Here is how I repaired a broken belt tensioner device on a Eureka Boss Smartvac 4870 from Costco. The steps include the removal and reassembly. Hopefully they will provide the guidance you needed.
If the brush roller stalls when it comes into contact with the carpet, it might be that the tensioner spring has broken off. This is a design flaw in the Eureka 4870. The symptoms are: 1) brush spins until it contacts the carpet then it stalls, 2) the brush lever for setting floor/carpet is loose and lacks a firm setting, 3) vacuum no longer has the feel of being self-propelled on carpet. It is not too easy to repair and I don’t know if a replacement tensioner is commercially available.
1. Remove the base plate by the 3 Phillips screws.
2. Remove the brush roller and belt.
3. Remove the black accordion hose connecting the motor housing to the clear vertical riser on the side of the vacuum. Unscrew it from the riser. Then disconnect the accordion hose from its black connector that screwed into the riser. Then unscrew the Torx T-20 screw that holds the bottom of the hose into the motor base. Then draw the accordion hose out through the underside of the vacuum.
4. From the underside, remove the 3 Torx T-20 screws that hold the red top cover in place. They are located in between the brush roller and the two small height adjustment wheels. The middle screw holds the height adjustment knob. The other two straddle the height adjustment knob.
5. Turn the vacuum upright and remove the red plastic cover. This is the most difficult step. Use a flat screwdriver to pry it loose in the hole where the accordion hose fed through. On the other side, where the foot operated upright release lever is, you will have to pry the red cover off. I broke the red plastic loop from here. But it still reseats OK.
6. Still upright, remove the belt tensioner by the 5 Torx T-20 screws, including the one connecting to the slotted arm (it has a wide cylinder under the head). Before removing the piece, note that there appears to be another mounting hole like the four standard mounts. This is the anchor for the spring which applies tension to the tensioner. The other anchor point for the spring has probably broken off, and the spring might be dangling loosely or even missing.
7. Remove the tensioner unit. Locate the other anchor point, which is probably a broken tab with a hole as the anchor point, broken through from the tension of the spring.
8. Drill a new hole near the broken tab. I drilled two, at right angles to each other. Drill small holes so as to not weaken the remaining plastic. I drilled ~1 mm. Holes should be between the two anchor points so as to not make the spring stretch longer than the original. Plus, a longer anchor point will interfere with the butting of the plastic edge when in the stretched position. If the spring is already lost then use a replacement that is ~1 inch long (total length) with hooks at each end.
9. Reassemble the tensioner device. Check the operation of the tensioner lever to ensure smooth, firm locking.
10. Reassemble the red plastic cover (3 screws including the height adjustment knob).
11. Reassemble the accordion hose, brush roller, belt, and base plate.
Walt K, July 2010
