Speedbrake Failure Mode

[exM20K]

I guess I should be glad they didn’t fail in the Up position.  This failure mode: push the button, they extend 2/3 of the wan, and then they snap right back to stowed.  Any ideas on how to troubleshoot?

-dan

[rgpilot]

The speedbrake controller located in the aft-belly will cause an ok speedbrake to retract if the opposite speedbrake does not deploy properly.

Peciseflight will tell you to send back both speedbrakes and the controller for repair. I did this and it turned out the controller was the problem.

[N201MKTurbo]

It seems the way they work is, when you push the button both clutches are energized and both motors are turned on and a timer is started. When each speed brake gets to its up switch, it’s motor is turned off. If both speed brakes don’t get to their up switches before the timer times out, both motors are turned off and both clutches are de-energized and the clock springs snap them back down.

The up switches are inductive proximity switches and should be very reliable. The usual cause is lack of lubrication on the motor and gears causing them to run slow. 

The timer is necessary to keep a stuck motor from running continuously and burning itself out.

Wiring and connections can always be a problem.

Ive always thought the timeout period should be about 50% longer.

[LANCECASPER]

22 hours ago, exM20K said:

I guess I should be glad they didn’t fail in the Up position.  This failure mode: push the button, they extend 2/3 of the wan, and then they snap right back to stowed.  Any ideas on how to troubleshoot?

-dan

The first thing I would do is pull both cartridges and make sure that the worm and worm gear have been cleaned & greased with Aeroshell 22. They specifically say not to use any spray lubricant. This is missed in most annuals although it's called for in the IAW in the speed brakes. This is especially true if the airplane has TKS. The fluid washes away the grease in the gear.

[N201MKTurbo]

The note about spray lubricants is because you don’t want to get any lubricant on the clutch plates. If you just stick the tube of your WD-40 down into the slot and spray you will almost certainly get lube on the clutch. 
 

If you disassemble them and strategically spray the pivot points, it should do no harm, but just to be safe, it would be better to use an oiler.  

[ArtVandelay]

The speedbrake controller located in the aft-belly will cause an ok speedbrake to retract if the opposite speedbrake does not deploy properly.
Peciseflight will tell you to send back both speedbrakes and the controller for repair. I did this and it turned out the controller was the problem.

Controller? That’s if they’re newer versions (2000 series?), the older electric ones don’t have a controller, just a 4 connection relay.
OP needs to figure out what they have first.

[exM20K]

18 minutes ago, ArtVandelay said:

Controller? That’s if they’re newer versions (2000 series?), the older electric ones don’t have a controller, just a 4 connection relay.
OP needs to figure out what they have first.

2009 acclaim. So likely the newer version. Thanks