What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Tire carrier issues

hammermachine

hammermachine

1/2 ton status
 Premium
Joined
Aug 23, 2005
Posts
2,496
Reaction score
21
Location
The East Coast Texas
I recently installed a jeep off road tire carrier rated for 39 tires. It's bolted to two 1 inch thick L brackets I made and the brackets are bolted into the frame with four bolts total. It seems like no matter how tight I tighten the bolts into the frame they slowly work themselves loose, causing more movement with the arm and tire. I installed locking washers and today while driving to work the bolts came losse again. I don't know if more bolts would help or just swiss cheese my frame. Any ideas?

tc2.JPG

tire carrier.JPG
 
Try some red Loctite. Or try putting some tack welds on them. Safety wire would work too.

What size are the bolts? If they are a small diameter, stepping up to a larger fastener would give more clamping force.
 
Bolts

Wow you must have read my mind, I just got some Loctite (red). I loosened the bolts (they are grade 8 1/2 inch stainless steel) jacked the bumper back straight, dropped some loctite on the threads and tightened them back down. I left the bumper jacked up while the loctite dried. I think I might have to fab some kind of support from the frame to the bumper. Not sure.
 
Are the holes in the frame slotted?
 
Get a better pic of the frame mount.

From what I see in the above pic the two bolts on either side are very close together. You need the bolts farther apart and perhaps 1 or two more per side.

A tire that weighs 100lbs. is putting a lot of force on the mounts. It's not uncommon to swinging tire mounts fail after a few years of service. The mounts and swing system fatigues and fails. I know you have a bit different system but it is the same basic concept.
 
I'd also question whether you really have grade 8 stainless bolts. Stainless is usually no better than grade2. If I'm wrong, where did you find them?
 
Bolts

bp71k5 said:
I'd also question whether you really have grade 8 stainless bolts. Stainless is usually no better than grade2. If I'm wrong, where did you find them?
Click to expand...


We sell them at work. We even sell grade 9 bolts but I went with the 8s. The tensile strengh is not as strong as regular alloy but they rate 100,000 psi. (compared to regular steel 150,000)
 
The problem has to be related to either the slotted holes or too small of a fastener in a hole(s).

I agree with miniwally, possibly spread the bolt pattern out some and use bolts that are a snug fit to the holes.
 
hammermachine said:
We sell them at work. We even sell grade 9 bolts but I went with the 8s. The tensile strengh is not as strong as regular alloy but they rate 100,000 psi. (compared to regular steel 150,000)
Click to expand...

Cool, I did know they made hi strength stainless fasteners but they are not as easy to find as the regular stuff.
 
More pics

This is what I'm dealing with. The L brackets were fabbed from a single piece of steel 1/2 thick I think. The holes were make to line up with my last Blazer, of course this truck frame rails are wider. So I put washers as spacers to fill the gap between the brackets and the frame. I think I will drill another hole in each side further back (towards the front of the truck as you stand behind it) (I hope that made sense). I think that will help stablize the whole thing more.

bump22.JPG

bump23.JPG

bump24.JPG

bump25.JPG
 
i think adding a 3rd bolt per side will do the trick for you - it will triangulate the load a bit.

however, were it me (and it's not so take it with a grain of salt) I think I'd relocate the brackets so that they didn't require spacers and preferably put the brackets on the outside of the frame rails and then make the bracket also go over the top of the frame rails and run a bolt through the top. this would give you a mounting point in a second plane and make it much stronger and would prevent any possibility of the leverage exerted by the heavy tire from rocking the bumper backward (with the exception of bending the frame and/or ripping through that top bolting point).
 
^^^^^^

What he said.

Those two bolts are way to close together. Not top flange going over the frame rail and the washers aren't helping things either.

Look at it this way.

Say the tire wheel combo weighs 100lbs. On a hard stop the tire keeps trying to go forward. It is mounted 3' away from the bolt surface. That makes for 300 ft/lbs of force trying to shear those two bolts or in this case rotate the tire mount around their center line.

By moving the bolts farther apart and adding a top flange you are giving a larger area to resist the tire trying to continue forward. More bolts also helps with clamping force (the washers are hurting this)which is what is going to help the most.

Same sort of principle applies with the down ward force of the tire as well. The forces just aren't as great since the distance from the tire mount to the bolts is smaller.
 
Bumper

Thanks for the help. But I am confused, your saying to change the brackets to include a over frame flange, forgive me how the hell do I do that? Do you mean if I create a piece of steel that goes from the top of the frame end to the top of the bumper? I think that would work. If that's it I just have to find/create a piece or pieces that will fit.
 
Can you get some pictures of the frame a little further forward?

The thing that will help the most is spacing the bolts out further, they are WAY too close together right now. You're giving the tire carrier TONS of leverage on your frame and the connecting bolts.

tirecarrier.jpg



In the top part of this picture, the lever on the left side (distance from the pivot to the center of the weight of the tire) is about a foot, the distance between the bolts is about 3". That means the weight of the tire/carrier is multiplied by four and exerted on the forward most bolt. When you hit a bump, that 150 lbs. of tire/carrier probably exerts several times more force than that, multiply that by four and you can understand why those little 1/2" bolts keep coming loose.

In the bottom part of that picture, the second bolt is more like 18" away from the pivot point. This setup puts 1/6 the stress on the bolts. It all has to do with leverage.

You don't need to make 18" brackets, I exaggerated the setup to show the point but spacing the bolts further apart would almost certainly solve your problem. Adding a third bolt on each side is even better.
 
Wow!

38377k5 said:
Can you get some pictures of the frame a little further forward?

The thing that will help the most is spacing the bolts out further, they are WAY too close together right now. You're giving the tire carrier TONS of leverage on your frame and the connecting bolts.

tirecarrier.jpg



In the top part of this picture, the lever on the left side (distance from the pivot to the center of the weight of the tire) is about a foot, the distance between the bolts is about 3". That means the weight of the tire/carrier is multiplied by four and exerted on the forward most bolt. When you hit a bump, that 150 lbs. of tire/carrier probably exerts several times more force than that, multiply that by four and you can understand why those little 1/2" bolts keep coming loose.

In the bottom part of that picture, the second bolt is more like 18" away from the pivot point. This setup puts 1/6 the stress on the bolts. It all has to do with leverage.

You don't need to make 18" brackets, I exaggerated the setup to show the point but spacing the bolts further apart would almost certainly solve your problem. Adding a third bolt on each side is even better.
Click to expand...


Thanks for the advice... I am by no means a engineer, but your explanation sure makes sense. If it's not raining tomorrow I'll try to fix it.
 
Chris is right on and way better with his explanation that I.

I would still look at getting something that ties into the top flat part of the frame and goes back to the bumper. Not your frame brackets but tied to the bumper itself.
 
After the rain

I was able to enjoy my day off and spend 90 minutes drilling through the two 1/2 thick brackets and K5 frame. I wore out a cobalt bit but there are new bolts & washers in place. I used locktite and placed the bolts as far back as possible (there are OEM holes near the very end of the brackets). I still haven't figured out how to fab a connection from the top of the frame to the bumper, one that would not get in the way of the swing arm. The two ends of the bumper is solid steel close to 3 1/2 to 4 inches (not drilling through that) so a support bracket would have to fit between the frame rails. I took the truck for a short ride afterwards and did not notice any movement. I'll have to test it further.

rebuild1.JPG

rb3.JPG

rb2.JPG
 
looks like there's already bolts through the top of the frame rails, how about adding to the bracket so that it fits up under the top frame rail?
 
You must log in or register to reply here.

Latest Posts

Top Bottom