JMortensen Posted June 19, 2006 Author Share Posted June 19, 2006 I'm not sure what the stock Ackerman is, but I believe it is close to 0. I know that when autoxing I drag the inside tire pretty bad. I think having a clevis machined would be more expensive than having the aluminum hex tapped for the 14 x 1.5mm, don't you? I mean you'd have to drill and tap the clevis for the metric threads on the rack, then machine the clevis. If they were just to drill and tap the hex for the 14 x 1.5, then they'd be done, and it would thread right onto the stock inner tie rods. It's pretty widely accepted that Z's handle better on the track with a LOT of static toe out (1/4" seems to be the going rate). I figure whatever Ackerman I can get will be an improvement on this as I will get dynamic toe out and can run static toe closer to 0. I was planning on getting as much as I could, then just running toe out until I don't get any more benefit from it. Since we've got the steering rack in front there really isn't much room to bend the steer knuckles laterally. I have to mock it up again, but I think it's only about 1/2" clearance before the knuckle hits the rotor. I had previously fixed the bumpsteer issue by raising the lower control arm pivot up 7/16". That worked fine and I was very pleased with the results, but I figure that if I can adjust the outer tie rod, then I can move the LCA up another 3/4" or so. This would allow me to try different roll centers in the front, but that means that I'd have to move the outer tie rod down 3/4" to minimize the bumpsteer. I'm not worried about the bending load on the bolt too much, the 5/8" bolt is way bigger than the stock tie rod and it should be 1" or less from the spacer to the rod end. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 19, 2006 Author Share Posted June 19, 2006 Still looking for some feedback on using the U-bolts... Quote Link to comment Share on other sites More sharing options...
Wiisass Posted June 19, 2006 Share Posted June 19, 2006 Is there going to be a joint in this hex stock? If not I highly recommend that you don't just thread that into the rack. You're going to need some type of joint at the rack so the suspension can move. Also about bending the 5/8" bolt, I've seen it done before on a 240SX with about 1" spaced down. That's why I thought I would mention my concern. It should just be an issue of making the bumpsteer spacers have a larger OD to take a lot of the bending load. When you say 0 ackerman, I'm guessing you mean parallel steer. About moving the outboard tie rod point laterally, I figured there might be some clearance issues, but depending on the length of the steering arm, you should still be able to get a little out of it. Your raising the inboard board LCA point correct? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 19, 2006 Author Share Posted June 19, 2006 Uh, yeah. There's going to be a joint. I'm not a retard. I'm using the stock inner tie rod end. The stock rack has 14 x 1.5 RH threads on one side and 14 x 1.5 LH threads on the other, which makes it harder because you'd need a RH and LH threaded tap to tap the hex aluminum. But the idea with the hex aluminum is to make a turnbuckle, which threads onto the stock inner, and a 5/8" outer rod end. This is the same idea that Cary had, except he modded a circle track 5/8" turnbuckle and welded in the 14mm threaded portion from the stock outer tie rod, so that would fit between the stock inner tie rod and the 5/8" rod end. I'm going to use the same bumpsteer spacers that everyone else in the circle track world does. I can't imagine that I'll have a problem. Sounds to me like maybe the 240SX needed a steering stop and didn't have one, so maybe it was using the power of the rack to try and bend the bolt or something. I've heard of people breaking tie rods, but never bending the bolt so that's just a guess. Right, parallel steer or really close to it is what the Z has. As I said before, I had already moved the LCA up. Now the intention is to move it up farther, but I need to move the tie rod down to minimize the bump steer. You can't move it too far with the stock crossmember, only about 1 1/8" from the stock pivot location, but I want to be able to use anywhere from stock to 1 1/8" up from stock and then space the tie rod to match if possible. Quote Link to comment Share on other sites More sharing options...
