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      01-23-2013, 03:22 PM   #1
beermeister kink
Enlisted Member

Drives: 2013 e93 m3
Join Date: Dec 2012
Location: Washington DC

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clock spring primer

wasn't sure where to put this, I hope this is fine - my thinking is, the slip ring exists to run wires to the buttons on the steering wheel, so it's electronics? All of my knowledge about slip rings is recently gained, I am in no way a mechanic or electrician. Well ok I'm both when I feel like tinkering but very much a beginner. So comments and questions and clarifications are good. Thanks!

Hey! There’s No Spring in this Clock Spring (or this Coil Spring), and No Slip in this Slip Ring!
A [Simplified!] Primer

TL;DR: The slip ring fits between your steering wheel and the steering column, and is what houses the wiring that connects any controls on the face of the steering wheel (such as the horn, and radio station and volume) to the rest of the car.

Oh, here's the kicker. As far as I can tell, if I want to add a button to the steering wheel itself, I need to do so through a connection in the slip ring. Example: I want to drill a hole in the back of the wheel around where my fingers could tap the 'meat' of the wheel while driving (hands at 10 and 2) and put a button in there. The wiring to that button will, AFAIK and that aint very F, need to go through the slip ring. I have yet to see anyone doing that although I have a functional prototype. Ok sometimes people who are retrofitting can use extra connections already in their slip rings to rig wires that do their bidding: But besides retrofit kits and the like, to do that you would need a slip ring with unused wires on it, usually one for model of your car that has some fancy extras like maybe a heated wheel that you don't have. I don't know how to go about ordering special flavors of slip rings but I assume it can be done.


Q: What IS this thing?
A: A slip ring, also called the clock spring or the coil spring, is a plastic piece about the size and shape of a large doughnut. It has an inner ring piece - which can rotate around the ‘hole’ of the doughnut - and an outer ring which is stationary when the whole thing is mounted. See pics below.

Q: That’s it? It’s a doughnut?? I didn’t even know my car was hungry. I've been told that "America Runs on Duncan" but does my car really need to be eating doughnuts?
A: You goof! It just looks like a doughnut, it’s not actually one, And yes, if you have controls of any kind mounted on your steering wheel (such as the horn and those that change the radio station and volume, or control the phone, etc), then you need a slip ring.

Q: Steering wheel?! Controls?? Who said anything about the steering wheel and controls??
A: That’s why this part exists, AFAIK. The controls on the wheel obviously need to talk to the rest of the electronics in the car, right? The wires that wrap around the “doughnut hole” of the slip ring provide the connections for this.

Q: Wires?!? What the? AHH!!
A: Slow down buddy! Take it easy. Deeeep breath. Having wires wrapped around the inside of the ‘doughnut’ is really just a way of running wire from the steering wheel to the rest of the car. Extreme simplification follows:

So you press the change station button on the steering wheel. The signal needs to travel from the button to, say, the radio. The signal runs from the button, down some wire. Just before the signal leaves the steering wheel to continue on it's way to the radio, it enters a connection to the slip ring's wires. SO the signal enters the slip ring near the doughnut hole, and travels along the slip ring's wire, which is itself wrapped a few times around the hole, inside the doughnut. As it wraps around the hole the wire overlaps itself and so gets closer to the outside of the doughnut. At the outside edge of the doughnut, the wire ends at a connector that's attached to, let's just call it the rest of the car. Anywhere else a wire needs to go. In our example, we've said the radio, so the signal leaves the doughnut at this outer edge connector, and gets on the wire that’s strung down along the steering column, to the car’s radio. It’s that simple.

Q: So what are the car designers putting in there for wires, like ethernet cable, or regular 22 gauge wire, or what?
A: The wires in slip rings are called 'flat flexible cables,' or FFCs. You can see them in the 3rd and 4th photos - they are the cute pink-and-white striped rectangular ribbon cables, although that pink coloring is actually the copper strips inside the FFC. They are called 'flat' because each cable is something like the thickness of paper, but don't quote me, I absolutely did not measure that. I made it up!

Each pink stripe is one wire, so the FFCs in the 3rd pic have, ummmm, 6 wires each, for a total of 12 connections (2 FFCs in the slip ring). There are typically two FFCs and a few blank plastic ribbons to protect the FFCs from damage from rubbing against the plastic shell, from what I've seen (all 3).

Q: Why do I need one of these things at all, if it’s just a way to run wires from the steering wheel to the rest of the car? There's wires running all over the car and I don’t see slip rings hanging everywhere! Ha! Gotcha.
A: Ah my friend, now we come to the crux of the matter. Well, one of them anyhow. Allow me to gently point out that the steering wheel spins. In both directions.

Q: So does your momma! And...?
A: And, well... Imagine, say, two wires that run along side each other for a foot or so. At one end the wires are connected to a point, like a nail that’s hammered into a board. At the other end the wires are connected to a steering wheel. Good functional example, huh? As the wheel spins one way, the wires want to twist. When the wheel is spun back, the wires untwist. Then if you keep turning the wheel, the wires will twist in the other direction. And if you go back and forth enough, eventually the wires will fatigue and break. And maybe even get really tangled, I haven’t actually tried it in real life.

