Landing PUCKS - When to replace?

[joekinnc]

Curious - they are rubber - and they will crack and age over time - how does one know when to replace them?

[Marauder]

5 minutes ago, joekinnc said:

Curious - they are rubber - and they will crack and age over time - how does one know when to replace them?

Start with the date code on them. (4 digits)

[Boilermonkey]

There's a guide in the service manual to measure the amount of play between pucks/disks and if they are out of tolerance then replace them.  While many may not do this, my rule of thumb is every 10yrs.

[RLCarter]

Maintenance Manual has the spec, date code as mentioned above and condition, mine met the specs but they were as hard as Chinese arithmatic. Shop around but they are roughly $100 (X 11) each

[DonMuncy]

The "down and dirty" way to check is to put the plane on jacks, wait 4 hours for the rubber to expand as far as they are going to, then try to rotate the discs by hand, It they turn easily or are loose, change them now. If they are a little tight, but you can move them, change them next annual. If you can't move them, don't worry about them. No true CB would change them on a "years in service" schedule.

[ArtVandelay]

From reports, the shorter,lighter models pucks last longer and heavier long bodies much less.

Very vague estimate: 25-12 years

 

Tom

 

[Hank]

My pucks were installed with the dates upside down. I thought they said "9-96" and they were quite hard, so I replaced them at annual in Dec 2012. Turned right side up on the workbench, they said "06-69"! YMMV, should have been done by the PO, etc., etc.

New pucks will really improve the quality of your landing, too. 

Edited March 5, 2019 by Hank

[N201MKTurbo]

I replaced mine last week. They finally failed inspection. I jacked the plane to change a tire and there was a gap.

They were good shock disks, they served me well. Date code 77

[N201MKTurbo]

2 hours ago, RLCarter said:

Maintenance Manual has the spec, date code as mentioned above and condition, mine met the specs but they were as hard as Chinese arithmatic. Shop around but they are roughly $100 (X 11) each

$118 last week

[Yetti]

if cracked you have to replace

[Shadrach]

Mine are not cracked and still expand to the point of being tight when the plane is on jacks.  I think the date code is late 70s.  I would not replace them based on age alone as they are not in the least bit hard, but then I can say that about almost all of the rubber on my bird.  The only rubber the seems to really degrade in short order is the vacuum tubing behind the panel.  If  your bird is new to you and you've not looked behind the panel yet, you should. 

 

[Marauder]

38 minutes ago, Shadrach said:

Mine are not cracked and still expand to the point of being tight when the plane is on jacks.  I think the date code is late 70s.  I would not replace them based on age alone as they are not in the least bit hard, but then I can say that about almost all of the rubber on my bird.  The only rubber the seems to really degrade in short order is the vacuum tubing behind the panel.  If  your bird is new to you and you've not looked behind the panel yet, you should. 

 

The electric gear planes with squat switches will notice the aging issue. When they don't expand fully, the squat switch doesn't get activated. I saw one plane where the Cheap Bast$#d of an owner kept adjusting the squat switch to be able to make contact. 

[N201MKTurbo]

28 minutes ago, Marauder said:

The electric gear planes with squat switches will notice the aging issue. When they don't expand fully, the squat switch doesn't get activated. I saw one plane where the Cheap Bast$#d of an owner kept adjusting the squat switch to be able to make contact. 

Getting the bolt in the collar on the side with the squat switch is one of the all time worse jobs on a Mooney. It is right up there with lock wiring the suction screen. 

[Shadrach]

36 minutes ago, Marauder said:

The electric gear planes with squat switches will notice the aging issue. When they don't expand fully, the squat switch doesn't get activated. I saw one plane where the Cheap Bast$#d of an owner kept adjusting the squat switch to be able to make contact. 

That does not make sense to me given my understanding of the gear assembly.  I have seen Mooneys with bad pucks.  The gear hangs slack regardless of whether the pucks fill the void or not. The slop in the collar and spacers will actually clank when you move the gear up and down on jacks, but the gear will extend to full travel even when the puck won't.   This reads like the stuff of "Cheap Aviation Bastard legend" not reality.

Edited March 5, 2019 by Shadrach

[Culver LFA]

3 hours ago, DonMuncy said:

No true CB would change them on a "years in service" schedule.

Absolutely correct, and a really thrifty CB may place the airplane on jacks when they know it will be sitting for a while to protect those precious rubber donuts.  

