Replacing shock discs

[1524J]

In trying to add photos I managed to somehow delete the thread.....technological disability rearing its ugly head. Anyhow here's photos I promised but couldn't take with greasy hands.

[1524J]

1st Photo is the difference between 20 year old discs and new. 2nd and 3rd are the nose truss with the 3rd from the backside of the truss showing the head of the bolt and collar that have to be pulled. 5th shows the main truss and the hole that needs to be lined up with the flat head bolt. 4th photo is the collar and bolt on the top main truss. 

[1524J]

This one shows the shaved bolt head that needs to be lined up properly to pull. You also have to pull the grease zert closes to the tire in order to fold the truss up. Changing shocks discs really is a straight forward job that most should be able to accomplish....with the blessing of your favorite A&P.

[carusoam]

Great Photo Maintenance descriptions, 1524J!

Thanks for sharing.

Best regards,

-a-

[pirate]

I agree doing them is straight forward I did my all disk in about  3 1/2 hours during annual,  NO special tools are required. 

Dont know if you taxied yours around yet but the ride is Soooooooooooo much better. 

[1524J]

I wanted to reorganize the photos and comments so it makes sense to someone searching how to replace their shock discs. Hopefully this is more organized and easier to understand. First and obvious, ya' gotta get the plane on jacks. Either hold down the tail with weights, pick up the nose with a lift or get Samantha from bewitched to twinkle her nose because no one wants to approve either. We'll start with the nose discs. With the front wheel off the ground remove the wheel. Remove the two bolts as shown. You'll need to use these bolts to attach the compression tool so you can remove the bolt at the top of the truss.

[1524J]

After removing the front truss bolts you'll need to remove the grease zerk shown on the backside. This will allow you to fold the wheel frame back and allow you to remove the bolt at the bottom of the disc stack. You've got to position the shaved bolt head so it'll slide out. 

[1524J]

Once the bottom bolt is removed you'll have to get your compression tool of choice and compress the discs so you can get the bolt and collar pushed up far enough that will allow you to get a 1/2 inch socket on the bolt head. I also came from the same side with a 1/2" crows foot to hold the nut on the opposite end.

[1524J]

When the top bolt is removed the disc shaft will slide down and you can remove the old discs and install the new. Take the time to inspect the collar and bolt. If the bolt hole is deformed you'll need to replace both the collar and bolt. Also be aware the hole in the collar may not be centered, it needs to go back as originally positioned. Reverse procedure and the front discs are done!

[carusoam]

Even better than before 1524J!

Best regards,

-a-

[1524J]

Now to the mains. The wheels do not need to be removed to change the mains shock discs although I pulled the inner gear doors . Set the plane back on the ground so the weight of the plane will align the hole in the truss with the flat head screw at the top of the truss. I had to use the jacks to relieve a little weight so the hole and bolt would align.

[1524J]

Once the bolt and hole are aligned, get In a position in the wheel well that's allows you to see the bolt and collar. The nut takes a 1/2" inch open end and use the biggest flat head screwdriver you can find to hold the bolt while loosening the nut. Once the nut is loose you can use the screwdriver to finish removing the nut form the bolt. I used a small phillips head screwdriver to push the bolt out the hole. 

[1524J]

When the bolt and collar at the top of the truss are removed jack the plane back up and remove the bolts at the bottom of the truss. This will allow you to lower the wheel and truss assembly down and out to remove the old discs. Have your new discs close so you can quickly swap them while holding the wheel. I had to hold the wheel because the brake lines are still attached and there's not enough slack to set the wheel on the floor.

[1524J]

Once you've got the new discs on the truss tower (make sure the top plate of the disc stack is in the proper spot as in the photo) reposition the tower back into the frame and GENTLY lower the weight of the plane back on the assembly. You've got to align the bolt and hole again and now the real fun begins. The collars on the mains have a 1/2" moon cutout. This faces forward and down. Once you've got the bolt positioned you have to get the washer and nut started. You cannot push the bolt through all the way. There's not room for the nut and washer. Push the bolt through just enough to hang the washer then I used 90 degree needle nose plyers to hold the nut. A better suggestion was to use the open end wrench and place tape on the backside to hold the nut and get it started. Once you've got the nut threaded it's all downhill. 

When you put everything back together now is a good time get the plane level with the front wheel on the ground and check the position of the front axle to a plumb bob hung over the front trunion bar. The line should split the axle. 

I wanted to add.....I always want to be involved with the maintenance on my plane....but I try to be realistic about my knowledge and abilities. I always get my A&P's blessing before I start a job like this and always have him inspect my work (he wouldn't sign my log book otherwise) afterwards. 

[Hector]

Excellent description and it could not have come at a better time. Mine are due for replacement!!!! This is something I have not done myself so I was starting to read up on it. Your photos and instructions are clear and exactly what I was looking for. THANKS.

[hoot777]

I think mine are the original. I see 7-67 on the disc and my m20 G is a 68. I guess it’s time to change them.  

[hoot777]

Great photos !!!

[hoot777]

I’ve got a 1968 :M20 G . I was cleaning up the belly and noticed 7-67 on the disk . Could these possibly be the original ??   

[AlexLev]

8 minutes ago, hoot777 said:

I’ve got a 1968 :M20 G . I was cleaning up the belly and noticed 7-67 on the disk . Could these possibly be the original ??   

Mine are on my 68 M20G.

[RobertGary1]

On 8/30/2019 at 10:59 AM, hoot777 said:

I think mine are the original. I see 7-67 on the disc and my m20 G is a 68. I guess it’s time to change them.  

Possibly. The manual describes how to measure them and provides the go/no go criteria  

this should be done each annual

-Robert 

Edited September 21, 2019 by RobertGary1

[carusoam]

That’s the date of mfg for the donuts themselves....

 

Somewhere along the way, the stack of donuts was changed from a 5 donut stack to four...

iirc Firestone made the 5 donut stack...

The logs would show where and when the donuts got replaced... if ever.

 

Hank taught us to look at the date code upside down as well...  some inverted date codes will look like a different set of numbers... 

 

The polymer guys have explained how the donuts compress irreversibly over time... cold flow, under weight, and warm temps...

Best regards,

-a-

[hoot777]

Thanks.  Makes sense I guess I have original. Glad I’ve got bladders.

[KB4]

Awesome descriptions with pics and arrows.  Thanks very helpful.

 

? What did you use to compress the nose pucks.  I know @Hank probably had his elves make up some CAD drawings to produce a 1 off compressor tool. That guy can make anything.  

[MV Aviation]

I’ve done my mains according to the way suggested here. It worked pretty well despite the fact that the collar bolts were put in the wrong way last time, which made it impossible to remove them without disassembling the gear doors. I recorded a little time laps…

[Shadrach]

On 3/19/2016 at 5:29 PM, 1524J said:

1st Photo is the difference between 20 year old discs and new. 2nd and 3rd are the nose truss with the 3rd from the backside of the truss showing the head of the bolt and collar that have to be pulled. 5th shows the main truss and the hole that needs to be lined up with the flat head bolt. 4th photo is the collar and bolt on the top main truss. 

Interesting.   My discs were 53 years old when I replaced them. The reason I didn’t do them sooner is that they were still within specs and seemed pliable…that is until I jacked the plane in February and I realized it took them nearly an hour to expand when cold soaked. Even so, the old ones only differed slightly from new when sided by side.