Technical Bump steer? But not really. Truck feels.......weird

Call Nostalgia Sid's here in Oklahoma and see what he has to say. He's a genius with dropped axles. Maybe he'll chime in on this as well.

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I finally found a couple old threads on here about the same subject in an f100.
What it gets down to is my ***umptions about the previous owner and the fact that prior to the rebuild, it did not do this.
But forget my ***umptions, I'm going after square one, and calling Sid's is a good idea.

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I could tell the caster changed on my truck when removing 3 out of the 7 leafs on the front springs. It doesn't take much lowering to make it drive different. I went from 2 to 4 degrees just to get it back where it was with a full set of springs. Lowering the rear changes caster also, just not as much.

If the pitman shaft/sector shaft moves up, down or sideways, the bushings are worn out. You need to correct that before it will drive better. Chevrolet used standard sized bushings which can be had from any bearing supplier, Ford may have used the same, so it would be worth measuring. I had room to add a longer bushing which made for a rock solid pitman shaft, again this is on a CHEVROLET, so don't be afraid to experiment. The tighter the steering box is, the better it works, and from there you work your way down through the whole system. Having an adjustable draglink sure helps to fine tune the steering to a dead ahead position. When driving with a correctly set gear box, very little steering input will be needed. DO NOT move the steering wheel to correct for straight ahead driving.

When you rebuild the steering box, us a 00 or 000 grade grease. CV joint , lawn mower transmissions, slow speed gear boxes, all use this type of grease. Tractor Supply has some, and John Deere corn head grease and both easy to get and cheap. Even a mixture of 50/50 gun grease and STP works if the seals are good.

 

i have a 59 and did all the rebuild stuff...then i installed power steering...it dose not ride as good as my 2008 driver but for a straight axel it is as good as it gets....i am local to you if you want to check it out....

 

also if you are running big fat front tires look at your tie rod if it is the stock one you mite be getting a little flex in it on a bomb..

 

When you drop or lift a vehicle with parallel springs you alter the drag link not the steering arm or the pitman. Mega drop or lift requires a Z in the drag link to maintain proper steering geometry.

If you are finding stiff spots in the steering with the box connected and not with the box disconnected I would suggest that before the rebuild it was so sloppy that is was less noticeable. A rebuilt box is probably in order.

Now off on a different rabbit trail, the slammer guys used to use a slammer shock. They actually built shocks that were built and valved for lowered vehicles. I like Suspension Technique Stilettos. You cannot imagine how much difference in ride and handling the proper shock makes. Actually when you think about it lifted vehicles use a shock that is also valved for the purpose, stock shocks work well on stock vehicles not modified vehicles.

Ok back on track I would suspect the box and if you are getting bump steer modify the drag link appropriately.

 

My cautionary comment was prompted by posts recommending the steering arm on the spindle, to which the drag link attaches, was much higher after the lowering job in relation to the drag link, therefore creating the upward angle of the drag link rear to front. Since it was ***umed the steering box and pitman arm were to remain in their present position, someone (or someones ?) suggested heating and dropping the said steering arm to reduce the drag link angle.

I was merely pointing out that doing so would hasten drag link interference with the axle beam as the steering arm rotated and that the OP should take that into account when considering following the recommendation. I did not suggest anything more than that. However, I am not sure a 'Z' in the drag link does anything to change the geometry of the steering linkage as much as it changes the appearance of it. It seems to me the relative position of the pivot points, not the shape of the connecting link, is the main determinant of the geometry.

Ray

 

I was just expounding on your comment.

You change the shape of the drag link to mimic the original angle on either end. Works like a champ; bump steer happens on vehicles with major changes in either direction. You lift one 6-10" for ground and tire clearance or you lower one 6" to fit in with the rest of the "slammer" crowd and you have seriously effected your steering geometry. On a parallel leaf suspension you change the form of your drag link to overcome it. Bending the steering arm lends to he problems that you suggested on a parallel leaf suspension.

One could apply this same concept to a lifted "g***er" with side steer. Back in the '70s before monster trucks were all the rage we did this with the street beasts once they got up to the nose bleed al***ude.

The Z goes in one direction for a lift and the other for a drop. I am not a suspension engineer but I have made a lot of cars drivable after the fact.

 

I would like to see pictures of the steering arms. I think they may be very flexable and causing the problems. As I said earlier, dropping the drag link arm would help with bump steer.
A Go Pro video of the suspension movement would be interesting.

 

Check caster, be sure steering box is good and double check those shocks are not already bottomed or nearly bottomed out.
Get that steering arm level.
Also do that Ackerman angle check previously mentioned.
I had a 59 F100 and boy in narrow highway lanes thru cities it was really hard to keep in lane...

 

The steering box NEEDS a rebuild. I just didn't think tightening up everything else would make me notice it quite this much.

I am leaning toward this. I plan to swap the engine in the future and a power box now might just be worth it.

What steering arms? The tie rod? The previous owner sleeved the stock tie rod with a stout piece of tubing. If that thing is flexing, then the whole truck is garbage.

Caster is high on the list. The p***enger side spring had a bunch of shims under it, but no rhyme or reason. There were angled shims, but placed both directions. I ***umed it was to correct height for the broken leaf. The driver had no shims.

