Mmmmm, New Donuts.

[Sven]

Sounds like a Homer Simpson line. We are in the process of removing the gear, sandblasting and repainting the gear. While we are there, we decided to change the donuts. You can see what a huge difference in height the old donuts and new donuts have. Can't wait to see if we can notice the difference. For the amount of $ we spent, I'm hoping we do.

-Sven

[crxcte]

Measure the distance in the old 4 donuts next time.  I just had mine changed.  I would like to compare.

[Sven]

Will do. I'll be out there tomorow. We just bought her two years ago and we have reason to believe these disks were new in 1991. We found a very faint date on one that looks like 11/91. I'd say it was about time. Since you just had yours changed, do you notice any difference? I'm interested to know if it affects taxiing and landing.

 

[flyby201]

It has been my experience in the past that I have encountered significant price differences when checking parts prices from the various Mooney Service Centers.  I had to buy a new lower cowl once and we are talking thousands of dollars in difference.  Just wondering if you checked around and, if so, where you got the best price.  I was looking at my shock discs yesterday and considering changing mine as well.  I'm also interested in knowing if you see a performance improvement.

 

Steve

[Sven]

We did a lot of shopping around on the net and finally settled on a full set of 11 for $900 shipped. I'm not exactly sure where they came from but I think they may have been from Texas. I'll check and get back to you, Steve. The old pucks from the nose gear were 1 1/32"  tall. The main gear pucks were 1" exactly. Here's a photo of the main gear pucks. They were visibly shorter than the nose gear.

 

[jezzie]

Regarding new donuts, I just went through sandblasting the gear and put new powdercoat finish on everything that had no springs or ball sockets, those parts I spray painted. I never thought of measuring the donuts. I was able to find some that only had 50 hours on them, and those are the ones I used. Just curious how thick the new ones are. I measured the old ones and they are between 1" and 1 1/32". If anyone can tell me how thick the new ones are I would like to know.

[Sven]

New donuts measure 1 1/8"

[carusoam]

The enemies of the donut=weight, time and temperature.  (not so much, hours flown or number of landings)

My guess...

The concern for donuts with only 50 hrs on them is....  The 50 hrs were the good hours when no compressive stress was placed on them and they were allowed to relax....

How many years out in the hot sun was 2,500# of airplane squeezing them down ever thinner and thinner???

Longer heavier mooneys are known/rumored to compress their donuts sooner than short / lighter mooneys.

Rubber is a visco elastic material.  Viscous = slow flowing (years),  Elastic = return to original form.  Over time, the compression force of the weight of the airplane will shorten the height of the donut.  Increased temperature will make it occur sooner.  The elasticity is also lost (harden) as the age of the rubber increases.

On an active mooney, with only 50 hours, the donuts, were used for a year or less?  On an inactive mooney, the 50 hrs does not tell much about how compressed or how old the donuts can be.

-a-

[jezzie]

Quote: carusoam

The enemies of the donut=weight, time and temperature.  (not so much, hours flown or number of landings)

My guess...

The concern for donuts with only 50 hrs on them is....  The 50 hrs were the good hours when no compressive stress was placed on them and they were allowed to relax....

How many years out in the hot sun was 2,500# of airplane squeezing them down ever thinner and thinner???

Longer heavier mooneys are known/rumored to compress their donuts sooner than short / lighter mooneys.

Rubber is a visco elastic material.  Viscous = slow flowing (years),  Elastic = return to original form.  Over time, the compression force of the weight of the airplane will shorten the height of the donut.  Increased temperature will make it occur sooner.  The elasticity is also lost (harden) as the age of the rubber increases.

On an active mooney, with only 50 hours, the donuts, were used for a year or less?  On an inactive mooney, the 50 hrs does not tell much about how compressed or how old the donuts can be.

-a-

 

Although I'm not a mechanic, I do have them on condition that they do work. The circumstances are that the donuts were on a Mooney for 2 years then had a gear up landing. They were removed from the plane and have been inside stored up till now, therefore not subject to heat and downward pressures. I did call a Mooney service center and they said that would have no problem using them. In any event I'm going to copy my AME with your comments cause the final decision is his.

 

Thanks for your help

 

Eldon

[Alan Fox]

Just some food for thought , the donuts are always compressed , when the plane is sitting on the gear the travel of the gear is on the upper limit , meaning that they do NOT compress at all unless you are landing or taxiing , When I replaced mine I had to jack the plane in a goofy manner so the weight of the whole plane was on one leg at a time to  get the top collar on, Also if your plane has not been converted from the Goodyears (5 0n the mains and four on the nose ) you have to replace the stack tubes also , Also very important , if you dont put the nose collar on correctly the plane will have nose wheel shimmy ... ( it looks like the bolt hole is in the middle , it is not it is a few thousandths to one side and the longer side has to face the truss and stack) 

[carusoam]

Quote: n74795

the donuts are always compressed ,

they do NOT compress at all unless you are landing or taxiing

[rgaines]

I replaced mine about 3 months ago. The difference was about 1".  Hard to believe but they were dated 1975. 

[DaV8or]

Speaking of donuts, I'm looking at a '66 F now that needs IMO new nose gear donuts. The logs mention replacing them in the late '60s and then later the nose gear trunion was replaced in 1992, so I'm assuming the discs were done then, but there is no specific mention of it. When I inspected them, I had a helluva time finding any date on them. They just looked pretty bad to me. I'm wondering what it costs to have them replaced? The main gear was done recent with log entries, so they're good to go.

[Sven]

The donuts themselves ran about $900 with shipping.

[DaV8or]

Quote: Sven

The donuts themselves ran about $900 with shipping.

[danb35]

Quote: DaV8or

Speaking of donuts, I'm looking at a '66 F now that needs IMO new nose gear donuts.

[DaV8or]

Quote: danb35

Just in case you're not aware, there is a spec in the service manual for this.  Page 5-22, Figure 5-13, specifies no gap between the collar and the upper retaining plate on the nose gear at static weight (full fuel, no pax).  See the attachment for a drawing.

Are you sure it's a '66 F?  There were very few (only 2) of those made, IIRC.

[N201MKTurbo]

When checking for the gap on the doughnuts, temperature and load have a lot to do with it. If you jack up any mooney on a cold winter morning there will probablly be a gap. Let the gear hang and warm up and the doughnuts will probably come back into spec. If you ever find a Mooney with a rotated top plate then it is time to replace the doughnuts.

[danb35]

The serial number is the most important, and the 66 indicates that it is indeed a '66 model year.  Like cars, the model year for airplanes starts at some point during the prior year, and the MFR YEAR is the calendar year of manufacture.

It would be a good idea to get a service manual for whatever Mooney you end up buying--my point was simply that there is an objective standard to apply when evaluating the shock discs.