8 cylinder front engine iconic vehicle
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By Mongo
#188768
A few months ago a mechanic discovered a leaking transmission overload protection switch leaking through the electrical prongs and into the wiring harness.

Merlin was such a great help via PM on what to do, and how to do it.

His thread is here for the process.

​​https://rennlist.com/forums/diy-928/...tml?styleid=25

With this thread I am adding more context to his DIY. I ran into an issue where a 36mm socket does not have enough leverage to break the protection switch loose.

Tools you need:

36mm Combination Wrench (Huge for leverage)
Dead Blow Hammer (Breaks the old switch loose)
Drain pan (You can lose up to 1 quart of ATF)
8mm Socket and Wrench (for heat shield screws)
Dow Corning 111 for new o-rings
4 jack stands (all 4 wheels need to be up)
Brake Parts Cleaner for Cleaning grime (if you go OCD like I did and clean everything)

The parts:

140 277 01 51 Spacer Ring To Reaction Valve
016 997 34 48 Transmission O-Ring To Rear Case Plug
005 997 80 48 Transmission O-Ring For Reaction Valve At Band B1
016 997 35 48 Transmission O-Ring For Overload Protection Switch
002 545 45 14 Protection Switch

Background: The transmission overload protection switch was initially used on the Mercedes 722.3 transmission to remove timing during hard downshifts and the upshift from first to second. Since the Porsche A28 automatic transmission shares similar components with Mercedes, you will notice these are MB part numbers and this process is referenced on many Benz forums.

Here is my leak. Pretty obvious what it is:
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Last edited by Mongo on Thu Dec 15, 2022 10:30 am, edited 1 time in total.
User avatar
By Mongo
#188769
Loosen the transmission protection switch cap. Mine was loose already and you may need channel locks to break loose.

Once it's off, you may discover ATF has infiltrated the wiring harness at the connector. Use copious amounts of brake cleaner to make sure the connector and wiring are clean. Mine sat to dry for more than 2 weeks.
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By Mongo
#188770
Here is my connector cleaned. Sucker had more grease than my Big Mac for lunch.

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By Mongo
#188772
You will see your switch next. If your leak is not out of the weep hole and up the harness, it's leaking between the switch and the case then.

If you have the latter leak, you will need to replace the o-rings on the reaction valve behind the switch. Either way you're screwed when you get the switch off and have to replace the o-rings on the valve.

So start drinking, or sniffing glue..... Chances are you smelled enough brake cleaner and ATF to get the same effects as both.

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By Mongo
#188773
Are we having fun yet? No? Well too bad. Now the real sh*t show begins. Did you buy that big 36mm monkey wrench? If not, you probably want to grind a socket down like I did so it sits flush against the switch. The hex part is only 3/16" thick and strips like a frat girl on White Claw.

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Now that you see what could potentially be a disasterous pan or transmission pull, don't use a socket. Grab your wrench, dead blow hammer and smack that sucker.
User avatar
By Mongo
#188774
Like I said, monkey wrench, hammer, a firm smack and grip on that wrench.


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Typically the reaction valve comes out attached to the switch. The small o-ring in the switch was so deteriorated, it never properly sealed the switch, causing the leak into the connector due to pressure.

Here is an image of the valve stuck in the transmission still. I used a chopstick from last night's Panda Express to pull it out.

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User avatar
By worf
#188828
Nice.

Assembly instructions forthcoming? Torque on the switch? Any WSM-recommended goop on o-ring? New crush washer anywhere?
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By Mongo
#188845
Installation is reverse removal. Just kidding...


Remove the cap on the reaction valve with a flat blade screwdriver. Most of them come out in pieces after all these years. The pressure pin should come out easily.


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By Mongo
#188846
Old o-rings next. They fall apart just as easily. Use a set of picks to take care of these.

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By Mongo
#188847
Pic of the o-rings. There are 2. Don't bother with the one on the old switch. You are replacing the switch anyways.

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By Mongo
#188852
Spray the protection switch with lots of brake cleaner, then wipe clean with a lint free shop rag. You don't want any contaminants in the transmission. I bagged mine once sterilized since I had to crawl back under and clean up the mess of ATF.


Now what is so hard about this job is how to reinstall the valve PROPERLY. Managed to snap a pic of the dimple in the brake band the pin of the reaction valve must sit in. I was lucky to have mine smack dead center.

Now I have heard some horror stories in the Mercedes forums where people have installed the switch with the valve attached, and torqued on. If you do this, you are guaranteed to screw up your brake band because more than likely you will not properly seat the pin in the dimple.

You need to get it in the hole properly. (What she said). There a tab on the switch and recess on the case to help straighten things out on install. Those instructions will be coming soon after my morning coffee and donuts. Sorry.

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By Mongo
#188859
Okay now that I've had one cup but no donut I can continue on..

Lay your parts out on a clean towel. Install the o-rings first. Take note that the pair on the reaction valve are different diameters. Not hard to screw this up honestly. Use Dow Corning 111 to keep them fresh.
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By Mongo
#188861
Pic of the o-rings before and after install.
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By Mongo
#188862
Next we will need to make sure the pin can hold position so that it's easier to contact the dimple on the brake band. Lots of Vaseline helps here. Don't worry it dissolves safely in the ATF so lube that pin up

(most of you should be good at this I assume. ) :lol2:

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Don't forget the little o-ring on your switch. Use Dow 111 on that too. Everything should look like this before installation.

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User avatar
By Mongo
#188864
Now that you're reaction valve is assembled, let's get this job done.

Make sure to align your pin the way your dimple on the brake band sits before inserting. I used the pic as orientation. Everything should go together easy. You don't have to force the reaction valve into the case. It will sit nearly flush against the case if you did this right. Note the reaction valve has a spring behind the pin internally that will keep it from being 100% seated. This is okay.
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Thread the switch by hand. Make sure it's not cross-threading. Because there is a cut recess for the reaction valve alignment, you can skip an entire thread and ruin your day if done in a rush. So take it slow!

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Torque the switch to 52 lbs/ft. I couldn't get my torque wrench to properly fit under the car since I don't have a lift. I used my combination wrench and made sure it was good and tight.

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After torquing and tightening the protection switch, plug the harness back in and screw the retaining cap back on.

Install the screws in the heat shield you loosened for more room to access the area. You are done with the install and will need to replace the ATF you lost on removal.

Congratulations. Some mechanics out there insist this job requires pulling the transmission. It does not and you can feel more satisfaction doing this yourself.

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