 6th. Going down hill in 4th especially with load doesn't provide significant engine braking and if I downshift to 3rd, torque converter is unlocked which means heat.
I downshift (i.e. do not leave it in D or 5 & 6th) to help the brakes. The car may already do this for me but I rather do it myself ...
If I have to downshift to 3rd or lower, I try to assist with brakes to kind of distribute the work (heat) knowing that under normal conditions my truck does not lock in 3rd gear.

You have to know your car, your load and your situation and adjust accordingly.
 
Messages
16,945
Location
NH
Sounds like a Tundra--mine won't lock up in 3rd. My guess, it doesn't need to, once well above stall speed, slippage is less, and of course, there's a good sized cooler with lots of airflow (one has to assume with high rpm comes with moving at a good clip).

IMO, everything causes wear. Upshifting causes wear too. Maybe we should drive around in first gear only?
 
Messages
4,426
Location
Southeast
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
 
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