Spring relocation problem

[74swangur]

Relocated my springs last weekend. All went well, but now when I drive over a hard bump in the road such as a split in the pavement or a pothole, there is a hard slam in the rear. Suspension travel is fine when I push the car up and down. I have to bounce it pretty hard to make the pinion snubber hit. The snubber has about 3" inches before contact. The hard slam doesn't happen when driving over rolls and dips in the road, only when hitting something hard. Didn't have this problem before relo with stock wheels and tires. After relo I am running 245/60R15's on 15 x 8 Weld Prostars. My springs dont have much arch. They are stock five leafs off of a four door smallblock car.
I'm concern that my shackle angle is not correct. Could this be the problem?
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[green67cuda]

I don't have witnessing knowledge about it, but have heard that if you tighten your u-bolts that hold the axle to the spring too tight, you'll get a booming noise in the car.  Did you torque them to specs, or just crank them down? 

[19swinger70]

your shackles may be letting the rear spring eye hit the frame. some people have had to address this issue.

[74swangur]

your shackles may be letting the rear spring eye hit the frame. some people have had to address this issue.

My shackles are very close to vertical. Have checked for any marks that would indicate spring eye hitting frame.   

[74swangur]

I don't have witnessing knowledge about it, but have heard that if you tighten your u-bolts that hold the axle to the spring too tight, you'll get a booming noise in the car.  Did you torque them to specs, or just crank them down? 

I just cranked them down. I'd like to hear more about this u-bolt to tight stuff

[70 Dustpan]

Are your rear shackles leaning to the front or the back of the car?

[Ryan (Strange246)]

Are your shocks too short? Thats what it sounds like, easy to tell, take em off and go for a ride, it'll feel bouncy but you'll be able to tell that way...

Ryan

[74swangur]

Are your rear shackles leaning to the front or the back of the car?

Shackles are straight up and down, top shackle hole is to the front about a 1/4" more than the rear spring eye.

[74swangur]

Are your shocks too short? Thats what it sounds like, easy to tell, take em off and go for a ride, it'll feel bouncy but you'll be able to tell that way...

Ryan

  I'll give that a try.

[Ryan (Strange246)]

Are your shocks too short? Thats what it sounds like, easy to tell, take em off and go for a ride, it'll feel bouncy but you'll be able to tell that way...

Ryan

  I'll give that a try.

No problem, I had an old camaro in high school that we put 6" lift springs in and didnt think about changing to longer shocks and it reacted EXACTLY the same way and that was the problem...

Ryan

[cu440da]

Are your shocks too short? Thats what it sounds like, easy to tell, take em off and go for a ride, it'll feel bouncy but you'll be able to tell that way...

Ryan

[guzzimike]

I don't have witnessing knowledge about it, but have heard that if you tighten your u-bolts that hold the axle to the spring too tight, you'll get a booming noise in the car.  Did you torque them to specs, or just crank them down? 

This is interesting. Anyone else care to elaborate..?

Could it be a Harmonic vibration..?

[daneddy]

If your rear shackles aren't 100% vertical that may be the problem.  You said the top bolt was about a 1/4" in front of the bottom bolt?  Did you weld the rear shackle mount to the bottome of the frame rails or did you drill holes in the fram and put bushing sleeves in the frame?  Reason I ask if you put the sleeves through the frame rails that will make the spring eyes much closer to the frame allowing them to hit without too much movement.

I think I'd also put some paint on the differential snubber and see if it's hitting, 3" isn't much clearence and a good solid bump can move the rear end more than three inches easily.

I seriously doubt that the shackle torque would be the casues.  While it's always a good idea to stick to the factory torque settings if you tightened them good there won't be any slack in those.

Also check for exhaust pipe clearences over the axial or exhaust hangers that may be broken.  Lots of simple things can make big noises and fool you.  You gotta out smart them.

Dan

[green67cuda]

I seriously doubt that the shackle torque would be the casues.  While it's always a good idea to stick to the factory torque settings if you tightened them good there won't be any slack in those.
Dan

that's not what I said.  it was u-bolts, and nota bout havi ng any looseness in them.  i'm still trying to find where I heard about this, but i think if the perches are too tight, then as the springs try to slide during acceleration or on bumps, the friction causes it.  absolutely not sure on that, which is why I've GOT to find it.  I know for sure that was in some manual somewhere that I have here at the house.

[dangerdawg]

in the mopar chassis book under rear suspension section g 3. "over-tighting can cause spring friction,which will produce a booming noise insidethe car."

[bOb shingler]

  with dangerdawg

[green67cuda]

in the mopar chassis book under rear suspension section g 3. "over-tighting can cause spring friction,which will produce a booming noise insidethe car."

yup.  i found it and came back to post.  my 9th edition doesn't have section G3, but it IS on page 316, last sentence on the left column, under the "shims and torque" topic.

I had skimmed the chapter looking for it, but didn't think it was there.  i was in the process of reading all my suspension literature fully. 

[74swangur]

in the mopar chassis book under rear suspension section g 3. "over-tighting can cause spring friction,which will produce a booming noise insidethe car."

yup.  i found it and came back to post.  my 9th edition doesn't have section G3, but it IS on page 316, last sentence on the left column, under the "shims and torque" topic.

I had skimmed the chapter looking for it, but didn't think it was there.  i was in the process of reading all my suspension literature fully. 

Is there a torgue spec on them there u-bolt nuts.

[green67cuda]

Is there a torgue spec on them there u-bolt nuts.

yep.

[74swangur]

Is there a torgue spec on them there u-bolt nuts.

yep.

I quess I forgot to ask if someone knew the spec!!

[green67cuda]

 



i think it's 40 ft-lbs.
i'm cetain there's a "range" and that it may vary by vehicle, but that's where I torqued mine.

[74swangur]

I'm sure mine are much tighter than that. I better losin them puppies and retighten with my clicker wrench. You feel pretty good about that torgue spec??(40 ft-lbs)

[Locomotion]

Sometimes in the kits the bolt for the front spring eye is smaller than the front bushing hole.
If the car unloads and loads the suspension while driving, that extra clearance could cause the noise.

[Ryan (Strange246)]

74swangur did you get it straightened out?

Ryan

[74swangur]

74swangur did you get it straightened out?

Ryan

  Thanks for asking. Having my stock springs re-arched. They were almost totally flat. I will probablly have to relocate my shackles in the frame after the re-arch. Also found that my shocks were bottoming out with two people in the car. Shocks work fine going over up and down dips in the road, but a quick hit from a split in the road or pot hole would bottom them out. Hopefully re-arching will increase the ride height and give the shocks more travel. If this raises the car I will have to get some lowering blocks to slam it back down. My tubs look to good when they are full of tire. Gotta have the car sitting low. Don't want it jacked up in the butt.