Automatic transmission HELP

mondeo

I went down the sticks with my friend today to help him check out a mitsubishi mirage with tiptronic auto gearbox. The car was in fantastic condition with new Nct and the tiptronic mode was great however I'm abit iffy about the automatic mode.

When your driving along in 'D' mode ( not tiptronic ) with a soft foot she goes up and down her gears fine, however if your driving along at 50 or maybe 60 kph and then FLOOR it she revs up very hard for a few seconds then downshifts and goes like a bat out of hell. Should she be revving herself up like this? The guy selling it said you hit a resister point and she will rev like that before downshifting as she knows your looking for some grunt!

Is this correct?

Cheers

Doesn't sound right to me.

tallaghtmick

I had that car in tiptronic and it does that,its just for when you want to over take a car and you need the extra speed it kicks in.

your friend should always use the car in tiptronic mode its so much easier.

mondeo

RoverJames wrote: »

Doesn't sound right to me.

When she is revving up after flooring it, it's like she is revving in neutral for a few seconds or somthing. Doesn't happen in tiptronic though.

krissovo

Sounds like old school "kick down" to me however that was on older generation gearboxes.

It used to be perfectly normal when you floor the accelerator the gearbox would change down.

SouperComputer

There is a "kickdown switch" which will give this behavior. Cars dont have the mechnaical switch anymore, but still need to peform the same function when you suddenly give it socks. Sounds like it might be exaggerated though. It has to rev the engine to match the RPMs of the lower gear its going to engage. Say you are doing 60Kph in 4th at 2000 RPM, if its dropping to 2nd and the RPM at 60KPh in that gear is 4000RPM then its going to have to get at least someway towards 4000 before it engages the gear. That's mostly what the pause is, rev matching. The other part is disengaging the torque converter lockup and of course actually engaging the gear it picks.

Over the internet its hard to say if the time that its taking to downshift is out of normal boundries though. Drive another mirage and compare.. Look at and smell the transmission fluid. If its dark or smells burnt. Walk away.

Stinicker

This is perfectly normal, when you floor the accelerator the autobox will change down and the engine will rev up

Reving for a few seconds prior to the downshift is excessive, I'd consider 3 secs to be a few.

mondeo

The fluid looked like it had just been changed. 110k kms on the clock, quite low mileage as she is a 00' car. The guy selling it said he has driven autos for years and guarantees me the box is perfect and would not have dragged us down there if there was a problem with it.

What's this 'resistor' thing he kept mentioning to us? When you floor her she hits a resistor. She was revving up to 5.5k before doing anything shifting..

mondeo

mondeo wrote: »

The fluid looked like it had just been changed. 110k kms on the clock, quite low mileage as she is a 00' car. The guy selling it said he has driven autos for years and guarantees me the box is perfect and would not have dragged us down there if there was a problem with it.

What's this 'resistor' thing he kept mentioning to us? When you floor her she hits a resistor. She was revving up to 5.5k before doing anything shifting..

sounds fecked to me, I have an auto at the mo and my old prelude was a slush box too, the resistor thing sounds like ass biscuits to me.

lomb

Sounds normal to me, but the kickdown should be fairly instant. That's the whole point of it. MMight be the make and model if there's a delay or the gearbox could be shot. Drove a cl 500 that there was a delay like you said and I reckoned it was shot. Somehow I doubt Mercedes flagship had a rubbish gearbox from the get go.

mondeo

RoverJames wrote: »

sounds fecked to me, I have an auto at the mo and my old prelude was a slush box too

I don't understand though why she drove perfect with a light foot, no probs going up and down her gears by herself but with a heavy foot changed her tune, you had to release the accelerator some what to make her pick herself up. Pitty if there is a problem as she was in great condition otherwise.

SouperComputer

He probably mightn't fully understand he's saying.. Basically the accelerator is connected to a variable resistor (sometimes call a potentiometer or "pot"). It works much like a volume knob on a radio. The ECU uses the signal from this to determine the throttle pedal position and make adjustments to things such as ignition timing, A/F ratio and autobox shift points. In some cases (maybe the Mirage, I dont know) it uses this reading to operate an electronically controlled throttle.

Anyway, I think what he's getting at is if the pedal is pushed past a certain position (say 75% throttle) to goes into kickdown mode. The behavior you describe is normal, the only question is weather the time its taking is unusually long or not. Does the gear engage pretty solid, or does it slip a little at first?

SouperComputer

mondeo wrote: »

I don't understand though why she drove perfect with a light foot, no probs going up and down her gears by herself but with a heavy foot changed her tune, you had to release the accelerator some what to make her pick herself up. Pitty if there is a problem as she was in great condition otherwise.

Think I'd pass on it for now based on what I bolded..... It should revup bang into gear and get moving. Might even be some youtube videos on it. Try 'Kickdown" as your keyword.

Take a look at these... http://www.youtube.com/results?search_query=kickdown+test&aq=f

mondeo

SouperComputer wrote: »

He probably might fully understand he's saying.. Basically the accelerator is connected to a variable resistor (sometimes call a potentiometer or "pot"). It works much like a volume knob on a radio. The ECU uses the signal from this to determine the throttle pedal position and make adjustments to things such as ignition timing, A/F ratio and autobox shift points. In some cases (maybe the Mirage, I dont know) it uses this reading to operate an electronically controlled throttle.

Anyway, I think what he's getting at is if the pedal is pushed past a certain position (say 75% throttle) to goes into kickdown mode. The behavior you describe is normal, the only question is weather the time its taking is unusually long or not. Does the gear engage pretty solid, or does it slip a little at first?

It engages fine in tiptronic mode, I didn't notice any slippage in this mode, I don't know enough about autos to be sure though:(.

Happened also when I was flooring her going up a hill she just revved herself out of it like she slipped into neutral for a few secs. I found it very annoying and if it is a fault or not I don't know. Halfway on the accelerator she was great in everyway at going up hills etc.

mondeo

Lads just out of interest is there anyone here from navan/nobber/carrickleck area who is familiar with automatics who could have a look at this car to determine if it has indeed a dodgy tranny? Good mechanic from the area maybe? Few quid in it for ya obviously:)

Thanks

Mr Benevolent

OP, that box is an INVECS-II and has a rep for very quick kickdown shifts. This is based on Googling, not real life experience, but it gives me the impression that something is wrong.

TomMc

If you floor an automatic in "D" (say while your trying to overtake) kickdown will engage and so the box will drop a gear. The revs and noise will increase and the car will take off like the clappers. If it didn't change down gears you simply wouldn't be able to overtake safely (in an underpowered car) if it was in a high gear, as progress would be painfully slow. After it hits a certain amount of high revs the gears will change up once more. It may take a second for kickdown to action after flooring the throttle and the gear change may feel somewhat jerky and engine revs somewhat manic but that is normal. So long as it isn't taking several seconds to kickdown or isn't holding the lower gear for too long. After changing down, the gear will usually change up again before you have fully completed your overtaking move.

Autotranz (a Meathman) or Conway transmissions (both based in Dublin) are the best people to go to with regard autobox issues. Having owned several autos down the years, I can assure you that the average motor mechanic wouldn't haven't a clue about same. It is very much a specialist field.