Cruise control issues - PeachParts Mercedes-Benz Forum

rwthomas1 · #1 04-04-2003, 10:17 PM

Okay, my cruise control has progressed from mild surging to a state where it no longer is tolerable. It acts like you are pumping the accelerator very quickly. I grabbed a cruise amp from an 82 SD and tried it out. It works okay for a few minutes but soon starts to surge intermitantly and especially on downgrades. I have tested the system according to GDL's instructions and all seems well. The only test I cannot do is the speed sensor test. My actuator is a little noisy and is pulling 180-185mA, the spec is 120-180mA so I am thinking it may be my actuator. Bottom line is this: These friggin' things are too expensive! GDL wants @ 1/7th the value of my car to rebuild my parts. Junkyard is an option but who knows if it'll work? I am considering replacing the MB system with an aftermarket cruise unit. I may even be able to wire the MB cruise switch to the aftermarket unit so I can retain the MB "look". I am unsure if I will be able to use a vacuum system? I know MB did in the earlier models. There is a possibility that there is an electromechanical aftermarket system available too. Prices I am seeing are $80-$120 for an aftermarket system and that sure beats the price of a rebuilt MB system..... Any thoughts on this? Thanks, RT

Diesel 924 · #2 04-05-2003, 09:44 AM

I fixed my surging problem with a reman amp from Ebay. A garage in California had ordered it for a customer who didn't show up for the work. I got it for $50. It wasn't the exact part number that the old one was, and the bracket didn't bolt to the car right(I used a wire-tie to hold it), but the connector connected. It works awesome. I tried the trick of re-soldering the points on the printed circuit of the old one before I bought this one, it didn't work. Plus, as soon as you open the case, the rebuilding companies don't want them anymore. One thing: make sure your linkages are set according to the factory manual and the pivot points are lubed with a little white lithium grease. It's too bad I didn't know you had this problem at the GTG, I would have taken out the actuator so you could have tried it in your car....process of elimination!! Just like the dealership techs do; "Substitute known good part!".

#3 04-05-2003, 01:10 PM

I would check to see if your speed sensor is not dirty where its picking up the speed of the vehicle. It might be lying to the amp which causes it to submit wrong information to the actuator

bjcsc · #4 04-05-2003, 02:09 PM

rwthomas1:
I went through all of this and you probably have read my post in the archives as I contains my entire experience. GDL will test and clean your actuator for a lot less than rebuilding it, but that slight increase in draw does not seem patholgical to me. I would suspect the amp. If you are even thinking about testing or cleaning the speed sensor, just buy another and replace it. They're cheap and it's not worth taking the dash out twice if you end up having to replace it anyway. As far as surging goes, it very well could be your linkage, esp. the rod that connects to the actuator. Pop the linkage of off the actuator arm and make sure that when the linkage is at rest, the arm of the actuator is at the end of it's travel. If it is not, shorten that rod until it is.