Hi All,

Any advice on fixing the cruise control on a '91 350SD? More specifically, how can you do it without spending $500 and going to specialty shops?

A quick search indicates the primary parts are the amplifier (about $240) and the actuator ($190). I know it's impossible to tell for sure without doing tests, but isn't it usually--I've heard "90%" of the time--a particular part (I had the same problem on my 300DT). If I know what part it is I feel confident enought in buying it (assuming a rational return policy) and going to a good local shop that'll put my parts in for me (they're good but they don't have parts access or the diagnostic equipment). Or how hard is it to replace these yourself? Also, any advice as to where to get the parts?

I've looked around this and another M-B forum and have seen discussions about aftermarket parts and customized systems--mine is a real nice car (perfect condtion, 123,000 miles) and I really don't want to go that route. I want to fix it properly but no way would I go to a dealer and I prefer not to go to a foreign, M-B, or specialty shop.

Thanks!

My Cruise doesn't work either.... I just bought a 1993 300SD with the 6 cyl. 603.971 turbodiesel. I drive alot for work and will be keenly interested in feedback on this subject as I would like to get my cruise working too. How does your engine run? At idle do you have alot of clicking/crackling noises? Mine sure does but at highway speeds is smooth as a gasser.... my old 300D with the 5 cylinder idled better but was loud as a tractor trailer going down the road.....

Also, do you have the antenna things in the back corners that are supposed to pop up if you get close to hitting something in tight corners? Those things don't work on mine either. Other than the cruise, these antenna things, the radio antenna and the trunk close assist, all else works flawlessly and my oh my, that is one beautiful, head turning vehicle!! I've gotten nothing but compliments since I bought it..... hope that 6 cyl. doesn't let me down. I now I gambled on it as all posts I read said they are trouble..... "rod benders" to be specific but this thing runs too good to be a bad engine.

Let me know what your experience is if you would....... there aren't many of us I'm finding!!

JMH

There was some tech advice in a Star column about the cruise surging, and that consisted of a factory fix I don't have any info on dead cruise. The star article was in 2002.

__________________
71 220D 169K wrecked
83 240D 118K sweet 4 speed
91 350SDL (one of the 60% good engines) 156K
84 300d (loaner to my sister) 189K
79 300SD (partswagen)
86 420SEL partswagen
70 220d (partswagen)
68 280s GASSER!!! under construction now
85 300sd 310K miles winter beater car retired
93 300d 2.5 turbo 168K wife's car
83 280SL euro 5 speed 155K
69 250S newest project 54K

Hi Pete! I too have the cruise dilemma. Just spent 50$ on a guaranteed used accuator w/ no luck. I am assuming this must be an amplfier problem, but have read from the search engine that the entire system is just not that good. Some members would differ, however there are plenty of non working cruise control units in these cars: 126, 123, etc... I have come to the conclusion that a quality aftermarket unit w/servo controlled accuator would be optimal. I am going to take the plunge and spend 249$ via jc whitney and install one of these units on my 82 380 sel. I will also try to pinpoint the wires for the control rod and hybrid this to the aftermarket amp and servo. This way, the system will look factory. Iam now having trouble w/ my service cd; the electrical schematics will not load up. Anyone want to jump in here? les

Most of the time its the amplifier on the 140 models. They can be bought rebuilt. Use the search feature.

GDL will test your amplifier and actuator....


I think it's $50-75 if everything tests out.

__________________
Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E

That's one vote for amplifier and one against actuator. For $50 you certainly became an expert! I'm inclined to buy the cheapest WORKING amplifer I can find and try and figure out how to put it in.

My 350 is as smooth as can be--the hood doesn't jiggle at all but you can definitely hear it. It reminds me of my former BMW 524td, but it is way, way more powerful. I like the distinctive sound. One thing I do is keep a container of fuel additive in the trunk and add it most of the time; I buy it at truck stops for about $15 a gallon. And I keep a small glass jar with it to pour it because it eats right through cups. I did the same thing, plus trying many other brands, with my previous Mercedes diesel and it didn't really do anything--the car was always rough at idle but smooth at higher speeds. I thought it needed new injectors.

I'd certainly like to hear of any flaws with this engine.

I also also keep a jug of DP in the trunk but I use an old pill bottle 8oz addit every fill up. What kind of milage are you getting? I love when you touch the pedal at 80 and it just pulls and pulls. Nothing like thepower of the 603

Questions:

Does the operating lever work properly, or is it floppy? If so, sometimes the lever slips out of the switch, so it does nothing. A bit of superglue will fix that.

