how do i trouble shoot my cruise control - PeachParts Mercedes-Benz Forum

ray m · #1 08-13-2007, 11:31 PM

1982 240d 4speed manual; My cruise control is not working. Is there anyone who can direct me how & where to check it out so I can fix it. I sure miss my cruise control. when you drive 25 minutes down a back road to get to work the cruise control is missed. Any links to DIY's etc. RAY M

lietuviai · #2 08-13-2007, 11:40 PM

A .22 cal usually does the trick.

There are lots of threads about the subject. Do a search on Google (or whatever you use) with mercedesshop.com in the search line.

cdplayer · #3 08-14-2007, 12:11 AM

My cruise stopped working awhile back too. Then I read in this forum to only use Oshram or Bosch brake light bulbs. Not the #1157 you get at your local parts store. The cruise system relies on a critical ground signal from the bulb to operate correctly. #1157 bulbs do not have this, thus the cruise system thinks the brake is applied, and therefore disengages.

I remember replacing a burned out lightbulb with one I had in the garage. Sure enough, no cruise. So I got myself several Oshram bulbs at the junk yard for $1.00. Got cruise. I hope your problem is as easy to fix.

If not checkout the DIY links by clicking on "shopforum" at the top left of this page. Arrow down until you find the link. Then look through them for cruise control. Good luck

Brian Carlton · #4 08-14-2007, 05:55 PM

Start here:

http://www.gdl-online.com/testproc.html

Follow the test procedures to determine whether the actuator or the amplifier is the problem.

These fellows also rebuild the unit for a reasonable charge.

bodyart27 · #5 08-14-2007, 06:56 PM

I used GDL and had nice service (maybe a bit slow - but super nice to talk to).

One thing that I REALLY liked on my 84 300sd is that you can send in both the under dash brain and the underhood actuator and they can bench test both units together. Before you start swapping / buying parts you at least will know what the heck failed!

I had my unit worked on programa thinking it was the brain - found out later through GDL it was the actuator.... lesson learned!

dieseldiehard · #6 08-15-2007, 01:54 AM

I always suspect the actuator, after learning the same lesson.
THink of this, every time you press the accelerator linkage the actuator gets "exercised" meaning the internal variable resistor sees some wear. If you have ever had problems with early film cameras where the exposures come out wrong because the exposure setting is faulty due to a worn ring resistor, its the same problem. The fine wire or, in some variable resistors a thin metal film, wears every time the wiper goes across the resistance surface. I learned this from a Nikon F I have (I still own it BTW) when it started having a jumpy needle in the viewfinder. An old German camera repairman showed me what they look like. Its amazing but these have a finite number of times they get rotated before the things wear thin and no longer are reliable. It seems that VDO actuators also suffer the same fate.

I spoke with General Development too, real nice guy and he confirmed this.
His rebuilds are all I use now and have had no problems with them. Incidentally he sold me a new actuator instead of rebuilding mine, on the 124 chassis its buried and a real PITA to R&R compared to the 123 and 126 cars. I didn't want to compromise, and a new one was sorta pricey but at least my cruise is good now on 3 of my cars.
Cruise on the '79 300TD has been disconnected though. It is the old vacuum actuator and with a late turbo engine in it its simply too much work to convert to the new electronics to get cruise working on that car. I've got too many other projects for now

Incidentally, someday I want to debunk the adage that brass or nickel bulbs

can cause cruise to not work or work, depending on who you talk to. This is a non scientific area that bears investigation (flame suit on).

DDH

ray m · #7 08-17-2007, 10:14 PM

Quote:

Originally Posted by cdplayer

My cruise stopped working awhile back too. Then I read in this forum to only use Oshram or Bosch brake light bulbs. Not the #1157 you get at your local parts store. The cruise system relies on a critical ground signal from the bulb to operate correctly. #1157 bulbs do not have this, thus the cruise system thinks the brake is applied, and therefore disengages.

I remember replacing a burned out lightbulb with one I had in the garage. Sure enough, no cruise. So I got myself several Oshram bulbs at the junk yard for $1.00. Got cruise. I hope your problem is as easy to fix.

If not checkout the DIY links by clicking on "shopforum" at the top left of this page. Arrow down until you find the link. Then look through them for cruise control. Good luck

Where can you get bosch or osram tail lights. I'm having difficulty finding them. Is there a certain # bulb I should look for. Ebay was no help.

#8 08-17-2007, 10:32 PM

Quote:

Originally Posted by bodyart27

I used GDL and had nice service (maybe a bit slow - but super nice to talk to).

I bought a rebuilt CCU from them, they were very good to work with.

ray m · #9 08-17-2007, 10:46 PM

Where can you get bosch or osram tail lightbulbs, brake light bulbs. I'm having difficulty finding them. Is there a certain # bulb I should look for. Ebay was no help.

wrench56 · #10 08-17-2007, 10:50 PM

try the benzbin.com. They carry lots of OEM parts. I think this website has a parts dept also.

ray m · #11 08-18-2007, 12:20 AM

does anyone know which is the right bulb on this link.http://www.vintagecarparts.co.uk/en/list+electrical~auto+bulb/

hey_allen · #12 08-18-2007, 06:33 AM

Quote:

Originally Posted by dieseldiehard

Cruise on the '79 300TD has been disconnected though. It is the old vacuum actuator and with a late turbo engine in it its simply too much work to convert to the new electronics to get cruise working on that car. I've got too many other projects for now

For what it's worth, there is an easy fix to the vacuum cruise issue, on a turbo car. All it takes is to add a check valve on the vacuum supply, and a reservoir on the actuator side of the valve. I've seen a few things used as reservoirs, but the simplest typically involves some thin PVC pipe capped off, with a couple of barbed fittings in one end.

This assumes that the actuator is controlled by something other than the level of the vacuum source, though.

dieseldiehard · #13 08-20-2007, 01:16 PM

Quote:

Originally Posted by hey_allen

For what it's worth, there is an easy fix to the vacuum cruise issue, on a turbo car. All it takes is to add a check valve on the vacuum supply, and a reservoir on the actuator side of the valve. I've seen a few things used as reservoirs, but the simplest typically involves some thin PVC pipe capped off, with a couple of barbed fittings in one end.

This assumes that the actuator is controlled by something other than the level of the vacuum source, though.

It's not that I don't have a vacuum reservoir, the vac system on my '79 is working fine but the engine is from an '85 and it uses a different type of accelerator linkage that was designed to use an electric actuator. I tried installing a catch plate for the vacuum actuator but it wore the steel cable through and the tip came out. The last thing you want on a cruise control is to have it jam up and stick wide open or something. I just couldnlt make it work so I disconnected it and also removed the control arm on the stalk when I found a New turn signal switch that didn't have the cruise arm on it (sure looks nice!

FWIW I use any kind of bulb as long as its the correct wattage and never had a cruise problem
The bit about nickel or brass bases seems to me to be an unfounded rumour