HP OfficeJet Pro 6958/6968/6978 Carriage Jam: Gear Only Moves a Few Teeth Then Hard-Locks (Printhead Stuck Right)

Question

I watched your video about the printhead/carriage stuck on the right for the HP OfficeJet Pro 6958/6968/6978 series, and it was very clear. My printer has a similar problem: the carriage won't move, but the gear looks intact.

I tried turning the gear the same way you did (pushing the teeth away from me), but I could only move it about five teeth before it locked up hard. Because of that, I can't move the ink carriage to the left to keep troubleshooting.

In your video, I saw the gear moving after the replacement, but I'm not sure how you ensured the two gears meshed correctly. I'm assuming something is binding with the gear that meshes with the gear you replaced.

Do you have any suggestions for getting the carriage out of the way so I can continue fixing the printer?

Answer

Now, based on what you described-the gear moves only a few teeth and then hard-locks-that detail is very important. When it hard-stops like that, it usually means the gear is not the root problem. Instead, it suggests the carriage drive system is encountering a mechanical block elsewhere. In other words, the gear is doing its job until it hits a physical "dead end" caused by another component.

Below are the most common causes on the HP OfficeJet Pro 6958 / 6968 / 6978 platform, and why they create that "5 teeth then locked" behavior.

Why the Gear Hard-Locks After a Few Teeth

1) The service station is mid-cycle (most common)

On the right side of these printers is the service station (also called the pump/cap assembly). It's the area where the printhead parks, caps, wipes, and sometimes pumps ink.

If the printer lost power at the wrong moment, the service station can be left mid-cycle, and that can mechanically trap the carriage or create enough resistance that the gear drive "hard locks."

How it feels:

• The gear turns a little, then suddenly hits a wall.

• The carriage won't slide left because it's effectively "hooked" or held by the right-side parking mechanism.

Why it happens:
The service station uses cams and linkages. If a cam is not returned to its home position, it can keep pressure on the carriage or keep the cap/wiper mechanism in a position that blocks carriage movement.

2) A jammed pump cam / cap mechanism on the right side

Very similar to #1, but more specific: the pump cam can bind due to:

• dried ink buildup

• paper debris

• a mis-seated part

• a partially broken cam tooth

• or a spring/linkage out of position

This can create a "partial rotation then lock" pattern exactly like you described.

3) A carriage lock tab or latch is engaged

Some models in this family have a mechanical latch that can hold the carriage at the right side (especially after certain error states). If that latch is engaged, the gear can move a little until the mechanism hits the lock point.

4) Encoder strip tension or snag (less common, but possible)

The clear encoder strip (with tiny markings) runs behind the carriage. If it's:

• misrouted

• snagged

• stuck to ink residue

• or pulled tight due to misalignment
  ...it can add enough resistance to stop movement and make the gear feel "locked."

This usually doesn't hard-stop as sharply as a cam jam, but it can contribute.

Safe "Big Rule" Before Any Mechanical Release Attempt

If you're going to manually rotate gears or try to slide the carriage:

• Power off the printer

• Unplug it from the wall
  This is critical because the carriage can unexpectedly energize or move when sensors change, and that's how fingers get pinched-or electronics get damaged if something shorts.

The Most Likely Fix: Relax the Service Station to Free the Carriage

Since your gear is intact and you're hitting a hard stop, the most likely path is that the service station is not in its home position.

What usually helps (conceptually) is:

• accessing the right side enough to reach the service station cam area, and

• manually rotating the pump/service station cam backward toward "home" to remove pressure from the carriage.

Once the service station is relaxed and no longer pressing against the printhead, the carriage will usually slide left more freely.

(Important note: Different revisions of the 6958/6968/6978 family can vary slightly in cover removal and cam access, but the underlying concept is the same: the carriage can't move left until the right-side mechanism releases it.)

About Gear Meshing: How to Ensure the Two Gears Engage Correctly

This is a great question, and it's also where people accidentally cause binding.

When you install/seat gears, the goal is not to "force align" tooth-by-tooth. Instead:

1. Seat the motor and driven gear fully and flush in their correct positions.

2. Confirm the gear shafts are not tilted and the gear faces are not rubbing the housing.

3. Then rotate the system slowly by hand and let the gears self-mesh and settle into the natural engagement path.

If the gears are properly seated, they will mesh smoothly with minimal resistance. If they bind immediately, it usually means:

• something is mis-seated

• a gear is crooked

• or the downstream mechanism (often the service station) is jammed-so the gears are fighting a locked system.

In your case, the fact you get only a few teeth of movement strongly suggests you're not dealing with "bad meshing" at all-you're dealing with the gears encountering a locked downstream mechanism.

Why You Shouldn't Force It Past the Hard Stop

If you force rotation past a hard stop, you risk:

• stripping a gear

• snapping a gear hub

• stretching or skipping the carriage belt

• cracking the carriage frame

• damaging the service station cam mechanism

A true hard-lock is the printer telling you: "something else needs to release first."

Addressing printer issues can be a complicated affair due to the hands-on nature of the problems. So, we're not able to provide remote troubleshooting, suggestions, or support for printer repairs. We offer an in-person evaluation and repair service via our local diagnostic facility: BCH Technologies Printer Repair Service (https://bchtechnologies.com/printer-repair-service). Given the high demand, we operate on a first-come, first-served basis. So, it might take a few weeks before we can get your printer in once you're ready to drop it off. Our services are structured to repair either a whole printer or specific parts, with clear instructions on how to proceed. However, we acknowledge that our rates aren't the most economical. Thus, we highly recommend that you resort to self-help via online research. You can start by checking out YouTube or visiting our YouTube channel's homepage (https://youtube.com/@bchtechnologies). Look for specific videos using the search icon next to "About" on the right-hand side of the menu bar. I receive dozens of queries every day asking about videos for specific topics. Having created videos over the past nine years, it's challenging to remember every single one. Therefore, using YouTube's search function would be most efficient. Plus, YouTube might suggest relevant videos from other channels that could assist you.

Thank you again for reaching out and for watching the video. I really appreciate your support, and I hope this explanation helps you narrow it down: when a gear moves only a few teeth and then hard-locks, the problem is usually not the gear-it's typically the right-side service station or pump mechanism being stuck mid-cycle and mechanically blocking the carriage.