Solid Axle Chevy Steering

[Bob_Sheaves]

OOPS- I meant "twisting it PARALLEL" not "normal". Sorry for the oops....the vector is normal, but the resultant (axis of rotation) is parallel.

Bob

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[K5Blazer]

Alright Im starting to get this. So If I switch from the stock style steering like Bob is suggesting to do, Im going to want to run a panhard rod that is an exact duplicate as the draglink at ride height with the steering centered. I also might want to consider running the haltenberger type linkage to get better steering response. I would also want to make sure the frame and panhard rod mounts are gussetted and braced very well in order to resist frame flex and to keep things from breaking from the added stress of the panhard rod. Is that what he said? cause it went right over my head.

[Bob_Sheaves]

You have understood the concept..... a couple of caveats however....

1. The Haltenberger linkage is used to create toe-in during rebound (commonly called "droop"-incorrectly) to increase the overall vehicle stability when launched airborne. This is one reason the TTB/TIB Fords are so easy to control when they land hard. Until the suspension moves to full jounce ("compression"), the vehicle understeers (travels straight and requires greater input at the steering wheel for the same amount of wheel turn) for that instant that the driver is bouncing around wailing on the steering wheel uncontrollably (or almost uncontrollably...LOL) from the impact of landing. The downside of this effect is that ntsqd is quite correct-the full jounce (full "compression") position can induce a dynamic toe-out condition to the front tires, leading to an oversteer condition.

By adjusting the distance between the right hand tierod end on the draglink and the "center" attachment tierod end on the tierod (which connects the left tire to the right in this discussion case) you can alter the amount of toe change and the sensitivity to the vehicle suspension dynamics.

2. To have a neutral suspension, you need to use a conventional "T"-shaped draglink/tierod configuration, with the draglink "ball" of the connecting tierod end on centerline of the 2 knuckle tierod ends (this means that you CANNOT have a straight tierod). This configuration will give you a neutral change, but be aware it is VERY tricky to handle on the street, as you have a uniform amount of steering wheel input, regardless of suspension compression or extension. Most manufacturers design in approximately 10 to 18 percent understeer to keep the driver out of trouble in "high suspension travel" conditions (one of the primary differences between a purpose-built race car and a street piece).

3.An engine cage will transfer the track bar loading (if properly designed) from the left to the right framerail and provide you with an alternative mounting position for the upper shock end (or coil over end if you replace the leafs with trailing or leading links-look under a Jeep XJ Cherokee or a Dodge BR fullsize pickup 4x4 for ideas here).

Best as always,

Bob

[ntsqd]

Bob,
Given that you could only have one but not both, which would you choose for stability; Castor gain in both jounce & rebound, or toe-in in rebound ?
I'd assumed until now that castor gain would be the preference, but your comment about the TTB/TIB stability with rebound toe-in (coupled with their obvious castor loss in rebound) has left me wondering if my assumption was correct.

Thom

TS

I used swerve around my halucinations, now I drive right thru them.

[Bob_Sheaves]

Simply put-caster gain has a higher priority than toe change for an offroad vehicle. For a street dirven vehicle, the reverse is true.

That being said, my PERSONAL preference is to design in (on a race car that does NOT use a TTB or TIB) a caster change to increase the castor about 25 percent at the limits of travel. In otherwords, if you have (at static ride height) 2 degrees negative caster, the increase at the limits goes to a negative 2.5 degrees (25% of the starting point). This is NOT to imply that I shoot for 2 degrees (the real number is higher than that, depending on the driver I am working with) but rather to illustrate the principle.

Best as always,

Bob

[ntsqd]

Bob,
Thanks for confirming my conclusion.

TS

I used swerve around my halucinations, now I drive right thru them.

[Stephen]

This is kind of an old one but since there's a bit more action on straight axle GM's going on I brought it back.
One thought on using stock steering with long travel springs: I tried the stock steering with a set of custom springs I designed a few years ago and the big problem wasn't bumpsteer but roll steer. This is the reason so many rock crawler/recreational offroad types go to crossover steering. The factory steering system places the draglink a few inches outboard of the leaf spring so when the axle articulates under the truck (steering the axle as a result) the draglink can't keep up. I tried running a locating bar from in the factory swaybar mounting locations on the frame and ubolt plate and the bumpsteer was minimal but the roll steer was still terrible. One solution I've seen was turning the box sideways like a dodge truck and running the draglink very close to the leaf spring.

The crossover system with a panhard bar referred to earlier was mine and despite a pretty nice mount on the frame it still tried to crack out until I field welded it to the crossmember that was touching it anyway. One inch of chicken poop applied with a battery welder ended the cracking problem. There is a problem with running a panhard with leaves in that leaves don't really want to move side to side very much so you're going to induce a lot of bind into the system. I had a sliding bushing at the front of the spring to give it about 5/8" of side to side motion without bind and it cycled through about 12" of travel pretty easily. I have some ideas on how to get that side to side motion in a more durable way but it doesn't take very much messing around with it to justify the universal answer: link and coil or coilovers.

[NTRoffroad]

I've read all this post and I think I am more confused than when I started. I am in the process of building a 78 Blazer. It will keep leafs all around for now and steering is a big concern. After talking with alot of people it sounded like x-over was the way to go if I really wanted to stay with leafs. Now what??

[Stephen]

go with crossover and live with bumpsteer (personally unacceptable but as always YMMV)
Add a panhard bar to crossover and have great steering at the expense of some spring bind. (probably the best overall solution)
Figure out some way to let the spring move side to side so that it doesn't bind with the track bar. (maybe barely practical)
Link it up and double shackle it and steer front to back with the steering box under the seat. (not really practical)

Stick with stock type steering and have some bumpsteer and probably a good bit of roll steer.

[ntsqd]

snip.....
Link it up and double shackle it and steer front to back with the steering box under the seat. (not really practical)

I've seen that type of steering done cleanly, and I still wouldn't want to race it. Too many failure modes.

My vote is also for cross-over, w/ or w/o the panhard bar.