Overdrive: Increased transmission wear or not?

[braverichard]

This just came to my mind today. My girlfriend and I flew to Baltimore to pick up her new Lexus RX400H - well actually, the car is used, but with just 900 miles on the clock when we bought it. The couple that bought it new just two months ago just stumbled across a great financial need and decided to sell it. We just arrived back here after driving it all the way back. The car's transmission has a very, very tall overdrive gear. It does 80mph at 2,100 rpm or so. As I drove through the Apalachian mountains at high speeds of around 90mph, it constantly had to downshift to a lower gear to get more power. This continued even after we left that mountain range and drove on flat highways. Basically, anytime I needed power to pass another vehicle or for any other reason the transmission downshifted. The downshifts were smooth, no questions about that, but I just started wondering if such a tall overdrive would increase wear on the transmission as it constantly had to downshift, perhaps more often than it would if the engine was spinning higher with more power available without a downshift.

I just want to hear your opinions on this. I'm sure all the automakers know what they are doing by introducing overdrive in all cars today, but it was a thought I decided to bring out for discussion.

[Jim H]

The 'wear' of gear changes is to clutch friction material as it slips to soften the torque as the next gear 'engages.'

Transmissions are designed with enough friction material to accommodate a certain number of shifts, depending on the transmitted torque during the shift.

Some have a shift selector that prevents torque converter lockup or 'overdrive' or delay shifts to higher gears for higher torque applications such as trailer towing or climbing steeper grades.

For the occasional journey to the hills, don't worry about it.

[Brian Carlton]

It's the typical problem with a gasser. No torque at low rpm's, but, very little is needed to maintain cruise on level ground. So, 1800 rpm's is fine.

But, need to climb a grade, even a small one? Sorry, no torque available for that. So, the drivetrain must downshift to get you the necessary torque to the pavement.

Every time it shifts, it exacts some bit of wear from the clutches in the transmission. Will the trans make it to 100K? Probably. But, some don't.

Natuarally, if you had a diesel and it was turning 3000 rpm at the same speed, you have all the power you need.......right on tap.

[braverichard]

Brian seems to have read me better. Jim, thanks for your post, but I am not worrying about wear on the transmission. It was just a thought that came to my mind. I was just wondering if there is increased wear due to the downshifts which wouldn't be there were the engine spinning faster. Like Brian said, some wouldn't make it past 100,000 miles. But even those that break down at 200,000 miles, I wonder if they could have lasted longer if not for the additional shifts required due to the tall overdrive gear.

[86560SEL]

Yeah, no cause for concerns. My Toyotas of the past were the same way and all had over 200K on the original tranny and still working perfectly. My Lexus LS400 would be at 2200 RPM around 65-70 MPH if I recall, but having the V8, it did not downshift that often on the freeways.

My mother has a 97' Oldsmobile with a small DOHC 2.4L engine, with a 4-speed automatic. It cruises at a very low 1900-2000 RPMS at 65mph. Also does a lot of "going out of O/D" when going up grades, even on the freeway. It now has 145K and still no issues.

Another example was my old 95' Suburban. It too was around 2000 RPMS around 65-70 mph, and did a lot of "hunting". It had 289K, but the tranny had been replaced at 179K.

[Hatterasguy]

Talk to the Lexus dealer and see what they say. The Toyota dealer said only use OD on the highway or you will blow the trans. My old Camry is still running on the original trans at 150k and I am probably the only one who ever changed the fluid.

This is typical of gassers with OD, you are too used to MB's.

[Brian Carlton]

Originally Posted by Hatterasguy

Talk to the Lexus dealer and see what they say.

.........duh.....what's a "transmission"??