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winchman
01-06-2010, 12:53 AM
I built a swing-out tire carrier a several years ago to go on the back of a Jeep. The fellow gave me a trailer axle stub and some tapered roller bearings. I machined a piece of tube for the bearing outer races to fit in to make the pivot, and welded up the rest. I remember the axle stub was welded to a custom bumper I also welded together for him.

It's been so long that I don't recall the exact details of how it was built.

He recently said the bearings were all messed up and one of the races had broken. I haven't seen them, so I don't know exactly what has happened. I suspect the constant pounding with no rotation to spread the grease around was responsible for the failure. He replaced the bearings and put it back together.

What sort of bearings would have been better in this application?

I know it probably should have been built with an upright so the pivot bearings could have been spread apart, but that's not the way he wanted it.

Evan
01-06-2010, 01:11 AM
Stick a grade 8 bolt in a piece of tubing with a little grease and call it good. You want some friction so it will stay put when you swing it out.

Willy
01-06-2010, 01:18 AM
Nylon bushings, self lubing and doesn't attract dirt, which is a real problem in the wake of a vehicle.

BadDog
01-06-2010, 01:22 AM
I built one using a trailer hub and spindle. It supported a mounted 35" tire, 2 full 5 gallon cans, and a tool box (containing mostly extraction gear) quite easily and operated one handed (level). A pin/plate at about 45* and 110* will keep it where it needs to be. Or get a broken axle (or make spline shaft) plus spindle/hub/lock-out from a light truck (CJ, Sami, etc) and use the lock-out to hold it anywhere you like. But as noted, hard to beat UHMWV for trouble free and cheap...

winchman
01-06-2010, 01:35 AM
Do you think making UHMW-PE bearings to go in place of the inner races and rollers would work OK? I'm thinking the contact pressure for a small area would be too high for plastic with the short distance between the bearings.

barts
01-06-2010, 02:53 AM
If you have some Delrin kicking around, that stuff works very nicely in this application - which is why it gets used for leaf spring bushings, etc.

- Bart

BadDog
01-06-2010, 11:17 AM
Not entirely sure, my knowledge of plastics isn't great. Maybe PU or delrin or something else would be better? I've never used the UHMW in that specific application, but in that configuration it seems well restrained and it wouldn't really be that small an area of contact pressure around the spindle. If you think it is an issue, you could always space upper lower a bit wider.

Also, a plastic bushing would typically be made wider than a typical bearing. So where a bearing race for that size spindle might be only 3/4" wide and 6" long (roughly), the same for plastic might be 10" long and with plastic bushing maybe 1 to 1.5" wide? You could also go from a maybe ~1.25" spindle up 2" or so? Not that I think it's necessary, and many of the guys here could/would calculate the specifics (and probably do a FEA!), that is something to consider. Me, for most stuff like this, I'm no looking for absolute minimal weight, and I sure don't want to deal with breakage on the freeway or 20 miles from the nearest pavement, so overkill is generally my preferred method of attack.

But the full weight + leverage is carried on the spindle only when you swing out. When closed, it would be supported on the latch side striker plate (or whatever you want to call it). You might also want to have a plastic pad there for smooth operation and to prevent rattle/squeak?

strokersix
01-06-2010, 11:59 AM
Delrin (trade name) or generic equivalent would be a great choice. Tensile strength is about 1/3 that of mild steel so it's pretty stout stuff and really works well as a bushing material, especially limited motion applications. Make the bushings beefy with relatively thick wall, don't try a thin wall insert because it may split under load.

Nylon is a poorer choice because it absorbs moisture and swells. UHMW is a poorer choice because it's not a strong. If you are buying material to make bushings check for ultraviolet resistance but I wouldn't worry too much about that because your bushings probably will be hidden inside the hinge and not exposed to light.

Carld
01-06-2010, 12:31 PM
what's wrong with loose fitting steel on steel or a loose fitting brass bushing.

BadDog
01-06-2010, 12:41 PM
Actually, I had pondered something like oil-lite or graphite impregnated bushings, but forgot to mention it while typing. But I don't think I would want loose fitting steel on steel. I think the weight and leverage would make short work of a (relatively) short hinge pin that would normally be found in this application, at least at the weight I typically see (up to 42" tires).

In my mind I would want smoother operation just for convenience. It would surely work, but who wants to horse that thing around every time they need in the rear hatch just to load a cooler with ice or whatever. And I think it would wear pretty rapidly making matters even worse.

I need to make a new front bumper and winch mount for my K5 expedition rig, and a swing out rear mount is next on the "major pieces" list after that. It will have some sort of easy access hinge as is being discussed, though I don't know the particulars yet. For one thing, my 18 yo daughter often drives it to work or up to the lake with the dogs in the back.

hitnmiss
01-06-2010, 01:15 PM
Mine has bronze or oil lite bushings.

Holds up a 33" tire and 5 gallons of gas quite well.

lugnut
01-06-2010, 04:10 PM
Back in my other life, I had a friend that was a avid Jeep person. He used to make spare tire and gas can carriers from the lower "A" frames and the associated attacting hardware of car suspensions. All the piviting hardware was pretty much already built into them. Just a thought.
Mel

Carld
01-06-2010, 05:44 PM
Thinking back in all the years that I have had trucks with steel on steel pivots on the racks none of them broke off, wore out or in any way were a problem.

How loose did you think I meant? 1/32" would work.

bborr01
01-06-2010, 05:59 PM
Oilite bronze. They can be bought off the shelf with or without flanges in a wide variety of sizes.

Thats what your car doors are probably hanging on.

Brian

John Stevenson
01-06-2010, 06:26 PM
You need ABEC 7's, if you don't use these you will get 1,000 of messages saying Your carrier won't swing to microns and the swing out will be unacceptable.

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