Replacing worn out rubber biscuits/donuts on M20B

[Wakeup]

Will need to replace these soon. Anyone have any thoughts, suggestions or materials?? I think the front nose wheel had already been done.

[BigTex]

Those on the mains are original and really only last 4-5 years. You will have to convert them to the newer 4 puck stack. SWTA generally have them in stock for around $95 each.

[Hank]

Those look like original biscuits! The setup was changed to 4 per main gear several decades ago. You nose has been converted to the new style. Don't know if you'll need additional parts or just new biscuits.

I just replaced the (new style) biscuits on my C--it's noticeable taxiing and landing. Life on our planes should be ~12 years, maybe a little longer. Check and see when your nose biscuits were replaced. Mine were $105.00 each, and a gear compression tool us required for the nose gear.

Find a shop that has done this, the more often the better. Duh, you're in Chattanooga, go see Joey Cole in Rome. He's an MSC and will know if you need anything else to do the conversion.

[rbridges]

Those look like original biscuits! The setup was changed to 4 per main gear several decades ago. You nose has been converted to the new style. Don't know if you'll need additional parts or just new biscuits.

I just replaced the (new style) biscuits on my C--it's noticeable taxiing and landing. Life on our planes should be ~12 years, maybe a little longer. Check and see when your nose biscuits were replaced. Mine were $105.00 each, and a gear compression tool us required for the nose gear.

Find a shop that has done this, the more often the better. Duh, you're in Chattanooga, go see Joey Cole in Rome. He's an MSC and will know if you need anything else to do the conversion.

 

Joey Cole told me around 10 years for the short bodies, less on the bigger planes.  I'm sure mileage will vary.

[Wakeup]

I will give him a call. I thought some one told me I would need to replace more then just the biscuits?? Maybe I can find that salvaged and buy new biscuits.

[Wakeup]

Just checked SWTAs site and they are on sale for 90/piece. Sounds like a great deal. Just wonder how many hours to install and if I need anything else?

[Hank]

The average to replace biscuits is about an hour each. This will be in addition to whatever is required to convert your mains from 5 to 4 biscuits each. Joey told me that a simple change might finish in one day but not to count on it.

[carusoam]

There are a few rubber bits that get old over a half century. Those are the most obvious, and expensive.

There are others that cost less and are less obvious...

There are similar rubber mounts supporting the engine, and the instrument panel...

Next take a look at brake and flap hoses.

Those were the areas that my '65C needed attention when I got it in 2000.

The wing leveler also has rubber bits.

The good news is the factory is open and parts are available.

The MSC is an excellent resource. Let them help put your plan together...

Best regards,

-a-

[N201MKTurbo]

If it were me and I wasn't in a big hurry and the mechanic could spare the jacks. I would have him pull the gear and him or you could completely strip and reprint the gear. Replace all the hardware. The bushings are usually OK.

It will do wonders for your plane and after you have the doughnuts off you are 80% disassembled anyway.

[mooniac15u]

You will have to replace the mounting hardware because the new discs are larger.  The Mooney Service Bulletin is M20-161 (http://www.mooney.com/images/pdfs/sb-pdf/sbm20-161.pdf).  You must also replace (or rework) a small bracket on the front of the gear bay to allow enough clearance to retract the gear with the new larger hardware (see item 4 on page 2 and figure 3 on page 5).

[Shadrach]

The donuts have been replace 1 time on my 46 year old bird. The current set are 22 years old.  There is a lot of talk about them wearing out but mine show no signs of wear. They still expand when the plane is jacked. They cannot be rotated by hand when the gear is extended to full travel and I can see that the nose gear is still very flexible every time I pull the plane over the position chock in the hangar.  Do most of you just replace them on a schedule regardless of their apparent condition?  Same goes for my PC system. The original hoses behind the panel where replaced 5 years ago (they looked pretty bad, but were still air tight), but all of the "boots/cans" are as soft and supple as ever.   

[Marauder]

The donuts have been replace 1 time on my 46 year old bird. The current set are 22 years old.  There is a lot of talk about them wearing out but mine show no signs of wear. They still expand when the plane is jacked. They cannot be rotated by hand when the gear is extended to full travel and I can see that the nose gear is still very flexible every time I pull the plane over the position chock in the hangar.  Do most of you just replace them on a schedule regardless of their apparent condition?  Same goes for my PC system. The original hoses behind the panel where replaced 5 years ago (they looked pretty bad, but were still air tight), but all of the "boots/cans" are as soft and supple as ever.   

 Mine were on for 24 years before I had them changed (plane has always been hangared). They still looked fine, but I was starting to have problems with them expanding and hitting the squat switch enabling gear retraction. With the new donuts, the ride is higher, the landings are softer and no more problems retracting the gear.

[Dcflyn]

We've elected to get new shock disks as part of our undercarriage rebuild on our newly acquired M20E. (Dang--missed the sale and already paid $105 ea.) The old ones actually looked really good--if anyone is interested in them, let me know. You can check out photos on my blog, http://n2690w.blogspot.com/.

[Hank]

The problem is that the volatiles are squeezed out over time, and the discs become permanently compressed. I was having gear retraction issues, although my discs passed all of the tests. The gear would retract all but the last few inches, squealing in the headset and causing much additional drag. I've only flown once with the new discs, but taxiing is nicer and both landings were much smoother.

