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50 years of MB
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5,046 Posts
hmmmm, $155 or just look to see if an oring or thread tape is needed......
 

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1988 Mercedes 500 sec
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1,344 Posts
Discussion Starter · #8 ·
I'm not penny foolish and definitely don't do things on the cheap lol just spent thousands on a full nut bolt restoration, I am generally asking how to check if it is faulty, if you have an answer, I would be happy to listen if you don't then don't waste time with silly comments
 

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'17 GLS450, '14 GLK250 "Grandpa's Roadster" Project Car, 350SDL (Sold)
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5,595 Posts
Clean it off and then try to figure out where the leak originates. It looks like it's leaking trough the sensor itself, buit it's hard to tell for sure with all that fluid there.

If it's leaking through the threads do not use thread tape unless the manual says to. It tends to degrade into tiny threads that can pass through screens and even some filters and plug up the works. If there's no o-ring or gasket and it's tapered treads, use thread dope to aid in the seal.
 

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1988 Mercedes 500 sec
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1,344 Posts
Discussion Starter · #10 ·
thanks, will give mercedes a ring tomorrow and see if there is an o ring, if not then its possible like you say it is the sensor itself
do you have a link, from the manual, on torque setting for installation
 

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'17 GLS450, '14 GLK250 "Grandpa's Roadster" Project Car, 350SDL (Sold)
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5,595 Posts
Why don't you take it out and look at it? Looks like a knurled nut; you tighten it with your fingers, not a torque wrench.
 

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1988 Mercedes 500 sec
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1,344 Posts
Discussion Starter · #12 ·
i have just serviced the transmission, changed all the seals that were leaking and now this has started, I assume I will lose most of the transmission fluid in the process
 

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'17 GLS450, '14 GLK250 "Grandpa's Roadster" Project Car, 350SDL (Sold)
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5,595 Posts
Can't tell where the sensor is on the trans from the picture. Unless it's in the bottom of the pan I don't think you'll loose much fluid.
 

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1988 Mercedes 500 sec
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1,344 Posts
Discussion Starter · #14 ·
Found a little more info, seems they can fail and leak through the sensor, normally where the two pins for the wires are located
Failure symptoms are slight misfire when driving at high speed high revs and I believe a 1 to 2 second delay in downshift, do the secs normally have a delay when down shifting or should it be an instant downshift when the pedal is fully pressed

What is the purpose of the knurled nut, I believe once this is removed the sensor has to be removed using a spanner or socket, but not sure what to torque it back to, if anyone has the relevant section from the manual, taht would be very helpful

I also found, to replace, the following parts may be needed

297 A 126 270 30 89 VALVE (REACTION VALVE) B1 (no need to replace)
298 A 126 277 09 75 PIN (no need to replace)
299 A 005 997 80 48 SEAL RING
300 A 016 997 34 48 O-RING
301 A 140 277 01 51 SPACER RING
304 A 016 997 35 48 SEAL RING
303 A 002 545 45 14 SWITCH TRANSMISSION OVERLOAD PROTECTOR B 1
Product Font Line Parallel Auto part
 

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1989 W124 260E
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7,306 Posts
Benz1 For starters, you never said that you had rebuilt the transmission, but if you had i would have known that your are no novice . So you must have missed a major part,, i would have thought a rebuild would include this vital sensor . . Lets hope it all works out in the end for you.
 

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1991 560 SEC
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11 Posts
Any ideas what this sensor is for, it is on the left side of the transmission and seems to have oil on it, not sure if there is an O ring that needs replacing or the sensor needs to be replaced.
From what I observed in your pictures....... The rubber boot with the wire going through it was attached where the knurling is on the part in question. It also appears to have a standard hex for wrenching the part on and off the vehicle. My own experience is when in doubt go to your MB dealership and get your questions answered in the parts department Here where I live they have always been very helpful
 

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1991 560 SEC
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11 Posts
From what I observed in your pictures....... The rubber boot with the wire going through it was attached where the knurling is on the part in question. It also appears to have a standard hex for wrenching the part on and off the vehicle. My own experience is when in doubt go to your MB dealership and get your questions answered in the parts department Here where I live they have always been very helpful
Additionally I don't see any leakage below the knurled area which indicates to me the leakage is coming from the center area of the device and not from its interface areas. This is a common failure with these type components
 
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