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Super Moderator UK 2002 SLK320 Blue
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2,759 Posts
Discussion Starter #1
So Silkie has run faultlessly since changing the battery - until yesterday. Once yesterday and once today, when cold, I shifted into reverse ... and nothing. If I turn the car off and restart her, I can get reverse. When she's warm, the car shifts perfectly. Forward gears are fine - it's just reverse. And then only when cold.

To give you some background:
  • Silkie had a tranny service in April 2017 (including filter/ATF/pilot bush) at 98k miles (she's now on 110k) so that should still be OK
  • There was some fluid noticed in the passenger footwell at the time (which prompted the tranny service) but this was cleaned up and none entered the TCU
  • There are no shakes or clunks when she changes gear, also idling when in drive is smooth and there's no hestiation in changing gear when going forward
Now I know need to gather up some evidence so that I understand what's going on, but I was wondering if anyone can point me in the right direction? My thoughts are to:
  • Check the ATF level
  • Check the pilot bushing again and see if there is ATF in the loom/plug/footwell/TCU
  • Check if there are any codes from the OBD
Anything else anyone can suggest - either as root cause or as steps to take to isolate root cause?

Thanks
 

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Premium Member 2002 SLK320
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615 Posts
"There was some fluid noticed in the passenger footwell at the time (which prompted the tranny service) but this was cleaned up and none entered the TCU "

I woud start here. It's a common problem (apparantly - I haven't encountered it). If there is ATF in the footwell or on the wiring loom you have to replace the seal. If you didn't do this it's probably happening again. I would suggest searching for ATF wicking wiring loom.
 

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Registered 2001 SLK320
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874 Posts
I had this issue in my 1992 E300 but cold was really cold. Like -20C cold. Once it warmed up it was fine too.
They changed the transmission under warranty.
How cold are we talking here?
 

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Premium Member 2005 SLK55 AMG; 2005 SLK350
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4,606 Posts
I'm not 100% sure but I don't think the common TCU failure due to oil ingress has any temperature sensitivity - when it fails it fails - hot or cold. This sounds more like a solenoid or wiring/conductor plate, or a worn clutch. It would definitely be wise to scan it properly first thing.
 

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Registered 2002 SLK320
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1,758 Posts
Hi @savcom ,

Reverse Gears on Autos have the pressure boosted as there are so many elements to engage, so that will be the first thing to show up if there is low pressure due to starvation.

Firstly make absolutely certain the Fluid level is spot on.

If that doesn't cure it get the Pan off and be absolutely certain that the filter is properly seated and sealed against the Valve Block, also was it a genuine Filter ? ..........

If not install genuine MB Filter.

If all that checks out you are going to be looking at either a Valve Block issue, worth checking the strainers beneath the Shift and Pressure Solenoids, failing issues there it could be something failing internally, although I would say that would be much more likely if it was a hot engagement problem, whereas the Cold issue you are experiencing is more likely a blocked strainer or bad filter, or low fluid / displaced filter ..................

When Engine starts and fluid pumps around it doesn't flow back to the Sump and Filter quickly enough cold, and results in starvation, a displaced Filter will need a higher fluid level to draw, etc etc etc etc ;)

HTH,
 

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Super Moderator UK 2002 SLK320 Blue
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2,759 Posts
Discussion Starter #10
Whew! Thanks guys. 😊 (y)

Let's start at the top:

If there is ATF in the footwell or on the wiring loom you have to replace the seal. If you didn't do this it's probably happening again. I would suggest searching for ATF wicking wiring loom.
Been there; contributed to those threads. I had ATF in the loom back in 2017. All cleaned up at the time, but of course the oil still in the loom will still wick. No evidence of any wicking in the footwell this afternoon.

Is this happening in both W and S modes or is it just W or S?
I'm only running in S mode at the moment - not tried it in W.

I'm not 100% sure but I don't think the common TCU failure due to oil ingress has any temperature sensitivity - when it fails it fails - hot or cold. This sounds more like a solenoid or wiring/conductor plate, or a worn clutch. It would definitely be wise to scan it properly first thing.
I scanned the unit this afternoon - no codes. Absolutely clean. (I cleared the codes after changing the battery - nothing noted since).

Reverse Gears on Autos have the pressure boosted as there are so many elements to engage, so that will be the first thing to show up if there is low pressure due to starvation.

Firstly make absolutely certain the Fluid level is spot on.

If that doesn't cure it get the Pan off and be absolutely certain that the filter is properly seated and sealed against the Valve Block, also was it a genuine Filter ? ..........

If not install genuine MB Filter.

