Control Yoke Universal Joint Failure

How to keep the Cessna 170 flying and airworthy.

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Re: Control Yoke Universal Joint Failure

Postby gahorn » Fri Dec 15, 2017 6:35 pm

The Ujoints are backordered if you look for them at McFarlane....and also if you look for them individually at Spruce.... BUT...if you order the "kit" from Spruce...they have them in the CA store. The "kit' is less expensive than the pair of Ujoints individually from McFarlane...and includes the two bolts and nuts to attach them as well as the dust-cover for which McFarlane ordinarily charges extra.

The Spruce "kit" is PN 05-04560 that contains ONE U-joint, two bolts, two nuts, and the dust sleeve. It's unknown at this time if the ones being offered by Spruce meets the requirements of the McFarlane SB9. Spruce is investigating and will report back and I'll post the info.
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Re: Control Yoke Universal Joint Failure

Postby brianm » Fri Dec 15, 2017 7:04 pm

It looks like both of my U-joints are not covered by the SB, but I want to add the dust cover anyway. The original Cessna part number for the cover is S1495-10, which appears to be 5/8" ID vacuum hose. Is that correct? I have some Aeroquip 306-10 on the shelf and it would save me from paying McFarlane $10 for 4 inches of hose.
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Re: Control Yoke Universal Joint Failure

Postby sfarringer » Fri Dec 15, 2017 8:04 pm

gfeher wrote:Understood and I generally agree. I don't know what the rivet itself was made of. That's what failed. Thought likely it was stainless as well. But in any event, after such a short period of use under the relatively light loads you feel when using the yoke, the galling explanation still doesnt make sense to me. There would need to be a heck of a lot of galling to cause that fairly large rivet to fail. Note that the accident report states that the NTSB retained the failed part for testing in its own labs. So i'm not sure how MCFarlane can be sure of the cause.


The slip is supposed to happen between one yoke and the center pin, and the other yoke and the two half pins.
If the yoke freezes to the center pin due to galling, then any movement of that yoke tries to shear the rivet (which passes thru a hole in the center pin). Note that there is quite a significant leverage available. Once the rivet shears, then the two half pins can fall out.
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Re: Control Yoke Universal Joint Failure

Postby gfeher » Fri Dec 15, 2017 9:04 pm

Got it. I was probably focusing too much on the galling causing excessive wear. Your explanation focuses on the lack of lubrication, etc freezing the pin. That make more sense. Thanks for the explanation.
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Re: Control Yoke Universal Joint Failure

Postby ghostflyer » Sat Dec 16, 2017 2:58 am

My universal yokes didn’t have covers when I got my aircraft so the universals were coated a in grease and heat shrink was placed over then and only the ends of the heat shrink were heated to seal it off with a plastic ty strap. Been good ever since .
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Re: Control Yoke Universal Joint Failure

Postby gahorn » Wed Dec 20, 2017 10:33 pm

gahorn wrote:The Ujoints are backordered if you look for them at McFarlane....and also if you look for them individually at Spruce.... BUT...if you order the "kit" from Spruce...they have them in the CA store. The "kit' is less expensive than the pair of Ujoints individually from McFarlane...and includes the two bolts and nuts to attach them as well as the dust-cover for which McFarlane ordinarily charges extra.

The Spruce "kit" is PN 05-04560 that contains ONE U-joint, two bolts, two nuts, and the dust sleeve. It's unknown at this time if the ones being offered by Spruce meets the requirements of the McFarlane SB9. Spruce is investigating and will report back and I'll post the info.


Spruce NEVER got back to me as to whether or not the U-joints they have in Kit "UMC-KT-1" is affected by this bulletin, but I have received them and they are from a DIFFERENT Job Order and are not affected. The ones I received are from Job Order 490039 and NOT AFFECTED.

I do not know why Spruce refused (I specifically asked them on two occasions to check the parts BEFORE shipment...and they did not seem to understand...they only replied ONE time, and that was for me to check the service bulletin or contact McFarland.

I'm installing them in the 172 we've bought for training purposes as the ones it has are loose and my 170 was restored with new u-joints which are also not affected.
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Re: Control Yoke Universal Joint Failure

Postby combahee » Wed Apr 18, 2018 5:48 pm

Hope you don't mind bringing this back up. I ordered the UJC-KT-2 kit from Spruce. MacFarlane says all the U joint kits have the sleeve. The Spruce description online said it didn't have the sleeve. So I called Spruce and the woman said she looked at the kit and it has the sleeve. The Spruce kit that had the sleeve was listed for IIRC $15 more. Just for the sleeve.
I ordered from Spruce as they are closer and I can put it in this weekend with my AP.
However a question I have is why two different bolts? The U joint should only be drilled with the smallest diameter hole for the smallest diameter bolt. Anyone that has the kit care to comment? Additionally I don't see Cessna or MacFarlane using a C washer, wouldn't that contribute to uneven clamping force, distortion of the yoke shaft? And even the hole in the shaft elongating?
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Re: Control Yoke Universal Joint Failure

Postby n2582d » Wed Apr 18, 2018 10:57 pm

The IPC shows the same length bolt, AN3-10A, on both sides.

