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Occasional HARD downshift to 1st. When going slow

11K views 16 replies 12 participants last post by  mlfun 
#1 ·
Hi there, 2002 ml320 that just doesn't want to be my friend. Made in alabama, brought to me through canada...

Is it a clunk of death or is it because I got my ATF changed before I knew better?

When slowing down, about 7mph-0, if done just right there is a noticeable clunk when the car shifts from 2-1 or 1-neutral?(I'm not sure what automatics do when they stop pulling)

if the deceleration is quick, (not slamming on the brakes but maybe not the most gentle caress...3-5 seconds lets say) you don't notice the downshift.

if the deceleration is not complete, or slower, like coasting thru a stop over 5 or 6 seconds, you can feel the shift. approaching a stop, that sort of thing. it doesn't happen as much without applying the brakes though... if the car is slowly coasting down under it's own power, it doesn't tend to happen.

sometimes it's never there. if I use the "manual" shifting I can get thru the gears with no jarring.

No jumps when upshifting


I towed a decent uhaul from Canada to California.
I had the fluids changed(i know, i know!) right after I bought it in Canada.
which i read can cause this if done improperly... but knowing this car...

I didn't notice when the problem started because I was towing almost 100% of the time that I got used to the car and only noticed when I began driving in the city regularly.

Thanks! things to check, tests...? I didn't have the fluids done at the stealer, but I ran it by one because I thought I should just throw $400 away... they said, "yeah, after you told us, we noticed. but it's weird. We don't want to open up your transmission because we're worried it'll break more." which isn't very detailed... hahaha
 
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#3 ·
There is a complete DIY on the 722.6 transmission. The unit is for all intents and purposes bulletproof. Just maintain it and be alert to the leaking 13 pin connector and the conductor plate. Change the filter and the gasket seal using ATF-134. It should be fine. And if the stealer said "We don't want to open up your transmission because we're worried it'll break more." You need to file a complaint with Mercedes Benz N.A. against the moron who said that and the dealership because they are incompetent. They're either stupid or don't give a damn and either is dangerous. ( sorry for the rant)
 
#4 ·
David, there is no reason why this transmission should break down after a ATF change. But the fluid has to be filled in the correct amount. DIY about this procedure is all over the benz forums. Under or overfilled transmission can in fact damage it. Therefore it has to be done correctly. If you buy the transmission dipstick, you can check the fluid too.

Second common fix is to replace the electrical connector that notoriously leaks. A $25 fix part replacement can do miracles to your transmission.
 
#5 ·
I would only use a genuine MB 13 pin connector. No aftermarket part for this situation.

As you will discover, when reading other posts, the test is to remove the connector and if wet with trans fluid, then time to replace.

If you need to replace without draining the transmission, you will need to substantially tip the car up otherwise it will make quite the puddle. Doable, but be safe and support the vehicle more than one way. I had to do this on my 98 E320. I'd replaced the fluid and filter and used a URO brand connector. Six months later it began leaking. 8(

So the connector and proper fluid level will make for a smooth shifting trans.

Skippy
 
#6 ·
And I thought it was just me that had this issue. It is very annoying.

What I did observe, after changing the 13 pin connector, was that the clunk went away completely. However, with the replacement seal and gasket, the oil doesn't fully stop leaking, ie, bone dry. Instead, it seeps much much less and is barely wet. I don't think this is enough to cause an issue.

However, very shortly after, the transmission went back to its usual clunking.

My next guess is a conductor plate, however, I'll be damned if I throw that kind of time/money into it, to have it keep happening anyway.

Aggravating, but doesn't seem like a cure is in sight.
 
#7 ·
If you have not done a scan with a scanner that read MB specific trans codes then you are shooting in the dark. The 13 pin connector should not leak at all.

If you you have not looked at the TCM for ATF wicking into it then the job is barely half done. Also the fact you still have leak is not a good sign about how the 13 pin connector was replaced.

No codes = a guessing game.

Did you use a genuine MB or Chrysler 13 pin connector or an aftermarket one? The torque for the 7mm bolt that holds it into the plastic threads on the conductor plate is extremely low on the order of 5nm. Many people strip them and then the seal is not tight so it continues to leak.

If you needed a conductor plate your truck would be going in and out of limp mode.
 
#8 ·
Completed all of the above. TCM harness had wicking, dried it out, removed the TCM, disassembled and inspected that as well. Have done everything but spent $$$ at the dealer to have codes read. My universal code reader sees nothing. No CEL's. Nada.

When you first R&R, the trans shifts nicely. Then, it reverts to it's first gear at 4mph clunk that I've known to love. Sucks, but really, not much more I can find other than taking it to MB to have codes read.
 
#11 ·
Drippy 13 pin was replaced, ETC module was cleaned. Codes reset...

still clunking on my drive home during slow, automatic, downshifts from 2-1.

If I do it "manually" no clunk.

Old code was P2000 before clearing and driving off. (how long till "new" codes are stored?)

Did the key/peddle combo to reset the adaptive transmission

Fluid level is right in the center at 80 degree C

Was told the motor mounts could be out... (would that cause this symptom?)

ANYONE WANT TO BUY A 2002 ML320 IN SF CA?
 
#12 ·
after driving around a bit more...

it really seems that the problem is just that the automatic downshift point is set for too low RPM.
it happens around (estimated from gauge) 7 or 800rpm, when I'm practically stopped, and dumps down to "idle" at 500.

If I control the shift point while coasting or braking to a stop, and shift down at about 900 or 1k, it's MUCH smoother.

how can that value be changed? can I teach a better downshift?

Also it's even smoother with ESP off (!) but that's about the braking system... can that be set or reset?
 
#15 ·
2-1 down shift shifting harness

You may have to go to a dealer , that knows Xentry tab inside & out. I recently & still have a tranny whine in 1st - 2nd & 3rd gears , but not in 4th or 5th which leads me to believe I have a Torque Converter issue . So I went to the local Good Guy Mercedes Dealer . The tech asked if he could hook up the Xentry & look at the line pressures . Mine was at 217 and was told that was boarder line good , the tranny is showing signs and may be starting to have Issues. ( Mine wasn't low) . but at 150 it would be good . I did ask about or what Hi pressures ? their cause & effects. I forgot his answer ?? I do know that on my Kleemann CLK with a kompressor & my 05 E-55 AMG I installed Blue Top Maybach Solenoids P/N 240-277-00-98 . They raised the line pressures and gave me abrupt shifts ln 1-2-3 gears all the time.

So what I think is happening here with your ML . has adapted extended shifts from your trip . And has not re-adopted back to your normal driving habits . The quickie ECU reset thing doesn't always work for the TCU. Have the Dlr go to the corrections tab with the Xentry , got to adaptions and just reset the TCU only. There also may be a software update too. I would drive the ML like granny , for a couple of hundred miles . Cheers Patrick T.
 
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