Automatic gearbox issue - jerk - downshift

[Comfortably Numb]

According to the Haynes manual, there are 2 wiring connectors clipped to the front of the transmission, which, once released from their brackets, should be twisted apart. The gearbox ECU will also show any stored faults if connected to T4 diagnostics. It is quite possible that the 2/3rd gear solenoid valve is the only one sticking, then suddenly activating/unsticking, causing the jerk. Changing the ATF (you may need to do 2 changes to ensure the majority of it is replaced), should help clean any sticky residues from the oil galleries and valves.My Audi A4 B5 used to change from 3rd to 2nd automatically with a slight jerk as it slowed down, but manually shifting from 3rd to 2nd, it would wait until the speed was reduced to the set parameters before dropping down fairly smoothly. My old Mitsubishi 4x4 (1991) does not seem to change down in this way, but always seems to be in the right gear when I re-apply the accelerator - smoothest Auto I know - as smooth and predictable as wife's tiptronic SLK box.

[trikey]

Originally Posted by Comfortably Numb

According to the Haynes manual, there are 2 wiring connectors clipped to the front of the transmission, which, once released from their brackets, should be twisted apart. The gearbox ECU will also show any stored faults if connected to T4 diagnostics. It is quite possible that the 2/3rd gear solenoid valve is the only one sticking, then suddenly activating/unsticking, causing the jerk. Changing the ATF (you may need to do 2 changes to ensure the majority of it is replaced), should help clean any sticky residues from the oil galleries and valves.My Audi A4 B5 used to change from 3rd to 2nd automatically with a slight jerk as it slowed down, but manually shifting from 3rd to 2nd, it would wait until the speed was reduced to the set parameters before dropping down fairly smoothly. My old Mitsubishi 4x4 (1991) does not seem to change down in this way, but always seems to be in the right gear when I re-apply the accelerator - smoothest Auto I know - as smooth and predictable as wife's tiptronic SLK box.

I reckon you are 100% with the diagnosis.

[xsport]

Originally Posted by Stanley008

Hi,
any idea what could cause jerk/small kick in automatic gearbox when downshifting? It is more obvious when the engine/gearbox is cold(less obvious or it even dissapears when the gearbox gets warm) and the thing happens only when downshifting and it seems that it only happens from 3 to 2nd gear around 40kmh/ 25mph? You can hear and feel the jerk / kick pretty obvious. But only from 3 to 2nd gear, other gears are OK. Any idea? Solenoid? Or it is just completely failing? The gearbox has 120 000km/ 75000 mil .

they all do it on the kv6 auto.change your fluid as you will probably find the solenoid is ok.i find in mine that it only happens when the brake pedal is operated for over a few seconds and like upwards changes you can to a degree influence the box changes. probably those who have the diesel variant dont have the snatch as much as the kv6 due to rpm and gear ratio differences. a fluid change wont go amiss anyway. regards xsport

[kaiser]

I changed my fluid, and it completely transformed the box and especially the upshift from 2 to 3, as far as I remember.

[genpk]

Had exactly the same symptoms after my car had been parked for about 4 weeks of no use.
First time i started it up the changes were terrible for about 15 minutes and then came good, next day same thing for about 10 minutes, next day ran perfectly and has done ever since ( 4 years ago)
Turns out the solenoids were sticking
A good oil change will probably fix it.
If not, solenoids can be changed without the auto being removed

[rustymotor]

We have run autos for past 20 years because my wife can't drive a manual, ATF changed every 3 years or 30K religiously last but one car had 300K miles no problems with the auto box, same on the Honda Auto she runs now. Considering the cost of a replacement box or a rebuild at £1200 it makes a lot of sense to me anyways.

[slovcan]

Originally Posted by rustymotor

We have run autos for past 20 years because my wife can't drive a manual, ATF changed every 3 years or 30K religiously last but one car had 300K miles no problems with the auto box, same on the Honda Auto she runs now. Considering the cost of a replacement box or a rebuild at £1200 it makes a lot of sense to me anyways.

The two KEY things for automatic transmission reliability and longevity are 1) as said, bi- or tri-annual fluid changes and, 2) use of an EXTERNAL ONLY transmission fluid cooler. This is different to what most manufacturers fit, which is actually a pipe/tank affair INSIDE a radiator tank. That OEM design ensures that your transmission fluid temperature is always at ~190F which is way too hot (by 15-20F).

Cheers,
Glenn

[SD1too]

Originally Posted by slovcan

The two KEY things for automatic transmission reliability and longevity are 1) as said, bi- or tri-annual fluid changes and, 2) use of an EXTERNAL ONLY transmission fluid cooler. This is different to what most manufacturers fit, which is actually a pipe/tank affair INSIDE a radiator tank. That OEM design ensures that your transmission fluid temperature is always at ~190F which is way too hot (by 15-20F).

Sorry Glenn but the evidence does not support your assertion. Neither my SD1 nor my 75 has had anything like bi-annual or tri-annual fluid changes and both transmissions are working perfectly. Also, my SD1 has an ATF to coolant heat exchanger inside the radiator which you consider unsatisfactory. It has functioned perfectly for 34 years!

Simon

[slovcan]

Originally Posted by SD1too

Sorry Glenn but the evidence does not support your assertion. Neither my SD1 nor my 75 has had anything like bi-annual or tri-annual fluid changes and both transmissions are working perfectly. Also, my SD1 has an ATF to coolant heat exchanger inside the radiator which you consider unsatisfactory. It has functioned perfectly for 34 years!

Simon

Hi Simon, I guess all automatic transmissions are not created equal. My experience is with the Nissan 4-speed one in the 300ZX and my old Infiniti Q45. The originals were famous for failing on long uphill drives (10-20 kms). In all cases it came down to excessive heat causing the plastic internal parts to fail. The dealers replaced mine under warranty for the original owner at about 60,000 kms. I did the external cooler and bypassed the in-tank heat exchanger (thanks, most people call it a cooler which is not quite correct) at about 120,000 kms. I sold the car with over 350,000 kms on it. The new owner drove it another 100,000 kms before it was written off after being rear-ended.

Chevrolet put an external-only cooler on my 3/4 ton 7.4 litre truck as part of the factory towing package. I am somewhere around 275,000 kms on that one and it has pulled a lot of weight (5th wheel camper) up the same hill that killed the Q45 transmission (Coquihalla Highway in British Columbia).

The autos in Audi A6's (I had one) are famous for failing solenoids. I have to wonder of heat (fluid at 190F) contributes to that.

Coolers are cheap as are fluid changes every 2 or 3 years. Lots of folks will plumb an external cooler in series so the fluid cools after it leaves the in-tank heat exchanger. This works but bypassing it works better.

Anyway, my experience.

Cheers,
Glenn

[rustymotor]

Hi, Having the auto box oil cooler in the rad caused Mercedes owners numerous and very expensive problems. So no amount of oil changes will fix that issue..fitting an external oil cooler has to be a good move especially towing a lot with an auto.