I replaced the leaf springs with 4/1 springs and now the truck shudders around 25 mph then goes away around 30. One of the top hanger bolts is tight against the frame since i got ones that were a bit too long. The other side I installed in the opposite direction with the nut facing out (like they originally were). I attached a picture of it. Would this have any effect on the vibration? Also, do the hangers need to move up and down or should everything be tight?

 

I'm planning on upgrading my rear springs to the heavier capacity springs from SDTruck Springs. Where did you get yours? I'm assuming you replaced all the hardware as you mentioned, but I would go with OEM hardware rather than aftermarket, unless it's from ARP. The fasteners should be the same length as stock. I don't see why upgrading your springs would cause a shudder. Perhaps they need time for a "break in" period? Try it with a heavy load in the bed to see if the shudder goes away.

 

This won't explain the shutter but the bolt seems to be hitting the mount and is starting to wear into it.

 

I got the hd springs from sd too. Got new shackles, hardware, u-bolts. I'm going to turn that bolt around today, looking back idk why I did it that way. Does the shudder have something to do with the change in height? Also I didn't use a torque wrench but I tightened them up good with the impact gun on a small compressor so not tight enough to do any damage. Could not torquing them to specifics make it shudder?

 

As a matter of fact, yes. Over/under torquing them can/will cause binding or flex. They're torqued to a specific spec right out of the factory, to the point where when the fasteners are removed Ford specifies you must replace them! Most don't because they do cost a bit of money. I had to remove the lower nut that attaches the rear shackle to the frame in order to mount my dual exhaust but I didn't bother replace the nut or bolt. But that's different compared to actually removing the entire assembly. And make sure they're the same size and mounted the same way as they originally were!

 

Alright I will torque them to specs but it seems strange that it would only be shuddering between 25-30 mph if that we're the case. I would think it would be doing it all the time.

 

Where can I find the torque specs?

 

I torqued everything to spec today as best I could. I read that the front eye bolt should be torqued to 220. Does this seem ridiculously tight to anyone else? Either way, the shudder is still there. Any other ideas?

 

Maybe spray some lithium lube between the leaves. Lift the frame to release the pressure from the springs and spray like hell.

 

Did you remove your drive shaft or pull the splines out and put it in differently. Thats a common issue.

Are the U bolts tight? Tires tight?