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Everything I have researched says that the steering arm must be heated and bent when installing a drop axle. Again, I ***umed this had been done based the preexisting ride quality and the drop axle being there.
I've driven this truck for 3 years now before rebuilding the front.
I think what I did was open a box full of cats and I just need to get them all back in.

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Just to clarify, steering arms bolt to the back of spindles. Tie-rods bolt to the steering arms. Pitman shaft is the same as a steering sector shaft, and the dragline connects the right steering arm to pitman arm.

All these have nothing to do with ride quality, steering yes, ride NO.

Bending steering arms back down is to compensate for the drop axle. The spindle location is now higher which places the steering arm higher. This makes the dragline angle all wrong. Bending the arm back down corrects the dragline angle. Yours does not seem be correctly bent. The draglink should be almost parallel to the leaf springs

If the steering arms have the wrong size holes for the tie-rod ends, that should be a red flag that something is wrong. Any give at all will cause problems. If done right, no problem, but if done wrong say soft material, you are asking for problems. Look at these really close, have someone turn the wheel while you watch for movement. If the linkage moves and the tires don't, you have a problem.

All those shims under the springs is wrong, caster shims are tapered, 2, 4, 6 degrees, depending on which ones you have. Fat end goes towards the rear axle, they tilt the axle forward. You should have one per side unless the axle is servilely bent, then you would need alignment tools to figure out what is going on. Never should you have two per side. Be sure the center pin of the leaf spring is long enough to p*** through the shim and still locate in the axle center hole.

 

Gotta heat and bend your steering arm. I had an almost identical 58 with a drop axle and mono leafs.

 

I think there's a few things going on here:
1) Somehow the caster got affected either by the re-arcing of the main spring or otherwise. These trucks had minimal from the factory for lower speed steering and it wouldn't take much to push it to the point where it will want to wander depending on the bump/speed/etc. The dropped axle caster may be adding to this too.
2) You may need a stiffer shock to compensate for changes in the spring. Here’s a thread where a HAMBer did some some improvements on his truck. https://www.jalopyjournal.com/forum...upgrades-that-made-a-huge-difference.1067517/
3) You may be experiencing bump steer due to an imaginary line drawn between the ends of the drag link not being parallel to one drawn from the spring end to the axle. If these are not traveling in the same basic arc you will experience bump steer. Look at articles about cowl steering and straight axles - same basic principle applies here. Even with a Z'd link it is still pivoting around those end points.
All of these at times can give you that weird loose feeling when hitting a bump or being at certain speed.

 

Why is the drag link bent? It should be absolutely straight to minimize buckling.

EDIT IN: being kind in my comments, a "Z" in a drag link is a poor idea...

 

It has a factory bend. Alot of heavy trucks are bent, too. Probably to maitain level through the arc of the pitman.

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This is the starting answer. I feel kinda sheepish now that I didn't notice this before posting. Otherwise I'd have just taken care of it.
Again, my ***umptions based on previous ride quality and faith in the previous owner.

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Correct. I wasn't sure what Andy meant by "bendy" steering arms.
The old shims were way off and I ***umed I'd need to adjust that slightly, but whoa, was the change ever drastic!

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Rough steering is probably the box. As far as drifting, the caster is probably out of whack due to all the spring changes. Put in some wedges. Also, if you are running bias ply tires those will drag your truck all over the road following cracks and ridges on the pavement. Changing from bias to redials makes an amazing improvement.

 

By a Z do you mean a double bend, so it looks parallel to the ground? If so I don't get it, the angle between the joints stays the same. What am I missing?

 

The effective angle of the draglink remains the same but it squares up the end of the draglink so it doesn't bind at some point of its travel.

 

Yessir.
Shims are going in.
I find bias wander to be totally manageable. My cars have always had bias plys and I don't find the difference in radials to be worth sacrificing the look of bias. (The price of bias may make me change my mind soon)

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One thing I noticed was that the front shocks may be too long and you may be close to the end of travel. When you get in truck is there any shock travel left?

 

Put the axle inside the spring with stock springs by welding a plate with the 4 holes in it on the bottom of the axle, both sides, put the stock tie rod drop back on, check the axle to pan clearance and put all new rod end parts and king pins. Adjust the steering box in the center position or replace it. these boxes are known to go bad fast.

 

I have built 2 f1 pickups with sids dropped axles and tie rod drops. The I beam axles have zero caster built into them, they all have to be shimmed. Factory spec is 4 degrees, when you end up with a slight rake, you need to compensate for that as well. I used 6 degree caster shims on mine, this was with reverse eye springs and every other leaf removed,leaves polished and greased. I had to heat and bend the steering arm back to level as well, an adjustable drag link would have been nice (to center the pitman arm), but it was not needed. I messed with toe in a bunch, ended up at 1/32 in running bias ply tires. It tracked nice on the highway and rode smooth.

 

I did consider this a few years ago. A truck front axle on top of a spring looks unnatural to me, but hey, I'm a diesel mechanic.

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An adjustable drag link has been mentioned a couple times and you may find it to be a necessary addition to enable centering the steering box.

 

De arching your spring lowered the front of your truck, lowering a vehicle at the front will change the caster. I suspect that may be part of your problem.