On my rod project, I'm running radius rods w/ heim joints; a typical t bucket set-up with solid front axle with a leaf spring. Anyways, if I turn about half-way either way, a wheel will start to want to turn the same direction by itself. Once it starts, I can't stop it, unless I stop the rod or turn the opposite way before it gets too bad; rather like it's being directed there on its' own. It dramatically slows the car down as well as may overturn it at any speed above 25mph. I am assuming it is due to a very bad caster angle. Anyone experience this?
Have you got any steering "stops" on the upper rear backing plate to spindle bolt? Excessive camber like on a dragster comes to mind as others said. Charlie
Are you doing this on jack stands or real time test driving? Sounds like it has to be up in the air with no load on suspension or tires for it to be 1/2 turn in or out and tire starts to turn based on radious rod length. Caster / Toe in & out? Sounds like a busy front end. You probaby already know this, but just incase. The only way you could be flip flopping (like a dragster) moving forward, is to have negitaive caster. Dragsters are set up with -7 to -9 deg caster and only flip flop the wheels / tires in reverse. Positive caster is top of king pins leaning back towards the rear tires. Start with axel strait and leave it alone at the rear radious hime joint, then do all caster adjusting the top or bottom hime joints in at the axle until you have negitive caster. Once done set the toe out. Good luck!!
By posting a photo of your front end,we can get a idea of what you got wrong. It's much faster then asking you many Q's .
Top of the kingpin leaning backwards toward the rear is positive caster. Dragsters run large amounts of positive caster.
It doesn't flop, it starts to drag a tire after I turn. The caster is neutral at best, unlike a drag car. It does it when I drive it, even at 2 mph. There are no steering stops. Originally I was aiming for a heavy amount of + camber, but the radius rods were too long and I couldn't adjust enough to get that out of it. I'll have to cut something shorter I'm afraid to be able to move it around properly. Although, it just hailed like there's no tomorrow here, so another day. I don't have any pics of the front end just yet, sorry. i'm going to try my best to work with the geometry I have and go for what you all say, more + caster. Toe in/out is normal, until it starts to pull, then obviously it's toed-in. Right about flopping only in reverse, that's what I was aiming for, but it's a tad hard to make it stable right now, I'll be working on it! Thanks everyone! Yeah, that's what I was thinking, anywhere from 6-9 degrees positive caster. I'm pretty sure the scrub radius and inclination would be fine once caster is set too.
If the toe in is changing your tie rod would have to be flexing. I'd be looking for something in the steering that is getting in a bind on turns. Or making sure that the tie rod and the rest of the steering was heavy enough to do the job. A tie rod that works great on a T bucket with 4 inch tires might not work right on a larger car with 7 inches of tread on the ground. I was also thinking Akerman issues on this one. Is the wheel base quite a bit longer than the car that the front end was origionally on? The front and rear wheels may be wanting to turn in different arcs and causing the problem. You could check that by finding an empty parking lot where you could run through a patch of water and then make a turn to see how the rear wheels track the fronts. There is a good explanation here: http://en.wikipedia.org/wiki/Ackermann_steering_geometry An article in the Natonal T bucket alliance http://www.nationaltbucketalliance.com/tech_info/chassis/ackerman/Ackerman.asp
I can't get pictures right now, as it's super wet and cold. Exactly, whatever it causing it to scrub is flexing the tie rod. I might double wall that soon actually. It's actually on a t bucket, and the tires are about 4.5" wide on Halibrand spindle wheels. The weight distribution is about 56/44 F/R. Ah, I meant I was "aiming for heavy + CASTER. Sorry about that.
as stated before sound like too NEGATIVE caster and an ackerman issue! see the new HRM Pit Stop column on that or on here, and post some pics of this setup so we can see if we can get ya figured out! Is this a cross or traditional steer style car??
I'd say a quick set at 1/8" toe in and 6 degrees Positve caster should help a lil along with bracing that tie-rod!
Your post #13 sound good to me! That's probably what I'll end up doing (if I can get up to 6 degrees + caster). It's traditional steering, push pull from front to back. The pic I have is not that great from when I stripped the frame.
