brake pedal switch

[SilverSaloon]

hi

i've been trying to figure out why i have intermittent cruise control on my R107. One suspect amongst others seems to be a faulty brake pedal switch.

so, i disconnected the switch, but then the brake lights dont work.

reconnecting the switch, and the brake lights work fine.

does this mean the switch is 100% working and i can eliminate it as a suspect? switch is only £5 but not worth replacing if the fact the brake lights work means its fine....

cheers

derek

 

[jaymanek]

no it doesnt... it could still be the switch... although more likely a speed sensor.

 

[SilverSaloon]

hi. thanks for that.

i've been doing a little more research into these switches and apparently there is a pin for the brake lights and a pin for cruise etc etc.

The switch on my R107 has 2 pins. Does anyone know if each pin provides a purpose (ie 1 for brake lights and 1 for cruise) and it gets its earth from its shell, or if one pin is + and one pin is -

thanks in advance.

derek

 

[A210AMG]

Hello

Is your car able to have the fault codes read?

When mine went in for the ESP/BAS/ABS the mechanics said it could be all manor of things and as he said even changing the brake switch (which mine didn't have by the pedal) could be a waste of £10 if it isn't that.

Then your going round changing other bits that may not need changing.

Mine turned out to be a corroded speed wheel sensor behind the rear wheel arch on one side.

Thing is again as they pointed out what causes it on my car could be totally different for the next 6 cars that have that problem.

I would if I were you just get it check at an indy, puts your mind at rest and hoepfully you will only be changing the part that needs changing.

I know I didn't like driving round with the lights on my car (for a week). Its annoying and I didn't have all the satftey feature the car should have.

 

[SilverSaloon]

I want to avoid taking it to a garage if possible to save on labour costs etc. I'm not sure how much info you can get from these old cars - this is for the 1985 R107 SL...

if i can find out for sure whether the R107 brake switch has the two pins for two functions each on it, or whether its just + and - i reckon i can know whether to replace or not. The switch is doing something (brake lights function with it but not without it) but is it just acting on that 1 pin. If the other pin also does soemthing (ie faulty cruise that is my issue here) then it would be worth replacing for the fiver it is.

 

[wobbly]

I would just like to say, its a huge pain in the a**e to change the brake light switch on a 107.

You have to lay on your back in the footwell, and try and get two spanners on the lock nuts, in cramped space. It took me well over a hour to change the switch.

Then a month latter, I had to do it all over again, as the crappy switch I bought from Eurocar parts failed.

 

[jaymanek]

Yes same as an SEC switch,,, very very fiddly.

There are only a few things it can be..

Wheel speed sensors are most common. trace the wires back from back of front wheels and from rear diff.. At the connector, undo it and put a voltmeter in line... spinning the wheel will give you a pulse.

If its not this then brake light switch can be the culprit..

If not then OVP if your car has one.

 

[SilverSaloon]

hi

thanks again. I've ordered a switch as its cheap anyway.

It does look tricky to change - i took the trim off last night to have a look at the switch and it was very hard laying across the footwell trying to reach up.

the cruise was working when i test drove the car (i was driving at the time so know this for sure) but the previous owner reckoned it only failed when it rained. Although i cant seem to get it to come on now in the wet or dry. so i assume its not a big problem.

i'll swap over the brake switch and then do Jays wheel test.

The OVP relay sits behind the glovebox - i've had this out and the fuse ontop is fine. It had a 201 part number. The ABS is working but no abs light - this could of course be the bulb in the cluster and may be nothing.

 

[jaymanek]

rain... there you go... bad connection at wheels or diff..

 

[SilverSaloon]

rain... there you go... bad connection at wheels or diff..

he just mentioned the rain issue. i cant get it to work now rain or dry..... i

it was dry when i tested it though on the test drive.

i'll change the switch anyway as its cheap and then check the wheels.

do you have a link to the EPC where the sensors are? i dont know what they look like. its for a R107 280SL

 

[jaymanek]

there arent any wires going down to the wheels apart from brake sensor so easy to identify and trace.. they bolt into the hub..

 

[alibally]

The cruise control on the SL uses the speed signal from the speedo. Its an electronic speedo , getting its pickup from a sensor on the gearbox. The car won't have speed sensors on the wheels if its not got ABS. A intermittant fault with the cruise is normally the thottle actuator motor under the bonnet or the control unit. A MB dealer has a cruise tester that plugs into the wiring for the control unit and tests the motor , speed signal and the switch etc. Hope this helps.

 

[SilverSaloon]

The cruise control on the SL uses the speed signal from the speedo. Its an electronic speedo , getting its pickup from a sensor on the gearbox. The car won't have speed sensors on the wheels if its not got ABS. A intermittant fault with the cruise is normally the thottle actuator motor under the bonnet or the control unit. A MB dealer has a cruise tester that plugs into the wiring for the control unit and tests the motor , speed signal and the switch etc. Hope this helps.

it does have ABS

 

[SilverSaloon]

i can always adjust the speed (ie accelerate the car) by pulling up on the cruise stalk..... but it just doesnt seem to maintain the speed..... it worked again today occasionally.....

 

[Smiley]

You could "fix" it by sawing off the cruise control stalk thingy

 

[Druk]

It could simply be a faulty stalk and the control unit is notorious for dry solder joints.