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MMT clutch slipping, workshop manual, & fix and tuning?


sceh
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I have a 2005 Yaris petrol with the MMT box.
It has started to show a slight slipping between gears, especially 3rd and 4th. In other words, when it changes the engine over revs a little before it changes. This is recent. Is this a known problem fixable by an adjustment I can make by chance?

thanks for any help or pointers

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On 7/30/2021 at 9:54 AM, sceh said:

I have a 2005 Yaris petrol with the MMT box.
It has started to show a slight slipping between gears, especially 3rd and 4th. In other words, when it changes the engine over revs a little before it changes. This is recent. Is this a known problem fixable by an adjustment I can make by chance?

thanks for any help or pointers

Yes,it`s a known problem. MMT boxes are notoriously unreliable and should be avoided.

What followed MMT was MULTIDRIVE an excellent CVT autobox which has proven to be very reliable indeed.

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5 minutes ago, john p williams said:

Yes,it`s a known problem. MMT boxes are notoriously unreliable and should be avoided.

What followed MMT was MULTIDRIVE an excellent CVT autobox which has proven to be very reliable indeed.

The box is fine John, it's the application of it's operation that is totally flawed!

I agree re the Multidrive. Many criticise CVT but I have no issues with it at all. Takes a little getting used to at first.  All fingers and toes crossed in the hope and belief that it will continue like that in my car.

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2 minutes ago, mrpj said:

The box is fine John, it's the application of it's operation that is totally flawed!

I agree re the Multidrive. Many criticise CVT but I have no issues with it at all. Takes a little getting used to at first.  All fingers and toes crossed in the hope and belief that it will continue like that in my car.

I take your point Peter. I used the word box incorrectly.

In addition to the examples of Marques I mentioned having problems with Electronic Manuals, I should have mentioned VW Group, Ford  Volvo and Mercedes(in A and B class models). Ford and Volvo have now reverted to Torque Convertors.

I have in our family, 3 Torque Convertor (2 Mazda and a Merc), one Multidrive (Yaris) and one ECVT (Lexus GS) and not had an ounce of a problem any. All are creamy smooth and sheer delight to drive. Not suitable for Audi, BMW and (new) Merc drivers though!

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It may just need a recalibration, there are known issues with the clutch motor and position sensor

INF12215_GB.pdf

 

The worse semi auto i have come across is the Vauxhall/Opel Easytronic they did drop it but decided to Use it in the Adam with disastrous results

 

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Brilliant document. I assume I can just calibrate the MMT ECU and then the clutch since I will not remove any parts and won't need to clamp the clutch?

 

Anyone actually done this? I am a bit apprehensive having once connected an ODB reader and completely wrecked the calibration just by reading codes..

 

 

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I wasn't trying to be a smart alec John - honest! Maybe a touch pedantic.:rolleyes:

I'm sure the description of Ford's Powershift most often used, i.e. powersh!t (my exclamation substitute), is most accurate.

I suspect Toyota's MMT is better than theirs, only just?

 

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17 minutes ago, mrpj said:

I wasn't trying to be a smart alec John - honest! Maybe a touch pedantic.:rolleyes:

 

Your comment was fine Peter. I detected nothing I didn`t warm to.😊

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The best automatic gearbox is one that doesn't exist.

Only after a specific gearbox has proven it is reliable is it to be trusted, but you need to wait to find out, is my experience. 🙄

If you don't expect anything from it, you won't be disappointed.

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It might just be that the clutch just needs changing - The MMTs is just a normal manual transmission but computers control the clutch and gear shifts, so they do wear out over time just like a normal manual clutch. If it's still on the original after 45k and you mostly drive it in start-stop traffic it's likely just wear.

 

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I do mainly drive in traffic so it could well be wear but this means the car is scrap since the cost of the clutch alone exceeds the car value even though I would do the work myself. I will try the initialisation procedures of the box and clutch and then see if we have a one way trip to the scrappy..

