Replaced rear bushings but still 'unstable'

[Tim240Z]

On my C20 Burb, I replaced the track bar and control arm bushings in the rear with urethane ones, but at speed the rear of the truck still seems very 'loose'...
Hard to put my finger on it, but it feels like the rear end is floating around back there.....never felt like this with my 71 truck....maybe just the way these burbs are? Very unsettling feeling especially on the freeway, going around a bend with a rough, or washboard type road surface....takes every bit of concentration to keep it in a lane.
I have replaced the steering box and the pitman arm in the front and all else appears tight and good....

Any suggestions? All shocks appear and feel to be good (paint still clean and the rears had lots of push to them when I did the rear bushings - unbolted the bottom mount - they were obviously done fairly recently by the PO)
Tim

[Hart_Rod]

Are you running bags or springs? How much drop? Do you have new shocks? Shock relocators?

[Tim240Z]

I mentioned the shock condition above...as for the rest:
Coils, no drop or relocation...all is stock. I'm sure that the springs are getting weak as they are approaching 40 years old, but I can't see that causing the problem?
Tim

[Hart_Rod]

Originally Posted by Tim240Z

I mentioned the shock condition above...as for the rest:
Coils, no drop or relocation...all is stock. I'm sure that the springs are getting weak as they are approaching 40 years old, but I can't see that causing the problem?
Tim

I missed that about the shocks. What type of tires are you running?

[Tim240Z]

245/70-17 BFG Rugged Trail, load range E, (off of a new Ram 2500).

Tim

[Hart_Rod]

I think some new springs would help, but I don't think that's the entire problem. How much air are you running in your tires? I had a similar problem when I let the pressure in my rear tires get low.

[Tim240Z]

50psi

[Hart_Rod]

Originally Posted by Tim240Z

50psi

Interesting. That seems high, but I'm not sure what is a normal pressure for those tires. I would suggest trying 40 psi and see what that does.

[Tim240Z]

I figured that since the tires had a very stiff sidewall, the high pressure could only help (max press. is 80psi iirc).
I'll try drop them, but my gut feeling is that it will just get more mushy?
Tim

[Hart_Rod]

Originally Posted by Tim240Z

I figured that since the tires had a very stiff sidewall, the high pressure could only help (max press. is 80psi iirc).
I'll try drop them, but my gut feeling is that it will just get more mushy?
Tim

You're probably right, but it's free to lower the pressure, . The only other thing it could be is the springs. Do you plan on upgrading them any time soon?

[smashingchuck]

Are you sure it's in the rear? Maybe it's the steering that's loose and you're just feeling the rear of the truck amplify the problem? Also I know in my burb it starts to feel kinda top heavy when you are pushing through the twisties just a little to fast.

[2tons of fun]

check your lower shock bracket, i tore mine apart and its was a stock truck that i babied.

they are a crappy single shear design and have a tendency to tear. weld a heavy spacer to the braket and it will bullit proof it.

[Tim240Z]

Originally Posted by smashingchuck

Are you sure it's in the rear? Maybe it's the steering that's loose and you're just feeling the rear of the truck amplify the problem? Also I know in my burb it starts to feel kinda top heavy when you are pushing through the twisties just a little to fast.

Like I said above, I replaced the box and pitman arm....everything else looks ok, except the bushings for the sway bar (only have the front one, no rear sway yet), which are mushy from past oil leaks.
I guess I could just replace the ball joints since they are likely original. I was hoping that I would feel a significant difference when I changed the rear bushings as the originals were shot, but I was very disappointed.

Originally Posted by 2tons of fun

check your lower shock bracket, i tore mine apart and its was a stock truck that i babied.

they are a crappy single shear design and have a tendency to tear. weld a heavy spacer to the braket and it will bullit proof it.

Everything looked OK when I was under there....where does it break?

Thanks guys!
Tim

[jrods70]

My fathers 71 suburban had a problem like this and it turned out to be loose u bolts on the axle years or rust ate away at the mount and bolt. Cleaned the mount up and put new u bolts fixed it.

[Tim240Z]

When I did the bushings, I loosened the U-bolts, then re-tightened again....they must have been replaced at some point as they are still quite nice....I guess they could have loosened, I will check tomorrow.....
TIm

[2tons of fun]

the break at the hole for the shock bolt.