Comparing the removed ones to new discs, the old ones were about 1/16" thinner after removing them inside a heated maintenance hangar. Note that I only had retraction problems during cold weather . . . If temps were ~50F or so, they went up smoothly.

[63C]

You will have to replace the mounting hardware because the new discs are larger.  The Mooney Service Bulletin is M20-161 (http://www.mooney.com/images/pdfs/sb-pdf/sbm20-161.pdf).  You must also replace (or rework) a small bracket on the front of the gear bay to allow enough clearance to retract the gear with the new larger hardware (see item 4 on page 2 and figure 3 on page 5).

Thanks for the link to the SB

[mooniac15u]

Thanks for the link to the SB

 

It looks like you own an M20C.  It's a different SB for C's, D's, and E's.  It is M20-139A (http://www.mooney.com/images/pdfs/sb-pdf/sbm20-139a.pdf).  You have to change out the bracket on this retrofit also.

[Shadrach]

The problem is that the volatiles are squeezed out over time, and the discs become permanently compressed. I was having gear retraction issues, although my discs passed all of the tests. The gear would retract all but the last few inches, squealing in the headset and causing much additional drag. I've only flown once with the new discs, but taxiing is nicer and both landings were much smoother.

Comparing the removed ones to new discs, the old ones were about 1/16" thinner after removing them inside a heated maintenance hangar. Note that I only had retraction problems during cold weather . . . If temps were ~50F or so, they went up smoothly.

Why the retraction problem?  I would think that if they were so compressed that the squat switch was triggered that they would not retract at all. What was the MOF?

[Hank]

Ross--

You'll need to get the full explanation from an MSC. Both D Max and Joey Cole stated that my partial retraction was due to old, inelastic biscuits. They had been converted to 4 per main and 3 on the nose at some point, but the manufacturing date molded into them was 6-69 . . . The new ones are 2-13.

What happened was simple, and only happened in cold weather--roll down the runway, rotate, pull the gear knob out and up, the green light goes out and in a couple of seconds it starts to squall. The floor indicator shows barber pole. Other pilots reported my gear partially hanging out. IAS and groundspeed were markedly slow. Eventually the gear would raise the last bit and thump home, the yellow "gear unsafe" light comes on and the squalling stopped. Instantaneous increase of 10-15 mph, and a need to input some Up trim. This whole thing could be avoided by putting the plane in a heated hangar for an hour.

[63C]

It looks like you own an M20C.  It's a different SB for C's, D's, and E's.  It is M20-139A (http://www.mooney.com/images/pdfs/sb-pdf/sbm20-139a.pdf).  You have to change out the bracket on this retrofit also.

Yes...I printed it out but did not look at it until today and then realized it did not include my bird. Thanks again for the link.

[carusoam]

Rubber is similar to both liquids and solids...

Under pressure, it will flow, over time....

More pressure, due to weight, they will flow more. Expect that under higher temperatures the flow would increase. I am not familiar with Southern donuts getting flatter faster than Northern donuts, though.

Physical properties will change with temperure.... The bounce will be less soft when they are cold.

It's possible that there is a transition temperature that they would get really hard / freeze under very cold temperatures.

Oxidation and UV cracking is another challenge for the donuts, but, the effect doesn't go very deep. It definitely looks worse than it is.

Since the rubber Mooney selected handles a range of weight for different models, and temperatures found around the world and Canada, and survives for decades without fracturing or over-oxidizing... I'm happy to replace a few donuts every decade or so.

You guys gave me the opportunity to talk about my other hobby, polymers!

Best regards,

-a-

[Wakeup]

Thanks for all the info... I have talked to 3 different people about cost to change main hardware and put new biscuits on. J Cole priced it around 5,000 before I bought the plane, SWTA had a set on the shelf for $2,300 per side plus labor and Don Maxwell said he could do for $1,000 total in parts plus labor in one day???? I even told him it wasn't converted to the new biscuits?? Am I missing something or is Don cheaper and faster then anyone. He even said he would fix my leaking wing for $600. If all that is true I need to fly South and have a beer at Gas Monkey Garage.

[carusoam]

Don is the guy to see, but I would make sure you are talking about the same thing, just to be sure.

He is genuine and easy to speak with. Since you know what you are asking about, it shouldn't be too difficult.

Don did the PPI on my O1. That's a longer conversation...

Best regards,

-a-

[Marauder]

Thanks for all the info... I have talked to 3 different people about cost to change main hardware and put new biscuits on. J Cole priced it around 5,000 before I bought the plane, SWTA had a set on the shelf for $2,300 per side plus labor and Don Maxwell said he could do for $1,000 total in parts plus labor in one day???? I even told him it wasn't converted to the new biscuits?? Am I missing something or is Don cheaper and faster then anyone. He even said he would fix my leaking wing for $600. If all that is true I need to fly South and have a beer at Gas Monkey Garage.

I had my donuts replaced in the Spring and it ran me around $1K. Before you sign up for any service, definitely check in with us. Many of us have been through everything you will encounter as a new owner.

Sent from my iPad using Tapatalk

[BigTex]

Don's the real deal.  He does all of my major work on my plane.  He did my shock discs but they were already converted to the new Lord discs.  Since they are the original, there's a chance when he pops out the old ones, he'll find some parts that will need to be replaced.

[Wakeup]

Thanks guys. I agree. Don sounds like a great guy and knows his Mooneys. Maybe my flight instructor would like to go cross country with me and land at lots of airports on the way for practice??