Vernier Mixture Cable

[Notatestpilot]

I have a vernier mixture cable in my experimental. Over 18 years of consistent usage…
When I was ‘turning’ the knob to (counter clockwise) lean it, I felt a bit of a tight spot. I turned the opposite direction and then back towards the same point - again I felt the same tight spot.
Now, when I pushed the button on the knob, I was able to freely cycle the control ‘smoothly’ in and out.
I’m guessing I may need to service the cable by pulling it out and apply grease/lubricant.
Thank you and I appreciate any and all comments/suggestions.

 

[Kenny Phillips]

Certainly start with lube; I used to have a device that clamped on cables and allowed you to use a can of spray lube without disassembling anything.
The one I have would work on bicycles, motorcycles, and the occasional automobile clutch cable. Looked like this, but mine was/is (haven't looked for it) somewhat larger than this appears to be:

 

[455 Bravo Uniform]

Just a thought: If it’s as old as you say, and it needs lube to continue to operate, perhaps it’s past its useful life and worth replacing. You can probably get more time out of it, and may be worth experimenting with, but as with all things aviation, try to stay a half step ahead of the machine. Harder on the wallet to do with certified, so I’m jeleaous.

 

[Bell206]

I’m guessing I may need to service the cable by pulling it out and apply grease/lubricant.

FYI: some vernier assist cables use a plastic/nylon/teflon liner and are designed to operate "dry." So you may want to verify that part as some liners can be damaged using various lubricants. However, it sounds like the vernier mechanism is the issue which a quick disassembly will show if it is worn or damaged depending on construction type. Over time if the cable is repeatedly kept in the same location the threads or pins/balls will wear on one side and cause the mechanism to hang up--unless it is a friction type mech. Lubing may give you a temporary solution but if it has a liner or the threads are worn your solution will not last long. Any idea what brand cable it is?

 

[Notatestpilot]

My RV6 drawing calls out a CT Red VMixture Control Cable.

 

[Bell206]

My RV6 drawing calls out a CT Red VMixture Control Cable.

Perhaps check with Vans or an RV forum to see if these cables can be lubricated? Unfortunately can't offer much more on these specific cables.

 

[Dan Thomas]

Some of those controls use a hard steel ball, inside the push-pull shaft, that is forced outward by a ramp on the pushbutton shaft. Pushing the button allows the ball to retract into the shaft and the control can be moved in and out without turning. The housing around the shaft has a tightly coiled steel spring in it that acts as the "threads" in a nut, and the ball runs in the "grooves" between the spring's coils. As Bell206 says, being in one spot for a long time, with vibration and all, can indent stuff and cause the control to hang up. The ball may even be galling on the spring.

Disconnect the control cable at the engine end, push the knob in and really carefully pull the thing out until the ball appears (could be anywhere around the circumference of the shaft) and see what things look like. Releasing the button will push the ball out. Catch it. You might get a light and look down that hole and see what the spring looks like. Hard to see much, though.

I don't think it will be a sticking wire in the housing if you can move it freely with the button in. More likely the ball and spring.

 

[steingar]

Needed a new tach cable. While installing it they broke my 60 year old mixture cable. Can't blame them, it was old. The upshot is I get a new shiny red (the old one was dull metal, easy to mistake for the flap release) vernier mixture. Hooray for me!

 

[bflynn]

My diagnosis would be a kink or small obstruction in the tube or at least in the channel. The control works by having a bearing ride in a spiral shaped channel in the tube the control slides in. When you push the button, the bearing retracts and you can push and pull. Otherwise you have to twist to move the bearing one direction or the other along that channel, moving the control in or out. If you get a small obstruction in the channel, it would show up as a tight spot.

Get a new cable, I've always seen them come as a prebuilt set. You can try lubricant, but it's unlikely to dislodge the problem. If it's a kink, nothing will fix it. You might find rebuild instructions for one if you look really hard.