CPP / Speedway PS conversion pics?

[mknittle]

i am not sure what the difference would be. Jeeps and solid axle 4wheel drive trucks trucks are all in front.

[mknittle]

I just looked it up in the herb adame chissis engeneering book. forntvs rear steering:"if all componentsinthe steeringsystem including the framemounting were and free of playit would not matter whethera carfront orrear steer"
I got to thinking if yoy made a steering arm of equal lingthes frim the center of th king pin one going to the back and the other to the front both left and right woth a tie rod on the front and one on the back it eould not inind because the arme are equal. so why would it matter what end the rod is on all things being equal?

I am not argueing just trying to see a reason it wouldnt work.

[mknittle]

Sorry about that i got into a fight with the computer and it got the upper hand I am a terable typist and when i went back to edit what i wrote all hell broke loose it should read more like this

I just looked it up in the Herb adams chissis engeneering book. fornt vs rear steering:"if all components in the steering system including the frame mounting were solid and free of play it would not matter wheather a car was front or rear steer"

I got to thinking if you made a steering arm of equal leingthes from the center of the king pin one going to the back and the other to the front both left and right both with a tie rod on the front and one on the back it would not binde because the arms are equal. so why would it matter what end the rod is on all things being equal?

I am not argueing just trying to see a reason it wouldnt work.

[yossarian19]

Hmm.
I don't know.
I'm having trouble conceptualizing how an ackerman angle is measured and how it would change if I flipped the steering arms around to put the tie rod in front of the axle instead of behind.
I tried my google-fu out on the problem and the terms "tie rod flip" bring up tons of results of people moving their tie rod higher (rock clearance, 4x4 guys) but not front to back or vice versa.
Worst case scenario, I try it out and discover my tires scrub, then switch to an F-body oil pan, put the steering back where it was & maybe add a leaf to the front packs.
Either way, this is probably not going to happen for a little while yet.

[mknittle]

this is pretty much it http://en.wikipedia.org/wiki/Ackerma...ering_geometry

[1project2many]

That's correct, but you will never see a straight axle truck with the factory steering box located on the shackle end of the spring.

Chevrolet and GM Trucks decided early on to put the fixed point of the spring on the same end as the box. This didn't stop other GM divisions from putting box and floating end together on cars, however.

Lots of homegrown steering setups work well enough for the driver and I don't argue against a vehicle that's safe, consistent, and driveable. Often what we build is a compromise between "right" and "good enough." But many people just don't know or understand "right" which means they get stuck if "good enough" doesn't work.

Regardless of which end the box is attached to, the axle always moves farther from the fixed point as a leaf spring compresses. And it always moves toward the fixed point as the spring is placed in tension. If the drag link is placed in parallel to a line drawn from spring eye to spring eye you will always have bump steer. Always. It may seem small because the change in effective length of the drag link is small but it will still bump steer. If your steering is loose, or you have a typical manual steering wide ratio box you may not notice it. Especially if you've made a change from a system which had dramatic bump steer. But it's there.

By lengthening the drag link you are lengthening the amount of vertical travel allowed before the change in effective length of the link becomes dramatic. You still have bump steer, you are just doing a better job of keeping it small through the range of vertical motion. Parallel, long link is a safe rule of thumb for guys setting up an axle who do not, or cannot, work out the geometry of the system.

However, by calculating the change in forward position of the axle as the spring moves through it's vertical travel one can determine proper angle and length of the drag link so the link will track the axle well through it's range. From that point it's a matter of doing your best to build the system so it matches the design.

20years as a CNC machinist building most ly one off scintific testing machines.

You must have built some cool stuff. I've known machinists over the years who've worked in production shops spending week after week making the same part. Ugh... I couldn't do it. Among the things I've done over the years I count the ten years on the pit crew of the vintage roundy round car as some of the best. We had a car that could turn times with late models and even modifieds on the short tracks thanks the the handles. Couldn't keep up on the long tracks... hard to out power a guy with 3X the engine budget and 40 year newer technology. We tried a lot of different things over the years and really, until the whole thing was done we never stopped playing with ideas. Sometimes we tried working in bump steer so it turned left on it's own, sometimes we pulled it out. Lots of different stuff. Even swapped out the beam axle for a modified Ford twin I beam at one point. Bad juju there. Ford indie truck suspension = bad, bad, bad. But maybe that was my semi-scientific testing machine??

