722.6 unrequested downshift

[Volker]

Hi everyone

Patient is 2001 CLK 430 with automagic transmission. It has about 155 000 miles.

For some time I notice occasional strange shifting behavior from say, a stop sign (braking then accelerating at 5 mph). Also 1-2 sometimes is odd if you let off the pedal.

But the past couple days noticed something quite odd. Past month I drove only in "W"-mode (starts in 2nd gear). Now not so much ice so put in normal "S" mode.

a few times when car is warm, crusing steady normal speed on the highway to work, will downshift to 4th gear from 5th on its own. Shift itself is very smooth, only notice the tacho jump up from 2750-ish RPM to 3600-ish RPM. Exactly like if you slapped stick to the Honecker direction (it is valid comparison as the extra gas burning is similar). I didn't move my foot at all and normally the car at this speed doesn't give you a shift as you can accelerate quite fast at this speeds (or rather I don't try to shred license by using so much foot, not in this country)

But, if I flip switch back to "W", shifts nice and back to 5th gear and normal engine speed. Exactly as if slapped stick right.

But I can't get gear back by moving stick in "S", but I can downshift some more.

I don't know what the "range" is as of course this small LCD display is broken on my car.

Anyone see similar issues before? I think to check oil, but alas dipstick missing. Does anyone have length of dipstick? I would \pick one from scrap Mercedes in j-y but probably it would be a 190 or W124.

Thanks in advance for any suggestions

[RichardM98]

First, there is no dipstick but a 'dipstick tool' used to measure the fluid level but not to be left in place (too long). They are pretty cheap online (~$30). Tip - if the locking pin (plastic) on the dipstick tube cap is black then the transmission has probably never been opened. If red then fluid addition and/or service has been performed.

If the ATF has never been changed, you might consider doing it. Although, only in very rare instances does a fluid change solve problems. Remove the pan to examine the bottom for debris as a sign of wear. Also, there are posts on various MB sites on how to reset adaptation values for the 722.6xx. Finally, see someone (dealer?) with the proper equipment to read the transmission controller values as a starting point for analysis.

[MAVA]

Like Richard said, obtain the "testing" dipstick. you can buy the actual Mercedes stick or buy a clone on FleaBay

722.6 transmission fluid dipstick in eBay Motors | eBay

Have your codes read, or buy a cheap Chinese reader-It is not OBDII reader..
Here is a how to get a reader, see post 11, and see the diagnostic data on post 7

99 S320 Transmission Rebuild - Mercedes-Benz Forum


Best of luck,

Martin

[Hirnbeiss]

Check or just replace the kickdown switch under the gas pedal, and check/replace the transmission connector plug. If it shows oil, also check the trans control unit for fluid that wicked up from the connector.

[MAVA]

One more thing about the 722.6, the 722.6 is known to blow the main transmission computer seals, and the fluid from it will wick-up to the computer-See pictures on post 5 of this thread

My attempt at replacing the transmission plug. - Mercedes-Benz Forum

If you find fluid, replace the connector at the beginning of the thread, but you need open up the transmission computer, and clean it with contact cleaner. Blot it clean and dry. Do it about six to eight times, and then let it dry for six hours or overnight...

Also, you could be on the verge of a new conductor plate. Just for kicks, I would check your coolant for cooler failure too..

MArtin