Otherwise, how many times have you used the cruise control switch for the turn signal? They only tolerate that so many times before the switch fails.....

Does it engage, the fade away, or surge a while then quit? If so, almost certainly the amplifier.

No action at all suddenly can be either actuator or amplifier, but you will be well served to have the current draw on the actuator tested betore installing a new amp -- if the actuator is bad, the current draw killed the amp, and a new amp will soon go the way of the old one.

The amplifier is probably behind the driver's side lower dash panel, held in by two screws with one large electrical connector. Typically, there is a chip in a socket beside the plug you will need to pull and swap into the replacement amp. Can't tell you how to get the panel off as I've never pulled one, though.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I think these fellows are a good place to start for anyone who needs assistance/parts for the cruise control. Clearly, they have the knowledge.

http://www.gdl-online.com/begin1.html#contents

Ouch! But how can you argue with 6,174 posts and a name like Peter? I've been at this long enough to have learned that it wouldn't be worthwhile if it were easy...

I don't think I've ever mistaken the cruise lever for the blinker. It doesn't flop and seems solid. I drove the car cross county and then used it locally there for a few months; when, after a while, I tried to use the cruise again and it didn't work. No symptoms, surging, etc. prior to that.

Thanks to all--this is a great site. I looked quickly at GBL but didn't see any easy answers there either; I'll go back and read everything. I'm not sure I want to take everything out in order for them to "bench" them; maybe I'll try that, but I suspect I can probably do it here in Denver also, and I'd rather buy something and put it in the hands of my trusty local mechanic... I'm eager for some road trips before winter!

I don't know, maybe 25 mpg or 650+ miles per tank of fuel? Not bad for a 5,400 pound car. But it has been a while since I've done any serious traveling in this one.

Edit: Here is the fast reply from GBL.

That sounds like classic cruise amp problems. At that medium mileage (it's not high for a Mercedes) it might not be a bad idea to look at the actuator as well. You can just pop them both out of the car and send them for evaluation and possible repair. The actuator should sit on the top of the engine on a diesel; we can email you a picture if you are unfamiliar. The actuator part number is probably an 002 545 86 32. If it has a longer-than-36-inch cord on it, it might be another part number. The part number is on the rectangular cover along with a date stamp.

Your amp, I believe, would be the 005 545 05 32 (with a coding plug.) You might ask your mechanic where these units are located in your car.

I hate to see you spend money on something that you don't need. That's why I recommend sending both units and we can make sure you're replacing the part that is actually the culprit.

Hope this helps. Please don't hesitate to email again or call our tech line (805 772-5127) from 0900-1700 PDT if you have any further questions or concerns.

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Their website says contact them and they can diagnose the problem. Their's is $195 plus shipping, but they also seem to offer a lifetime warranty, so I don't quite follow the interaction thing. The site also has thorough instructions on how to remove it.

Second edit: The lifetime warranty at GBL only applies if you replace them both and, of course, buy from them; you have to pay $150 extra for it. I don't understand the interaction thing but I believe those who know more than I do. Nontheless, I'm going to "risk" it and try replacing just the amplifier.

I don't think buying the amplifier is risky...

I talked with Peter at GDL online. He was very nice and suggested: If you get an amplifier rebuilt- install it and drive 50-60 mph down the road. Activate the unit.. if it doesn't work right. Turn it off and don't do it again and again. He said a bad actuator will fry an amplifier. I've got a system apart right now and am battling a similar thing.

I know on my car the amplifier was bad.. low mileage and both had been replace by 60,000 miles.
Maybe I've got a bad speed sensor or switch.

Michael

__________________
Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E

I think those "antennas" should only pop up when you have the gear in reverse, to make you see better where the corners are. Forerunners to the PDC...

Thanks samiam4 and good luck! I bought a rebuilt one for $155 from www.benz-store.com and it'll be here in a few days. Only $25 core and I'm tempted to keep the old one--I've heard it can be a simple soldering job and it might be worth experimenting on.

If you have any further tips on making the exchange I'm all ears! I see that the instructions from GDL start after removing the kick panel, and a quick look suggests I don't even know how to do that!!

Alright, I'm slightly embarassed to admit it, but I bought an amplifier and it still doesn't work. Should I take out the actuator and try replacing it? Or have it and BOTH my amplifiers benched? I'm now out $200 and have nothing. This tries my patience, but I still like the car...

I know there are some experienced folks lurking around this forum and I would REALLY appreciate advice on next steps.

P.S. I still believe some folks here are "over opinionated." I think the rod bender thing is not so clearcut, especially in '90s and '91s (I'll deal with that another time), and Slick 50 makes a great bicycle chain lubricant!