When replacing a blown power steering pressure hose on my W211 about 2 years ago, i broke off the electrical connector to the SPS solenoid. for those of you that Dont know, this is the solenoid valve on the rack that controls the speed-variable power steering on just about every Mercedes-Benz from the late 90's to present day. when the valve is energized, it makes the steering wheel easier to turn by changing the fluid flow/ pressure in the rack. So the valve is energized when moving slow or when stationary, and de-energizes when driving to make the steering a little stiffer and harder to turn.
So for 2 years, i basically just dealt with steering that was very heavy. UNTIL NOW. i finally decided to tackle that problem and rebuild the solenoid coil since new valves are around $400. FOUR HUNDRED DOLLARS.
**WARNING** This is not a job for the faint of heart or the ill-equipped. This requires access to a lathe and a few other specialized pieces of equipment. i am an auto electrical rebuilder by trade, so i have all the equipment and knowledge to do this. if you lack the tooling or the ability to do this, i will rebuild these solenoids for you guys for $200 plus shipping.
But for all of you that wish to tackle this project yourself, here it is, a complete guide to rebuilding these SPS solenoids:
Here's a picture of the valve in question.
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to press the valve core out of the outer housing, support the bottom of the valve leaving the center of the core open to be pressed out. using an arbor press or the gentle tap of a hammer, press or tap on the center of the back of the solenoid. it doesn't take a ton of pressure, the valve will push right out.
From here, the two ends of the valve gently pry apart from the solenoid coil in the center (black tube). in the back end cap, there is a plunger that can be pulled out.
here's what the valve looks like pressed out of the housing with all individual pieces separated.
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On the inside of the bobbin (solenoid coil) there is a metal sleeve. this sleeve is the outer wall of the valve. be careful not to score it or deform it or harm it in any way. pictured with it is the electrical connector that i broke off this coil.
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Now was the timing consuming part, which i have done for you guys: figuring out what gauge and how many turns of wire there are on the coil. there are 550 turns of 27 gauge magnet wire on the bobbin.
Next step was to clean up the bobbin and get it ready for rewinding. that involved setting up a tool to be able to safely turn the bobbin on center. i used a metric bolt with cintered brass bushings i pulled from stock that perfectly fit the ID of the valve and the OD of the bolt.
heres a pic of that chucked up on the lathe along with the winding rig i have set up for winding custom coils at work.
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Now, CAREFULLY machine off layer by layer the top layer of the plastic covering the coil, leaving a 1/4 to an 1/8 of an inch on each side of the plastic bobbin. Don't be afraid to cut into the wire, i already counted and documented the number of turns.
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finish removing the wire and machining a nice bobbin for rewinding.
Next step is rewinding! i ended up using 28 gauge wire instead of 27 gauge because i had a roll laying around at work. that requires reducing the number of turns for a smaller wire in order to match resistance and current draw. 28 gauge is 26% smaller in surface area than 27 gauge, so that means reducing the number of turns by 26%, changing it to 409 turns.
after carefully rewinding 409 turns and wrapping in fiberglass tape....
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I decided rather than re-affixing a poor designed and fragile electrical connector that i originally broke off, i figured i would change the design a bit. i attached and epoxied in place a 6" lead for each wire with high temp 16 gauge braided wire, holding it in place with heat shrink tubing.
After reassembling the valve and pressing it back together, Here's the finished project!
![]()
I got it back on the car tonight, topped of the system and started the car..... and IT WORKS!!!!! Yay Easy steering when parking again!! so happy
So for 2 years, i basically just dealt with steering that was very heavy. UNTIL NOW. i finally decided to tackle that problem and rebuild the solenoid coil since new valves are around $400. FOUR HUNDRED DOLLARS.
**WARNING** This is not a job for the faint of heart or the ill-equipped. This requires access to a lathe and a few other specialized pieces of equipment. i am an auto electrical rebuilder by trade, so i have all the equipment and knowledge to do this. if you lack the tooling or the ability to do this, i will rebuild these solenoids for you guys for $200 plus shipping.
But for all of you that wish to tackle this project yourself, here it is, a complete guide to rebuilding these SPS solenoids:
Here's a picture of the valve in question.
to press the valve core out of the outer housing, support the bottom of the valve leaving the center of the core open to be pressed out. using an arbor press or the gentle tap of a hammer, press or tap on the center of the back of the solenoid. it doesn't take a ton of pressure, the valve will push right out.
From here, the two ends of the valve gently pry apart from the solenoid coil in the center (black tube). in the back end cap, there is a plunger that can be pulled out.
here's what the valve looks like pressed out of the housing with all individual pieces separated.
On the inside of the bobbin (solenoid coil) there is a metal sleeve. this sleeve is the outer wall of the valve. be careful not to score it or deform it or harm it in any way. pictured with it is the electrical connector that i broke off this coil.
Now was the timing consuming part, which i have done for you guys: figuring out what gauge and how many turns of wire there are on the coil. there are 550 turns of 27 gauge magnet wire on the bobbin.
Next step was to clean up the bobbin and get it ready for rewinding. that involved setting up a tool to be able to safely turn the bobbin on center. i used a metric bolt with cintered brass bushings i pulled from stock that perfectly fit the ID of the valve and the OD of the bolt.
heres a pic of that chucked up on the lathe along with the winding rig i have set up for winding custom coils at work.
Now, CAREFULLY machine off layer by layer the top layer of the plastic covering the coil, leaving a 1/4 to an 1/8 of an inch on each side of the plastic bobbin. Don't be afraid to cut into the wire, i already counted and documented the number of turns.
finish removing the wire and machining a nice bobbin for rewinding.
Next step is rewinding! i ended up using 28 gauge wire instead of 27 gauge because i had a roll laying around at work. that requires reducing the number of turns for a smaller wire in order to match resistance and current draw. 28 gauge is 26% smaller in surface area than 27 gauge, so that means reducing the number of turns by 26%, changing it to 409 turns.
after carefully rewinding 409 turns and wrapping in fiberglass tape....
I decided rather than re-affixing a poor designed and fragile electrical connector that i originally broke off, i figured i would change the design a bit. i attached and epoxied in place a 6" lead for each wire with high temp 16 gauge braided wire, holding it in place with heat shrink tubing.
After reassembling the valve and pressing it back together, Here's the finished project!
I got it back on the car tonight, topped of the system and started the car..... and IT WORKS!!!!! Yay Easy steering when parking again!! so happy