Wiisass Posted June 19, 2006 Share Posted June 19, 2006 I didn't think you were an idiot, i was just under the impression that you were trying to replace the whole tie rod rather than just the end. That is why I suggested the clevis. Alright, I see what your doing now. Tapping won't be too hard, either pay someone to do it on a lathe or do it at home on the vice and just be careful. If you don't want to be concerned with the bolt breaking, then that's fine. But I'm just bringing it up because when you space it too far the bending in the bolt gets very high. If your putting high forces through the tie rod, the moment your creating when you space down the outboard tie rod point too far can be higher than the bending strength of the bolt. It's a cantilivered beam, it should be something to be concerned with especially when you space it a lot. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 20, 2006 Author Share Posted June 20, 2006 Allergies are kicking in big time so I'm on mega doses of drugs today and I got about 4 hours sleep last night after attempting to drink myself into oblivion last night to get away from the itching. Probably shouldn't be doing anything with power tools at all, but it sucks even worse just sitting here being miserable. So I went out and tore up my spare rack and crossmember, and this is what I've come up with so far. This is just kind of mocking everything up to mount the rack with the clamps. I really think that mounting this way with the clamps is going to be plenty strong, and nobody has said otherwise, so I think this is the way it's going to go. I just tacked the brackets on to see what kind of height I could get on the rack. I measured the stock rack at 1 7/8" from the table to the bottom of the tube. When I tacked the brackets to the crossmember I got 1 1/2" inches. I could move the brackets up another 1/2" or so, but I can't really do anything in between. I think that moving them up would be better than leaving it where it is, because moving it up means moving the rack that much farther back, and the lower position will require more spacing on the tie rod end. I'm worried about rim clearance on the tie rod if I use a big spacer. I want to stay with 15's if possible. When I get the rack mounts finalized I'm going to cut a pipe lengthwise and weld it in to fill in the hole I ground out for the pinion housing clearance. One weird problem is that the rack doesn't appear to be sitting straight on the crossmember, or maybe the crossmember isn't straight. If you look at the last 4 pics you can see that the boot is going to interfere with the driver's side of the crossmember. They overlap by about 3/8". On the pass side they will barely rub. Don't know what to make of that. I'd hate to put the rack on crooked, and the mounts appear to be the same, and they're both welded to the crossmember the same way. I'm going to have to check that out really closely and try to measure as many ways as I can before I weld those brackets in permanently. The flange on the driver's side does appear to be about 1/16" wider than the passenger's side flange. Anyway, that will have to be dealt with when the time comes. Quote Link to comment Share on other sites More sharing options...
tube80z Posted June 20, 2006 Share Posted June 20, 2006 Allergies are kicking in big time so I'm on mega doses of drugs today and I got about 4 hours sleep last night after attempting to drink myself into oblivion last night to get away from the itching. Allergies here too. I know this all too well. I just tacked the brackets on to see what kind of height I could get on the rack. I measured the stock rack at 1 7/8" from the table to the bottom of the tube. When I tacked the brackets to the crossmember I got 1 1/2" inches. I could move the brackets up another 1/2" or so, but I can't really do anything in between. I think that moving them up would be better than leaving it where it is, because moving it up means moving the rack that much farther back, and the lower position will require more spacing on the tie rod end. I'm worried about rim clearance on the tie rod if I use a big spacer. I want to stay with 15's if possible. Some things to think about. Ideally you want the rack to be at the same level as the LCA inner pickup point. If not you'll get some bumpsteer from that. Did it raise a lot more than your pickup points? If you had studs that were in the crossmember you could use spacers under the rack mounts to move it up and down. Along with your slots this would allow for some variability in the front RC. But it may be a little hard to get the rack any lower that you currently have it. You can use a couple of plumb bobs to align the rack and crossmember. I have yet to see a Z that is straight as far as crossmember alignment is concerned. I think it has to do with how old the cars are these days. My bent race car had the crossmember cocked to try and straighten it out. You also need to weld a tab to the mount near the rack pinion. The aluminum appears to be pressed to the tube and I had one that came apart after a lot of use. You can bolt through the tab to the lower ear of the aluminum mount. Or that was the solution I used. You could probably drill a hole and use a set screw into the metal rack housing but that would be more work and the rack would need to come apart. I think you'll have to clearance more of the rack for the tie rod. I had to remove some of the flange on my old car. Be careful you don't have oil pump clearance when moving the rack. I had the motor set back and this was a major issue on my car. Cary Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 20, 2006 Author Share Posted June 20, 2006 Some things to think about. Ideally you want the rack to be at the same level as the LCA inner pickup point. If not you'll get some bumpsteer from that. Did it raise a lot more