Wiper set on fast run same speed as slow...

[somecarguy]

Today I noticed that my wipers run the same speed (slow) when set to slow or fast. Intermittent works fine. What are the likely culprits?

[snow663]

Are you driving it or sitting still. They go faster when you start moving, could be a host of things but i would start by looking at a diagram of the wiper control module and see if its getting the speed sensor input? Idk if it works off of speed directly or if something else controls it.

Sorry just read this is an 89. Don't listen to me.

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[Kershaw]

Relay might be bad.

[somecarguy]

Should have checked Bentley first - they have a very good diagnosis section on wipers. Will run thru that and let you all know what I find.

[ELVA164]

Are you driving it or sitting still. They go faster when you start moving, could be a host of things but i would start by looking at a diagram of the wiper control module and see if its getting the speed sensor input? Idk if it works off of speed directly or if something else controls it.

Sorry just read this is an 89. Don't listen to me.

Thank goodness these wipers don't work off vacuum. What a silly idea that was.

[snow663]

Thank goodness these wipers don't work off vacuum. What a silly idea that was.

Haha i am not familiar with anything older than 91 but i remember reading somewhere the 80s models have vacuum to the ECU for the econometer which is also pretty redundant. But yeah this isnt a model T with vacuum actuated wipers that was probably the worst invention ever.


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[ELVA164]

Haha i am not familiar with anything older than 91 but i remember reading somewhere the 80s models have vacuum to the ECU for the econometer which is also pretty redundant. But yeah this isnt a model T with vacuum actuated wipers that was probably the worst invention ever.

Forget the Model T, they were making vans with vacuum-operated wipers into the 70s! I remember my dad telling me a story of driving home on the highway and having to choose between going slowly with no wipers and speeding with some visibility in the rain

[Kershaw]

Weren't most things still vacuum actuated in Mercedes' through the 90s? Not the wipers, but things like door locks.

[somecarguy]

I removed the wiper relay and jumped the relevant terminals for fast and still got only slow. I suppose having a look at the motor and its connections is the next step?


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[ELVA164]

I removed the wiper relay and jumped the relevant terminals for fast and still got only slow. I suppose having a look at the motor and its connections is the next step?

Motor, connections, linkage, and ground if you weren't including that as a connection.

[Kershaw]

I removed the wiper relay and jumped the relevant terminals for fast and still got only slow. I suppose having a look at the motor and its connections is the next step?


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Yeah. Over time the worm gear gets covered in grease and the contact isnt great. It gets slower and slower until it barely drags itself across the screen. It's fairly simple to drill out the rivets, wipe the contacts down, and use bolts to reassemble the motor. The tricky part is getting the wipers realigned properly.

[somecarguy]

Is the motor as much of a bear to remove as it sounds to be?


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