Thumping / Gear Noise – HP Laserjet  5si, 8000, 8100, 8150 Printer
One thing that I’m hearing more often on HP Laserjet  5si, 8000, 8100, and 8150 Printers is a thumping or gear noise in the left side of the machine. These machines unfortunately are starting to get older and some of the less common problems in the past are starting to surface more often with the age and high number of prints most these machines have by now. In this article I will discuss the thumping / gear noise generated in the left side of the machine and give some advice on troubleshooting and diagnosing the problem as well as providing instructions on replacing some parts if needed.
HP Laserjet 5SI / 8000 Fuser Maintenance Kit C3971-69001
HP 8100 / 8150 Fuser Maintenance Kit , Brand New C3914A
Troubleshooting the Thumping / Gear Noise in the HP Laserjet  5si, 8000, 8100, 8150 Printer
The thumping / gear noise in the left side of the machine is usually causes by the fusing assembly or the face down delivery assembly. The best way to check this out is to remove the fusing assembly. See below. Let cool 10 to 20 minutes before removal.  Alright with the  fusing assembly  removed rotate the gears. If the pressure roller is flat spotted or the two bushings for the hot roller have worn out the gears will not rotate smoothly and that will cause the thumping noise when the machine is running at normal operating speed. Also if the bushings have worn out there will be a lot of metal bushing dust in the fuser. Removing the  fusing  unit  and tilting it will usually cause the dust to fall out leaving your hand or floor covered in a dark-colored  powder. If this happens then the fuser  probably should be replaced even if it seems to be rotating smoothly because its only a matter of time before the bushings start to cause problems. Remember a lot of these fusers  have been rebuilt so a lot of these units have bushings in them that have been reused one or two times. If the fuser gears and roller rotate smoothly then we need to check the gears.
 Three gears  generally wear out in the back of these printers resulting in the thumping / gear noise. There is a small gear in the front of the  fusing unit  that meshes with a gear on the main drive assembly. The teeth can wear out causing the fuser  not to properly rotate anymore. The second gear is on top of the fuser. About the same size as the one in front. This gear drives the face down delivery assembly. Again this gear can wear down resulting in the delivery assembly not functioning right and paper jams in the assembly. The third gear is inside the printer cavity. The gear on top of the  fusing assembly  meshes with a white gear on the left side the drops down and drives the face down delivery assembly. With the fuser  out it should be easy to find as its located at the top left corner inside where the fuser  sat and is located right above where the top gear on the fuser  would be. If the  fusing unit  gears are broke obviously the fuser will need to be replaced. If the gear on the face down delivery assembly is shot then the assembly will need to be replaced to solve the thumping / gear noise in your machine.
RG5-1874 Delivery Assembly, 5si, 8000, 8100, 8150
HP Laserjet  5si, 8000, 8100, 8150 Printer Parts Removal for Thumping / Gear Noise
Fusing Assembly
1. Open the Diverter Assembly access door, and remove the Duplexer if installed.
2. To release the Fusing Assembly rotate the upper levers down.
3. Â To remove the Fusing Assembly lift up on the finger handles while pulling outward.
 Control Panel
1. While pushing in on the center area, lift up on the forward edge of the control panel to release the plastic retaining tab.
2. Â Press down on the back while pushing up on the front of the Control Panel to free it from the chassis.
To Reinstall: Plug in the cable, replace the cable in its retainer, insert the rear edge of the control panel under the top cover lip, and press down on the forward edge to snap it into place.
Formatter Assembly
1. Â If the Formatter is to be replaced, make sure to note the page count.
2. Â Loosen the two captive screws, and slide the Formatter PCA out of the chassis.
AC Access Cover
1. Remove the Formatter PCA.
2. Â Remove 3 screws.
To Reinstall:
1. Â Insert the panel edge inside the back cover (if installed).
2. Â Be sure to insert the three alignment tabs into their slots before replacing the screws.
 Top Cover
1. Â Remove the Control Panel, then remove 1 screw.
2. Â Open the Diverter Assembly access door, and remove 1 screw.
3. Â Open the top cover door, and remove 1 screw.
CAUTION Be careful not to damage the Face-down Bin Full sensor flag when removing the top cover.
4. Â Lift (and hold) the top cover door up, and carefully pull out on the cover to release the retaining tab.
5.  Hold the Face-down Bin  down while carefully and slowly lifting the top cover straight up until it clears the Face-down Bin Full sensor flag and the Delivery Unit.
Be careful not to damage the Face-down Bin Full sensor flag  when replacing the top cover.
1. Â Hold the top cover door up and the Face-down Bin down while lowering the cover into position.
2. Â Slide the Face-down Bin under the Face-down Bin Full sensor flag, and make sure that the cam at the rear of the top cover door is properly positioned while lowering the top cover into place.
3 Â Make sure that the top cover is seated properly and that the retaining tabs are in place before replacing the screws
Delivery Unit
RG5-1874 Delivery Assembly, 5si, 8000, 8100, 8150
1. Â Unplug and re-route the fan cable out-of-the-way.
2. Â Remove 1 screw to loosen the grounding strip.
3. Â Remove 1 screw, and remove the metal fan shield.
4.  Open the Diverter Assembly access door, remove 2 screws, release the plastic retaining tabs (figure  6-12, callout 5), and remove the metal mounting bracket
5. Â Remove 2 screws and 1 screw
CAUTION Â Be careful not to damage the plastic sensor flags and gears on the left end of the Delivery Unit.
6. Lift the left end of the Delivery Unit approximately 1/8 inch to clear the alignment pin, and carefully rock it forward and backward  while sliding it out of the chassis.
To Reinstall:
CAUTION Â Be careful not to damage the plastic sensor flags and gears on the left end of the Delivery Unit.
1.  Place the plastic edge on the right end of the Delivery Unit into the chassis. Make sure that the plastic support tab on the right  end of the Delivery Unit slides on top of the chassis.
2.  Make sure that the plastic sensor flags and gears on the left end of the Delivery Unit can move freely. 3. Replace the metal mounting bracket before replacing the Delivery Unit screws. Make sure that the plastic  clips are snapped into place before  tightening the mounting screws.
Conclusion about the Thumping / Gear Noise in the  HP Laserjet  5si, 8000, 8100, and 8150 Printer
Wow, I’ve replaced both the fuser  and the face down delivery assembly on these printers more than I can count. I didn’t realize there was so many instructions. Anyway, I hope that has helped people walk through the thumping / gear noise  repair in their HP Laserjet  5si, 8000, 8100, and 8150 printers. Like I tell everybody these machines, right now are some of the cheapest machines to own and operate. Rebuilt toners have come a long way since this machine first came out. So running a rebuilt toner in these machines typically don’t cause too many issues. Lots of these machines have been retired and parts suppliers have broken them down and have really cheap reliable refurbished parts available. Plus these machines are work horses. I have at least twenty in the field that have a million prints or more on them and still running good. I would recommend to anybody to have these machines repaired and keep them running as long as possible, until parts are no longer available.
HP 8100 / 8150 Fuser Maintenance Kit , Brand New C3914A
HP Laserjet 5SI / 8000 Fuser Maintenance Kit C3971-69001
RG5-1874 Delivery Assembly, 5si, 8000, 8100, 8150
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