than your pickup points? If you had studs that were in the crossmember you could use spacers under the rack mounts to move it up and down. Along with your slots this would allow for some variability in the front RC. But it may be a little hard to get the rack any lower that you currently have it. I guess I'm not following here. The rack is currently 3/8" lower than it was before I started, I was going to raise it up so that it will probably be 1/8" higher than stock. I figured that as long as the tie rod and LCA remained parallel then the height of the inner pivot wouldn't matter. Am I missing something there? You can use a couple of plumb bobs to align the rack and crossmember. I have yet to see a Z that is straight as far as crossmember alignment is concerned. I think it has to do with how old the cars are these days. My bent race car had the crossmember cocked to try and straighten it out. I don't really know how to do this. I did the TC mounts by tape measure so maybe I'll bolt this rack in and do the same. On the TC mounts I measured from the center of the rad support, from the top of the frame rail, and from the bottom of the frame rail, and that seem to work out pretty good. I was kinda thinking about butting it up against a wall and trying to measure distance from the wall to the rack. Then measuring from the bottom of the inner tie rod to the table to make sure it is level. I can also change the spacers that locate the LCA to change the pivot position fore/aft if necessary. That's about all I can think of to do, so if you have instruction on how to do something better with plumb bobs I'd love to hear it. You also need to weld a tab to the mount near the rack pinion. The aluminum appears to be pressed to the tube and I had one that came apart after a lot of use. You can bolt through the tab to the lower ear of the aluminum mount. Or that was the solution I used. You could probably drill a hole and use a set screw into the metal rack housing but that would be more work and the rack would need to come apart. This I can do, thanks for the heads up. I think you'll have to clearance more of the rack for the tie rod. I had to remove some of the flange on my old car. Be careful you don't have oil pump clearance when moving the rack. I had the motor set back and this was a major issue on my car. Engine is in the stock location. Not moving it as the plan when I blow it up is to go to an LSx so it just isn't worth the hassle to move it at this point. Once I get it all figured out I'll check clearance on my engine which is on the stand right now. I have the AZC aluminum pan, but I'm not going to be raising the rack very much, so I'm hoping that this won't create any issues. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 21, 2006 Author Share Posted June 21, 2006 Went back out and figured a couple things out. First I flipped the mounts around and found that it doesn't work that way, the tie rods are hitting the crossmember. I also figured out that there is only about 6" in the middle where the crossmember is straight, and I had previously had the clamps in the beginning of the curved area. So I moved them into the straight area of the crossmember and now it's just barely different at one end and the other with respect to the boots rubbing. I think basically I didn't have it straight before because of the curve in the crossmember, now its closer but still not exactly right. So I'm going to play with it a bit more, but I think its basically going to come down to setup before I weld. I think the crossmember is pretty straight, and I will definitely have to grind some of that flange off the ends for clearance. Quote Link to comment Share on other sites More sharing options...
Wiisass Posted June 21, 2006 Share Posted June 21, 2006 For zero bumpsteer, ideally, you would have the inner lca pivot at the same height and lateral distance from the centerline of the car as the tie rod pivot. Then the outboard points would also be at the same height and distance from centerline. This will assure that the outboard points move the same amount. Just having the arms parallel won't work. You have to take into consideration the inboard and outboard points for the LCA and the tie rod. You should be able to find the exact location everything needs to be with a simple kinematic analysis. I've seen several different methods for solving this in different suspension books. One way is to determine the instant center of the LCA, tie rod and strut. It's actually for an SLA suspension, but since we're talking MacP, I'm guessing using the line perpendicular to the strut axis as the top line is fine. This will determine the angle that you want the tie rod to be. Once the angle is determined, you need to figure out the length and where the pivots will be. This can be done graphically. Since you're working from a car that already exists, your constrained differently. Are you considering changing the inboard tie rod pivot location? If so, that gives you another place to play with. If not, then you'd be best to just make sure the tie rod follows the line that it should and you might have to accept whatever bumpsteer is now inherent in the suspension. