Hey All,

Maybe someone knows what these symptoms mean.....

The cruise control will not hold a speed, if I hold the control stalk on accel, the car accelerates. When I let go, it acts like the cruise is off. However, sometimes it works! Then the problem is it "remembers" one speed setting and resumes that speed and does not reset to the current velocity.
Does anyone have an idea what I can check or possibly repair myself?

BTW, it's an '85 turbo, thanks!

__________________
Ed "Don't Benz's just feel better..."

Current wives...
2000 ML430 Skyview "The Mel"
2000 CLK430 Cab "The Cab"
85 300D Turbo "The Diesel"

Past wives...
92 300E
85 190E

"One should as a rule respect public opinion in so far as is necessary to
avoid starvation and to keep out of prison, but anything that goes beyond
this is voluntary submission to an unnecessary tyranny, and is likely to
interfere with happiness in all kinds of ways."
Bertrand Russell

You need a new or rebuilt cruise ECU...I had mine rebuilt by General Development Laboratories (www.gdl-online.com)...current price is $185. Works like a charm. GDL was very good to do business with...highly recommended. They also provide detailed diagnostics info.

Good Luck

__________________
1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)

Greetings Dude,

As mentioned in the previous post it is most likely your cruise amp that is causing your problem. With age the soldered joints become brittle and seperate from the board just enough to dislodge that joint or connection. Just curious, does your cruise seem to want to work in the early morning while the interior of the car is still cool to cold? If you get good results during this climate then it can almost be sure that one or more of your cruise amps connections are bad. Several on this post have removed their cruise amps and have reheated all the soldered connections within and have gotten good results and a like new cruise control working again. There are many connections on the board if you choose this route. This is no guarantee that it will work for you, but some think they have nothing to lose by trying this first. If you are wanting it rebuild or resoldered by a professional firm, then that is also mentioned in the previous post and they are extremely successful in what they do. They may not rebuild your amp if you burn a hole through it while trying to resolder the connections. So this will strictly be your call on that issue.

Charles

__________________
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan

Hey Guys,

Very interesting.... it would work sometimes and not others huh?
Where is the ecu, how can I get at it and try to fix it myself?

Thx, Ed

__________________
Ed "Don't Benz's just feel better..."

Current wives...
2000 ML430 Skyview "The Mel"
2000 CLK430 Cab "The Cab"
85 300D Turbo "The Diesel"

Past wives...
92 300E
85 190E

"One should as a rule respect public opinion in so far as is necessary to
avoid starvation and to keep out of prison, but anything that goes beyond
this is voluntary submission to an unnecessary tyranny, and is likely to
interfere with happiness in all kinds of ways."
Bertrand Russell

I have an 85 300d with cruise. Mine was acting up a little while back. I checked under the hood for bad vacuum lines. Found one that was disconnected. Now the cruise works perfectly.. Also I found if I just pushed the lever for a second, instead of holding it, then let off on the gas, it worked a lot better.

__________________
Gary
85 300D Ivory, 202,000
Beatus exsisto Jesu, verus et Deus verus Vir

Hey Gary,

I've experienced that too, the thing acts up and a touch works where a normal application does not. I looked for vacuum lines but didn't see any disconnected, where exactly did you check. Will you describe the fittings which actuate the cruise.

Thx, Ed

__________________
Ed "Don't Benz's just feel better..."

Current wives...
2000 ML430 Skyview "The Mel"
2000 CLK430 Cab "The Cab"
85 300D Turbo "The Diesel"

Past wives...
92 300E
85 190E

"One should as a rule respect public opinion in so far as is necessary to
avoid starvation and to keep out of prison, but anything that goes beyond
this is voluntary submission to an unnecessary tyranny, and is likely to
interfere with happiness in all kinds of ways."
Bertrand Russell

Greetings Dude,

Here is the removal process and the I.D. of the cruise amp or as someone called it the ECU (electronic control unit) none the less it's a cruise amp. www.gdl-online.com/remove.html

Based upon what you describe I think it is still the amp that is at fault. You can check your vacuum fittings and hoses all you like but your year car should contain an all electrically controlled cruise control system. The early models had vacuum going to the actuator under the hood, my '80 does, but my '84 doesn't. Try the resolder job unless it's more than you want to undertake, then I'd send it to GDL for testing.

Charles

__________________
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan

Greetings Can-do,

Thanks for the link! Where was the amp for your 84, mine's probably in the same place! Any other gotcha's on the removal?

Thx, Ed

__________________
Ed "Don't Benz's just feel better..."

Current wives...
2000 ML430 Skyview "The Mel"
2000 CLK430 Cab "The Cab"
85 300D Turbo "The Diesel"

Past wives...
92 300E
85 190E

"One should as a rule respect public opinion in so far as is necessary to
avoid starvation and to keep out of prison, but anything that goes beyond
this is voluntary submission to an unnecessary tyranny, and is likely to
interfere with happiness in all kinds of ways."
Bertrand Russell

Greetings Ed,

Once you get the kick panel off you will most likely see the cruise amp on the left side of the steering column. Pretty hard to miss seeing as it's one of the largest items under the dash.

Charles

__________________
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan

Check out the GDL site that can-do mentioned. It will tell you everything you need to know. The two phillips screws holding the amp in can be ABSOLUTELY impossible to get loose, besides you can't even get to the one closest to the fire wall. Fear not! GDL has a tip on getting it out. I have five used ones from the werecking yards in the last week and a half, three do nothing at all, one will accelerate only, and one works some of the time and today it started competing for attention over the radio. I think that going to GDL is probably the way to go, not only that...I believe that they have a special going right now that offers a free lifetime warranty if you ask for it. Cant beat that.

Ernie

Well, I haven't found the problem with the cruise yet, but, I ran across an interesting article on diesel cruise repair. In it the writer states that using non-OEM brake bulbs could fry the cruise control unit beyond repair. I did install some 50w bright brake lights awhile back, what's the connection with the brake light circuit and my cruise control unit module?

http://mbca.org/MBCA_Troubleshooting_cruise_cont.htm

__________________
Ed "Don't Benz's just feel better..."

Current wives...
2000 ML430 Skyview "The Mel"
2000 CLK430 Cab "The Cab"
85 300D Turbo "The Diesel"

Past wives...
92 300E
85 190E

"One should as a rule respect public opinion in so far as is necessary to
avoid starvation and to keep out of prison, but anything that goes beyond
this is voluntary submission to an unnecessary tyranny, and is likely to
interfere with happiness in all kinds of ways."
Bertrand Russell

Greetings Dude,

If you look at your electrical schematic you'll see that the cruise shares the same ground that your brake lights do. A lot of aftermarket bulbs aren't quite up to spec with MB requirements and the ground is incremental.


Charles

__________________
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan

Just wondering, is it possible to rewire the CC amp and the tail light grounds so they're separate? Has anyone tried this?

It'd be nice to be able to get a light bulb at a truck stop in an emergency and not worry about blowing other parts up...

Thanks!

__________________
2001 VW Jetta TDI, 5 speed, daily driver
1991 Ford F-350, work in progress
1984 Ford F-250 4x4, 6.9l turbo diesel, 5 speed manual
Previous oilburners: 1980 IH Scout, 1984 E-350, 1985 M-B 300D, 1979 M-B 300SD, 1983 M-B 300D
Spark-free since 1999

Greetings,

I believe the brake lights system plays a part in the disengagement for the cruise in a panic state. You apply the brakes and the the cruise is disengaged.

Charles

__________________
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan

Take a look at this conerning the light bulb myth.Click here to see what Peter has to say about it.
Ernie