Shock discs

[eaglebkh]

What are the signs that new shock discs are needed?  Do they compress much over time?  My prop clearance is a little low in my opinion (8"), especially for a 3-blade.  I can't find any entry logging a replacement, but I wouldn't think they're 45 years old.

[KSMooniac]

There are some inspection criteria spelled out in the maintenance manual, but I don't remember them off the top of my head.  One check I think is to jack up the plane and see how they respond once they're unloaded...they should expand and not leave any "slack" in the assembly.  They very well might be 45 years old, and if that's the case you should replace them!  I don't remember the "normal" prop clearance either, but 8" sounds very low.  Also, the 3-blade props STC'd for Mooneys are the same diameter as the 2-bladers, except for the MT.

[mooniac58]

Mine were very mashed looking (being rounded at the edges) and they were also very cracked looking.  Installing new ones did raise the aircraft about 1 to 1 1/2 inches though.

I believe mine were 10 years old when replaced them right after buying her, about twice as long as it should be.

[Magnum]

Replacing them gives you a smoother ride on the ground, too. You'll need a special tool to change them at the nose gear.

[Magnum]

To change the discs at the main gear you don't need the special tool, you can use the weight of the aircraft (at least worked for me). Before jacking remove the bolt at the retaining collar. Lift her up, replace the discs and put her back on the mains to insert the bolt again. It won't work with the nose gear, as the weight isn't enough.

[eaglebkh]

Yes, I noticed the 3/5 disc arrangement as well.  Umm...

The engine mount and lords were replaced at annual last year (cracked engine mount!).  It could very well be the nose wheel rigging.  A visit to an MSC may be in order in the near future.  Any recommendations for the N. Alabama area?  I need a general rigging of all controls as well.

[Seth]

I just replaced my main gear discs at this last annual.  They can go bad simply from one bad landing but usually its a more gradual wear.  The Freeway Aviation MSC, in Bowie, Maryland, recommended the replacement.  When on the jacks, you could see that they were compressed, and about a half inch of play was noted in the landing gear system as opposed to it being ready for a good landing (similar to a ready spring).  It is hard to describe, but if you look at the picture a few posts ago, and the diagram even further up, you can see that the Mooney wheel sits at an angle under the discs.  The discs compress, when there is weight, but do not spring back when your discs are ready for replacement.  They spring back a whole lot less and you can literally pick the wheel up with your hand at an angle (when on Jacks) for the first half inch or so of movement (the excess play involved) - this means they are dead and its ready for replacement.  I realize this is not the most efficient way to explain the information, but I really cannot figure out a better way to put it in words.

Also, if you have discs that are date stamped, you can look at them and figure out what year they are from.  My mains were from 1984, my nose gear discs are much newer and did not need replacement.  Many hoses are date stamped as well so you can see what year they were installed if you can't find it in the log books.

Also, if you have discs that are date stamped, you can look at them and figure out what year they are from.  My mains were from 1984, my nose gear discs are much newer and did not need replacement.  Many hoses are date stamped as well so you can see what year they were installed if you can't find it in the log books.

[GeorgePerry]

JimR

That's a nice looking main...New Lords disks, shinny new rotor and caliper.  Looks like you've put some time, effort and funds into keeping your bird ship-shape.  Where did you get the calipers?  Are they rebuild and painted or new?

Mine's going in for annual next week.  Shock disks for all three wheels on order from lone star.  $650 for the set isn't too bad considering my local MSC wanted over $1000 for the same parts. 

 

[KSMooniac]

Yeah, that pic makes me envious.  My mains are showing 32 years of use and muck, no matter how much I clean them.  I hope when I get the plane painted they end up looking like new again.

[MooneyPilot231]

This may have already been mentioned but if you can spin the disc between the rubber with your hand while the plane is jacked then you need to replace the rubber. Not sure where I got that info but it came from a Mooney site somewhere.

[Seth]

That makes perfect sense that if you can spin the disc between the rubber with your hand while it is jacked up, you need to replace it.  This is similar to the extra half inch of play that the gear shouldn't have when jacked up. 

[Mooneyland]

The last set of shock disks that I purchased were from Southwest Texas Aviation and he had a bunch of them for about $50.00 each. Not sure if they still have that price but check them out because they have been cheaper traditionally than other suppliers. You can talk to Russell Stallings: 800 749-SWTA. They're in San Marcos Texas midway between Austin and San Antonio.

Hope this helps.

richard zephro Mooneyland

[GeorgePerry]

Another thing to watch out for if shock discs haven't been changed in a while is piting in the shock tower.  My plane just came out of annual and I had the lords shock discs replaced.  My plane had the "updated" discs and towers installed back in the late 90's.   The good news is that Aerodyne went over it with a fine tooth comb and the plane got a clean bill of health.

The bad news was that since it had been about 11 years since the discs had been updated / swapped the shock tower's that go up through the holes in the discs had become badly pitted and needed to be replaced.  Each tower was about $500.00.  Ouch...that's an expensive piece of metal.  I asked my shop if this was normal and they told me that they had seen it before.  Some of the castings from the late 80's and 90's were not good quality and it's not unusual to see this type of deterioration on cast steel parts of that era.  I spoke with Mooney about this to see if there was a SB that addressed the problem and they said no.  The customer serviced rep went on to say they were aware of the problem and the newer shock tower castings are of a much higher quality.

I'm passing this along for those who had the disc / Shock tower update performed back in the late 80's and 90's.  If your discs need to be replaced...I would recommend inspecting the shock tower struts too.