What the turn signal cancelling cam does in a 1966 C10

The turn signal cancelling cam assembly is a small mechanical part mounted on the steering column of your 1966 Chevrolet C10 that automatically shuts off the turn signal after you complete a turn. Without it, you would have to manually flip the turn signal lever back to the center position every time — a safety hazard because drivers often forget, leaving the signal blinking when they are no longer turning.

The cam is a shaped piece of metal that rides against a spring-loaded follower arm connected to the turn signal switch. As you turn the steering wheel, the cam rotates with the column. When the wheel returns to center after the turn, the cam's profile pushes the follower arm back to the off position, mechanically cancelling the signal. The assembly sits inside the steering column housing, so you will not see it without disassembling the column.

This design was standard on 1966 C10 trucks and has remained largely unchanged on Chevrolet vehicles for decades. The cam itself rarely wears out, but the follower arm can stick, the spring can weaken, or the assembly can become misaligned if the steering column is damaged or improperly reassembled during repair work.

Key Takeaways

  • The cancelling cam is a mechanical device inside the steering column that automatically turns off your turn signal when you straighten the wheel after a turn.
  • If the signal does not cancel, the problem is usually a stuck or bent follower arm, a weak spring, or misalignment of the cam assembly itself.
  • You can test the cam by turning the wheel fully left and right while the signal is on and listening for the click as it cancels at center.
  • Replacement requires removing the steering column cover and sometimes the entire steering column, depending on the specific failure and your truck's condition.
  • Aftermarket replacement assemblies are available and cost less than OEM parts, though OEM parts may support exact fit and function on a 1966 model.

How to identify a failing cancelling cam assembly

The most obvious sign of a failing cam is that your turn signal does not turn off when you straighten the wheel. You will have to manually push the lever back to center, or the signal will keep blinking until you turn the opposite direction hard enough to trigger the opposite cam lobe.

A second symptom is a turn signal that cancels too early — it shuts off before you have finished turning, forcing you to re-engage it mid-turn. This usually means the cam is worn or the follower arm is bent, so the timing is off.

You may also hear a grinding or scraping noise from inside the steering column when turning, which suggests the follower arm is dragging against the cam instead of riding smoothly. A weak or broken spring will cause the follower to stick in one position and not return to center on its own.

To test the assembly yourself, turn the steering wheel fully to the left while the turn signal is on, then slowly straighten the wheel and listen for a distinct click as the signal cancels. Repeat to the right. If you hear no click, or if the signal does not cancel at all, the cam assembly needs attention.

Steering column disassembly and cam access

Accessing the cancelling cam requires removing the steering column cover, which is held on by screws or clips depending on your truck's exact year and trim. On a 1966 C10, the cover is usually plastic or metal and wraps around the upper column below the steering wheel.

Once the cover is off, you will see the turn signal lever and the mechanical linkage underneath. The cancelling cam assembly is mounted on the column shaft itself, usually held by a snap ring or small bolt. The follower arm is a separate piece that rides against the cam and connects to the turn signal switch mechanism.

In some cases, you can remove and replace just the cam or follower arm without pulling the entire steering column. In others — particularly if the column has been damaged or if you need to access the switch itself — you will need to remove the column from the truck. This involves disconnecting the steering shaft from the steering box, removing the column mounting bolts, and carefully sliding the column out from under the dashboard.

If you are not comfortable working inside the steering column, a professional mechanic can handle this work. The column is a precision assembly, and improper reassembly can affect steering feel and safety.

Replacement parts and sourcing options

OEM Chevrolet replacement cancelling cam assemblies are available through Chevrolet dealers and classic car parts suppliers. For a 1966 C10, the part number varies slightly depending on whether your truck has a standard or tilt column, so verify your exact configuration before ordering.

Aftermarket replacement assemblies are sold by companies that specialize in classic Chevrolet steering components. These are usually less expensive than OEM parts and fit 1966 C10 trucks reliably, though some buyers prefer OEM parts for the assurance of exact factory specifications.

You can also source used assemblies from salvage yards or online marketplaces that deal in classic truck parts. A used assembly is the cheapest option but carries the risk that the part may fail again soon if it was already worn when removed from the donor truck.