If all that checks out you are going to be looking at either a Valve Block issue, worth checking the strainers beneath the Shift and Pressure Solenoids, failing issues there it could be something failing internally, although I would say that would be much more likely if it was a hot engagement problem, whereas the Cold issue you are experiencing is more likely a blocked strainer or bad filter, or low fluid / displaced filter ..................

When Engine starts and fluid pumps around it doesn't flow back to the Sump and Filter quickly enough cold, and results in starvation, a displaced Filter will need a higher fluid level to draw, etc etc etc etc ;)
Hi @Dave2302. To answer your points:
  • ATF level measured at 80° this afternoon. The ATF is at the minimum on the dipstick (see photo). I think it's time for a small top up.
  • All MB parts used during the service including the ATF. I even swapped the lock on the filler cap to the red one to show it had been done.
  • Your last point makes the most sense. I can reverse when starting off - it's within the first few miles I have the issue.
A little light (cough) reading for you Savvy ..
Yep. Got that thanks @M4rCu5. Will be reading that shortly.

Two photos:
ATF level on the dipstick
571829


View under the car - looks like the pilot bush o-rings have gone (again!)
571830


I can get the bush and replace it - that's easy. It's getting the car up high enough to do the deed on the drive. Hey ho.

At least I filled the screenwash / pumped the tyres / found the buzz on the passenger door while the car was warming up. :giggle:

Got to get round the garden now to prepare the place for Storm Ciara
 

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Super Moderator UK 2002 SLK320 Blue
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2,759 Posts
Discussion Starter #12
Let's hope that's all it is and you've dodged a bullet (y)
Thanks @M4rCu5 - although I did dodge a bullet when I replaced the battery and found the air filter not clipped down. Fingers crossed this is all it is. Question is: how much ATF to add? It seems to be to add a little (200ml) at a time and remeasure.
 

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Premium Member 2001 SLK200K/2001 SLK320
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1,494 Posts
Thanks @M4rCu5 - although I did dodge a bullet when I replaced the battery and found the air filter not clipped down. Fingers crossed this is all it is. Question is: how much ATF to add? It seems to be to add a little (200ml) at a time and remeasure.
That's it, small increments until you're happy - THIS THREAD - for "how to" & "why" .. post 13 is particularly good 🙃


Hmm .. engine covers and air filters .. go bigger on that 320👌 .. different topic lol :cool:
 

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Super Moderator CA 2012 SLK55 AMG w/P30
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11,968 Posts
I think @Dave2302 mentioned less than 200ml in a recent thread.
I remember thats why my indy needed overnight (something about needing a complete drain?) when he did the fluid change. Next day, add a bit and measure. Add a bit and measure. There may have been another action taken after that little refill but I don't remember. Time consuming but required.
 

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Super Moderator UK 2002 SLK320 Blue
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2,759 Posts
Discussion Starter #16
Thanks all.

When the storm has passed (i.e. Tuesday) I'll put 200ml in at a time and re-test. Then I'll check again next weekend and see if this cures the reverse issue.
 

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Registered 2002 SLK320
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1,758 Posts
Hi,

Hmmm doesn't look mega low to me, that said lets hope the Fluid low, cold morning might be the problem,

Put in around 100ml when it's getting near the top, 200ml to start with when it's proper low ;)

The thing to remember when dipping is after each little top up ............
Whip it out, wipe it, whip it in, whip it out again, wipe it again etc etc about 8 - 10 times after each top up to get an accurate reading ;)

HTH,
 

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Super Moderator UK 2002 SLK320 Blue
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2,759 Posts
Discussion Starter #18
Hmmm doesn't look mega low to me, that said lets hope the Fluid low, cold morning might be the problem,
I know - that was done warm, of course. I'll do a cold check, just in case, but it won't hurt to top it up a little and get the pilot bush replaced when I can. If topping it up fixes the problem then that'll do for the moment.
 

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Registered
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159 Posts
Hi Dave. My understanding around the absence of a transmission dip-stick is that it is it is an MB dealer/specialist/independent workshop job that requires the transmission fluid to be at a particular temperature and a pre-measured amount and that there are three different choices of stick depending on gearbox details.

The ability to get the car at a comfortable working height is essential for H&S in the workplace;having the rather expensive garage equipment for draining and refilling the auto transmission and the ramp that ensures that the car is level and fully supported is paramount.

The transmission service on my SLK 230 auto some 4,000 miles ago was not a mind blowing cost at £202.00 including fluid,filter,gasket and labour.
 

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Registered 1997 SLK230 Kompressor
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218 Posts
Any further details available on that.....

The "that" being the 3 different dip-sticks previously mentioned. Still struggling a bit with the new web site on my Android.
 
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