Is it easy to change the speed senser in a 1991 300sl ??
is it an easy fix ?? are the parts expensive ?? where is it located ??
any idea's please post , once again thank you very much .

thats the ones I'm talking about , the ones for the tires .

The speedometer receives it's signal from the ABS unit as an average of the signals it receives from the four wheel sensors. If you are having problems with your speedo first check that all the connectors and wiring are secure from the wheel sensors and the ABS unit, then check the wiring connections at the rear of the instrument panel.

were is the ABS unit ?? and were are the sensers located ??
thank you

The ABS unit is mounted in the engine bay on the right hand inner wing as you look from the front. The ABS wheel sensors are mounted on each wheel hub behind the brake disc.
Really, if you need to ask such elementary questions I don't think you should be working on the braking system, it is not something you take on as a first project. The consequences of a mistake are too dire!!!.
Sorry, Geo.

once again , Thank You , I'm just trying to learn , and I'm also trying to save a little money , this car is costing me too much , I don't mind spending some money sometimes on a (fun car) , its a car that I drive only once in a while , its a good fun summer car , ya know driving with the top down , but its not fun when the top doesn't go down , I'm hoping it was something That I could fix ,Thanks