And crown them ‘King of CBs’ if they made the jacks for less than $100!

[Releew]

If you see visible cracking, cuts and or deterioration, OR if the plane is on Jacks with the wheels OFF the Ground and you can move the gear in a vertical position.  If you have rear door fairings you mas see some rubbing (marks) too.

Rent the tool to replace the donuts or have it done by someone who has a clue.  The compression tool makes it effortless!

Rick

[Shadrach]

I would add that if the plane has been sitting in extreme cold for a while it may take a bit of time for the pucks to expand.  My annual this years was done in January.  The plane had been sitting for over a month and was cold soaked from temps in the low teens over the previous night.   When I jacked the plane initially the pucks were loose.  My IA showed up a few hours later and I immediately mentioned that the pucks weren't expanding. When I tried to demonstrate, they made a liar out of me and were as tight as ever.

[Marauder]

 

I would add that if the plane has been sitting in extreme cold for a while it may take a bit of time for the pucks to expand.  My annual this years was done in January.  The plane had been sitting for over a month and was cold soaked from temps in the low teens over the previous night.   When I jacked the plane initially the pucks were loose.  My IA showed up a few hours later and I immediately mentioned that the pucks weren't expanding. When I tried to demonstrate, they made a liar out of me and were as tight as ever.

This is what I am talking about. When you take the load off of the wheels, the donuts are supposed to expand and activate the squat switch. On electric gear planes, when those donuts don't expand, the electric gear "unsafe" warning comes up and the gear isn't able to retract. I saw this repeatedly when I lived in Buffalo. The donuts weren't that old either. If you let the donuts age long enough, the expansion doesn't happen and the same thing happens. 

To deal with the cold weather issue, I installed the J model's override switch.

That white plate underneath the squat switch is what gets moved up with the donuts. I have seen some planes where the owner had lowered the squat switch.

 

 

[skydvrboy]

34 minutes ago, Culver LFA said:

Absolutely correct, and a really thrifty CB may place the airplane on jacks when they know it will be sitting for a while to protect those precious rubber donuts.

I believe a previous owner of my plane fit into that "really thrifty CB" category.  When I changed my pucks, there were 5 different date codes, ranging from '67 to '94.  I believe he measured each puck and replaced them individually on condition.  They now all have 4/18 date codes. 

[Shadrach]

29 minutes ago, Marauder said:

 

 

This is what I am talking about. When you take the load off of the wheels, the donuts are supposed to expand and activate the squat switch. On electric gear planes, when those donuts don't expand, the electric gear "unsafe" warning comes up and the gear isn't able to retract. I saw this repeatedly when I lived in Buffalo. The donuts weren't that old either. If you let the donuts age long enough, the expansion doesn't happen and the same thing happens. 

To deal with the cold weather issue, I installed the J model's override switch.

That white plate underneath the squat switch is what gets moved up with the donuts. I have seen some planes where the owner had lowered the squat switch.

 

 

Interesting, so the position of the pucks is what activates the squats switch, not the position of the gear?  Forgive my ignorance I’m a manual gear guy.

[Marauder]

38 minutes ago, Shadrach said:

Interesting, so the position of the pucks is what activates the squats switch, not the position of the gear?  Forgive my ignorance I’m a manual gear guy.

Yep. The plate is attached to the top of the donut stack. When the weight of the plane is removed, the donuts should expand and push that plate up into the squat switch. You can see the movement upward is about a half inch of expansion.

Edited March 5, 2019 by Marauder

[N201MKTurbo]

3 hours ago, Yetti said:

if cracked you have to replace

My '77s had no cracks!

[Guest]

Replacement per the manual.

[Ragsf15e]

1 hour ago, Marauder said:

Yep. The plate is attached to the top of the donut stack. When the weight of the plane is removed, the donuts should expand and push that plate up into the squat switch. You can see the movement upward is about a half inch of expansion.

All true for models with squat swithes, but lots out there with electric gear only have an airspeed switch.  I looked for my squat switch for a real long time.  Finally realized I was on a wild goose chace.  M20F, 1968 = airspeed switch only.

[Marauder]

10 minutes ago, Ragsf15e said:

All true for models with squat swithes, but lots out there with electric gear only have an airspeed switch.  I looked for my squat switch for a real long time.  Finally realized I was on a wild goose chace.  M20F, 1968 = airspeed switch only.

That was a test.  Al Mooney wanted to make sure we stayed on our toes.