I am wondering if anyone knows off-hand what size of u-bolts are supposed to be in the rear of a 79 F100 short box. Even if you don't know the height but only the width and diameter, it would help greatly. I can't measure the old ones because they are in the back of my other truck, and my friend has it at the moment. I can measure the height of the spring stack, since I've got that handy, and I know that the total height just has to be the width of the axle pluss the spring stack pluss 3/8 for the block on the axle.


Any help would be greatly appreciated!

Thanks in advance,

Chris

 

9/16"-18. I think the tube is 3".

 

Yup! 9/16"-18 and a 3" tube. I just bought a whole new set for my 78 - $7 each.

The length will depend on weather or not you have lift blocks on the axle and the spring pack. I had stacked blocks and removed one when I flipped the rear shackle. That's why I needed new u-bolts. I bought 12" long ones to be safe and ended up cutting 1" off each just because I didn't like them sticking up. I think the next size down was 10" and that would've been too short.

Just get the longer ones but make sure the threads are several inches long. Mine were threaded 3/4" of the way down.

Good luck.

Kevin K.

 

I measured my 1971 F-100 4x4 with the 9" with the factory lift blocks and 9 leaf spring pack and the length is about 11 1/8 inches with thread to spare.

 

You flipped your shackles? By that I assume you mean you flipped them to the bottom of the axle? That is something I have wanted to do, but I don't really want to try to cut the perches of the axle.

 

I flipped the rear shackles to gain 3" of height so I could remove the 3" blocks.

I did, however, cut the shock mounts off the axle and move them up for more clearance. It took about 5 minutes to do both. Welding them back on is a little tougher because the axle tube is either cast steel or too thick for my little welder to penetrate.

Kevin K.

 

The shackles? The metal piece that connects eye of the spring to the mount on the frame, allowing for the horizontal lengthening of the spring when it compresses, correct?
Do the ones on your truck have several holes in them to allow height adjustment?

Chris.

 

Sorry. The rear shackle bracket is what I flipped which also flips the shackle. No, it doesn't have multiple holes - it's the stock shackle.

However, a long time ago I had a 68 Mustang with sagging rear springs. I bought some shackles which were just thick pieces of steel with multiple holes in them for adjusting the height. Don't know if those are still available, but they should be.

Kevin K.