Gear Doughnuts

[Releew]

Going through my annual and AP says its time to replace the shocks!  Says there is about .25" of up play with the plane on the jacks.  But...... he did this as soon as the plane was in the air.  Is there a reasonable time period to allow for decompression for the rubber, OR should there be NO PLAY as soon as the wheel leaves the ground.  Is .25" of play acceptable?  They look good, meaning no cracking or brittle in appearance.  I've also had a Go-pro on the gear and you can visually see the weight transfer and shock absorption but I know that means nothing if they are out of specification!  

Thanks for any input advice is appreciated.

Rick

[Alan Fox]

What is the cure date on them... ???

[Hank]

The cure date is molded into the edge of the donuts.

Re time period betwern javking and measuring play:  how long is it when you takeoff before you raise the gear?

[DonMuncy]

Most Mooney gurus I know wait a while after jacking to check for clearance. My take is that if the donuts expand so they are not "free to move" within a half hour or so, you are good. If they take much longer than that, you should consider replacing. If they don't expand to that extent after a couple of hours, change them now.

[N201MKTurbo]

If there is 1/4 inch above the stack of pucks then I would have to agree with your mechanic. I've always thought that any space there was unacceptable. I have '77 pucks and there is no space even just after jacking. 

If it is real cold they may be slow to expand. I live in Arizona so it is rarely real cold. It is a little chilly today. It only got to 85.

[thinwing]

If all your landings were perfect..your pucks could be made of metal!....worst case total deterioration of puck rubber...happened last year on an amphib Husky.....these guys are hard to check and wipline doesn't have the checks we Mooney guys use...one day noticed 3 degree lean..wipline puck which looks identical to our lord mount puck had totally blown out!I mean rubber chunks!...

[Vance Harral]

Factory specifications for shock disk replacement should be documented in the maintenance manual for your airplane.  I have a 1998 M20J maintenance manual, and the relevant details are in Section 32-81-00.  No jacking is involved.  The procedure is to leave the airplane on the ground, fill the tanks, and measure the gap between the retaining collar and the top retaining plate.  Basically, you're measuring how much the disks compress with weight on the wheels.  The allowable gap is 0.60" for the mains, and 0 (no gap) for the nose.

The amount of play after jacking, how long it takes the disks to uncompress, the date code on the disks, etc., are all reasonable things to consider.  I don't have any particular beef with mechanics using those factors to recommend replacement.  But that's not how the factory spec'd it.

 

[N201MKTurbo]

2 hours ago, Vance Harral said:

Factory specifications for shock disk replacement should be documented in the maintenance manual for your airplane.  I have a 1998 M20J maintenance manual, and the relevant details are in Section 32-81-00.  No jacking is involved.  The procedure is to leave the airplane on the ground, fill the tanks, and measure the gap between the retaining collar and the top retaining plate.  Basically, you're measuring how much the disks compress with weight on the wheels.  The allowable gap is 0.60" for the mains, and 0 (no gap) for the nose.

The amount of play after jacking, how long it takes the disks to uncompress, the date code on the disks, etc., are all reasonable things to consider.  I don't have any particular beef with mechanics using those factors to recommend replacement.  But that's not how the factory spec'd it.

 

Never mind...

Edited May 19, 2017 by N201MKTurbo

[Sven]

Here's a little before and after shot for you taken when we changed ours out.

[Guest]

8 hours ago, Vance Harral said:

Factory specifications for shock disk replacement should be documented in the maintenance manual for your airplane.  I have a 1998 M20J maintenance manual, and the relevant details are in Section 32-81-00.  No jacking is involved.  The procedure is to leave the airplane on the ground, fill the tanks, and measure the gap between the retaining collar and the top retaining plate.  Basically, you're measuring how much the disks compress with weight on the wheels.  The allowable gap is 0.60" for the mains, and 0 (no gap) for the nose.

The amount of play after jacking, how long it takes the disks to uncompress, the date code on the disks, etc., are all reasonable things to consider.  I don't have any particular beef with mechanics using those factors to recommend replacement.  But that's not how the factory spec'd it.

 

I built a set a gauges based on these numbers for each model. It makes measuring quick and easy.

