Why such little bearing engage on the yoke to driveshaft bearings?

/ Why such little bearing engage on the yoke to driveshaft bearings? #1  

LightningCamaroGuy

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Tractor
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The cross joint on my bush hog came apart the other day. I noticed the vibration, but before I could hit the PTO Kill switch, it came apart on me. I’ve never built one of these before, but I knew that they had kids to do so. I cleaned up the sleeves for the bearings in the yoke and on the driveshaft and when I replaced them, I realized how how little material was contacting the bearings. I’ve never noticed this before, but rebuilding the thing I noticed it now. Looking at other examples it seems common for the yoke and driveshaft connection point that connects to the PTO on the tractor to have these thin of walls on the castings l, and I’m wondering why they need these thin walls on the castings, and why they use bearings that are mostly unsupported? You would think they'd invent a cross joint that doesn't have so much bearing material exposed. There are spots that are likely only contacting the bearings for a 1/4 inch or so when you account for the snap rings.

IMG_1278.jpeg
 
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/ Why such little bearing engage on the yoke to driveshaft bearings? #2  
An engineer decided it was adequate, and more open space makes changing it easier.
 
/ Why such little bearing engage on the yoke to driveshaft bearings? #5  
Wrong cross-too small I bet
Let’s see the outside, where the snap ring is.
 
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/ Why such little bearing engage on the yoke to driveshaft bearings?
  • Thread Starter
#7  
It very much looks like this. See how thin this is up top.?

Also going off the lists of availability Cross joints it's the only one that will fit. This is a Series #6. 30.2MM bearing diameter, and 92MM overall length. IDK the new joint looks the same as the old OE joint other than the seals are a little different designs.

Here's a picture of a snap ring, and what I have of the old cross joint that came apart.
IMG_1277.jpeg
IMG_1279.jpeg
 
/ Why such little bearing engage on the yoke to driveshaft bearings? #8  
Way too recessed, IMO. Do all 4 caps have the same recessed depth?
Is the yoke “splayed” open?
Do you cut a lot of excessively (edit) steep angles , like where you can here the yokes slappin?
Somethings not right.
I’d call Maugansville AG and send them a couple pics of what you have.
If they can’t fix it, nobody can.

If that’s the way it was built from factory, I’d be thinking about a whole new assembly of yokes and U-joints on your driveshaft
 
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/ Why such little bearing engage on the yoke to driveshaft bearings?
  • Thread Starter
#9  
Yes it is fairly recessed, but I think it looks recessed more in the picture than it does in person. No it's not splayed. It's just casted this way. If it was even possible for this thing to work at a 90* angle it looks like it would have the clearance for it. My dad bought this cutter new probably 20 years ago, and this is the factory yoke and driveshaft. It's a 7' Howse.

This yoke is the same series 6 as the one I have and could be used in it's place.

Here's a cross joint to fit it that looks very similar to the one I bought.

This picture is of a Series 4 yoke, where mine is a Series 6, so the size is different, but the basic shape is the same, and it gives you an idea of what it looks like from a section view.
IMG_1280.jpeg


I'm wondering if I had lost a snap ring and it took a will for the bearing to come out. It looked like it hadn't had anything in it for a while based off buildup and corrosion, but IDK for sure.

I don't use it at any weird angles.
1000004029.jpeg



BTW the other end with the clutch that mounts to the gearbox has a bigger/beefier looking cross joint, but I haven't taken it apart to check for sure.
 
/ Why such little bearing engage on the yoke to driveshaft bearings? #10  
I wonder if you got a series 5 mismarked as series 6? They both share the same ID of cap (30.2mm), however a series 5 is 79.4 mm cap to cap and a series 6 is 92mm cap to cap.
 
/ Why such little bearing engage on the yoke to driveshaft bearings?
  • Thread Starter
#11  
I wonder if you got a series 5 mismarked as series 6? They both share the same ID of cap (30.2mm), however a series 5 is 79.4 mm cap to cap and a series 6 is 92mm cap to cap.
No, that couldn't work. The bushing to snap ring clearance is a few thousands. 92MM-79.4MM is 12.6MM. Basically a 1/2 inch difference. 1/2 inch is 12.7MM.

