Manual gearchanges using an Autobox

mike65

Does it hurt the gearbox to change manualy?

Mike.

Anan1

No, provided you don't use too low a gear for the speed you're doing.

unkel

Anan1 wrote:

No, provided you don't use too low a gear for the speed you're doing.

Surely the rev limiter would kick in?

ffocused

autos will still shift down automatically in manual mode. (at least they have on all mine)

Captain Trips

You might balls up the torque converter and whatever electronic memory exists that learns your driving pattern

In my auto MB, the autobox gears just change the revs at which the engine electronics change the gears - you don't have any real control over it except for this. Lower auto gears, like say selecting 2 or 3 instead of D, simply means the gears will change at higher revs, which is where the higher torque kicks in and at the higher BHP. It's useful if you are towing and need the extra torque which you don't get when it's changing gears at 3,000RPM.

The learning thing learns how heavy your foot is basically, so if you start changing the autogears on the fly, the car won't know what the fsck you are at, or at least, I've found that in mine, and if I go back to D, it takes a short while to stop changing at 5-6000RPM and start changing at 3000RPM again. That's my experience anyway!

nialler

Doesn't appear to harm the engine, if it did why would they have it there?

Generally on national roads I'll use the tiptronic or whatever ya call it, slap the lever twice to the left to drop it to D3, you'll see the revs jump to around 4k, floor (not kickdown) and sail by a few cars, then hit brakes to slow down again, double slap back to DS.

Wouldn't bother on a motorway, the kickdown usually sorts it before going back into left lane.

mike65

Thanks for the feedback, my box is an early example of the adaptive style with no fancy sport/economy stuff it - just learns and usually changes well but I've noticed its weak spot is 30-40 mph traffic, when in 4th its rather slow to drop a gear unless you give it a good prod.

Mike.

AMurphy

Does it hurt the gearbox to change manualy?

Mike.

Captain Trips wrote:

You might balls up the torque converter and whatever electronic memory exists that learns your driving pattern

......!

It depends on the gearbox and control mechanisms and the speed you were doing and which gears you shifted between, pretty much as with any manual gearbox.
Under normal conditions you'd not shift a manual box from 50mph forward to rev, same for an AT. On many Electronic AT, the electronics will prevent such a change from occuring until the speed range is within an acceptable range, eg, my van will not shift from For to Rev at speeds >8mph. I can move the shifter, not that it makes any difference. Not quiet the case with manual ATs

Assuming you did shift a manual AT abruptly at speed, I'd not expect the TC to get damaged, but clutches within the box to be subject to excessive loading and wear. And/or at worst some sun gears to get stripped. The Wheels may lock up and skid on a RWD vehicle.

nialler

Considering AMurphy that a lot of cars will do over 100k (close to 6000rpm) in 2nd there's little risk in that happening, the engine management system will not allow you to force a gear when doing it manually.

damo605

Only last week I was asking a local mechanic friend what would happen if you fired an automatic into reverse while driving along and he told me about a guy with a 50euro Carina II from the early ninetys who was finished with it so decided to try and kill it - Apparently what he did, numerous times, at speeds up to 50 or 60 mph fired it into reverse, into park, tried everything.... Only result was a loud clicking noise and the car slowing down. Back into drive and away it went again fine each time!!!
Now I'm not suggesting for one second anyone try this in a car worth more than 50 euro or without a crash helmet but I thought it was interesting

Anan1

unkel wrote:

Surely the rev limiter would kick in?

The rev limiter only cuts fuelling, the engine would be overrevved by the momentum of the car even with no fuel at all. An even more immediate concern would be the locking up of the driven wheels.