Cruise control surge
 

'88 190E 2.6, five speed manual tranmission, 72K miles

The cruise control surge is intermittent and seems to correlate directly to an intermittent speedometer needle flutter. I recall from looking at the cable some years ago that it appears to be sealed with O-rings at each end, so the normal cleaning and relubrication that will usually solve speedo flutter on my older GM cars doesn't appear to be an option.

Both my speedo head and speedo cable were replaced under warranty, but they was about 10 years ago, so I figure the needle flutter, which is the likely cause of the cruise control surge is probably just an age phenomenon.

Has anyone else experienced this problem? Does anyone know if the cable can be lubricated, or is the fix to install a new cable.

Duke

I think that the surge is due to your cruise control suffering the pains of old age, and not the speedo cable at all.

The speedometer is probably just recording the erratic speed that the cruise amplifier is causing.

My cruise control did thisa once about a year ago, and when I inquired about this at GDI, Peter told me that the amp was in the process of dying.

I haven't had it fixed yet, because most of the time it behaves.

Still, lubricating the cable, if done properly, can't hurt and may solve the problem more cheaply.

My cable is sealed like yours and any amount of lubrication, at best, would be a temporary fix if any even got in there. If I were you, I'd replace the cable. It is the least expensive component of the cruise system, other than the speed sensor, and can certainly cause the symptoms you describe, esp. if you are noticing a correlation. If it doesn't work, you could send your amp to Peter at GDL and have it bench tested.

buy european bulbs and put them in the tail lights and brake lights first. Must have nickel bottom, not gold color.

Austin

I have read about your suggestion of the proper light bulbs before, but why? Hows the improper light bulb influence the cruise control?

Haasman

The resistances of the US bulbs are different than the resistance of the european bulbs. Give it a shot.

duke2.6

i'd check your tailight bulbs, nickel base only. MOST likely it's the cruise amp.

www.calibermotors.com 1.800.252.6877

wholesale m.b. parts, it's where mine came from

peter

I'm mystified by this bulb discussion. As far as I know the tail/stop light bulb spec is SAE 1157. So what's with "European bulbs"? All the bulbs in my car are original - never changed any.

The cruise control surge is worse in the freeway cruising speed range of 70-80. The speedo needle flutters intermittently with the cruise off or engaged, and when engaged the cruise control only surges when the needle starts fluttering.

In the 60-65 MPH range there is no needle flutter and no cruise control surge. This is why I'm convinced that the needle flutter is the cause, not the effect. The cruise control keys off a speed sensor in the speedo head.

I'm going to add a new speedo cable to my list of parts to get/things to do, but I'd like to get to the bottom of this bulb business.

Duke

The impression is that the cruise control amplifier circuit reads the resistance from the brake light and due to MB's "design" a difference in the resistance can cause damage to the amplifier circuit. Since the OEM bulbs are so cheap, why risk it. The most common problem with 80-90's MB cruise controls is the fragile circuit boards and their tendency to break solder joints (age, vibration). Over time, the weakening joints slowly deteriorate the electrical connection on the board, showing up as eratic cruise operation, until eventual failure.

Stoplight bulbs and ctruise control
 

The Cruise control shuts off when you tap on the brakes, and the way it knows this is when the brake light comes on.

Presumeably, if the resistence of the specific brake light bulb is not what the Cruise control expects, then it won't work.

I don't think this could logically cause the sort of problem you are having. I am not an electrician, so please don't take this as gospel.

Now that you say that the speeedo nedle bounces even with the Cruise Control off, it seems more possible that the speedometer cable or one of its connectors is at fault. A new speedo cable is sure to cost less than an overhaul of the CC.

Good luck getting this to work.

Dont use 1157 1156 or any other american bulbs, they dont work right.

www.sylvania.com
http://www.sylvania.com/auto/carapp/


which is really osram who makes bumbs for mercedes

High & low beam headlamp
Part number = 9004


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Parking light
Part number = 7528






Front turn signal
Part number = 7528






Rear turn signal
Part number = 7506






Tail light
Part number = 5008






Stop light
Part number = 7506






Fog/Driving light
Part number = H3-55W






License plate
Part number = 6418






Back up light
Part number = 7506






Front sidemarker
Part number = 7528






Rear sidemarker
Part number = 5008






Glove box
Part number = 6418






Map light
Part number = 64111




Part number = 6418






Dome light
Part number = 6411






Trunk/Cargo area
Part number = 6411






Instrument-general
Part number = 2721






Hi-beam indicator
Part number = 2721






Seat belt indicator
Part number = 2721






Brake warning
Part number = 2721






Automatic transmission indicator
Part number = 2721






Directional signal indicator
Part number = 2721

7506 is the number you want from sylvania, you can get them at checker or autozone. I dont like wagner bulbs, I only buy syvania or hella bulbs.

if you guys want to read more on this 'nickel based' bulb theory, do a search.

i found it mentioned A LOT when i was re-searching my cruise problems.

maybe there is something to this, maybe not.

if my car prefers nickel based bulbs, so be it.

it's just as easy to grab those, as it is the 'brass' looking ones.

peter

Or you could go to the mercedes dealer, and tell them you want bulbs, and they come in these really cute card board boxes or a plastic pillow for 6 dollars each...

Autozone 3.99 I believe for two.

Duke2.6:
The tailight bulb theory is often compared to urban myths, but there are people who claim them to have been the problem. Whatever you do, if you decide to change the bulbs out don't go drinking with any attractive women and pass out in a hotel room...you'll be sure to wake up missing a kidney, but with a nice suture line:D. Search for it here and see for yourself. Like Richard, I doubt your symptoms are consistent with any of their experiences. One of the reasons these cruise systems are such a PITA is because they are very accurate. The speedocable has a magnet on it, and the speed sensor picks up the frequency of that magnets rotation past itself. The cruise system is actually trying to maintain that frequency of rotation, thus, if it is intermittent as you describe, the cruise control will stay busy trying to adjust it and surge as a result. Be careful to not burn up your actuator, it's working overtime due to the fluctuating signal. My money's on the cable...