ORIGINAL REAR SPRINGS WITH LIFT BLOCKS?

 

find a puddle in a parking lot or hose the street in front of your driveway, drive straight through the water and at least a full vehicle length.
view your wet tracks, front and back inline or are your dogtracking.

 

That's a great tip!

 

The problem with the OEM specs is they have a wide range and using the wrong combination of caster,camber and toe will still result is poor handeling.

To me, ( and this is just a educated guess ) it sounds like the split between your left and right caster is more then 1/2 a degree.

Question, Does it behave the same on a road that is flat as compared to one that has a more pronounced crown ?

 

I would have to agree with Seijirou about the shifting axle situation. I believe in a diff, the right rear is the first to get power which if you have an axle that could move, it would send you left on acceleration. The right may be the one getting the initial torque when deacclerating which again could torque your rear axle. If your left rear spring is allowing movement, it could possibly create those types of directional changes. Just a thought since rear steer is a real issue where you hit a big pothole or bump, the axle torques and off you go where you were not planning. On a flat road, it could track straight. You have a higher center of gravity With a 4 inch lift, you have created additional leverage of the body/engine against the chasis and springs. If it did not do it before the lift, there's your answer.

 

I disagree. ( but do not dismiss the notion )

When you lift either the front or rear or both you change the caster angle of the front axle. Caster is the single largest factor to make solid front axle track straight.

You could install the rear axle crooked by 2" and still track straight down the road. The rear end would be be crabbing off center but would still go straight down the road. it would actually track straight down the road better then it would handle a curvy road. Curvy road it would have better "turn in" one direction and worse "turn in" the other giving it a quick or slow feeling.

 

But to watchers point,

In the rear you want to check your leaf spring bushings.
A very loose/worn out or missing spring eye bushing could give the results you
described.

 

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I'm still working out caster effects in my head. It relates to angle and distance from the rotational center of the front wheels to the most forward steering linkage--is that a fair description? If you raise the vehicle, you would increase the angle from the front wheels to the steering linkage-correct? I get the effect of caster angle in general on tracking but what about caster angle-which would be a constant whether good or bad-would cause acceleration forces to vector one way on acceleration and the opposite way on deacceleration in a consistent manner? Again, just trying to understand that relationship.

I would agree on the improper angle of a rear axle install and the crabbing. However, if that angle changed when force was applied, it would create the directional changes being experienced, would it not? I am just going off the basic concept that a direction change would be preceded by a change in orientation of another component. I really enjoy learning which prompts my questioning.

 

I've been thinking about this too, and on the front the only thing I can come up with is a stack of 3 things happening to cause the effect as originating from the front.

1. Caster is significantly different side to side
2. Bump-steer is great enough to transition one side or the other from negative to positive toe
3. The front suspension is not compressing and rebounding evenly.

The wheel with greater enough caster will be dead ahead, in extension bump-steer will pull the other wheel's toe to one direction and in compression push it the other way. Normally toe auto-balances to neutral forward but if you have enough caster in one wheel it will not. Of course bump steer is a geometry thing so it also cancels out on both wheels equally, unless the movement is uneven side to side.

I see all of that as an unlikely combination, but I might be missing something, and like you I enjoy learning too.

 

Of course bump steer is a geometry thing so it also cancels out on both wheels equally, unless the movement is uneven side to side.

Since your directional pull is consistent on acceleration and braking, I tend to think in terms of a common cause. Unless you have a limited slip differential, the right rear receives power first. If axle moves, rt rear goes forward and pushes you left until the left rear catches up. On stopping because of the same scenario could occur BUT ONLY IF the rear axle can be torqued enough to allow this movement. Could be rear torque on start, uneven brakes on front, could be...?????? All you can do is start eliminating the eaasiest things first

 

I don't understand bump steer "canceling out."

Leaf springs do a poor job of locating an axle side to side. In part, it is the caster that helps locate the axle as you drive down the road. However, in our trucks, we have a track bar, which runs laterally from frame to the passenger side of the axle near the knuckle.
The drag link runs from the pitman arm to the tie rod, with both mounting points and angle mirroring the track bar.
When you hit a bump, the suspension cycles. The track bar pushes the axle towards the passenger side as it cycles across its pendulum of travel (as it is not level at ride height but slightly downward pointing, and approaches level at full suspension compression). The drag link being a similar length and angle, this keeps the squat of the leaf springs from causing the drag link to level out, pushing the passenger knuckle (and therefore both knuckles, connected by the tie rod as they are) and causing the vehicle to steer towards the right under suspension compression, like during braking, or after hitting a bump.

As you accelerate, the vehicle squats and lifts the nose, drooping the suspension and, without proper drag link/track bar geometry, can cause the vehicle to steer left.

A change in caster (often caused by lifting the vehicle) can make the vehicle less stable and less self correcting, which amplifies any bump steer.

Post a picture of your front suspension taken dead on from the center.

It's an extreme common issue after installing a poorly designed or pieced together lift kit, and has probably sold thousands of add on dual and quad steering stabilizer kits over the decades.

It is not self canceling, unless you mean the track bar, when properly installed in relation to the drag link, will cancel the push and pull on the tie rod during suspension travel.

 

You're right, I was considering a tie rod assembly where the tie rods can pivot.

All the more reason I keep coming back to the rear in my mind.

 

If this was a vehicle with control arms, I'd suspect control arm bushings. Likewise on a straight axle I'd suspect the leaf spring bushings or the shackle bushings, on either axle.
Pulling to one side while braking alone would suggest a calipers not working equally.

 

Did you check the leaf Spring bushings yet like Pirate 4x4 suggested?
I have also seen where U bolts were not tight and the axle would move on the leaf springs. Lay underneath and compare all the different attachment points, look for things that look dissimilar between either side, shiny spots, or rust powder (meaning something isn't tightened enough, leaving a rust trail).

 

This thread had continued on and I appreciate all the responses. It's been slow because of a lot of work. Saturday I'll finally get to replacing all the brake like with SS braided lines. I'll check all slider pins and ensure they're lubed. I still have to get around to replace all the leaf spring bushings & bolts as I mentioned in the first post.