Does engine braking an automatic wear out the transmission?

Question

My question is a variation on these two:

• Engine braking with an automatic transmission
• What are the “1” and “2” or “L” gears used for on an automatic?

I recently bought an automatic transmission 2012 Mazda 3 after driving a manual for a number of years. As was my habit with the manual, rather than braking on a highway off-ramp, I downshift all the way to 1 to use engine braking (applying brakes right at the end).

When downshifting from 2 to 1 around 30 - 40 km/h the car has a jerk of deceleration and revs to about 4k rpm. I assume this is because a large amount of momentum is transferred through the transmission to the engine block while the clutch is engaging. Is this putting strain or wear on the transmission?

Am I saving wear-and-tear on my brakes at the cost of an eventual transmission replacement?

Answer 1

Sorry for bringing up an old thread, but I'd just like to add my personal experience with this. Long story short, I recently took up the practice of engine braking on an automatic minivan, and my transmission is now dead at 100k miles. Could just be a coincidence, but here's the long story for what it's worth:

On a drive up and down the Rockies a bit, 1 year ago, I decided to try engine braking while heading down hills. We're talking about 40-50 mph in 4th gear (the gear just below my OD) and 30-40 mph in 3rd. 3k rpms max, usually closer to 2k. After about 1.5 hrs of doing this on the way back, I noticed a whirring sound. It worried me, but after getting home and checking the transmission fluid, everything seemed fine. I figured I was just being paranoid, that the sound had already been there and that I was just worried that after trying this new thing I was prone to think I did something wrong. But...

After about a year of frequently doing this, not just in the mountains, but at red lights, etc., the 3rd gear suddenly now has a terrible time shifting. And 4th seems like it's about to go as well. The transmission mechanic says the fluid looked fine and everything else is checking out. My "clutches" are going out, he says. Time for a transmission rebuild.

I'm sure it's not that rare for a 10 year old transmission with 100k miles to go out all of a sudden, but I can't help but think that it was the engine braking that made it happen so soon. Whether or not the whirring sound was already there will remain a mystery, but I'm fairly certain it wasn't. I don't want to build unfounded fear for engine braking, but the saying "better to wear out a $150 part than a $3000 part" is really hitting close for me.

Answer 2

Basically, yes. Automatics don't have a clutch per se, but you're causing additional wear and tear on the internals. Basically you're reversing the power flow -- instead of the engine driving the wheels, you're driving the engine with the wheels. Obviously this occurs normally when you decelerate, but by downshifting you're increasing the amount of force that normally goes through the transmission in that way. There's no way to accurately predict how much additional wear you're putting on your drivetrain, but doesn't it make more sense to put the wear on an easily-accessible part that's designed to be replaced than on an expensive one?

Answer 3

You should leave the downshifting to the transmission. Sounds like you're doing it wrong anyway. The abrupt "jerk" that you speak of means you're going Too Fast for the gear you've selected. Of course if you're towing a heavily loaded trailer, you could manually downshift to assist the cars brakes to avoid the possibility of overheating them. But the engine revving to 4k on the 2-1 downshift is really being abusive.

There are clutches in an automatic transmission, but for this discussion, you have no direct control over their operation, and should realize instead, that you're no doubt over-revving your engine.

The "1"-"2" & "L" mean that you're selecting that gear manually, and the transmission will only shift automatically between "1" and "2" if you select "2" on start-up. "L" means Lo/Low gear and there won't be an upshift at all. Same is true when you select"1". The transmission will remain in "1" or "Lo". This manual selection is useful for towing at low speed for short distances, and can help when braking on super slippery surfaces.

Additionally, there are always exceptions. A rear wheel drive vehicle will realize theoretically, an advantage when braking on ICE over a front wheel drive vehicle because the proportioning valve sends as much as 67%-70% of the braking force to the front wheels anyway. Yet, a too high Idle speed will have the rear wheels pushing while the fronts are forced to lock-up in their effort to stop the car. A.B.S. does NOT stay with you until you come to a complete stop. On top of all this, braking forces applied to each front (or rear) wheel are not guaranteed to be equal, so from a moderate speed on ICE , engine braking can conceivably help, but you MUST have a good "seat of the pants" feel for what's going on under you as conditions vary.

Answer 4

Downshifting to prevent brake fade on a long steep grade is one thing. Downshifting repetitively to slow the vehicle at every stoplight is another. Ultimately you want the shift to be as smooth as possible. In a manual transmission as well as a motorcycle this is easy.. just rev the engine RPM up right before you let the clutch out. Note: that on rear wheel drive vehicles, mainly motorcycles and pickups, engine braking will wear the rear tires out rapidly as there's not much weight back there.

Answer 5

I would say the wear and tear is less than accelerating particularly when hard acceleration is used. The thrust on bearings is not limitless and neither are the splines on a gear. However manufacturers tend to format in long descents and use of engine braking with the assistance of brakes as well. The fuel use is less and more control available especially if you need an emergency stop. The wear and tear is certainly not as much as hard acceleration particularly from cold asa many do from my witnessing locally