Leaf spring U-Bolt tightening specs and ideas

[6 packin]

I have seen soom past posts on loosing the back u-bolts I guess for weight transfer? If some one could explane a little in depth about this. I have read that the U-bolts must be torqued, i cant seem to find any specs on this. maybe some specs on how tight and how loose the rear ones need to be would be awsome.

[amxauto-x]

The only thing I can think that you are refering to would be the straps around the rear portion of the rear leaf springs. You know the straps that hold the leafs together. Take them off to loosen up the leafs so they can bend more and let the rearend squat more, hence weight transfer. The u-bolts should be torqued, but I don't know what value that would be. That must be it the shop manual someplace.

[amxauto-x]

This page contains a reference chart of torque values for tightening u-bolt nuts on vehicle axles. It assumes a light coating of machine oil on the threads has been applied.
The figures represent ultimate torque values for the size thread indicated. Actual torque applied to u-bolt nuts is also dependent on the ability of the anchor plate to take the pressure without deforming. A lot depends on proper tightening as the leg of the u-bolt must be stretched to do its job, but as in many mechanical systems final judgement falls to the technician and his knowledge.
An example would be of a Pickup Truck Rear Suspension using 5/8" diameter u-bolts passing through a 1/4" thick anchor plate (a plate which will deform with much less torque applied than near the ultimate figure on the chart). This situation requires a lesser torque than the published values. However, a three ton dump truck using 7/8" diameter u-bolts anchored with a heavy iron plate will require full recommended torque, and be retightened after a few hours service.
Since this chart gives ultimate values of torque, our shop has found ninety percent of the figures to be sufficient for final torque on a given size u-bolt. For example: 1800Lb/ft torque is recommended for 1-1/4" Grade 8 equivalent u-bolts; 1890Lb/ft would be ninety percent of the maximum allowable figure of 2100Lb/ft.

U-Bolt Torque Chart - SAE Bolt Size;;; and Thread Grade;;; Max.Torque (FtLbs)
1/2 - 20 ;;; 5 ;;; 92
9/16 - 18 ;;; 5 ;;; 131
5/8 - 18 ;;; 8 ;;; 256
3/4 - 16 ;;; 8 ;;; 446
7/8 - 14;;; 8 ;;; 710
1 - 14 ;;; 8;;; 1057
1-1/8 -12;;; 8;;; 1522
1-1/4 - 12;;; 8;;; 2107

Source: Triangle Auto Spring Co.

[amxauto-x]

U-bolt torque chart
Rod Diameter 3/8" 7/16" 1/2" 9/16" 5/8" 3/4" 7/8" 1" 1-1/4"
Torque 30 ft-lb 45 ft-lb 65 ft-lb 90ft-lb 125ft-lb 300ft-lb 480ft-lb 730ft-lb 1240ft-lb
Husky Spring U-bolts are made from Grade 5 strength equivalent material in the 3/8", 7/16", 1/2", and 9/16" sizes.


Important Note: U-bolts should be retorqued after 20 miles of use after installation. If they are found to be far under the specified torque, they should be checked a second time after driving 20 more miles. This is critical because initial settling in of the spring leaves may cause a loss of torque values. If not properly retorqued, flexing in the center section of the spring may result in spring breakage or in some cases the center bolt may shear or bend with axle shifting being the result.


From Husky Spring co.

[rumblefish360]

MoPar rears are not to be squating. They should rise under power.
The more power, the more rise.
If your ccar squats, somethings wrong.

[deadhorse66]

I agree with rumblefish. If you watch a car that has the rear spring clamps cut, you will see the rear of the spring unfold and the front will bend upward, and as the car rises, it will almost look the spring is unloaded. That is the spring actually trying to pick the front of the car up due to the torque back from the axle. Mine squatted, but it was heavy, geared high, and devoid of any traction improving mods. It also spun. A mopar that still has factory style suspension and hooks on it does not squat, or at least I have never seen one that did, but I am just a youngster.

[cuda66273]

Factory manual says "40 lbs"

I use steel rollers top and bottom on the shackle eyes and tork to "Zero", I use a 1/2 nylok nut and bring the clearance to about .030-.040 and call it good, I want it to be loose and free to arch with the suspension so there's no bind...rattle a bit...I think....although with open headers and a helmut on there as quite as a mouse....LOL

[FearThe4Doors]

do cal-trac bars help it to lift? or do they just keep everything rigid? or do those bars enter everything into a whole different ballgame?