Bump steer (change in wheel orientation due to unintended linkage interaction from vertical suspension motion) is just one aspect to consider. All you guys putting on fatter radials and improving the brakes... has anyone ever stopped to consider how the axle torques and the springs wind up under braking? This also causes the wheels to turn. Anyone consider adding strut rods? Are they a good idea? And now we're talking about the Ackerman angles and mainting factory relationship but is that really the best thing to do? How do you know the factory setup was right? Hmmm?

Ackerman is the result of the change in effective length of the distance from kingpin to tie rod as the spindle rotates. A person might have luck picturing this by imagining the tie rod end attached to the spindle in a slotted hole. As the tie rod is moved closer to the kingpin, the spindle will turn through a greater arc when the tie rod moves. As the tie rod moves farther away, the spindle moves through a smaller arc. This is how the natural change in distance from spindle to tie rod changes as the spindle rotates. Engineers calculate where to place the tie rod so this natural change works in the truck's favor and keeps the wheels tracking close to what they really need to be during a turn. Since there was only one spindle available for several different wheelbase trucks, you know darn well there was a big compromise going on there.

Anyway, tie rod back or front doesn't change Ackerman by itself so front steer or rear steer, either works. A spindle is formed with tie rod attaching points inboard of kingpin. As mounting point is rotated away from center of truck the distance from kingpin to tie rod increases (tie rod moves "out" through slotted hole). As mounting point is rotated toward the center of the vehicle the distance from kingpin to tie rod decreases (tie rod moves "in" through slotted hole). The effect is that a wheel rotating away from the center of the vehicle (as observed from front of wheel) turns more than the wheel turning toward the center of the vehicle. Regardless of whether the attaching point is on the front or rear of the vehicle, as long as the attaching points are inboard of the kingpins this will happen.

If you or I angle the shocks and ride improves the shocks are too stiff cantilevering {angeling} gives the axle leverage aginst the shock makeing its dampening less effective the more angle the less effective the shock.

But... Remember the previously mentioned axle roll during braking?? Changing shock angle can help dampen this effect. As the front end dives during braking the shock applies force to the axle. If the force is purely vertical it can only work against the vertical motion of the spring. If some of the force is directed horizontally it works along the strongest part of the spring and helps the spring resist torque.

And just maybe that's the reason the steering box is attached on the same end as the fixed spring eye. If you start with the idea that the box had to attach below the cab, the question is where to attach the fixed point? If the fixed point is in the front, as vehicle dives during braking the axle moves toward the box and the vehicle tends to steer left. But with the factory dropped axle combined with larger weight on trucks, brake torque can cause a fair amount of axle rotation which in turn causes truck to steer right. The combination of truck vertical motion from weight transfer and axle rotation from torque is much harder to keep consistent. In order to prevent the left turn from winning over the right turn, the fixed point was placed in the rear where the truck will always self steer right whenever it's braked heavily. Previously mentioned swap of box and fixed point to front of axle creates self cancelling effect during braking. If gemoetry is right this combination can stop hard with little self steering.

there is no reason to make it more complicated than it is.

You know, if we just attach a steering rack to the axle and put a sliding pivot joint between axle and frame that will completely eliminate any need to worry about bump steer or brake torque steer.

[Denee007]

My photo from up above, since that photo, I had moved the steering gear forward 6"'s in an attempt to lessen bump steer. I had Sid@dropped axles make me a new drag link or the adjustment sleeve. The photo shows a steep angle placed on the pitman arm, the truck is up on jackstands allowing the axle to sag, but when on the ground is much better, plus no engine/transmisson is installed. I may have Sid twist my pitman arm for less angle on it, but not there yet. ; )

I was looking at the rack with the sliding pivot joint, but "they" were saying it would have bump steer too! I forget who "they" is! lol I should have gone by my first instincts.

[mknittle]

project2many,
All good points. i apologize for being onery The medication or brain surgery makes me that way. and i hate it!

