Chamberlain 3850PC Manuale Utente

6

•  

Remove the two washered bolts mounted on top of 
motor unit.

•  

Align rail and styrofoam over belt pulley. Cut tape from 
rail, belt and styrofoam.

•  

REMOVE STYROFOAM.

•  

Insert both washered bolts through the rail into the 
motor unit. Tighten bolts securely.

•  

Position belt over the motor unit belt pulley.

To avoid SERIOUS damage to opener, ONLY use bolts 
mounted in top of motor unit.

•  

By hand, thread the spring trolley nut on the threaded 
shaft until it is finger tight against the trolley (Figure 1). 
Do not use any tools. 

•  

Insert a screwdriver tip into one of the nut ring slots and 
brace it firmly against the trolley (Figure 2).

•  

Place a 7/16" open end wrench on the square end. 
Rotate about 1/4 turn until the spring releases and 
snaps the nut ring against the trolley (Figure 3).

This extends the spring for optimum belt tension.

Washered Bolt
5/16"-18x1/2"

Rail Hole

Motor Unit
Belt Pulley

Rail Hole

USE ONLY THIS

TYPE AND SIZE 

BOLT

Trolley
Threaded
Shaft

Spring/Trolley Nut

The Chamberlain Group, Inc.
Liftmaster Synchro Drive
Spring Trolley Nut Assembly
3/5/92 - 5/16 /92 - 5/21/92 - 6/2/92
6/11/92

Nut
Ring

Trolley
Threaded 
Shaft

Nut Ring
Slots

Square 
End

Nut Ring

Trolley

Nut Ring

Trolley

1" (2.5 cm)

1-1/4" (3.18 cm)

BEFORE

AFTER RELEASE