Are transmissions less stressed by highway driving

[mareakin]

Full title: Are automatic/manual transmissions less stressed by highway driving or city driving?

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With engines, the near-consensus is that highway driving is less stressful--engines like to be revv'd at a constant rpm.

What about transmissions? Is the opposite true? With transmissions city driving means slower speeds (=less heat=good) but also entails a lot of gear changing (change in speeds and also reversing for parking)

What says you?

 

[Shannow]

In a manual, every gear change is a major fatigue event (versus gear meshing) and adds up to reduced life...highway, there's a downshift or two, followed by some steady state or acceleration.

Would give highway FTW in general.

 

[Silk]

In earlier times of rear wheel drives,top gear was direct drive manual or auto,so much less stress. These days of overdrives and indirect gearboxes there is always a gear train involved,so no longer applies.

 

[exranger06]

In an automatic, most of the heat comes from the torque converter. On the highway, the torque converter is locked up, which greatly reduces the heat. Also, heat builds up every time the transmission shifts, so just cruising in overdrive doesn't generate much heat. Furthermore, every time the trans shifts, the clutch packs get worn down and the trans's life is reduced a little. Just cruising in overdrive = little to no shifting. In conclusion, highway driving is way less stressful to a transmission than city driving.

 

[OldCowboy]

At 60 mph, a typical car needs 10 to 20 horsepower simply to maintain its speed. (http://auto.howstuffworks.com/one-horse-engine.htm). OTOH, accelerating to 60 mph will require significantly more than this, depending on how quickly you want to reach 60 mph. So, driving at a constant, reasonable speed puts less stress on the transmission.

 

[hounddog]

In a short answer. YES.

 

[meep]

On the highway, the AT in our minivan will sit at 110F for a looooong time if it stays in lockup.

Around town, or climbing hills or aggressive driving, it quickly reaches and fluctuates between 150F and 180F.

After being on the highway for an hour+, with the Air on in the summer and all the temps equalized, it *might* reach 150F and stay there.

 

[mareakin]

Why does Haynes manual recommend 20 minutes of highway driving to get "up to temp" before measuring the automatic transmission fluid level?

 

[eljefino]

Because Haynes cuts and pastes advice from 1970 and the era of non lockup convertors.

Look at their "body work" section if they have it; they're bondo-ing up a 1975 plymouth!

 

[dparm]

Shifting is what stresses the transmission. Sustained speeds, especially with good airflow, do not.

 

[Torino]

Yes. John--Las Vegas

 

[01rangerxl]

Highway driving is probably the ideal condition for the transmission while in use. It's getting the best cooling possible, it's not shifting as much, and with an AT the TC is probably locked.

Vehicles that put mega miles on ATs usually see mostly highway miles. The million mile E-Series comes to mind.

 

[Nick R]

Put it this way- highway driving is the ideal driving situation for pretty much every part of your car.

 

[mechtech2]

Unless extreme speeds are encountered on the highway, it is better [as mentioned above] for most systems and parts of your car.

 

[JHZR2]

Originally Posted By: OldCowboy
At 60 mph, a typical car needs 10 to 20 horsepower simply to maintain its speed. (http://auto.howstuffworks.com/one-horse-engine.htm). OTOH, accelerating to 60 mph will require significantly more than this, depending on how quickly you want to reach 60 mph. So, driving at a constant, reasonable speed puts less stress on the transmission.



This.

Mechanical systems life are effected by time at load/time at temperature.

The end result is that the more torque applied, the lower the life. Stop and go is likely the worst, but the more rolling the hills, the more steep mountains, the heavier the payload, etc., the more of an issue. Extent of over design will determine how much of a difference it makes.