front wheel hop (crazy feeling)

[fastwillie 696969]

DRAG RACER please check in ,when i driving down the hwy and if i jump on it ,sometimes the front wheels feels like there hopping left to right ,almost to the point the truck is uncontrollable until i back off the throttle then it stop and i can continue cruising
this happens when i launch off the line too get about the 1/8 mile and then the wild ride starts until i get off the pedal .

my set up in the rear is coil over adjustable springs .4 link ,rear tires 31x18.5 x15 pressure set to 30 lbs
front suspension cpp tubular a arms with springs and cpp front shocks
i try different setting on the rear shocks .no difference ,

maybe I'm just reading to much into this ,maybe i just need to power thur it or i just run 1/8 runs

any help would be appreciated

[Super73]

First thing that comes to mind is asking what spring and shock you have in thefront end.


Next, Is the truck porpusing? In other words oscillating front to back. I have heard of this issue happening when spring rates are the same front/rear or even in cases where certain speeds there is a harmonic causing an oscillation.

Dave Morgan talks a bit about it in his seminar I have on DVD. I have also seen some posts about it on road racing forums. Somewhere I even saw a calculator someone put together on a road race forum that allowed you to put your info in and it would tell you what speed this would happen.
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[fastwillie 696969]

its more left to right than front to rear bounce ,it feels like the body is twisting back and forth

[Super73]

Do you know anything about the springs? Rate, length? Are they a "lowering" spring?

When I had their lowering springs, they were short and heavy spring rate. As soon as I switched to a softer longer spring which is more conducive to drag racing, the ride got a million times better. The rough farm roads in this area did not like the short stiff spring. It would shake the truck to pieces at any speed.
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[vin63]

Originally Posted by fastwillie 696969

DRAG RACER please check in ,when i driving down the hwy and if i jump on it ,sometimes the front wheels feels like there hopping left to right ,almost to the point the truck is uncontrollable until i back off the throttle then it stop and i can continue cruising
this happens when i launch off the line too get about the 1/8 mile and then the wild ride starts until i get off the pedal...

...any help would be appreciated

My first question is what are your front end alignment specs? It sounds like when load is taken away from the front end, you might be going into a severe bumpsteer condition, which can dart the front end around...sometimes violently.

[raceman6135]

Originally Posted by vin63

My first question is what are your front end alignment specs? It sounds like when load is taken away from the front end, you might be going into a severe bumpsteer condition, which can dart the front end around...sometimes violently.

Bumpsteer due to poor geometry was also my first thought, especially when OP says that it steers better when he lets off the throttle, which would transfer weight back onto the front, minimizing the bumpsteer.

[fastwillie 696969]

Originally Posted by vin63

My first question is what are your front end alignment specs? It sounds like when load is taken away from the front end, you might be going into a severe bumpsteer condition, which can dart the front end around...sometimes violently.

i thought about that myself since the a arms and front suspension was changed ,im going to ask the shop if they did the alignment ,or i might just take in and have the alignment check out and get the printout

[vin63]

Originally Posted by fastwillie 696969

i thought about that myself since the a arms and front suspension was changed ,im going to ask the shop if they did the alignment ,or i might just take in and have the alignment check out and get the printout

Ah...are you able to take a straight on photo of the drag link, tie end rods and lower control arms in the same photo (one at ride height and another maybe with the front end jacked up so the wheels drop) for geometry purposes? If the tie rods are not parallel with the lower control arms, it will cause a bump steer condition. But, a bad alignment (or no alignment) can cause a lot of similar problems, too.

[Super73]

Not discounting the alignment or geometry comments because they are very viable.

The CPP lowering spring however will not allow of weight xfer due to how stiff they are. So bump steer through the arc of suspension travel is going to be minor for the simple fact the front suspension won't travel or will have very little travel. However, if it is off even at a settled position, well that will be aroblem. By the 1/8 weight that did xfer to the rear is more than likely coming back on to the spring bringing the nose down a bit (if it went up at all).

I wish I could find a video of my truck first time at the track when I had CPP lowering springs in it. 12.33 with dead hooking a 1.89 60'. Sure it's not ubber impressive, but it literally left flat as a board with zero weight xfer.

Super smooth roads were no issue 70+ mph. Semi bumpy roads were horrible even at low speeds. A bump under the right tire would shoot you left. A bump under the left tire would shoot you right. There are a lot of farm roads in my area that have had pot holes patched and they were no fun even at 40mph. as soon as the 600lb ish rate spring found its way to the shelf and a mid 240lb rate took its place, what a difference.
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[D13]

My 99 did that, found the steering box was worn. Front wheels whould go into side-to-side oscillation at certain loads and speeds, usually on acelleration when the weight on the front would decrease. Let off, would load up the tires and they would put tension on the linkage, problem would go away. Took ma about a month of it getting progressively worse before I sorted it out. new box, no more problem.

[fastwillie 696969]

Originally Posted by D13

My 99 did that, found the steering box was worn. Front wheels whould go into side-to-side oscillation at certain loads and speeds, usually on acelleration when the weight on the front would decrease. Let off, would load up the tires and they would put tension on the linkage, problem would go away. Took ma about a month of it getting progressively worse before I sorted it out. new box, no more problem.

i will have them check it when it goes in for alignment ,i wanted to replace that box ealier ,but was talked out of it because it was turning ok and no leaks ,i might just order the cpp 500 box

[82chevylsx]

i would try putting a sway bar on it if it don't have one.....my 82 chevy did that and i didn't have a sawy bar and it sure helped it out......just my opinion.....

[vin63]

Originally Posted by 82chevylsx

i would try putting a sway bar on it if it don't have one.....my 82 chevy did that and i didn't have a sawy bar and it sure helped it out......just my opinion.....

In a drag race application, a front sway bar would be the last component I would add to a suspension. If the front sway bar mitigated your suspension issue, I would guess it created enough of a bind to mask the problem temporarily. My approach is to always to fix the underlying suspension problem when it comes to geometry and/or alignment because those issues only tend to get worse and more dangerous.

[Super73]

Originally Posted by vin63

In a drag race application, a front sway bar would be the last component I would add to a suspension. If the front sway bar mitigated your suspension issue, I would guess it created enough of a bind to mask the problem temporarily. My approach is to always to fix the underlying suspension problem when it comes to geometry and/or alignment because those issues only tend to get worse and more dangerous.

I started to type this response almost word for word a few hours ago but didn't want to get in to it being a bandaid for a bigger issue at hand.
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[fastwillie 696969]

it has a sway bar ,i called the shop where i had the work done ,they didnt do a alignment ,they said they told me about 2 months before they finish the work that i was going to need the front alignment done ,either i was stoned or i didnt hear it or just thought it would be part of the suspension work .so thats on me . its going alignment tommarow at my friends dealership ,they have that laser machine by bear ,so for a case of beer cant beat that deal

[Super73]

When I have alignments done on my truck, I have the raise the front 1 1/2" so it is more like it would be going down the track.
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[fastwillie 696969]

my front end is up already ,i got stock height spindles ,

[vin63]

What Super73 was referring to is be sure and check alignment, particularly toe, when load is removed from the front springs by an inch or two - similar to when the vehicle is under acceleration.

[BR3W CITY]

Originally Posted by fastwillie 696969

either i was stoned or i didnt hear it

I can't count the number of times I've uttered this statement. Either about the truck or the girlfriend

[fastwillie 696969]

Originally Posted by vin63

What Super73 was referring to is be sure and check alignment, particularly toe, when load is removed from the front springs by an inch or two - similar to when the vehicle is under acceleration.

yeah got it