Thats how I run mine stable enough at 125mph and still steet driveable! I had problems with my traditional steer setup flexing the tie rod too but when I redid the front end I went with a cross steer setup. Yeah I'd just set it up and trim what you gotta to get the 6-7 degrees positve caster and run that then I was wondering if it was a cross steer setup cause I have seen some geometry between the center and drag link cause some binding if not parallel but that doesn't apply in your situation! Good Luck-Paul
I just quickly skimmed this post, but someone up the way said Akerman issues... We have a winner! With you tie rod out front and and the angle on your steering arms combined, you have a situation where you wheels are steering on different, non complimentary arcs. In a normal Akerman situation, the inside wheel will turn in a tighter arc than the out side wheel to track evenly throught the turn. Where your at, one wheel is turning so far out side of the natural arc that it is dragging or "over centering" and not letting the wheels return forward. This could be solved one of two ways, Either turning the spindles around so that the tie rod is behind the axle where the arms are fairly close to being rightly posistion, or making a wider tie rod and bending the steering arms out ward beyond the king pin axis... I would say the first would be a bit easier. If this is truly a drag car that will not be called appon to go through turns on a daily basis, you could just limit the spindles turning radius so that it can't turn beyond the point where it "locks". I always prefer to side with correct geometry rather than band aids myself though. Never know when having things right will save your tail.
If you look CAREFULLY at the frontend on my t-bucket, you can see how the ackerman has been corrected to allow the use of a tierod out in front of the axel. The steering arms must 'point' to the center of the pumpkin to get the arc proper.
I looked very carefully at this one and have to conclude that ackerman has not been corrected. To get the straight line through the tie rod end and the king pin to align with the centre of the rear axle would demand the tie rod end being about 2"-3" closer toward the disc. At the moment that imaginary line probably goes outside the rear tires. Check the schematic below.
The thing is with this car my spring hangs instead of being normally set-up like choppedtudor's rod's spring. I don't think I have enough room under the frame to flip my tie rod around. I can bend the steering arms, but what exactly does having them outside of the kingpin axis do when they would be inside that axis when the wheels are turned? Right about a band-aid. I don't want to be on a freeway, make a lane change, and have it flip. Been there, done that (not my fault though, vehicle was faulty). Crushed my ribcage mid-last year after the thing rolled on top of me (topless car). Not able to move much at age 24 for 6-8 weeks stinks; I'll say that much. Thanks for all the info guys, I really appreciate it. (I'm fine now though, more or less). =) @ choppedtudor: I don't understand why having the arms point to the diff makes it work differently? I thought as long as the point in space where the tie-rod end connects in relation to where the spindle base is, is what really counts? In other words, you can eat from a spoon, even if it's bent type of thing, as long as the end of the spoon and the handle line up. Or did I miss something? Aren't your steering arms inboard of the kingpin axis? Very nice rod by the way. Then again, I think the steering arms are adjustable with a locking nut on the rear to allow rotation! Ill look as soon as I can! *fingers crossed* If they are, then can I just rotate them until they are parallel or slightly outboard of the kingpins?
Oh ouch, I don't think I can go that far with the bending, haha. I'll look into limiting it slightly and bending/adjusting them as far as they'll go. I won't bend anything until I'm sure it will help, and if I'm not sure, I will go with trying to flip the tie rod behind the axle instead, as from the diagram you provided, that's what it was set-up for originally, but some joker decided he knew more than anyone else and built it wrong...
OH! I just did some visual steering in my head and I can understand why it works now to turn the outside wheel less! Love it when that happens... The outside wheel makes a larger arc, and that's what Akerman is all about right? I hope I can get it right with the geometry I have. It's almost like an elongating lever idea. The longer it is, the more leverage, and the less it moves on the outside wheel. Apparently, mine is working backward of what it's supposed to be.
(I typed too slow while you since figured it out) That's not what was meant. You need the imaginary line from the center of kingpin and the steering arm tie rod mount hole, to travel back from each side and end up at the center of the rear axle. It's a goemetrical equasion by the Ackerman dude This makes the car be able to go from 1/8" toe-in when straight, to ever-increasing "toe-out at turns". Toe-out at turns lets the two front tires turn at different turning circle diameters, which is what you want. You want the toe-out to keep increasing as you turn a even tighter circle. With the Ackerman angle being exactly reversed, one tire will fight the car. My son has an antique tractor like that, and one tire will peel the sod on the lawn in a turn, no matter how careful or slow he drives.
You are correct. The Ackerman on that T has not been corrected. I have seen this many times where the arms are bent so they point at the pumpkin, but the center lines of the tie rod ends and the kingpins are not in a straight line as shown in the diagram. Sorta like the guy who wanted to build a stepped or Z'd drag link so it would be parallel with the radius rod and, therefore, eliminate bump steer. You can't mess with the imaginary line
Now you've got it! Its about the relative degree of turning, when a car turns the 'pivot' point is the centre of the rear axle, the front wheels have to follow a relative arc around that point, if your ackerman is wrong, the arcs are off, and one front tyre will scrub, or put forces back into the steering that will cause what you experienced.
Get the geometry correct. If you don't understand the relationships, then seek someone who does. I may sound like I am coming on strong, because I am. Your life and that of anyone who may come near your car is in jeopardy. The advise and info that has been posted needs to be seriously considered. Good luck.
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