The Stovebolt Site Forums The Shop Area Driveline Loose U-Bolts

The other day I was riding down the highway when my truck started vibrating pretty badly. I got under it and found out that the nuts on the front leaf spring U-bolts were really loose. All eight of them. Both sides. This is the second time this has happened. I tightened them back up and that fixed things but I also had to re-adjust my steering because all of a sudden there was a lot of play in it. So now all is good but I can't figure out why these things have worked themselves loose twice now. I am using lock washers. The u-bolts are new, installed around three years ago. The nuts I think are a combination of old and new. I know there was a big long discussion about this some time back, whether it's wise to re-use old fasteners. Not everyone agrees, I know. If it makes any difference, I got the u-bolts from a trailer supply place, not one of the usual vendors. Can't see how that would make a difference but thought I'd mention it.

I don't know if it is wise but I have seen jam nuts used on rat rods.
My trucks have fine thread u-bolts with deep nuts.

U-bolt stretch?
https://beattiespring.com/blogs/knowledge-center/the-biggest-u-bolt-question-we-get

Locktite

Some things to check...

Are the U-bolts the exact size for your axle tube?

Are you using the correct nuts?

Are you using Grade 8 washers?

Are you torqueing the bolts to the proper torque setting?

Is the leaf spring centering bolt head lined up with the hole in the spring perch?

Is the leaf spring centering bolt broken?

Mike B

I did not use the deep nuts. I think that's where I went wrong. I just looked at a picture of the replacement nuts and I now recall that the originals were deep nuts. There is no torque specification that I can find for these nuts (1956). Manual just says secure firmly. The centering bolts on both leaf springs are lined up with their holes. Don't know if I used grade 8 washers or not. Also, I think these U-bolts are probably not fine thread.

If you don't have a torque value, you can torque by thread count and diameter. Loctite, maybe. Jamb nuts, that'll do the trick. Torque them, them mark them with a paint stick or similar. Keep an eye on them to see if they are starting to back off.

Like Mike said, if the spring bolts are not seated properly upon tightening, when they do get properly seated, the spring U- bolts will all be loose, not a good situation. Always check carefully if they are seated and long enough to work with any shims that might be there.

ED

There a few extra steps I take when I install the an axle on leaf springs.

I make sure that the u-bolts are perpendicular to the springs. If you are not careful they can sometimes get some angle to them. As the spring works the u-blots move and get loose.

I start the assembly by getting the nuts finger tight while I jiggle the u-bolt so it will seat itself. I work a cross pattern and tighten each leg just a little bit at a time.

I finish tightening the nuts with the vehicle on the ground. This pushes the axle up against the bottom of the springs.

If the axle is above the springs I let it hang while tightening the nuts.

A good practice is to retorque the u-bolts after a few miles. Only takes a few minutes for peace of mind.

I put in the new springs almost three years ago, but I'm pretty sure I recall that the spring bolt on the driver's side was not long enough to go into the hole in the perch. The shim is too thick to allow it to go all the way. We are talking about the peg that sticks out of the bottom of the leaf spring, correct?

I've decided I'm going to remove the u-bolts and replace them with the correct ones (nuts as well). But here's my problem. I currently have 4 degree wedges under the axle. They're about 1/2 inch thick at their thickest end, which doesn't allow the pin in the leaf spring to go down into the hole in the axle. I put these in on the advice of another forum member because I was having a problem with seriously uneven front end height when I installed the new springs. The 4 degree wedges fixed most of that problem. Don't know why, but they did. Anyway, if the wedges are too thick to allow the u-bolt pin to go into its hole, should I go to thinner wedges? Is there a way around this? The truck rides well with the wedges now. Also, I've always worried that since the pins are most likely not in their holes that the axle may have moved some and may never have been centered at all. If I get the pins in the holes on both sides, doesn't this automatically mean that the axle is positioned correctly under the truck?

Used to be that kits came with a little piece of paper or a sticker that said "Retorque after 100 miles."

Whoa! Go back. "Seriously uneven front end height after installing new springs"?
That doesn't sound right.
If I remember correctly the spring pack can only go on one way (can't install backwards).
Maybe the pack was assembled wrong.
Pictures?

You need to remove everything that you have and go back to original design parts. Those "wedges" are designed to set your caster, not adjust ride height. They are called cater shims.
For u-bolts, take some originals with you to a spring shop and have new ones made. They will come with the correct nuts.

Yes, I know that the shims are for caster and that they have nothing to do with ride height. It was just during the trying to figure out why the truck sat unevenly that the shims came into the discussion. The truck sits fine now. My main question, really, is if the caster shims are too thick to allow the u-bolt pins to go into their holes, should I go to thinner shims? The truck seems to be fine with the shims that are there now. If I get the pins in the holes on both sides, doesn't this automatically mean that the axle is positioned correctly under the truck? The whole thread about uneven ride height is here: https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/1270094/1.html

http://chevy.oldcarmanualproject.com/1929_57chevyparts/57cmpc0585.htm
I don't think the original shims were that thick.
In my area I go to a shop that does straight axles for big trucks.
They do 1/2 tons as well.
The first check, for an old unknown truck, is to make sure the axle is not bent.
Then check that the camber is correct.
Shops that do this kind of work day-in and day-out know what to look for.

Thanks for posting that diagram. I agree, the original shims were much thinner. I still have them.

If the shims are too thick for proper spring bolt engagement, remove them until getting spring bolts with longer heads. The spring bolt head is the only thing that positively locates the axle.

One can make extensions to lengthen spring bolt heads when thick shims are necessary.

Ed

If you don't have a local spring shop you might try Plattsburgh Spring Inc...

www.UBoltsDirect.com

I got 8 U-bots for my Jeep project for less than $30 with about $10 in shipping. They will custom make whatever you need (bolt size, axle diameter and length). You might ask them about your wedge issue as well.

Mike B

thanks, Mike.