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Hi. I have a 79 crew cab 4x4 with 4" lift and my differencial moves when moving from a stop. It rocks up and down about 1inch or so.
my ? Is: i have torqued the long u bolts (it has 4" blocks for the lift) now 3 times and there stretching a bit i guess. When i tighten them it moves less. Now is there like a huge amount or torq needed to the u bolts? I have torqued by hand with a regular ratchet at very firm torq but maybe it needs more? Thanks in advance
A long wheel base and blocks are somewhat of a perfect storm for axle wrap and wheel hop. Give us some more pics of the underside of your lift both front and rear.
From the definitions below can you give us more clarity on your issue?
Axle wrap is a problem that plagues leaf sprung vehicles with soft springs, particularly those that are set up SOA (Spring Over Axle). Axle wrap is something different than wheel hop. Wheel hop is when an axle on your 4x4 rapidly hops up and down. Axle wrap is unwanted suspension movement that allows the pinion angle to change. Wheel hop is annoying and could cause drivetrain breakage, but usually it's not the actual hopping that breaks parts, it's the axle wrap that results from the hop that causes drivelines to bind and breaks yokes, drive shafts and sometimes even pinions.
You need to determine if the axle is moving from something loose or just spring deflection. It is normal for leaf springs to twist under load, blocks put a 'lever' into this action and make it a little worse. If you are not experiencing binding at the u-joint or vibration it may be okay to leave it like it is. The solution is ladder bars or something attached to the axle and then the frame to stop that motion.
Just an inch? Four inch blocks you say? Long Short bed crew cab I see? Springs do flex. You are good candidate for some bars.
I torqued mine at 100 ftlbs, in steps, evenly, with no blocks using 9/16" U-bolts (per U-bolt manufacturer's spec) ... then after a few weeks and re-torques, I added 8 more nuts on excess ends, and flush cut (smoother and so less likely to get cut by thread ends) .
U bolt torque depends entirely on the thread pitch and material used. The factory pitch and u bolt material might call for ~100 pounds but aftermarket u bolts could be completely different. I did spring bushings in my crew cab last year and had a semi truck shop cut and bend a set of u bolts because I couldn’t find any online and they have me torque then 220 pounds because the material they use doesn’t stretch like other u bolts.
This is a very long winded way of saying pitch the old no name used u bolts and get some correct new ones. Bolt everything down how it should be then see what your problem is.
Also, figure out exactly if it’s wheel hopping or axle wrapping.
Wheel hop will make it bounce like a ghetto hooptie car. Axle wrap changes the angle the driveshaft comes into the axle from the front. Both can have similar causes but if you’re not bolted together right you’re not gonna diagnose anything.
Just an inch? Four inch blocks you say? Long bed crew cab I see? Springs do flex. You are good candidate for some bars.
I torqued mine at 100 ftlbs, in steps, evenly, with no blocks using 9/16" U-bolts (per U-bolt manufacturer's spec) ... then after a few weeks and re-torques, I added 8 more nuts on excess ends, and flush cut (smoother and so less likely to get cut by thread ends) .
Yes that's correct. If you need any help finding a set just say. Post the GVWR that's on the warranty sticker of the driver side door pillar. It gives the front and rear axle ratings also.
There's like 7" between the spring and bent spring perch with three blocks in between, no wonder it rocks. The miracle is the U-bolts still holding that "Dagwood" together.
I agree that you should at the very least toss the non-factory blocks. That one with the "ear" pointing towards the inside of the truck is factory. The ear is what the bumpstop will hit provided you flex the suspension enough to do that.
Lift springs would be great for giving you that lift back without the use of block. I also agree with getting new spring perches. Those should be nice and flat.
U-bolts will have different torque specs depending on their size (diameter) as well. I used aftermarket 5/8" u-bolts when I had the lift done on my Bronco and I believe that specs for those was something around 145 lb ft. It's also normal to have to retorque them a time or two after the first install once they get a few miles on them.
My setup is different now, but here's a couple shots after I had new spring perches put on. Nice and flat and the springs sit nice and flat on top of them. I've since done a lift, but those same perches are there, but my u-bolts are thicker now.
There's like 7" between the spring and bent spring perch with three blocks in between, no wonder it rocks. 
The miracle is the U-bolts still holding that "Dagwood" together.
