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Johnson Bar - hard to secure in gear down position

bgpilot1

By bgpilot1
in Vintage Mooneys (pre-J models)

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bgpilot1 Community Regular

bgpilot1

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My friend recently purchased a 1968 M20F which seems to be in very good health overall.  But he is having problems getting the Johnson Bar locked in the gear down position.  It operates smoothly until about an inch or two from where the handle meets the floor.  Then, it takes a whole lot of effort to get the bar down the last inch and secured.  I don't think flight speed is the issue.

 

Ordinary mechanics put the plane up on jacks and cycled the gear.  They didn't spot any issues.  So I'll assume the gear doors closed properly.  The main landing gear springs look good, no corrosion.  My next suggestion is to grease all the points.  But I'm no expert.

 

Anyone have any ideas why the bar would be so tough to secure once it's 2 inches from the floor? 

 

Thanks,

Barry

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Bob_Belville Grand Master

Bob_Belville

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The bar needs to get very close to the floor. The point right behind the hole is probably the nip point and because of the leverage, for lack of a better word, any carpet or anything else on the floor at that point will hold up the end of the bar several times the thickness of the interference. Someone had glued my boot with something that hardened like hot melt. The 1/4" wad of glue/boot resulted in an inch of struggle at the latch end.

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danb35 Mentor

danb35

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The next obvious step is to check the landing gear preloads--they're supposed to be checked at every annual, and if set too high they could cause this problem.  There's a Mooney Service Bulletin (M20-155, I think, but I don't have it handy) that reduces the values from what's specified in the service manual.

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Alan Fox Grand Master

Alan Fox

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The next obvious step is to check the landing gear preloads--they're supposed to be checked at every annual, and if set too high they could cause this problem.  There's a Mooney Service Bulletin (M20-155, I think, but I don't have it handy) that reduces the values from what's specified in the service manual.

It is my understanding that that bulletin increases the preloads....

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danb35 Mentor

danb35

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It is my understanding that that bulletin increases the preloads....

Just pulled it up (it can be found at http://www.mooney.com/images/pdfs/sb-pdf/sbm20-155.pdf for those playing along at home).  From the SB: "Caution must be taken to insure that the lower gear rigging value be used . . .".  This bulletin calls for a nose gear preload of 100-130 in-lb, mains of 250-280 in-lb.  The introduction to the SB begins, "[a] reduction in the force required to place the manual gear retraction lever in the gear down and locked position can be realized . . .".

 

Mooney developed a newer design of landing gear links which allow more overcenter travel and thus require less force to hold them in place.  These parts were introduced during 1967, and aircraft built after that time (including the '68 F that's the subject of this thread) included the new-design parts.  Older aircraft could be retrofit with the new parts.  However, for whatever reason, the service manuals kept the old preload values.

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bgpilot1 Community Regular

bgpilot1

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Ah, thanks everyone for your ideas.  And we've made it this far without any Johnson Bar jokes!  Perhaps we should create a new message board for these...we can start with Hugo's reply.  :)  But back to the topic.

 

Anyone know a mechanic near Memphis,TN that would have the gear rigging tools?  Are these standard or Mooney specific?

Barry

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N601RX Grand Master

N601RX

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The problem he is having is that the gear is getting tight as the wheels go up into the wheel wells. I don't see how the gear preload could affect this. This seems to be more of a binding or rubbing problem to me. I would suggest jacking the plane up and disconnecting the gear doors so you can see what is going on. You could also disconnect each wheels control rod from the jbar and swing and lub each wheel indivudally to see if you an find out what is binding. It could just be that it hasn't been lubed in a long time.

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N601RX Grand Master

N601RX

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From the first post: "he is having problems getting the Johnson Bar locked in the gear down position."

Yes, but the text describes the problem as when the J bar is down close to the floor.

"Anyone have any ideas why the bar would be so tough to secure once it's 2 inches from the floor? "

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Urs_Wildermuth Rising Star

Urs_Wildermuth

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Barry,

 

something is weird here. You say, you have trouble in the gear down position, however that is when the Johnson Bar is vertical and locked into the bottom of the panel. If it is "close to the floor", that would be the up position. Both are fundamentally different in terms of what the last inch of travel is. Can you please clarify this?

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mikesalman Collaborator

mikesalman

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Hi folks, the problem is getting the Johnson Bar down / getting the gear up that I am having so much trouble with. I have put it up on jacks and cycled the gears until my arm felt like it was going to fall off. We could not see anything wrong, keeping in mind the mechanic did not remove the doors either. I have made 25 landings in the past 3 weeks since I have purchased this airplane and it is not getting any easier.

 Now Berry was kind enough to take me up in his M20F with a Johnson Bar and he let me retract the gear (bar down) it was so easy two fingers is all it took, mine is like a wrestling match trying to get the Johnson Bar down and locked. And I even removed the carpet and that did not help.

 

  Mike

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N601RX Grand Master

N601RX

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Get your mechanic to get it back up on jacks and disconnect the gear doors and see if that helps. If thats not the problem, then the belly needs removing and everything needs lubing. With the belly off each wheel can be disconnected from the J-Bar to determine which one is causing the problem. With the disconnected, you should be able to move each gear leg freely from under the plane. This is also how to to work the oil into all the rod ends and joints.

After getting everything moving freely the preload will need to be reset.

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