What the turn signal cancelling cam does and why it fails

The turn signal cancelling cam is a small rotating part inside your steering column that automatically shuts off the turn signal after you complete a turn. On a 1966 C10, this cam sits on the steering shaft and has a shaped edge that catches a lever connected to the signal switch. When you turn the wheel far enough, the cam rotates and pushes that lever back to center, killing the signal.

The cam fails because it wears down over time. The edge that catches the lever becomes rounded or develops flat spots, so it no longer pushes hard enough to reset the switch. You'll notice the turn signal stays on after you finish turning, or it clicks off inconsistently. Replacing it is a steering column job, not a quick fix, but it's doable in a home garage with basic tools and patience.

Key Takeaways

  • The cancelling cam sits inside the steering column on the steering shaft and wears out from repeated use, causing the turn signal to stay on after turns.
  • You must remove the steering wheel and the horn pad to access the column, and you'll need a steering wheel puller to do this safely without damage.
  • The cam itself is a small part that slides onto the shaft; replacement takes two to three hours if you work methodically and don't rush the reassembly.
  • Chevrolet part number 3869469 is the correct cancelling cam for 1966 C10 trucks, and you should also replace the turn signal switch lever spring while you have the column apart.

Tools and parts you'll need before you start

Gather everything before you begin, because you don't want to have the steering column half-disassembled while you're hunting for a tool. You need a steering wheel puller (a three-jaw puller works, or a dedicated steering wheel puller from a parts store), a socket set with a 9/16-inch socket for the steering wheel nut, screwdrivers (both Phillips and flat-head), a small hammer, needle-nose pliers, and a flashlight or work light.

For parts, order the replacement cancelling cam (Chevrolet 3869469 for 1966 C10), and pick up a new turn signal switch lever spring while you're at it—they're cheap and often worn by the time the cam fails. You may also want a new horn pad gasket if yours is cracked or dried out, since you'll have it off anyway. Get a small container to hold the screws and small parts as you remove them; losing a screw inside the column is a frustrating setback.

Removing the steering wheel and horn pad

Disconnect the negative battery terminal first. This prevents accidental horn honking and electrical shorts while you work. Then remove the horn pad by prying gently around its edges with a flat-head screwdriver. On a 1966 C10, the pad is usually held by small clips or screws around the back. Once the pad is off, you'll see the steering wheel nut underneath.

Use your socket and wrench to loosen the steering wheel nut—don't remove it completely yet, just break it loose. Then thread the steering wheel puller onto the wheel following the tool's instructions, and tighten the center bolt slowly. The wheel will pop off the shaft. Once it's free, remove the nut completely and set the wheel aside in a safe place where it won't roll.

Accessing the cancelling cam inside the column

With the wheel off, you can now see the steering shaft. The cancelling cam sits on this shaft just below where the wheel was mounted. You'll need to remove the turn signal switch assembly to get to it. On a 1966 C10, this means removing the screws that hold the switch housing to the column—typically two or three screws on the side of the column.

Once the switch housing is loose, gently pull it away from the column. You may need to disconnect a wire or two; take a photo with your phone before you disconnect anything so you remember where it goes. The cancelling cam will now be visible on the shaft. It's held in place by a small pin or a press fit. If it's pinned, drive out the pin with a small punch and hammer. If it's a press fit, you may need to carefully tap it off the shaft using a soft-faced hammer and a small block of wood to distribute the force.

Installing the new cancelling cam

Before you install the new cam, clean the steering shaft where the old cam sat. Any dirt or corrosion will prevent the new cam from seating properly. Wipe it down with a clean rag and a little penetrating oil if needed.

Slide the new cancelling cam onto the shaft. It should go on smoothly; if it's tight, tap it gently with a soft-faced hammer and a wood block. Once it's seated, find it with the pin (if your truck uses a pinned design) by driving the pin back through the hole. Make sure the cam rotates freely on the shaft and that the shaped edge faces toward where the turn signal lever will contact it. Reassemble the turn signal switch housing, reconnect any wires you removed, and tighten the mounting screws.

Reassembling the steering wheel and testing

Slide the steering wheel back onto the shaft and thread the nut on by hand first to avoid cross-threading. Then tighten it with your socket and wrench—it should be snug but not over-torqued. A 1966 C10 steering wheel nut typically torques to around 30 foot-pounds, though check your service manual if you have one. Reinstall the horn pad and reconnect the negative battery terminal.

Now test the turn signal. Turn the wheel fully to the left and set up the left turn signal; it should click on. As you straighten the wheel, the signal should click off automatically. Repeat on the right side. If the signal doesn't cancel, the cam may not be seated correctly, or the lever spring may be too weak. Go back and check that the cam is fully seated on the shaft and that the lever spring has tension.

Common problems during reassembly

The most frequent issue is the steering wheel nut spinning without tightening. This usually means the shaft is turning inside the column. To prevent this, have a helper hold the wheel steady while you tighten the nut, or use a strap wrench on the shaft below the column to keep it from rotating. If you've already tightened it and the wheel is loose, you'll need to remove it again and check that the shaft isn't damaged.

Another common problem is the turn signal lever not returning to center after the new cam is installed. This usually means the lever spring is too weak or the cam isn't making full contact with the lever. Check that the cam is fully seated and that the spring has adequate tension. If the spring is visibly bent or corroded, replace it now rather than taking the column apart again in a few months.

Frequently Asked Questions

Can I replace just the cancelling cam without removing the steering wheel?

No. The cam sits on the steering shaft directly under where the wheel mounts, so the wheel must come off to access it. Trying to work around the wheel risks damaging the horn pad or the column itself. The wheel removal is the longest part of the job, but it's straightforward with a steering wheel puller.

What if the cancelling cam is stuck on the shaft and won't come off?

Spray the shaft around the cam with penetrating oil and let it soak for 15 to 20 minutes. Then tap the cam gently with a soft-faced hammer and a wood block, working your way around the circumference. If it's still stuck, you may have a press-fit cam that requires more force; a small gear puller can sometimes work, but be careful not to damage the shaft.

Do I need to remove the entire steering column from the truck?

No. The cancelling cam replacement is done with the column in place. You only need to remove the steering wheel and access the switch housing. A full column removal is a much larger job and isn't necessary for this repair.

How do I know if my turn signal problem is actually the cancelling cam and not something else?

If the turn signal works when you set up it but doesn't shut off after you complete the turn, the cam is the likely culprit. If the signal doesn't work at all, the problem is probably the switch itself or the wiring. If it works sometimes and not others, the cam is probably worn unevenly, and replacement will fix it.