I bought my universal joints and saddle washers from Pegasus as seen on page three of this thread.
Last edited by n2582d on Sat Apr 21, 2018 4:02 am, edited 1 time in total.
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Re: Control Yoke Universal Joint Failure

Postby gahorn » Wed Apr 18, 2018 11:22 pm

I also installed two McFarland kits ordered thru Spruce and the bolts are AN3-11 and -10 and are correct length...however they were oversized. It was as if they had been plated two or three times oversized. Comparing them with a digital caliper to new stock in my inventory it became very obvious. I would have had to drive them thru the yoke shaft and the joints using a clamp or press and didn't wish to do that so I substituted new bolts from my own stock and complained to Spruce who refunded the difference between the complete kits versus the u-joints only (about $35 each kit.)
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An originality nut (mostly) for the right reasons. ;)
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Re: Control Yoke Universal Joint Failure

Postby ghostflyer » Thu Apr 19, 2018 7:00 am

Some where in the back of my brain [very empty space] its come to me that those attach bolts holes are supposed to be reamed to size. I have found some [bolts] over the years loose in the shalf. I would have a read of the lastest cessna structural repair manual.
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Re: Control Yoke Universal Joint Failure

Postby gahorn » Thu Apr 19, 2018 4:45 pm

The McF universal joints are "FAA-PMA", and the bolts are standard (AN) parts. The bolts included in the kit were packaged in McFarland plastic bags and identified on the individual packaging. The ones supplied by McF in the kit (headstamp "PA" over "X") measured .1895 - .191 in diameter and any/all of the new AN bolts in my stock measured .1865 - .188 and fit snugly.
I think that indicates a standard parts mfr'r problem. (The McF instructs had no mention of reaming.)
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight.
An originality nut (mostly) for the right reasons. ;)
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Re: Control Yoke Universal Joint Failure

Postby combahee » Sat Apr 21, 2018 1:01 am

Got the kit in today and the sleeve is in the kit. Also the bolts both fit easily in the U joint. One is just longer than the other. I still wonder about the clamping force and also about whether the shaft holes are elongated, we'll see tomorrow when I install it.
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Re: Control Yoke Universal Joint Failure

Postby wabuchanan » Sat Apr 21, 2018 3:10 am

I ended up ordering my U-Joints from Yingling aviation. They stated they get theirs from the Cessna warehouse, there were 18 of them in stock. Mine came with a manufacture date of 2015 on them.

I had to order the bolts and nuts separately as they did not come in a kit. He looked up the bolts and they were the same length, as were the original bolts. My aircraft had a washer on the forward bolt to space the nut the correct distance from the bolt head for grip. Without the washer, the nut bottoms out the threads before clamping force is achieved, so those of you that have two different length bolts are likely getting the shorter bolt for the forward hole.

No dust covers.

Installed:
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Re: Control Yoke Universal Joint Failure

Postby ghostflyer » Sat Apr 21, 2018 6:09 pm

Why no dust covers ? And a touch of grease. As said in a previous statement , I used heat shrink over my universal joints and this was done about 6 years ago and due to this discussion i have checked them out very recently and they are as good as the day I refitted them . The control cable chain needed a oil on it as it had dried out only after about 9 months . Some times its good to do a detailed inspection add hoc on a part of the airframe . A/p,s and IA,s can miss items during a 100hrly due outside pressures ,and familarity. People doing inspections doing the same item time after time have a expectation in their brain of what they think they are seeing but the reality is they miss the problem issue as it doesnt register. This is one of the reasons why I like owners to get involved in the servicing of the aircraft . I know people will bring up about occupational health and safety issues with owners in the workshop but a little training before hand is good. PLUS the owner hopefully will then realize why it costd so much to have a 100hrly. Sorry about the subject hijack.
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Re: Control Yoke Universal Joint Failure

Postby lowNslow » Sat Apr 21, 2018 7:30 pm

I notice that Spruce also sell MIL-SPEC universals. Are these legal to use (if they fit)? Actually I think we discussed this very issues here:
viewtopic.php?f=24&t=6213&hilit=universal+joints
Last edited by lowNslow on Sun Apr 22, 2018 2:09 am, edited 1 time in total.
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