Liftmaster Jackshaft 3800

[dbertheau]

Hi,

I've just installed a Liftmaster 3800. Works good but I have a couple of questions.

1. when the door is closing, and about 5 inches from the floor, the opener/door starts to jerk a bit as it slows down. Is this normal? Or, is there something that I need to adjust to smooth it out.
2. when the door is open and then push the button to close, after about 3 to 4 inches of travel down, the cable where the cable tension monitor is located gets some slack --just for a second and then will tighten back up. This only happens to one side, the other cable appears to be tight at all times. When the cables are adjusted are they done one at a time, or do both cables get adjusted at the same time? Not sure how do adjust, I may need to call someone to come out???

Thanks,
Dave

[gdoorpro]

Lm3800

The LiftMaster 3800 is probably one of the smoothest running operators on the market. If their is jerking toward the close position, then the door is probably a little to tight against the jambs, or the track is pinching the door.

There should be a little play if you pull on a hinge while the door is in the close position. Perhaps an 1/8". You should also be able to spin the shaft of the rollers. You can move the track in or out by loosening the bolts on the jamb brackets and sliding it in or out.

Also check the vertical tracks to make sure they are wide enough. You should have at least a finger width away from the edge of the door, but pinch the door at the bottom to make sure it sits in the same position. If a roller is hitting a track bolt or at the joint, this should be adjusted.

The cable being loose on one side is usaully due to the door being off level. Make sure the door is level. IF not you can adjust this, but it probably would be safer to have a door professional do it because of the enormous torque on the torsion springs. If you have a curved jaw vice grip and wrench i can walk you through slipping a drum to level the door if so desired.

Ryan

[dbertheau]

Liftmaster Jackshaft 3800

Hi Ryan,

Thanks for your reply.

I'll take a look at the door tomorrow evening and will let you know how it goes.

Thanks again,
Dave

[dbertheau]

Liftmaster Jackshaft 3800

Looks like the all three of my doors have the same issue where the top section of each door is pretty snug against the jambs. As you move down the doors there may be up to a 1/4" of slop. I'll adjust all brackets, from top to bottom, so there is approximately 1/8" of play.

Dave

[dbertheau]

Liftmaster Jackshaft 3800

I've gone through and tuned up all three doors. One of the doors was considerably out of balance. I balanced the door by tightening the torsion spring using half inch steel rod.

So, I have a good understanding on how the torsion spring and bar works with the drums and cables. I still have one door with one cable that is slightly slack. I think I know how to adjust, but, just to be sure: is slipping a drum a two person job? If one person uses one of the steel bars to hold the torsion spring in place, and the other loosens the set screws on the drum. Once the set screws are loose, the torsion spring and rod is backed off a bit until both drums/cables are the same - then tighten the set screws on the drum.

Is this the concept of slipping a drum?

Thanks,
Dave

[gdoorpro]

slipping a drum

To do this you only need a vice grip, prefferably a curved jaw 10" vice grip, 7" will work. Assuming you have a standard set up, use the vice grip to hold the spring shaft steady, by setting the vice grip against the wall on the underside of the shaft, or by suing the track to hold the vice grip steady.

IF you are not sure you can set a vice grip on the top and bottom to keep the shaft from spinning either direction. Then loosen the set screws on the high side of the door, do so slowly and don't loosen the first one all the way, then do the second screw, It should slip slowly if you are gentle with it. If you let it slip too, far you will have to correct the other side.

Note; The drum on the left side, looking out will give you a little more slack as you retighten the set screws, while the drum on the other side will actually tighten the cable. This has to do with the direction the set screws turn, anytime you set the cables on a new door you always start on the Left side looking out, and then move to the right drum.

It should be easily done by one person.
Let me know if this helps.
Ryan

[dbertheau]

slipping a drum

Thanks Ryan.

Ok, so I understand how to adjust the level now. But, As I look at the door, the bottom is in fact parallel to the floor and is level. So, something else is going on for the cable to be slightly slacking as it starts its way down. I'll look closer to see if the verticle rails are to tight.

Dave

[dbertheau]

LiftMaster 3800 - Loose Cable

Hi,

I've now installed a 3800 on all three of my doors. And all three work perfect except for one thing: they all three get a loose cable about 1 to 3 seconds after starting down --it's like the doors cannot keep up with the torsion bar at the start of the down cycle. Is there a way to adjust or slow down the initial downward motion of the motor??? Not sure what to do - except to tape a nut on the back of the cable monitor so it never detects a loose cable!

Thanks,
Dave

[gdoorpro]

Adjusting the track

I find that installing the horizontal track so that it is going up hill a couple of inches seems to help with keeping tension on the cable, because the door will want to help itself go down.

This usually entails raisng the back of the track up and also adjusting the track at the radius, their are usaully a few screws that can be loosened to help keep the track from bowing.

Ryan