Any way the rack and pinion of the right ratio could be a cure all for alot of situations.

it's all a compromise any way ya do it sometimes the tough part is picking the best one.

Yeah, I really miss the way that machine shop was. the shop and the office/main assembly were 15 miles apart. the best few years there was just me and one other guy. we got along really good too. I did most of the mill work and Scott did most of the lathe work there were times that we didn't see the boss for a month!
One of the biggist machines we made was a 4 axis load frame for John Hopkins university.Used for plate tectonic studys {our nick name was the earthquake machine}
I forget how many hunderds of tons it pressed. It was 14 feet high and a bit wider.it was ran by two desk top computers that interpreted what our computer did. The computers fit into a 4'X4'X6' cabnet
all made in by our sheet metal/fab guy.
The hard part was it had to be designed so once build it had to come apart in pieces small enough to fit in a frieght elevator to go in a below ground level and be re assembeledexactly as it was.
The way it works is they take a block fo specil formuleted plastic of a known dendensity and fracture it under controlled conditions. then x-ray it then using our machine put very controled pressure untill it shatters then study it.I like to say there are parts all over the world that have my fingerprints on them.
enough hijacking the thread

[Russell Ashley]

" A spindle is formed with tie rod attaching points inboard of kingpin."

Well I wasn't going to make any more comments on this thread but the above statement is only true when the tie rod is behind the axle. In the case of a front tie rod the tie rod attaching points on the steering arms are by necessity outside of the kingpin. Refer back to one of the previous posts describing the ackerman principle.

The ackerman principle is seldom if ever perfectly adhered to by manufacturers but it can't be too far off or excessive tire scrub and wear would result.

[yossarian19]

I'm learning a lot from all the comments back & forth.
I still haven't decided on how to make this all work.
From looking at my Jeep parts under the work bench and the Chevy parts on the truck, I can see that they do design things differently for a front steering vs rear steering axle. The Jeep parts have the steering axis to the inside of the steering point, the Chevy has the kingpin outside the steering point. Though there is def. compromise from the manufacturer depending on wheelbase (the same parts are used on different wheelbases) I'm going to assume that inverting the ackerman angle is not going to work the way I want it to. So, no steering flip for me - I'll figure something else out to clear the oil pan.
That leaves a new oil pan, lift springs, or a new front axle as options. I suppose the other item on the list is to drop the motor in place & add a spacer between the bump stop and frame, bounce up and down on it and see what happens.

[yossarian19]

So, if I haven't said it before: thanks, folks, for all the replies! It goes a long way with me to be able to learn from others this way. Much appreciated.

[mknittle]

This is how my jeep is set up. I don't have problems with bump steer but the locker in the rear and the springs being pretty close together can be exciting at times

[1project2many]

mknittle, wow. And cool machine. Again wow.
I've got thick enough skin that a bit of ornery doesn't hurt. No worries.

" A spindle is formed with tie rod attaching points inboard of kingpin."

Well I wasn't going to make any more comments on this thread but the above statement is only true when the tie rod is behind the axle. In the case of a front tie rod the tie rod attaching points on the steering arms are by necessity outside of the kingpin. Refer back to one of the previous posts describing the ackerman principle.

Yep. I screwed that up. Realized what I'd done while I was pulling a trans and transfer case today. I have no justifiable reason for making that mistake although maybe getting chewed out by my wife for drawing chalk circles on her kitchen floor had something to do with it. Sheesh... I told her I'd clean it up.

Denee007, if you attach a rack to the frame you will have issues. It won't be bump steer. It will be changing toe with axle movement. Like the parallel drag link, you can play with geometry to try and minimize it but it is going to be there. If you attach the rack to the axle there is no change in geometry because the relationship between the steering rack and axle never changes. The only issue is to allow for the rack to move fore and aft and vertically with slip joints and U joints. High end over the road trucks are built like this. Supermodifeds run this way, too, and you know steering better be right on an 800 hp car doing 140+. With this article as a guide, I'd bet a guy could build and install an axle mounted rack then sell the CPP parts to recover some $$.

Freightliner truck with rack and pinion "on the beam."

[mknittle]

They also run those stupid azz hub pilot wheels!