M20J - Potential Vacuum Leak

[WheelPantsOff]

Good evening,

I hope everyone had a safe and joyous Christmas and is thoroughly enjoying the holiday season.  I think I have a vacuum leak and am wondering where I start troubleshooting or having the shop investigate.

First, the SBS on the left side retracts significantly slower than the right side.

Second, when pressing the extend/retract button, the pitch of the sidetone changes significantly through the headsets.

I only have the idiot light on the panel so I can't say what the vacuum is actually pulling.  The pump is about 5 years old and ~350 hours.

Thanks in advance!

[M20F]

Your speed brake (vacuum) on the left retracts slower than the right?

What does your idiot light say?

Do you have any vacuum instruments?  If so how do they work?

[WheelPantsOff]

1 hour ago, M20F said:

Your speed brake (vacuum) on the left retracts slower than the right?

What does your idiot light say?

Do you have any vacuum instruments?  If so how do they work?

Correct.

SBS light is too dim to be meaningful.  Even in the nighttime, it's of marginal utility.

Yes, ADI.  It seems to work as intended and no obvious issues.

The left side retracting slowly happened during the runup and in-flight.  I flew it for 6-00 earlier and that's the only squawk I have for it.

[M20F]

32 minutes ago, WheelPantsOff said:

Correct.

SBS light is too dim to be meaningful.  Even in the nighttime, it's of marginal utility.

Yes, ADI.  It seems to work as intended and no obvious issues.

The left side retracting slowly happened during the runup and in-flight.  I flew it for 6-00 earlier and that's the only squawk I have for it.

I will let smarter people than me comment.  If your vacuum AI is working per normal and your right speed brake works fine, I would say not a vacuum issue. 

[PT20J]

How much slower is "significantly"? I have electric speed brakes and the left is maybe a second slower than the right (I haven't timed it). It doesn't make any noticeable difference in the way the airplane flies.

[IvanP]

I suggest looking at the cable and the brake box on the affected side. The vacuum speedbrakes are both activated by a single vacuum actuator that pulls on cables connected to the brakes. If the issue would be with the vacuum actuator or pump, it would affect both sides and generally would affect the deployment of the brakes, rarther than retraction. When you disengage the brakes, vacuum is released and springs retract the blades. If your deployment is OK but retraction is slow, it is likely either cable or spring. If the spring is broken, the blades will still retract by gravity, but slower. I had similar issue occur few months ago on 1990 Bravo with vacuum speed brakes. Squirt of TriFlow in the cables fixed it. 

[WheelPantsOff]

11 hours ago, PT20J said:

How much slower is "significantly"? I have electric speed brakes and the left is maybe a second slower than the right (I haven't timed it). It doesn't make any noticeable difference in the way the airplane flies.

At least 10 or 15 seconds, or at least the time it would take me to process the thought, 'I wonder if this is going to retract by itself or if I'm going to need to rock the wings a little bit' and 'I hope the rental car is at the FBO when I get there because it's a bitch to get these people on the phone.'  If I didn't do something, who knows if it would have retracted on it's own.

11 hours ago, IvanP said:

I suggest looking at the cable and the brake box on the affected side. The vacuum speedbrakes are both activated by a single vacuum actuator that pulls on cables connected to the brakes. If the issue would be with the vacuum actuator or pump, it would affect both sides and generally would affect the deployment of the brakes, rarther than retraction. When you disengage the brakes, vacuum is released and springs retract the blades. If your deployment is OK but retraction is slow, it is likely either cable or spring. If the spring is broken, the blades will still retract by gravity, but slower. I had similar issue occur few months ago on 1990 Bravo with vacuum speed brakes. Squirt of TriFlow in the cables fixed it. 

Excellent.  I will look at that this weekend.  Thank you!

[LANCECASPER]

17 hours ago, WheelPantsOff said:

First, the SBS on the left side retracts significantly slower than the right side.

Second, when pressing the extend/retract button, the pitch of the sidetone changes significantly through the headsets.

What year is your J? Are you sure you have vacuum speed brakes and not electric?

[RolexRootBeerGMT]

3 hours ago, LANCECASPER said:

What year is your J? Are you sure you have vacuum speed brakes and not electric?

Hell, I thought they were all electric.

[WheelPantsOff]

7 hours ago, LANCECASPER said:

What year is your J? Are you sure you have vacuum speed brakes and not electric?

1981 and these were installed prior to my ownership sometime around the mid 1990s.  I'd have to grab the manuals to be certain of the date.