Cruise Control Anomalies

'87 300 SDL W126

Cruise worked A+ for first 200k.

Now it 1. is difficult to engage
2. disengages uncommanded

In a jam here, as I must needs go from MI to FL and return shortly. Somebody please help the boy!

Thank you in advance.

Medical Dave
aka Almost Cruiseless in Michigan

[P.E.Haiges]

Dave,

I wonder how people got to FL and back before cruise control? LOL

TRY: http://www.gdl-online.com/begin.html

P E H

Hey, P.E., you're missing the point here! If it's on this German's car it darn well better work and work right! Do you pump a water handle when you're thirsty or push a faucet lever? hmm...

It's probably the amp failing, as that seems to be the primary cause of cruise control failure. There was supposed to be a "cigarette butt" fix mentioned before that you should be able to find in a search.

I also agre with you Dave. If it's a piece of equipment in any one of my cars, it needs to work correctly.

[psfred]

Usual cause is failing solder connections in the CC amp. You can replace it or re-solder it. There are several sources for rebuilt units, check the old postings about CC.

Also, check the condition and age of the brake lights -- the CC grounds through the lamp filaments, so if you have one going flaky, it will cause the CC to disengage intermittantly.

Peter

[diesel don]

Welcome aboard Dave!

PSFred:

On most of my MB's the cruise engages but is very uneven. So much so that you can't use it. Kind of like someone punching the pedal.

Would that indicate faulty connections?

Don

[P.E.Haiges]

Hey Guys,

Go to the GDL website I listed above and read. They explain how the cruise controls work and why they don't. They also have rebuilt components to replace malfunctioning ones. I think they will diagonose your entire system and rebuild it for you. They also explained why the rear light bulbs do not affect the cruise control.

The cigarett fix is for the tachometer, not the cruise contrl.

P E H

[psfred]

Oh, but the rear stop lamps DO affect the cruise control! If the connection is dirty, it can prevent the CC from working -- the operating ground is through the lamp filament. Type of bulb, according to them, isn't significant, but I always use Osram on the advice of my professional mechanic friend. A bad bulb will also prevent the CC from working correctly, too, as well as lighting up the lamp out signal lamp. IF the current from the CC isn't sufficient to make a connection through a dirty bulb socket, no CC.

Surging isn't usually the amp, I don't think -- on 86-87 turbodiesels, it can be the air recirc valve on the turbo causing the surging -- there is a refit kit to smooth out the signal to the ALDA to prevent excessive power bursts. Mine did this before the tranducer died and I left it dead -- did fine on the flat, but would overrun the set speed on hills by 5-10 mph and osccillate down 5, up 4, down 4, etc until it stabilized. Annoying.

Otherwise, the usual suspect is dirty linkage, causing the actuator to stick. If this is the case, it will intermittantly disconnect when the actuator doesn't reach the correct posistion in time. Can be cured by cleanign the swivels in the linkage.

Peter

[Thomaspin]

Here's how I replaced my cruise amp with a reman unit.

Wherever you get yours, the key is to remove the common bracket holding the amp and the buzzer. Chances are you may have to use an impact hammer of some sort to loosen the Philips scews holding the amp to the bracket - mine were seized solid.