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 21, 2006 Author Share Posted June 21, 2006 That hasn't been my experience with bumpsteer Wiisass. The inner tie rod is nowhere near the LCA pivot on the stock rack on a Z car. I just took a quick look and I would estimate that the centerline of the inner tie rod is about 1.25" higher than the stock LCA pivot hole on the crossmember. Same deal on the outer end, the tie rod is higher than the ball joint. I don't think that it would be physically possible for me to move the LCA into line with the inner tie rod with the stock rack mounting, even with a rod end pivot on the LCA. There just isn't enough room inside the crossmember for that by the looks of it. I don't think I'll be able to do it on mine even with the rack slightly lowered. I fixed the bumpsteer previously by moving the LCA pivot up 7/16". I did this on a home made bumpsteer gauge, without using any modeling software. I just slotted the hole and moved it up until the bumpsteer went away. Did the same thing on both sides, and it turns out my front suspension wasn't bent so it was the same on both sides. I was able to move the suspension thru about 3" or 4" of travel with no sign of toe change whatsoever, so I called it good at that point. As long as the LCA and tie rod follow the same arc the bumpsteer should be eliminated (on macpherson strut suspension) as far as I know, and that was the case with the previous setup insofar as I tested it. I'd like to know if there is more to it than that, but if you or Cary can put it in plain terms that would be great. I know Cary has this idea to have the rack and LCA move together which would keep the angularity constant, and I think that was part of what he was talking about. I won't be doing that this time around, so my emphasis is on getting the Ackerman in there and getting the bumpsteer minimized again. What I can do is measure the change in the LCA pivot height and add an equal amount to the bumpsteer spacers at the tie rod end, so that was the plan. Quote Link to comment Share on other sites More sharing options...
Wiisass Posted June 21, 2006 Share Posted June 21, 2006 When I was talking about having them both at the same height. That's just ideal, it makes things a lot easier. Like if you had complete freedom in where the pivots were, but I know this isn't the case with production cars. I might have been mistaken about things being parallel and being close enough to not matter. Without plotting all this stuff, it seems like if the arms are parallel and the inboard and outboard lateral locations are close for the tie rod and lca it will work out pretty well. It's when those locations are different where it will start to hurt you. For example, if the tie rod pivot is an inch further outboard that the lca inboard mount, then the arcs will have different radii and it will create some bumpsteer at the top and bottom of the travel. I think that's right, I'm trying to picture all of this in my head. It should be pretty easy to do this graphically. You would just need the distance from pivot points of the tie rod and lca and then the height differences of the inboard points and the outboard points. And then just use a compass to trace an arc for each. You would then need to draw vertical lines at several different points on each arc, you could do it at points that represent a half inch in vertical wheel travel and then measure the distance. If the distance stays the same between the two lines throughout the range of travel you should have no bumpsteer. But no matter how you do it, if you measure it and it measures zero or very little bumpsteer then it's working fine. Depending on how your adjusting ackerman, you could do it so bumpsteer is minimally affected if at all. By moving the rack forwards and backwards, if you keep the inboard pivot at the same height and lateral position and the outboard stays the same as well, then there shouldn't be much if any increase in bumpsteer from the previous setup. You mentioned something about the LCA, what are you planning on doing with that and was that in reference to the Ackerman changes or to the bumpsteer adjustment? if it's the bumpsteer part, then don't worry about explaining it, but if it's for ackerman, I would be interested in what your trying to do. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 21, 2006 Author Share Posted June 21, 2006 I was more thinking that I could move the LCA pivot fore/aft to try and compensate for any bend in the crossmember, but I really don't think that's a problem with the one I'm using after looking at it again yesterday. I think the rack wasn't straight because I just welded the brackets on in the wrong spot. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 21, 2006 Author Share Posted June 21, 2006 Got the brackets welded on. What I did to ensure straightness was to pull the boots off and pull the rack all the way to the left. I measured the distance from the crossmember to the inner tie rod. I also measured from the bottom of the inner tie rod to the table. Then pulled it all the way to the right and measured the same dimensions. Right off the bat it was pretty close, with about 1/16" difference in the tie rod to crossmember, and about 1/16" difference on the tie rod to table. So I welded the brackets on, then used a scotch brite pad inside the bracket to fix the difference. It took a while, but I now have the inner to crossmember dead on at 1 3/16", and the table to inner is off maybe 1/32" higher on the passenger side at 1 19/32" vs 1 9/16" on the driver's side. I also measured these dimensions on the stock rack and the passenger side tie rod was 1/8" lower than the driver's, and the other dimension was off 1/16". I guess that's probably just a bit of settling in the rack bushings. So mine is more accurate than the stock rack dimensions, and obviously won't have any bushing flex. I also gave clearance for the rack boots. That was pretty easy to do with a grinder and a sanding disk. Now all I need to do is fill in that hole in the crossmember with some pipe. I will also have to open up the centermost holes in the bottom of the crossmember to access the nuts inside, and drill out the holes for the U-bolts. Then I can measure it all up again and make sure its still all correct. I'm a little concerned about welding the pipe in, think I might bolt the crossmember into the frame before I do that just to prevent any warping. Quote Link to comment Share on other sites More sharing options...
