The International Cessna 170 Association

https://app.ntsb.gov/pdfgenerator/Repor ... m&IType=LA

This just happened recently when one of the brand new McFarlane universals installed a year ago failed at the time of flair, everyone beware, I need help posting the pic that I acquired of the actual part failure associated with this incident thru a friend of the guy to whom it happened to.

Here it is Dave.

Well, that is interesting.

I just called McFarlane to order a couple and they told me they were out until February, so have a couple coming from Yingling. I would hope they might have a different manufacturer source. Or at least a different batch.

We installed one from Mcfarland last November. I will be giving them a call Monday.

pmel22 wrote:We installed one from Mcfarland last November. I will be giving them a call Monday.

Wow... me too...

What is the criteria for replacing the original U Joint?

What can be done to prevent original from wearing out?

MoonlightVFR wrote:What is the criteria for replacing the original U Joint?

What can be done to prevent original from wearing out?

Grady the criteria is discretion. If you have any fwd or aft movement in the yoke when you hold the other, the universal should be replaced. usually it is only the left side that wears out. Generally a worn out universal will also have slop in the roll of the yoke also. This was a new replacement because the old one was worn out. here is a picture of warn out universals. I replaced mine 10 yrs ago but the ones I took out looked like they were original. Attention to detail but this is not a known failure area but treat it like a tailwheel spring. If you dont have record of replacing the universal in the log book you may consider replacing it because it is likely 60+ years old.

Spoke to McFarlane today, a service bulletin will be out in a day or so....

Here is the McFarlane Service letter SB-9 dated Dec. 11,2017 for anyone that has recently replaced the universals.

I’m impressed at the quick thinking of this pilot who saved the plane in the flare by using the opposite yoke when his failed.

It’s interesting to see Doug’s picture of the failed universal joint which looks gold in color to me and then to read the following from McFarlane’s Service Bulletin:

Note: ALL McFarlane manufactured U-joints are made from heat-treated stainless steel and are therefore not coated. U-joints that are yellow or gold in color are NOT affected McFarlane parts. No further inspection is necessary.

Hmm... I hesitated writing this but decided to go ahead for any of you who may have one of the affected U-joints. I have a lot of respect for McFarlane and its parts, but its explanation of the failure ("lock up," galling of the parts, then failure of the rivet and separation of the halves, caused by similar metals, improper lubrication and/or particle contamination) just doesn't make sense to me. Clearly the rivet failed, as the parts separated. But caused by galling? Over just 2 years (max) of use, given the lot dates? Looking at the exploded view of the assembly, that doesn't make sense to me. In my mind it was more likely caused by a defective or defectively installed rivet that failed and worked itself out over the 1-2 years of use. But I'm glad to see that McFarlane is giving credit for labor, etc for replacement of any units that fail inspection. If I had a unit in one of the affected lot numbers, I would immediately replace it whether or not it passed the inspection. Just my 2 cents. But its only worth just that.

New Replacement Parts That Fail

I have a suspicion.

Universal Joint failure. new replacement part mfg from high grade stainless tool steel. That's nice, SS vs common steel.

Really why did a brand new replacement part fail in one year of below normal service?

I expect several Centuries of service from SS tool grade.

Now we have a SB that STATES replace within 100 HOURS!

Am I alone in being suspicious?

Really 100 hours vs 60 Year old installed part!

Galling of stainless steel on stainless steel is a very real issue, and seems like a very plausible cause to me.
Changing material to stainless steel is not always an improvement!

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.

Seems plausible to me; I haven't heard or seen the Cessna parts failing but I imagine if never addressed they will. I think we have all found slow wear and the control becomes sloppy.. On stuff I work on, the parts, high grade steels or stainless, often pickup occurs when disassembling and the loads to pull them apart skyrocket because the materials are really hard. Possibly there's a sharp edge somewhere that initiated the deformation and the process of the parts binding, commenced.