8 3/4 housing U-bolt torque

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Duster_71

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Hello all, rebuilt the 8 3/4 rear end and starting to put it back together. I couldn't find the torque spec for the U-bolts for the housing to the spring. Little help please.
 
It's either 40 or 45 LB FT. It's nowhere near as tight as you think, because the springs need to be able to flex. If you over tighten the U bolts, the rear suspension will pound you to pieces.
 
This is from 70 service manual. Suspect 71 would be the same
Screenshot_2018-04-26-21-24-56.png
 
Do the spring leaves actually slide relative to the other leaves at the center of the spring between the two halves of the u-bolts during the springs range of motion?
 
Do the spring leaves actually slide relative to the other leaves at the center of the spring between the two halves of the u-bolts during the springs range of motion?
They slide at the ends as they arch and de-arch. (for the lack of a better term) The center bolt keeps them aligned in the middle. Because the leaves are arched, they lengthen as they get flat and they do slide. That's why there are pads on the ends of the springs. Because Mopar springs are quite short on the front section most of the sliding happens on the rear section.
 
They slide at the ends as they arch and de-arch. (for the lack of a better term) The center bolt keeps them aligned in the middle. Because the leaves are arched, they lengthen as they get flat and they do slide. That's why there are pads on the ends of the springs. Because Mopar springs are quite short on the front section most of the sliding happens on the rear section.

That's how I understand it as well. So how does over-torquing the U-bolts cause a stiff ride then?
 
That's how I understand it as well. So how does over-torquing the U-bolts cause a stiff ride then?
I wonder if the housing moves around a bit in the u bolts. I know that if you overtorque the u bolts you can dent/ distort the axle tubes.
 
I know that if you overtorque the u bolts you can dent/ distort the axle tubes.
I figured that was the reason for the relatively low torque spec. I never quite understood how over-tightening the u-bolts would make for a rough ride. To me, there'd only be two way- either it makes the spring bind, or it increases the spring rate. I just don't see how either of those could happen.
 
I just installed my Caltracs and mono leafs and they wanted 75 - 80ftlbs. I torqued them to 75 and I can feel the threads and bolts stretching. I found the factory torque spec in my manual somewhere. I think the guys above are correct with 40 - 45.
 
I just installed my Caltracs and mono leafs and they wanted 75 - 80ftlbs. I torqued them to 75 and I can feel the threads and bolts stretching. I found the factory torque spec in my manual somewhere. I think the guys above are correct with 40 - 45.

New 1/2" u-bolts???
 
Some new U bolts are not flat on the inside. This puts a point of pressure on the housing (greater PSI) where the U bolt contacts the housing tubes. Too much pressure and you might crimp the tube. Factory had the area of contact on the U bolt flattened applying much less PSI to the tube.
 
I am going to order a new set after reading the thread. Calvert sells 1/2” grade 5 7” long for $35.00. Thanks for the post. Andrew
 
Make sure the weight of the car is on the axle before you torque the nuts to 40 ft.-lbs.

If the reason the torque spec is only 40 lbs is to let the leaves slide, why does it matter if the weight is on the axle when you torque them? Won't the leaves still slide at 40?
 
I dunno. Do whatever you want... That's just the correct way to tighten them. It's standard practice for anything with leaf springs.
 
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