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1987 560SL
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Discussion Starter #1
My cruise control or tempomat is innacurate and varies by 5-10mph, meaning if I am holding a steady 70mph and push the stalk up to engage it, the speed will vary between 60 and 70, and sometimes but not always the setting will be lost (control disengages).

The stick appears to function correctly, pull back accelerates quickly, push forward kills it, up sets it, down resume. The slowest speed that it engages is about 45 mph, what is the slowest speed you can hold?
I searched this forum for cruise control threads but have not found anything like this. Is there a cruise control calibration procedure? How can I tell if the cables are properly set?

This string was found but it is not the same problem:
http://www.benzworld.org/forums/r-c107-sl-slc-class/1911257-cruise-control-problem-1980-450sl.html
 

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300sl 1987
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742 Posts
I remember a few Tempomat threads... Actually I write a few. Even an article.

My suspicion/advice would be:

A. Get the amplifier out and resolder all solderings because of the infamous soldering problem
B. Replace the electrolytic capacitors (hope they named so in English)

Regards
 

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1983 380SL, ivory/dk brown, 46k miles, dual roller timing chain. 1986 560SL, red/white, 190K mile.
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6,642 Posts
Make sure everything is plugged in.
I went to the trouble of pulling my Cruise Control Amplifier and
touching up all the solder joints with my soldering iron - takes
about a hour or a little more. Later I found what the problem was - the
connector from the Cruise Control actuator on top of the Engine was
disconnected. On my 560SL, that connector plugs into a receptacle
on the right side Radiator support - very well hidden by the ABS controller.
You don't have ABS on your 450SL, but you might want to look at the
simple stuff first.

Also, there is a procedure to test the CC Actuator with pictures:

http://www.benzworld.org/forums/r-c107-sl-slc-class/2128338-cruise-control-amplifier-soldered-but-no.html
 

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Premium Member
1987 560SL
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2,292 Posts
Discussion Starter #5
I remember a few Tempomat threads... Actually I write a few. Even an article. My suspicion/advice would be:

A. Get the amplifier out and resolder all solderings because of the infamous soldering problem
B. Replace the electrolytic capacitors (hope they named so in English)
Regards
Bereng, thanks. Do you mean capacitors within the amplifier, part number 5 in the EPC diagram below? Or are these capacitors somewhere else in the system?
Make sure everything is plugged in. I went to the trouble of pulling my Cruise Control Amplifier and touching up all the solder joints with my soldering iron - takes about a hour or a little more. Later I found what the problem was - the connector from the Cruise Control actuator on top of the Engine was disconnected. On my 560SL, that connector plugs into a receptacle on the right side Radiator support - very well hidden by the ABS controller. You don't have ABS on your 450SL, but you might want to look at the simple stuff first.
Also, there is a procedure to test the CC Actuator with pictures:
http://www.benzworld.org/forums/r-c107-sl-slc-class/2128338-cruise-control-amplifier-soldered-but-no.html
Carl, thank you very much for the link. I very much agree with starting with the simple stuff first. I will check the integrity of connections and hopefully my pins are numbered the same as your 560.

Nonetheless, I suspect my issue may not be electrical, as I do have a working cruise control, it just does not maintain a steady speed. I thus suspect a mechanical, vacuum, or electromechanical issue. But of course my suspicion is with zero knowledge and I welcome guesses from anybody who has experience with these tempermental tempomats.
 

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1983 380SL, ivory/dk brown, 46k miles, dual roller timing chain. 1986 560SL, red/white, 190K mile.
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6,642 Posts
Hmmm. I wonder if, wild ass guess, the Cruise Control Actuator motor
works in one direction but not the other is the reason for your Cruise
Control not maintaining speed?
 

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Premium Member
1987 560SL
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2,292 Posts
Discussion Starter #7
I will test the actuator motor.
The best procedure I have found so far is by George Murphy, that is referenced in the MB Maintenance Manual by Steve Nervig; so the answer to my question is already on my own computer! The same file is also online at article number 12 in this table of contents:
00 Miscellaneous Reference Articles

Statement number 8 by Murphy, pasted below, has me wondering if it applies to the 1980, as I might have 1157's. Do you think this an issue for the 450SL tempomat?

8. IMPORTANT: If you are not sure, check that the brake light bulb in each tail light unit of your car is an original equipment OSRAM or BOSCH bulb. DO NOT USE U.S. TYPE 1157 BULBS - THEY CAN DAMAGE THE CONTROL UNIT BEYOND REPAIR! The correct bulbs are available from your M-B parts supplier.

