Cruise control
 

On my 84 the cruise worked for a moment when I first bought it. Now no go. What is the most common issues? I've read the 928 international write up. I'm planning on Dyoxit the plugs. Has anyone run into it being as simple as that? Let me know what you found was wrong with yours.

On my 83 I had a bad vacuum connection. It would engage but slowly loose speed as the vacuum failed. I fixed that connection in the engine bay near the booster, removed, cleaned and lubed the unit with silicone and it worked for a while but now I have to clean the contacts in the engine bay as when it engages it sets off the center console warning light. The unit is in the front driverside panel behind the wheel well panel.

I have good vacuum. My problem seems to be electric.

I have an issue where the vacuum acceleration part works but the part where it maintains constant speed does not in my 81.

Most of the problems are inside of the metal box under the HVAC system that is essentially the brains of the cruise control where resistors wear out and such.

If you have good vacuum next would be to check input signals to the CC module per service manual. If it checks out OK there is something wrong with the CC-module. I would pull the unit out and send it to David Ruberg, the "speedometerrepairguy dot com" in Winona, MN. About $100, quick turnaround, lifetime warranty. Makes no sense to screw around with it unless you know what you're doing.

Just applied deoxit on all the connections in the system. We will see if it helped

So the cruise accelerates and pulls hard but as soon as I let off the lever the cruise cancels and doesn't hold the setting. When I pull the vacuum line off the booster that vacuum has held and escapes. Not sure what to do from here.

Well, if it's working at least some of the time, then I'd think that the tempostat (brain box) isn't totally toast.

Have you done the diagnostic procedure in the WSM?
All the way through?

Joe, I respectfully disagree.

I've had two instances of accelerating 'properly' with a push of the stalk, only to not hold the cruising speed. A new tempostat brain cured the problem both times.

The problem for me was that each 'new' (read:used) tempostat only lasted a year.

I'm thinking of sending my latest tempostat brain to Winona, MN, like others have advised.

I disconnected and clean the connections for the clutch pedal bypass circuit that is under the dash. Now because my car is an automatic there is just two wires bridge together. Since this is the last connection for the repair manual I can only assume that if the cruise does not work after this my only choice will be too have the circuit board of the cruise brain repaired. Has anyone removed the board from the box and done the soldering themselves?

Thanks Scott.

I haven't dug too far into mine yet. I was under the (apparently mistaken) impression that the tempostat was an "all or nothing" sort of thing.

Wrong again :icon501:

i repaired mine by removing the "brain box", and reflowing all the solder contacts with a soldering iron. was amazed when it actually worked again!

not difficult (and free if you have a soldering iron), just takes some time as there are a bunch of solder points.

Cruise links
 

This was a common concern aback in the nineties on the email listserv, there used to be a mercedes specialist that would address the 'brains' for a reasonable cost...not sure of the status of that...but it was very common subject of discussion.

More recently, someone on here followed posted instructions to re-flow the board using a household overn..

Some additional info, I don't recall whether the unit is actually M-B or just similar. It'll be some time until I go after the one in my '86.

http://www.peachparts.com/shopforum/...-articles.html

http://www.benzworld.org/forums/w201...pair-14-a.html

http://www.cruisecontrolrepair.com/

And of course the 928 vendors probably have rebuilds.

I do not recommend Autoecu.com. They had my 86.5 CC brain three times last year and could never get it to work. They are also very disorganized and it took numerous phone calls to get them to send it back to me the last time, and get a refund. They had a Ebay sale for the service at the time.

This is one issue where there's no good solution in my opinion. I didn't have the patience to reflow 1000 tiny solder joints, but some have been able to fix their brains this way. For some reason, the CC works perfectly in my 87 and it's NICE!

Also,
 

https://rennlist.com/forums/928-foru...rol-issue.html

and,
https://rennlist.com/forums/928-foru...ol-module.html