Tire Carrier Sheared OFF!

[cruiseroutfit]

Thanks for the drawings but they are unnecessary, I'm well aware of what trailer bearings are and are not designed for (EE but working on ME for double major). Nevertheless that design is destined to fail and I would never have left the shop with that. IMO, single shear should be avoided whenever possible. Hope you didn't pay too much for that fab work or bumper design. I do like the new design, and if I were to do it all over I'd probably go with something so easily serviceable as that over a unit bearing.

Though I completely agree that a double shear setup should be used... there are thousands and thousands of these setups in use. You have to look at it from a probability of failure aspect. I know of a few that have failed (I can think if 3!), out of how many I personally know exist (hundereds??). So say we have a 1% failure rate AFTER many years of use and abuse (range not specified), then some would be just fine with it.

Someone mentioned they are starting to see it more? It is occuring with a higher failure rate (and MTBF) or are there just so many more in use that you see the problem more? I know of shops (Cruiser Outfitters for example) that were using derivations of trailer spindles for tire carriers almost 15 years ago now... can't say I know of one that ever failed. At least a dozen different manufacturs and countless retailers (RL4x4 for ex.) sell this setup... I'd say that the failure rate is under 1%...

Its like telling everyone they should have a built Dana 60 under their rig... afterall, a D30 is destined to fail sometime right? Everyone should have DOM steering rods, DOM driveshafts, 1410 joints, etc... everything else is just waiting to die...

We make allowances based on judgement all the time... I know I would be more likely to break a stock shaft than I am to break a tire carrier spindle, yet I still don't have Dana 60's, the risk doesn't outweigh the increased cost. I'm more likely to break a 3/8" winchline than I am a 1/2" winchline, but I don't run out and swap it.

You had probability/reliability yet?

 

[sjbrownie4x4]

Yes I have, I have been out of school for almost 7 years now . I understand what you are saying not everyting needs to be BIG, DOM, D60 to be sucessful. I am not advocating that it needs to be.

I do however belive in superior design :greg: , and in this case I think it can be done safer and cheaper than the stub axle shaft.

3 years ago you didnt see any failures of this type. I dont think this is an infintile failure, and I would expect that the MTBF is constant and that we are starting to approach that Mean number. Sure mine is an outlyer, but there are others and I belive there will be more as we approach the MTBF.

Today you can get on the just about any BB out there and find a few documented failures. For every documented one I am sure there are many others that went un-recorded. The % of people who have stub shaft carriers and are active enough online to post a failure online is likely very small.

It is not a rampant like plague of failures but some of the failures have resulted in other people hitting the now free floating carrier at high speed and doing real damage and that is what really scares me. If I knew that the D30 under my XJ had documented accounts of shearing all attachement to the vehicle and leaving its self on the highway without me even noticing, for some one to have a nasty run in with, I might be considering putting something different under the front end. Breaking a d30 on the trail is in my mind very different. It really only affects me, I now have to replace the stub outer to keep wheeling. Its something I know can happen and I can plan accordingly.

It's when we find those dangerous pieces on our rig that should drive us to furter action. I got lucky that when it failed the rest of the system held it. For me, I do not want to be the cause of some big or small accident because of a flaw in design.

I also think people should understand the risks of using something in a manner it wasn't designed . When someone says this is a #2000 Axle shaft (#1000 per single side) it seems beyond reason to most people that there could be any possibility of failure because their tire & carrier could only weight a couple hundred pounds at most. I know that motion has a big effect on stress fatigue cracking (its how you actually test for fatigue) and that not all carrier designs are created equal in thier ability to resist the constant vibration that can occur.

In my design I belive it can be done better, cheaper, and simplier than the welded tralier stub shaft. I am going to start by building 4 or so for everyone I know who knows mine failed and are now concerned about the structure of their own stub axle carrier. Who knows maybe I will be all set when all these others reach their MTBF and I can provide a nice little replacement package for their sheared stubs of metal....

 

[sjbrownie4x4]

The bumber and carrier came with the scrambler when I bought it. I actually flew up to AFW where the vehicle was and it was there he told me he built it.

I dont know however, how long the carrier had been in service before that.

For me it sat for a year in the garage while I worked on it. I trailer towed it moab. Opened the carrier once, maybe twice while there. Towed it home and commuted with it for about 6 days. It was on the 6th day that it failed while I was on 7th east.

Needless to say I do not have a lot of confidence in the system now. And as you put it, I also belive it is destined to fail. My next one will be an evolution / improvement of the first.

Thanks for the drawings but they are unnecessary, I'm well aware of what trailer bearings are and are not designed for (EE but working on ME for double major). Nevertheless that design is destined to fail and I would never have left the shop with that. IMO, single shear should be avoided whenever possible. Hope you didn't pay too much for that fab work or bumper design. I do like the new design, and if I were to do it all over I'd probably go with something so easily serviceable as that over a unit bearing.

 

[cruiseroutfit]

Yes I have, I have been out of school for almost 7 years now . I understand what you are saying not everyting needs to be BIG, DOM, D60 to be sucessful. I am not advocating that it needs to be. ...

I know you have... I was wondering if Brad has. We discussed this very subject (well not tire carriers) ALOT... Its funny how much this happens in the industry (substandard) design at the risk of premature failure and liability, all to save a buck!