Clarence

[LANCECASPER]

When they are in good shape the discs absorb a lot of the shock, when they aren't in good shape the airframe does - your choice. You will notice a much more stable feel when taxiing after the discs are replaced. Don't go by whether they are cracked. The rubber gets hard from age and loses it's elasticity. You won't see them cracked very often unless the airplane has spent its life outside. It's probably going to run $100 per year on a short or mid body for shock discs. More like $130 per year on a long body. (labor not included - it usually runs <$500 for labor to replace all 11 discs)

[Vance Harral]

2 minutes ago, LANCECASPER said:

It's probably going to run $100 per year on a short or mid body for shock discs. More like $130 per year on a long body. (labor not included)

That's probably about right at current prices, but the darn things seem to inflate in cost about $5/disk per year.  The first time I ever looked into it (over a decade ago), you could find 'em for about $80 apiece.  Next time I looked they were $95, then $100, then $105, etc.  We replaced our mains at annual this year and paid about $115 each.

Moral of the story: if you think they're getting close, just replace 'em now.  They'll probably be more expensive next year.

[LANCECASPER]

Find an A & P with an Aviall account - they are the only Distributor. Everyone else buys from them so they have the best price.

[highlowfastslow]

If the pucks are more than 15 years old, I'd probably change them if there is any doubt. Spend the 2 AMUs and extend the life of your fuel tanks and the 10 AMU re-seal (less shock to break down sealant etc). I'm doing that this annual even though I probably could have stretched it another year or two. 

[RLCarter]

Generally if I question something's condition I just repair/replace as needed. Takes the doubt out of the equation 

[RobertGary1]

1 hour ago, highlowfastslow said:

If the pucks are more than 15 years old, I'd probably change them if there is any doubt. Spend the 2 AMUs and extend the life of your fuel tanks and the 10 AMU re-seal (less shock to break down sealant etc). I'm doing that this annual even though I probably could have stretched it another year or two. 

Or just learn how to land.

 

-Robert

[Hank]

1 hour ago, RobertGary1 said:

Or just learn how to land.

 

-Robert

Or never go anywhere with less-than-excellent runway and ramp surfaces . . .

[Releew]

Thanks for all the great comments.  Got back in town and had the opportunity to look in the manual.  It indicates .60 of travel when the aircraft is suspended.  I am less than .25".  I do not see any indication of the tire creating any sort of abrasion in the wheel well.  But.....Bottom line is... if he wants them changed they will be changed....

Safe than Cheap any day!

Rick

[LANCECASPER]

5 hours ago, RobertGary1 said:

Or just learn how to land.

 

-Robert

Wow it's nice to know that at least one person makes a perfect landing every time.

[Releew]

Got about about 3K landings....  By far not an expert but I think Mooney's are easier to land than a 150.....and a cakewalk compared to a Tomahawk....

Just a well handling airplane.....

Rick

[N201MKTurbo]

I helped re seal the nose gear on a Cherokee 6 last weekend. Thank God we have doughnuts!

[Vance Harral]

19 hours ago, Releew said:

Got back in town and had the opportunity to look in the manual. It indicates .60 of travel when the aircraft is suspended.

Are you sure about that?  I've never seen a Mooney maintenance manual that specs anything about "travel when the aircraft is suspended".  As far as I know, every maintenance manual spec on the shock disks specifies having the aircraft on the ground, with full tanks.

Respectfully suggest you double-check.  As others have said above, if you have 0.25" of play when the gear is first retracted on the jacks, there's a good chance you have more than 0.60" of compression when the weight is on the wheels.

[Releew]

You are correct....  I was wrong.  Bottom line is they need to be replaced. They can be rotated with no compression load on them.

Thanks for your input.

 

Rick

 

[N6758N]

On 5/19/2017 at 2:05 PM, RobertGary1 said:

Or just learn how to land.

 

-Robert

Let me guess, you have original 60's or 70's era pucks on your airplane?

[Alan Fox]

On ‎5‎/‎19‎/‎2017 at 11:53 PM, N201MKTurbo said:

I helped re seal the nose gear on a Cherokee 6 last weekend. Thank God we have doughnuts!

True , the ten dollars worth of seals on the oleos , that fail every 20 years or so are far inferior to the 1200 dollar donuts every 12 tears....