Q: How does winding the wire around a doughnut hole stop the wires from twisting?
A: The wires are wrapped around in the slip ring so that when you turn the steering wheel, the wheel turns the inner part of the slip ring. The inner part turns and pulls the wires. The wires either unwind more or get wrapped around the ring in the other direction. Example: When you turn the wheel to the right, the wires wind around the doughtnut, clockwise. Then, when you go back to the center, the wire unwinds from the center of the doughtnut, and remains loose in the doughnut. This is key, because then, when you turn left, the wire can begin to wind counterclockwise around the doughnut hole. The wires just wind and unwind around the spindle of the slip ring and don’t get tangled or twisted.

Q: But how do the electric signals even get to the wires inside the slip ring?
A: There are connectors on the outside edge of the dlip ring - the ones on the bottom right of it in fig 1 - and also connectors by the 'hole.' The connector near the doughnut hole gets plugged into a connector on the steering wheel, and the other side gets connected to the wires that go to the rest of the car (inside the trim that covers the steering column).

Q: Why would I ever need to know this?
A: If the buttons on your wheel, including the horn, stop working or become erratic, or if you’re getting odd warning lights on the dash of your car, the problem could be with the wires inside of the slip ring. The part itself is small and easy to replace because it just sits between the steering wheel and the steering column, and plugs into the existing wiring in the car. I've seen them run from around $120 to like $20 depending on make/model of car and new/used.

Q: How did you come upon this wealth of knowledge?
A: On a trip to ancient Tibet I made friends with a poor porter who was assigned to me, to carry my bags to my room and back to the bus during my travels. Perhaps he was just in need of someone to recognize his humanity - my constant attempts to say thank you in his native tongue, combined with my general unwillingness to let him carry everything unaided, must have come at just such a time when a kind gesture went so very far. One night I stumbled back to my room after had I drank too much of the local rice wine. I had a pulsing hangover and I hadn’t even gone to sleep yet! The room light was on, which was very odd - sometimes the power didn’t come on at all - but even more strange was this creased and folded brown square of paper on my bed. I stumbled over to the bed and moved it aside, noting even in my stupor that the square was in fact a folded oiled linen, aged to a sandstone brown. I fell on my face. I awoke to a stream of painful sunlight. Hours later, in the late morning, my porter friend didn’t show up, and I never saw him again, which kind of sucked because I had to carry my bags around after that. Oh, and the linen square turned out to be an ancient map that I had dated to the time of Kublai Khan. It’s wizened script was difficult to decipher even with the very expensive help of local officials, who, with the national holidays approaching, had a need for presents both familial and official and so were open to modest corruption. With their help and my hard currency, I gained access to those in charge of museum restorations and forensic examinations, who in turn had access to modern tech for x-raying art, or performing microscopic examinations and the like. With the map somewhat restored, I set about exerting even more cash influence to find someone to read it. Oh wait, I thought you asked about my wealth of ancient mystic fighting knowledge.

A: I was aiming to install a Valentine 1 radar detector in my car (“Albert”). I wanted it be be a ‘stealth’ install, where the wires and display and even the detector itself were all out of sight. The detector would go inside of the rear headrest (diy found through google); I’d take the display apart and place the important parts in the instrument cluster; and finally I’d put a mute button on the steering wheel, where my pinky rests when I’m driving. Lots of people install remote mute buttons all around the driver, so that they can press it if they want to silence the detector’s audible warnings - I’ve seen them on the control stalks (like that for high beams), and on the center console, by the driver’s leg.... But why wasn’t anyone putting them in the most obvious spot (to me) - on the steering wheel itself? So I looked into it.

Q: And? Why DON’T people put buttons on their steering wheel?
A: Who has the time to waste to figure it out? Oh, except for me. Over time I got 3 different slip rings and took them apart to see how they work, so I never touched the one in my car. That's 3 more than most people! It's not tough but exploring such thing takes some time and diligence and patience. Also messing with such things can look scary, but I think there is only a small danger in experimentation with actual use. Such dangers would be: Some buttons stop working until you replace the part or fix it (but the part is inexpensive (relatively). That's it! Even if the wires to the airbags become disconnected or go bad, from what I've read, the only thing that will happen is that an air bag light will come on or maybe an error code gets generated, but the car won't stop turning or running, and the air bag won't suddenly deploy.

Q: Are there any springs in the clock/coil spring?
A: Not in the one we're talking about! The wires inside just look like a clock's spring when it is wound. Oh and if you take the top off of our slip ring quickly, then the wires may come flying out. But said wires are not under tension in a way that would make them tough to put back into the slip ring.

Link to my 'coil spring cartridge' at

1: slip ring vs doughnut (this is a bmw e93 m3 slip ring) (Oh, and a hostess regular-sized doughnut)
2: where slip ring fits against steering wheel
3: inside of slip ring
4: inside of a different slip ring (acura)
5: connectors on outside of slip ring
6: inner ring (that rotates) and outer ring, pointed out.
7: How to wind the slip ring. Warning: Extremely well-executed technical schematic. I may do a photo pictorial at some point. Number 4 on my carefully-considered artwork is the key here - the flexible flat cables that are the wires in the slip ring bend back on their winds just before you put their connectors back into the slip ring. This allows the wires to wind both clockwise and counterclockwise! The connectors are plastic housings with metal headers that fit into molded parts of the actual slip ring.
Attached Images

Last edited by beermeister kink; 01-23-2013 at 07:41 PM.