Cruise control disengaging. 1989 300SE

[stwat]

I've just been to stock up on important items (beer) and on a nice long stretch of road I flicked the cruise on. All was well for a mile or so but then the cruise decided to switch its self off. (Maybe it's very clever and realised I was getting close to the shop)

Shop done and back driving the car, I try cruise again but it almost instantly disengages. It did the same a few more times till I gave up.

Cruise control is something I have never worked on, so any tips and pointers would be gratefully received.

Ta,
Stu

 

[stwat]

Having had a think on this, the brake light switch seems to be the logical first port of call.

 

[moonloops]

Having had a think on this, the brake light switch seems to be the logical first port of call.

Either that or your tyre sizes are mismatched.

 

[stwat]

The tyres are all the same make and size and only a few months old.
I havent checked the pressure in a while I must admit But would different pressures cause this issue?

 

[moonloops]

The tyres are all the same make and size and only a few months old.
I havent checked the pressure in a while I must admit But would different pressures cause this issue?

It's the wheel speed sensors that kick cruise control out most of the time, so tyre sizes or actual faulty sensors are worth investigating along with the brake switch.

 

[stwat]

Wouldn't I get the ABS light with faulty sensors?

 

[John Jones Jr]

Wouldn't I get the ABS light with faulty sensors?

I'd guess it would.

 

[stwat]

So that's the sensors out of the equation.

Is there an ECU for the cruise control? Or a relay?

 

[John Jones Jr]

Should have said, check out the interweb for faulty Cruise Control Amplifiers. That's what went on my W124.

 

[stwat]

Ooo I hope it ain't that. It sounds expensive, even in second hand form

 

[John Jones Jr]

Ooo I hope it ain't that. It sounds expensive, even in second hand form

From what I recall it's a very common fault. Mine was cured with a used replacement amp that had been repaired and from what I understand they are very easy to repair too according to guy that fixed my C/control.

 

[Stratman]

The most common fault with the CC amplifier is cracked joints, where the connector is soldered to the board. If you're in any way handy with a soldering iron it's worth resoldering all the joints and giving it another go.

 

[stwat]

Thanks gentlemen. I've repaired a few OVP's and ECU's in my time, so I'll g.I've it a go.

 

[John Jones Jr]

Was having look over the pond and found this while I was there. I'd say you won't get a better insight in 80's M-B C/control issues. See post #7.

http://www.benzworld.org/forums/w126-s-se-sec-sel-sd/1649283-cruise-control-amplifier.html

 

[gbjeppm]

Was having look over the pond and found this while I was there. I'd say you won't get a better insight in 80's M-B C/control issues. See post #7.

Cruise Control Amplifier - Mercedes-Benz Forum

Thats a really good find JJJ, thanks, another job I need to do at some point. Although its at the bottom of the list.

 

[stwat]

Was having look over the pond and found this while I was there. I'd say you won't get a better insight in 80's M-B C/control issues. See post #7.

Cruise Control Amplifier - Mercedes-Benz Forum

Brilliant. Thank you