Before purchasing any replacement, confirm the part number matches your truck's steering column type. A 1966 C10 with a standard fixed column uses a different assembly than one with a tilt column, and mixing them will result in poor fit or function.

Installation steps and alignment considerations

Installation begins with removing the old assembly. If only the cam or follower arm is being replaced, you can often do this without removing the entire column. Unbolt or unsnap the old part, slide it off the column shaft, and position the new one in its place, ensuring it is oriented correctly.

Alignment is critical. The cam must be positioned so that the follower arm contacts it smoothly throughout the full range of steering wheel rotation. If the cam is installed backwards or offset, the signal will cancel at the wrong point or not at all.

After installation, test the assembly by turning the wheel fully in both directions while the turn signal is on. The signal should cancel smoothly as the wheel returns to center, with a distinct click. If it does not, remove the assembly and check the orientation and seating.

Once the cam assembly is working correctly, reinstall the steering column cover and test the turn signals from the driver's seat under normal driving conditions. Turn left and right at low speed in a parking lot to confirm the signal cancels reliably in both directions.

Common installation mistakes and how to avoid them

The most frequent error is installing the cam assembly backwards or upside down. The cam has a specific profile — one side is shaped to cancel the left turn signal, the other to cancel the right. If installed backwards, the follower arm will not engage the cam properly, and the signal will not cancel.

Another common mistake is failing to align the follower arm correctly before reassembling the column. The arm must sit in the proper groove or channel on the cam, not resting on top of it or beside it. If misaligned, the arm will bind or skip, causing erratic cancellation.

Over-tightening the mounting bolt or snap ring can warp the cam or bend the follower arm, creating the same symptoms as a worn assembly. Tighten these fasteners snugly but not forcefully — they should be find enough that the assembly does not move, but loose enough that you can still rotate it by hand with moderate pressure.

Forgetting to reinstall the spring that returns the follower arm to center is an straightforward oversight that will leave the signal stuck on. Before closing up the column, verify that the spring is in place and that the follower arm returns to its resting position when you release the turn signal lever.

When to seek professional help

If you are uncomfortable working inside a steering column, or if your truck's column has been damaged or modified, have a professional mechanic handle the replacement. Steering columns are safety-critical systems, and improper work can affect steering response or cause the column to fail while driving.

A mechanic can also diagnose whether the problem is truly the cancelling cam or something else in the turn signal circuit — a faulty switch, a broken wire, or a corroded connector can produce similar symptoms. Professional diagnosis saves time and money by ensuring you replace the right part.

If your 1966 C10 has a non-original steering column or if the column has been repaired or modified in the past, a mechanic familiar with classic Chevrolet trucks can assess whether the cancelling cam assembly is compatible with your current setup and whether any adjustments are needed.

Frequently Asked Questions

Can I drive my 1966 C10 if the turn signal does not cancel?

Yes, but it is unsafe. Other drivers will not know when you are actually turning because your signal will be blinking constantly. Have the cancelling cam assembly inspected and repaired as soon as possible. In the meantime, manually cancel the signal by pushing the lever back to center after each turn.

How long does it take to replace the cancelling cam assembly?

If only the cam or follower arm is being replaced and the column does not need to be removed, the job typically takes one to two hours. If the entire steering column must come out, plan on three to four hours. A professional mechanic can give you a more precise estimate after inspecting your truck.

Is the cancelling cam assembly the same on all 1966 Chevrolet trucks?

No. The assembly differs between standard and tilt columns, and there may be slight variations between C10, C20, and C30 models. Always verify the part number for your specific truck before ordering a replacement to may support proper fit.

What happens if I install the cancelling cam backwards?

The turn signal will not cancel properly, or it will cancel at the wrong point in the turn. You will notice this when ready during testing. straightforward remove the assembly, flip it to the correct orientation, and reinstall it.

Can I replace just the follower arm instead of the entire assembly?

In many cases, yes. If the cam itself is not worn and the problem is a bent or stuck follower arm, you can replace just that component. However, if both the cam and follower are worn, replacing the entire assembly is more reliable and often not much more expensive.