8KCAB Brake disk rubbing on gear leg

Big Ed

N50247 - '79 Super D
Joined
Jul 20, 2020
Messages
420
Location
Tampa, FL
Took my wheel pants off today to investigate a suspicious noise and found this. The brake disk is making intermittent contact with the gear leg. From the looks of it, this has been going on for a while. Has cut a notch into the edges. The top surface of the gear leg is slightly concave, so only the edges are affected. My IA says he thinks a spacer is missing. The A&P who works with him says it needs to be shimmed for alignment. Neither are sure because we don't have a parts diagram. While I am chasing down a catalog, does anyone know the answer?

How alarmed should I be?

PXL_20201210_164041470.jpgPXL_20201210_164033532.jpg
 

Helo pilot

Active member
Joined
Sep 7, 2020
Messages
26
Location
Florida
Here you go. You might want to check the brake disc for being the correct one. The parts manual says p/n 164-5 (164-00500)IMG_2556.jpg











0
 

Big Ed

N50247 - '79 Super D
Joined
Jul 20, 2020
Messages
420
Location
Tampa, FL
From the photos it looks like I am missing part #35. Do you have the item list for that page?
 

Helo pilot

Active member
Joined
Sep 7, 2020
Messages
26
Location
Florida
You need to check wheel alignment. Specs are 0 degrees to 1 degree towin. No more than three shims should be used.
 

Bartman

Administrator
Staff member
Joined
Mar 27, 2018
Messages
1,631
Location
New Jersey, USA
check your caliper attach brackets, they are flat plate with what look like spacers on each side. the thing is though, the spacers are thicker on one side than the other and the plate can be flipped, mounted, and you would never know it is backwards.

if they flipped it they might have messed with how the wheel is mounted to make the disc line up with the caliper. in my case they flipped it and then put shims between the caliper halves to keep the disc from binding. found it during the rebuild and made it all symmetrical and it works the way it is supposed to now.

good luck Ed. too much of a notch in the gear leg is a problem. I have the guy's info in WA that reconditions gear legs and can post it in the AM.
 

Big Ed

N50247 - '79 Super D
Joined
Jul 20, 2020
Messages
420
Location
Tampa, FL
Sure looks to me like I am missing the shim plate that goes between the gear leg and the torque plate that the brake caliper attaches to. Are parts like that standard for the wheel/hub make, or is that a Citabria/Decathlon specific part?
 

Big Ed

N50247 - '79 Super D
Joined
Jul 20, 2020
Messages
420
Location
Tampa, FL
If anyone has the parts catalog page with the parts number listing for the wheel and brake assembly, would greatly appreciate if you would post a screenshot or scan. I have the service manual with the drawing posted above, but parts numbers are not included, so I cannot cross reference to any parts listing from today.

From initial research, it does not appear there is such a thing as a flat shim, eg a spacer that does not change camber or alignment. I meant to call the factory but dawdled too long and now they are closed.

Headed to the airport to pull the wheel and examine closer.

Big mystery is how long this condition has persisted. Kinda shocking that it would have passed an annual in June and a pre-buy in July without this getting noticed, especially as the wheel pants were off. I rotated the tires and repacked the bearings under the supervision of an A&P in
September. It is possible we reassembled it wrong, but hard to see how that could have happened. I will check the parts diagram when I pull it to be sure, and take some photos so the experienced eyes here can judge.
 

Big Ed

N50247 - '79 Super D
Joined
Jul 20, 2020
Messages
420
Location
Tampa, FL
Ok, broke down both wheels with my A&P/IA. Still can't figure out exactly what thr problem is, but did get some insights.

1. The problem is not recent. Someone has previously dressed the edge with a file to take a prior groove out. Judging from the rust, it was a while ago.

PXL_20201211_232041946~2.jpg

2. The grove only affects the edge and does not extend across the width of the gear leg. I'm hopeful the IA will be ok with dressing it again if we can find the problem.

PXL_20201211_225613616~2.jpg

3. We could not find an obvious cause. All parts on the wheel, axle, and brake are identical to the other wheel, which has plenty of clearance. The bearings and races are fine. I even flipped the axle over in case it was bent upwards.

4. The only thing I can see is the portion of the gear leg below the bend appears to be longer on that side. It could just be the gear leg was fabricated out of spec.

I will call the factory on Monday to see if they have any ideas.
 

Bob Turner

Well-known member
Joined
Apr 4, 2018
Messages
1,299
Why not make a spacer? A drill press, a hacksaw, and a 1/8" piece of aluminum and a half hour's work. Might need longer screws, but AN-4s are cheap. I think they are 4s.
And seriously polish that blemish. Don't just file it - make it shine! Then paint it. No more stress raiser.
 

Bartman

Administrator
Staff member
Joined
Mar 27, 2018
Messages
1,631
Location
New Jersey, USA
@Big Ed Look at the end of the gear leg, the face of the steel leg below the axle that faces the ground, there should be a serial number there. I have seen black market gear legs that look identical to factory but without the serial number. unless you can really jack it up you'll probably have to use a mirror and a flashlight. might not be the case but it's another possible explanation.
 

Big Ed

N50247 - '79 Super D
Joined
Jul 20, 2020
Messages
420
Location
Tampa, FL
Did you swap wheel?
Nope, rotated tires last month but did not swap wheels. Not a bad idea to try; would identify whether the issue is with the wheel or gear leg. I would need to scrounge up another jack adapter, or do some hillbilly wood blocking.

I did check all the wheel and brake part numbers, and they are identical on both sides. My IA and I looked closely at both wheels and axles for any issues with assembly, mounting, or bearing condition. IMO most likely issue is with gear leg. I think it might just be poor QC during manufacture. Looks to me like the bend is higher up on the leg. Would only take about 1/4" variance to cause interference.

Starting to research options for repair or replacement. Potential options:
  1. Fabricate axle mount spacer and dress the notch.
  2. Exchange for reconditioned legs from Rainbow Ron.
  3. Buy new Aluminum gear upgrade kit from ACA.
  4. Does ACA still sell steel gear legs?
Now that I have started paying attention, these airplanes do have a track record of spring steel gear failures. I have found at least 10 stories on the internet of people having their gear or mounting bolts break, always resulting in severe prop strike and significant fuselage or wing damage. I'm sure there are more.
 

Big Ed

N50247 - '79 Super D
Joined
Jul 20, 2020
Messages
420
Location
Tampa, FL
Why not make a spacer? A drill press, a hacksaw, and a 1/8" piece of aluminum and a half hour's work. Might need longer screws, but AN-4s are cheap. I think they are 4s.
And seriously polish that blemish. Don't just file it - make it shine! Then paint it. No more stress raiser.
I might do that, but only if A) the factory says it is OK, and B) my IA agrees to sign off. Could be some engineering issues I am not aware of.

There must be a thickness limit, because the service manual allows no more than 3 shims.
 

Helo pilot

Active member
Joined
Sep 7, 2020
Messages
26
Location
Florida
Where there any shims on the other side? Like I said before you may want to check the alignment. Someone in the past may have lost a shim. I have never seen any SDs or citibria without a least one shim. If the alignment is good, you may want to add two shims. The shims are tapered and with two oposing you could have no taper and be in spec and compliance.
Aluminium retrofit legs are very very expensive.
How deep is the damage? I don't think ACA is going to allow any damage to the gear leg without some sort of repair scheme.