-12.6/25.4=.496".

-92/25.4 = 3.622" (most common GEN3+ SBC LS/LT crank stroke, but noone says, "LS engines uses a 92MM stroke," it's always referred to as 3.622".)

-79.4/25.4 = 3.126"

So basically one has a spread of 3.625" and the other a spread of 3.125". Engineers are always trying to mimic common fraction #'s with metric #'s.

As a tool maker/die builder for the last 22 years, other than figuring out the ID for any particular thread size I hate the metric system and I’ve worked at companies that used metric exclusively, but tool makers always seem to convert metric back to imperial. If I say 1” you instantly have an idea of how long that is, but if I say 25.4MM people try to convert in their head how long that is in inches. To convert metric and standard numbers you need to remember 25.4. 25.4MM is 1”. 1MM = .03937 (1/25.4) Example 5L(metric) Coyote has a 3.937" bore spacing, or 100MM. 100/25.4 = 3.937". To covert imperial to metric you multiply the standard # by 25.4. for examples .300x25.4 = 7.62MM, or .22x25.4 = 5.588 (5.56/25.4 = .2188)
 
/ Why such little bearing engage on the yoke to driveshaft bearings?
  • Thread Starter
#12  
The cross joint is in there with little slop or side movement. It's not tight, but not sloppy loose either. I just don't understand why there's so much bearing surface not being used. We've cut 3.5"+ trees with this cutter, and it's just surprising that a bush hog would use a yoke and driveshaft with such little bearing contact, on implements that take such a heavy load as a bush hog has to handle. It's like this much clearance to achieve more articulation seems unnecessary for the angles the joint should experience, and that just wastes a bunch of surface area (overall strength in the joint) on the bearing surfaces and material thickness on the yoke and driveshaft. IDK, just seems oddly minimalistic for a HD PTO implement.
 
/ Why such little bearing engage on the yoke to driveshaft bearings? #14  
I have a Howse 7' but mine is pushing 30 years old and looks to be made heavier.
It's yoke and cross looks like you would expect. Not like yours. Notice it has the snap ring grooves in the cups. They are still the original u-joints even. Cutter has been setting mostly unused since I got a 12' batwing. It only get used for the real rough stuff or where the 12' don't fit.
 

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/ Why such little bearing engage on the yoke to driveshaft bearings? #15  
Don't know for sure but you stated the joint next to the gearbox appears larger than the one you are having issues with, is it possible someone gave you the wrong half of the drive shaft?
By the pictures you have posted it appears the cross is the wrong one for the yokes.
Here is some info from Weasler, noot the only manufactuer of PTO drive shaft though.
 
/ Why such little bearing engage on the yoke to driveshaft bearings?
  • Thread Starter
#16  
I believe Howse just used a budget DS for this mower. It's pretty much a medium duty cutter. Certainly not the most beefy bush hog, but nowhere near the lightest duty cutter I've used either. In looking for DS's to replace it with the more expensive ($600/$700+) seem to be made in places like Italy, etc, and I'm sure a beefier than this DS. To be honest this is a 20 old cutter, or there abouts, and we've used it a pretty good bit, but I've never had to rebuild a joint in one either. While some DS's are asking high 3 or even 4 figure $, some are only $120-$200, but they all look identical to the point that I've pretty sure they are the same DS that comes off the same Chinese assembly like, but gets a different brand slapped on them. For example everyone's seen Vevor the past few years start selling pretty much everything from wrenches to air gun pumps, a fuel and siphoning pumps, to tractor implements, etc, etc. I found these Vevor DS's from Lowes that look identical to the one on our cutter. Everything from the castings on the yokes, to the bolt patterns, to the clutch, to the plastics down to the strength ribbing is identical. Gareenteed that these $120 Vevor brands DS's came off the tooling that produced the one on our Howse. Everything is too exact when looking at unmachined castings for them not to be. I also noticed that these DS's are having the bushings exposed like on mine, but just like a new tractor comes with the filters painted, these exposed areas on the bearings are also painted so they don't stand out.