I also am unable to locate the figures that Murphy references in article 12. If anyone has a better copy with illustrations please share it. Cheers.
 

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One of the BW Old Guard/R129, W204 Moderator
1997 SL500- 40th Anniversary
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7,148 Posts
I will test the actuator motor.
The best procedure I have found so far is by George Murphy, that is referenced in the MB Maintenance Manual by Steve Nervig; so the answer to my question is already on my own computer! The same file is also online at article number 12 in this table of contents:
00 Miscellaneous Reference Articles

Statement number 8 by Murphy, pasted below, has me wondering if it applies to the 1980, as I might have 1157's. Do you think this an issue for the 450SL tempomat?

8. IMPORTANT: If you are not sure, check that the brake light bulb in each tail light unit of your car is an original equipment OSRAM or BOSCH bulb. DO NOT USE U.S. TYPE 1157 BULBS - THEY CAN DAMAGE THE CONTROL UNIT BEYOND REPAIR! The correct bulbs are available from your M-B parts supplier.

I also am unable to locate the figures that Murphy references in article 12. If anyone has a better copy with illustrations please share it. Cheers.
I recall this was dis-proven...
 

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Well just throwing out a quick question.............. Did this problem all of a sudden just come up?
Did you happen to just put new tires on your car? Just front tires or just rear tires?
My 2 cents on this is I had similar problems after I put bigger diameter tires on the rear of my car.
 

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1980 450SL named Freya. 202,000mi
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1157 is wrong no matter what brand.

8. IMPORTANT: If you are not sure, check that the brake light bulb in each tail light unit of your car is an original equipment OSRAM or BOSCH bulb. DO NOT USE U.S. TYPE 1157 BULBS - THEY CAN DAMAGE THE CONTROL UNIT BEYOND REPAIR! The correct bulbs are available from your M-B parts supplier.
I recall this was dis-proven...
That sounds kinda odd. While we know the cruise controller is disconnected by braking, and so shares the brake switch, there is no reason there should be a permanent malfunction.


FIRST OF ALL, we'd never be putting 1157 bulbs in, those are the bulbs with two separate filaments, and two separate contacts at the base, and they are wrong for all lamps in the tail, period. 1157 are only used in the front turn signal lights.

The correct tail bulb is 1156, a 26 watt bulb (typically brass base). The other bulb cross reference is the 7506, a 21 watt bulb (typically nickel base). These are the bulbs with a single filament and a single base contact. The BRAND is of no consequence.

It is advisable to not mix 1156 and 7506 bulbs (use all 1156 or use all 7506).

None of this should have any effect on the cruise controller.

When the brake switch is OFF, the cruise controller pin 6 is pulled to ground through the stop lamps.

When the brake switch is ON, pin 6 is pulled high (to 12 volts) and that disengages it.

Thus, pin 6 must be low to engage, and high causes a disengage. A float state (disconnection) would probably also be a disengage.

There is no reason that the lamp wattage should have any effect on the controller. It's not sending any significant current out pin 6 or the stop lights would be on all the time!!


If you put 1157 lamps in both stop light holders, the lamps won't work, because they are not making a connection with the middle prong. Because they are not making a connection, the cruise control pin 6 would not be brought low, and therefore it would not engage.


MYSTERY SOLVED!

Obviously, some monkey stuck in the wrong KIND of bulb (two contact), the cruise control stopped working, and an urban legend was born.

Monkeys!!!!:bash:
 

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300sl 1987
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I will agree on the advice and check for the obvious first. Light bulb, good connnections etc.

I wouldn't be surprised electrical gremlins could be causing what you describe, but this is personal opinion on experience, I might be well wrong. Check the obvious first and if nothing comes up go down the soldering route.

As if this is part 5 of the diagram or not I must admit this diagram looks awfully different from my 300sl setup. Please check with similar period owners just in case your's is some sort of mechanical gadget or God knows whaat and then you find ther's nothing inside to resolder etc. This amp doesn't look at all like mine.

The bulb legend is what you've just been fantastically well explained in the previous post. Grounding the pin makes the difference when brake is actuated.
 

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1987 560SL
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Discussion Starter #12
Problem solved. As suspected it was mechanical; the cable (92) from the actuator to the throttle linkage had way too much slack in it. I turned it until the cable was tight and the speed variance went away. Works as it should now.

Also checked the rear light arrangement; the brake light is 1156 silver base; the festoon lamps were replaced with LEDs. Thanks for the informative discussion.
 
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