B737 Undifferentiated or Other Model
Maintenance Airframe; Maintenance Powerplant
Confusion; Time Pressure; Training / Qualification; Workload
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy
General Maintenance Action
Human Factors
While doing a routine Transit inspection on Aircraft X; I noticed Number 3 & Number 4 MLG (Main Landing Gear) tires needed to be replaced.  Unable to do this task alone I notified my crew chief to send additional manpower to complete both tires efficiently. Three coworkers showed up.  One of my coworkers went to acquire all the tooling and parts needed for the tasks.  Once the Number 4 tire change started I pulled off the hubcap and proceeded to take the bolts out of the axel nut.  Another coworker loosened the axel nut and removed it.  [Two coworkers] removed the tire; and during the removal of the tire one of the wheel bearings fell out and landed on the ground.  Not thinking much of it; because this has happened quite often when I have seen 737 tires being changed; we continued on with the task.  The same two coworkers placed the new tire on the axel and began torqueing it.Something seemed off because the axel nut seemed to sit further in then it did before the new tire was placed on.  After reviewing the sequence of events; I felt like it had been done satisfactory and redressed the tire with its hubcap.  Number 3 tire was removed and replaced without any issue and I signed off the tires per the AMM (Aircraft Maintenance Manual).  After leaving for the day and coming back into work that night I mentioned something being slightly off about the Number 4 tire change to another lead and asked if he had ever encountered this.  He knew a bit more about 737 tire changes then I had and mentioned that there is in fact a washer that sits immediately behind the nut which could have been overlooked when removing the tire and when it was put back together.  That's when I realized it must have been missing and it had probably been mixed up in the wheel bearing pieces that fell out in the initial removal of the tire from the axel.This was one of the few 737 tire changes I have been involved in; so this was pretty new to me.  Also I was not involved in the actual removing and installing of the axel nut and believed it was done correctly and per the AMM.
B737 Maintenance Technician reported reassembling the main landing gear wheel assembly incorrectly during a tire change.