This DS looks identical to mine:

Just to go on another little rant, many times these American companies that source parts from China want to slap their brand on them, and claim, "designed in USA, by American engineers, and made in China with foreign materials." Then they sell them to us for X amount with their brand on stamped on them, but the 3rd party Chinese manufacture will take the branding off the side of a part and sell the same thing on EBay for 1/4-1/3 the cost. I've seen this a lot with things like intercoolers, or oil/transmission coolers and things like this. Then these American companies claim that even though these parts look the same, it's just that other Chinese companies copied them exactly in the looks department, but internally they're not as good. BS, they are the exact same part, just withiut your brand logo and #'ing. I've had aftermarket intercooler companies claim I was wrong on this, and when I say them prove it. Buy a $200 EBay intercooler, and use one of your $700, Chinese made I/C's, saw both open, and compare them. I'm telling you they are the same part, made on the same assembly line. They refuse to take me up on that, but they claim their inner cores are better, and that justifies the 3.5x's the $ increase. I have no issue with American companies sourcing from China and asking whatever they want on the American market as long as they're honest about when compared to the Chinese sourced parts that skip the middle man, and sells directly from China for less $. That's what happens when you bight that fruit of using China to make your product to then sell for likely 5-6 X's profit for what you paid for them in bulk.
 
/ Why such little bearing engage on the yoke to driveshaft bearings? #17  
The yokes are not castings - they are steel forgings. Not to say they did not mix up forgings at the supplier. Think it through - everything assembled with proper clearances. The cross does not slop back and forth an excessive amount once assembled. The bearing cup is the real support for the needle bearing. I've attached a photo of an exemplar u-joint. The bearing cups are the hardened cases for the needles and provide the support. If the cross ws designed with more width so not as much bearing cup would be exposed, the needles would be shorter - higher load per needle. In short, the bearing cups are the real load carrying parts. The cross needs to be open to provide clearance. Your cutter is designd by a company that selects an off the shelf driveline rated for the load the cutter is designed. I don't see a proble with what you have realizing the bearing cup is the main load transfer. The machined cross is the shaft for the needles. The yoke is there to transfer load and if forged from the proper steel, is not really significant in how much of the bearing cup is supported as the bearing cup is the prime element - provided they don't get unreasonable.
 

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/ Why such little bearing engage on the yoke to driveshaft bearings? #18  
Yes it is fairly recessed..

Then the U joint does not properly fit the yoke. Change one or the other to correct the problem.

You either get another yoke so they both fit correctly or measure both and find the proper conversion u joint.
 
/ Why such little bearing engage on the yoke to driveshaft bearings? #19  
The yokes are not castings - they are steel forgings. Not to say they did not mix up forgings at the supplier. Think it through - everything assembled with proper clearances. The cross does not slop back and forth an excessive amount once assembled. The bearing cup is the real support for the needle bearing. I've attached a photo of an exemplar u-joint. The bearing cups are the hardened cases for the needles and provide the support. If the cross ws designed with more width so not as much bearing cup would be exposed, the needles would be shorter - higher load per needle. In short, the bearing cups are the real load carrying parts. The cross needs to be open to provide clearance. Your cutter is designd by a company that selects an off the shelf driveline rated for the load the cutter is designed. I don't see a proble with what you have realizing the bearing cup is the main load transfer. The machined cross is the shaft for the needles. The yoke is there to transfer load and if forged from the proper steel, is not really significant in how much of the bearing cup is supported as the bearing cup is the prime element - provided they don't get unreasonable.
I respect your conclusions, but the amount of exposed cup on the inside of the yoke did look “unreasonable”, at least to me it did. In my memory, I have never seen a driveshaft with that little support on any of the 100+ machines with PTO shafts I have owned.
I’d be a lot more confident in a cross where the cups were a lot more immersed in the yoke.
My guess is Howse got a good deal on a large quantity of those driveshafts as long as they passed the specs they needed to operate their mowers.
 
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