I fully agree with everything else... thus why I still have a Toyota axle and a two pivot tire carrier Mostly playing the devils advocate (you know the business executive they warn you about in prob/reliability )

 

[Caleb]

my only issue with your arguments of the weight are you are assuming the tire carrier is open driving down the road. Most people close their tire carriers when they drive down the road If you have a properly designed carrier then it will spread the weight between the hinge and the latching mechanism. That makes your argument not worth it. Like Kurt pointed out the failure rate is very very low. You make the point that not all are reported in a BB, but I am willing to bet that most the people that are using the spindles found out about them on the internet, or from a buddy that heard of them on the internet. Say your buddies spindle breaks, and he's never on the net, next time you hear about someone else's spindle breaking chances are you will chime in saying your buddies broke too so it will infact get "reported". Even still I think you are WAY over analyzing this. The ones I have seen that have failed (either in pictures or in person) almost all have had imperfections in the middle area of the spindle. This makes you wonder if it's a bad piece or a bad design.

Just for the record I have never been a fan of a single spindle hinge setup (search my posts and you'll see I have voiced my opinion in the past on them). The thing I don't like about your proposed setup is one you use a bolt (I may be wrong but I don't think a bolt was ever intened to be a hinge, and you're taking the same approach as going to a larger spindle, throw a large enough chunk of steel at it and it'll hold), second thing is it will, after a while, get slop in it. Either in the steel, or the bushing, but it will get slop. I'd rather go for something like a double spindle setup, or something different all together (I don't know what yet) I also like the fact of having tappered roller bearings and the spindle setup is rebuildable with just a little bit of grease.

Also, your setup is either as much or more (depending on where you get it) than a hinge setup...so explain how it's cheaper

 

[sjbrownie4x4]

Of couse I am I way over analizing this, I am an engineer, its what we do!

Several of the failures, after the stub axle failure caused a failure of the clamping attachment point. This allowed the device to detach. Like I said mine was done up and I belive I got a little lucky.

The double taper is a great bearing and is usually meant for things that are spinning, in fact they can take properly designed loads that are spinning very very fast.

Bolt as a hinge.... depeding on what you drive you have many bolts that act as hinges. Shackles, control arms, Spring pivots all have some sort of bolt and perform a rotation function every day. Now ask a bolt to be part of a rotating system that has some real velocity and you will have some trouble.

Your 100% right I went with a huge bolt. It is very likely that is way overkill for the application. 1" would probally be fine. Someone earlier said they used 3/4" and have had no trouble. I am not yet set on the 1 1/2 bolt, I just was putting the concept out there for comments.

Slop, again your right, thats why I used the bronze bushings. These are industrial bad boys and are used on heavy duty tool and die stamping machines. The great thing about bronze on steel is that its the bronze that wears not the steel, so for rebuild you may need to buy new bushings years down the road, though from their rating I think it will be many years.

Cost

RockLogic sells a complete kit for $45

I think you can put a kit together yourself for about 30-35$.

Now thats unfair because you can do most of the trailer stub axle parts yourself except for the outer that needs some turning to accept the bearing races. Obviously RL is making some margin on their kit. But if you look at what the conventional thinking is leading some people to do after failure is go to the next stub axle up (1750# rated) now you are looking at the 60-90 price range. Now you are talking a big savings when you look at this double shear system.

I am also looking at an upper pivot and upper clamping, probably either of which would allow you to run the orgional size stub and keep an almost infinite fatigue life. But either way I have to buy / make a new stub to replace my broken one and it simply can be done better and more cost effective.

 

[Caleb]

Of couse I am I way over analizing this, I am an engineer, its what we do!

you could have stopped right there


Keep us updated on this as you get some put together. I know there is a better way to do it than the spindle and I think you are off to a great start.

 

[RockMonkey]

Maybe I'm under-analyzing this, but... The top of the trailer spinlde is threaded. You could make it double-shear. My dad has a tire carrier with a trailer spindle that he's been happy with, and I'm happy with mine.

 

[Brad]

You had probability/reliability yet?

Yes. But while probability is low, liability is high with a 100+ lb. object hanging off the back of the Jeep, as you know. When putting mine together I kept in mind that 80% of my driving is freeway speeds where the probability that someone will hit it before I can retrieve it is rather high. I don't want to be responsible for the accident that that could cause. Peace of mind for me was a simple matter of additional bracing and gusseting.

 

[cruiseroutfit]

Yes. But while probability is low, liability is high with a 100+ lb. object hanging off the back of the Jeep, as you know. When putting mine together I kept in mind that 80% of my driving is freeway speeds where the probability that someone will hit it before I can retrieve it is rather high. I don't want to be responsible for the accident that that could cause. Peace of mind for me was a simple matter of additional bracing and gusseting.

Safety chain...

 

[Jared]

Roof rack. Picked up a used one cheap and haven't looked back. Did I mention how nice it is to see out my entire back window?

Jared

 

[Herzog]

Roof rack. Picked up a used one cheap and haven't looked back. Did I mention how nice it is to see out my entire back window?

Jared

Yeah, but the problem with roof racks and mounting tires up top is the extra weight... ALL the way up there. It for sure heightens your COG, but is also dependent on the size (read weight) of the tire.

 

[cruiseroutfit]

I'm still advocating the safety chain method...

 

[spaggyroe]

Here's my approach.

I didn't start with an off the shelf trailer spindle. rather 1.500 inch material.
I did however use 3500 lb trailer bearings.

The "hub" is machined from 3.00" .375 wall DOM tubing.