Great results! Hopefully it drives properly now.

And I understand that time is money. If I could get a new cruise unit for $100, slap it in, and be done with it I would. But not for triple that... I'll try to fix it first

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

For me it's more the principle and the hobby. I just love fixing things myself, when I can find the time. Plus I take pride working on an old Benz - I am, indeed, from Stuttgart!

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

I agree but I do not have the patience you have! I love fixing things especially on my old Mercedes but I opted to try a used replacement CCA on Ebay this time. Guess I am not from Stuttgart!

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1989 300E

2005 Acura TL

2011 Hyundai Elantra Limited

Swing hard! Take chances!

Well, I received the used CCA from a 1992 300E (mine is a 1989 300E). It seems to work fine without a hiccup. Hope it will last for awhile! Didn't cost much for it.

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1989 300E

2005 Acura TL

2011 Hyundai Elantra Limited

Swing hard! Take chances!

OK, not only did the cruise control act reliably, but it seemed to be much, much smoother than before! I don't know about the circuitry, but it was so smooth you almost could not tell it was on! I never had it like this!

A couple of notes:

(1) The electrolytic capacitors have polarity. For anyone doing this, make sure you put them in correctly, unless you want them to pop like small firecrackers.

(2) Putting the unit back in was a real pain, because the screw (10 mm bold) that bracket holds on to by the pedal will keep on retracting as you are trying to mount this. After a couple of hours trying, in really tight space, I gave up and bought the same bold almost twice the length. This allowed me to install the unit in minutes - I just let it hang on the super long bolt as I screwed the nut on top. There is plenty of room for the longer bolt, and it will save you tons of time and bad language.

So the conclusion is: When you re-solder, replace the electrolytic capacitors!

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

Woot! Glad to hear its working well. And I know what you mean about smoothness. I never had cruise feel so "intelligent" before. On some cars one engages, but the car drops maybe a mile per hour when you take off the pedal. The cruise sees that and suddenly engages causes a small jerk in movement. Not the MB setup, its very smooth and smart!

As for the module. There is a MUCH easier method for removing and reinstalling. Since I was removing mine A LOT, I found this tip helpful. Simple bend back the aluminum case tabs that are bent in on the pin side. When one does this the board simple falls out if the connection is removed. Then you can just slide it back up in (within the rails for the board) and bend the tabs back. Saves a ton of time.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

Unbelievable! My problem in the past was that the thing would disengage suddenly after a few minutes. But otherwise it seemed to "work". I had no idea, though, that beyond disengaging it was really not working the way it was designed to. All I wonder is what the role of the capacitors was. It would make sense that it would drop out when one capacitor is intermittent, but this totally new feel just because of a couple of capacitors still befuddles me.

Yeah - you made it easy for yourself if you have to service the box again. I am saying that hopefully I won't have to touch the thing again for the next decade.

Oh yes - the parts list was a real killer $5.something, including shipping, and buying DOUBLES (i.e. instead of two capacitors I bought four of each). I'll post a picture of the finished board with the new units tomorrow.

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

How about getting a couple kits together. I would not have an issue paying $10 plus flat-rate shipping for a "kit". Mind you I dont need one, but when I was hunting around and reading up I would have much rather had a kit. Of course keep in mind this kit would be specific to certain years and not all W126. I think 86 and up. The board you pictured looks just like mine in my 91.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

I know the ~88 and 91 boards I have are not identical. I'll dig them out tomorrow and take pictures... I might desolder the caps too and test them, find if they are the problem.

-J

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

I'll see if I can grab a pic too. To be certain. I will be taking most of the inside of the car apart anyway.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

Read the capacitor markings on all of those if you could. The kit idea might be fun. The principle is the same: You wash the solder side of the boards with acetone, using a toothbrush, re-solder all the connections except for the transistors (you need to do those carefully with a heat sink if you are going to touch those) and the ICs, and scrap & replace the electrolyte capacitors.

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

Below is the circuit board with the new capacitors. For future reference to anyone who wants to use these instructions, I have added the polarities to this image.



CORRECTIVE NOTE: "nF" in this image should be read "μF"

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

Here is a picture of the board from my 91, made in 1990. It looks nearly identical to the one you pictured:



I see a couple small differences though.

I checked the two 22nF caps and according to my meter they were each about 26nF.

Did you do any checks on the resistors in the coding plug?

Also, I wonder why all the caps are "high" voltage? Surly the module runs at 5-12v internally?

-Jason

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

The higher voltage generally means the capacitors last longer under heavy use. I wondered about this too, and looked it up in my electronics text books. So theoretically a 22 μF 12v capacitor will go bad before a 22 μF 63v capacitor, even though the circuit never goes above 12v.

As per checking anything else, I did not, because logic would dictate that I would have to remove each component first before testing (since the current from the meter can travel other routes in the circuit if the component is still installed...)

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

I checked all the caps you had listed and they each tested close to their rated value (I unsoldered one leg). Bummer

-J

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.