I am still  curious as to why Toyota designed a box which clearly has issues and why they didn't simply sign a volume contract for proper auto boxes since these would be cheaper and more reliable than this experiment which has no advantage to the end user. Odd

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The problem is we're too miserly - Most car automatics used to use torque converters, and indeed the Mk1 Yaris originally had a 4-speed automatic, but the problem with torque converters is they waste a lot of energy which means they're thirstier and  attract higher car tax (When car tax was still based on CO2), and people didn't want to pay £100 more tax and have to fill up more over the manual version.

That's why most automatic gearboxes, not just Toyotas, are now single or double-clutch automated manuals like the MMT, Tiptronic, DSG etc.; These have similar efficiency to a manual gearbox, but they do wear out. Some cars use belt-driven CVT for their autobox, but these are not popular because they don't feel nice to drive (The classic press accelerator, engine revs up, car doesn't accelerate complaint).

But all autoboxes are expensive to repair compared to manuals - That's one of the reasons I avoid them. Just be glad it's not a DSG gearbox! Yours is at least potentially repairable without a 4-figure outlay!

The problem you're going to have is all gearboxs will need some refurbishment or repair when a car gets that old - Even torque converters and modern CVTs, which typically require a lot less maintenance than automated manual boxes. The only cars that won't are EVs and Toyota hybrids, because neither have gearboxes as such.

 

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I'd say auto boxes are more reliable in the long run than manuals and if you did need to swap one out, the cost of a refurbished unit plus labour would be less than fixing and MMT I suspect.

Today I will try the clutch reset procedure to see if it makes any difference and if not, scrapyard..

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Oops...I did it. Reinitialised the clutch using the procedure.

I did not get all the the buzzer to confirm so I tired again and still didn't get it but when I pumped the brake at the end I did get it.

Started the car, pressed the accelerator and nothing happened! The N was flashing so I switched off and on again. Same result. Third tie lucky, no flashing N and the accelerator revs the engine. Put it in gear (E) and the engine revs slightly higher than previously before engaging so it implies something has happened clutchwise. I have not road tested it yet until I get a bit of feedback. The N no longer blinks which implies the MMT learning is complete.

 

Any advice before I hit the road? Did I do it right?

 

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AFter a VERY short drive (ie up and down my long drive) I notice it revs to 2500 or so before engaging the first gear and less so for second. Longer drive tomorrow but I am worried!

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BTW, since I only initialised the clutch and not the box and therefore did not delete the old memory, should it not simply follow what it had before?

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So, did a test drive and got back safely! I will do a few more miles tomorrow but I notice already that to start it needs to rev to 3000+ before the clutch slowly engages. Then in second gear (using the manual ****) it revs to about 2000  once engages and then settles down. The other gears seem OK. So it seems to over-rev as though the clutch is either engaged and slipping or engaging slowly.

I tried it in E position and it seems slightly better but still the sensation of over-revving

Any ideas here?

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It still revs to 3000+ when it changes gear manually or automatically. It is better is 3/4/5 but still not right. It is driveable with care but if this slipping continues it is a matter of time before the clutch is burnt out. Any manual adjustments I can do?

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and as an ancillary question, if I buy an ODB reader instead of paying 80 euros for the pleasure of hearing it from Toyota, which is best? I had one years ago with some software from a Canadian company and it completely wrecked the electronics..

And will an ODB reader tell ma anything useful?

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It will give you the error codes, you can either Google them or a good reader will have the definition of them too.

Then when you go to the dealer you'll know if they are being truthful on what's wrong.

A good one shouldn't damage your electronics.  It should have a scan mode that's read only and separate from any programming mode.  

A lot of people have success with doing things like setting auto lock, or doing test cycles, but I've always been wary of doing that.

Also a good one can display real time info like O2 levels, true engine temp, even yaw and roll of the stability sensors.

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  • FROSTYBALLS changed the title to MMT clutch slipping, workshop manual, & fix and tuning?

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