tube80z Posted June 22, 2006 Share Posted June 22, 2006 Sounds like you have it nailed Jon. For welding the pipe I would clamp it to a section of you TC tubing if you have any left. That should be good enough. Cary Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 23, 2006 Author Share Posted June 23, 2006 Alrighty then. Done with the crossmember, unless I need to grind some of the welds around the slots flat. I did bolt the crossmember in and weld in the pipe. Just some oddball 2.5" pipe I had laying around, worked pretty good though. Then I made the stop for the rack. For this I just used 1" wide piece of angle iron. It fits right in where the bushings go on the rack. Also you'll see that the clearance between the pinion housing and the pipe is pretty close, basically I don't think the rack is going anywhere. I then slotted the holes on this crossmember and made some 1/8" plates to go over the slots. This was something I had intended to do on the last crossmember and never got around to. I was just running a washer on both sides of the slot on the last one, not really good enough, but luckily for me it never caused a problem.First pic is an overhead shot so you can see how the rack moved. I think I'm going to call it good and not mess with bending the steer knuckles for any further Ackerman. Too much hassle and I don't have an oxy/acetylene torch. Quote Link to comment Share on other sites More sharing options...
Guest SS-Z31 Posted August 1, 2006 Share Posted August 1, 2006 In a search for some more info on bumpsteer and ackerman steering geometries I came across some potentially useful things... This doesn't talk about Datsun specific suspensions but the general info might be useful to someone... http://www.steeda.com/PR/Mustang/techQA/BumpsteerInstallation.htm http://www.auto-ware.com/setup/ack_rac.htm http://www.eng-tips.com/viewthread.cfm?qid=117106&page=1 GOOD stuff http://www.auto-ware.com/software/asgp/asgp.htm some suspension software Quote Link to comment Share on other sites More sharing options...
tube80z Posted August 2, 2006 Share Posted August 2, 2006 If you're looking for a single thread that sums up everytyhing that I've seen on Ackmerman it is http://www.clubracer.com.au/articles/ackerman.asp Cary Quote Link to comment Share on other sites More sharing options...
JMortensen Posted August 2, 2006 Author Share Posted August 2, 2006 Well I'm finally ready to dive back into this, so it's kinda nice that the thread just popped back up all on its own. Got the coleman racing swaged tubes in a few days ago. Got a set of old tie rods to cut up. First thing I did was to cut the threaded ends of the tie rods off. I cut it a little long, so I ended up including a bit of the curve that is on the stock tie rod at the end. I then ground that curved end off. That's where I'm at now. What is immediately apparent is that the end is larger OD than the ID of the tie rod. Cary, what did you do about this? I know you said cut a slot down the side of the tube, but it seems like the thing to do is to grind down the OD of the tie rod so that it slips into the tube. The pic that you showed of Kipperman's car is small, but it looked to me like the tie rod was a lot smaller than the tube and the tube had to be crimped down to fit, so I was pretty surprised when I found the opposite this morning. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted August 2, 2006 Author Share Posted August 2, 2006 Well I took my grinder with a sandpaper flap wheel and I've "turned" the end piece down. Turns out those end pieces aren't really tapped straight, probably because the only part that turns in the stock piece is the inner end, so if the outer end isn't straight it doesn't really matter. So I've pretty much got the end to where I can weld it on. Plan is to do 4 plug welds, 2 far, 2 close at 180 degrees from each other, then weld around the top. I think it will be strong enough. Cary had told me to preheat the pieces, but I can't find my MAP gas torch and I don't think the propane will heat it enough to make much of a difference. Besides, the wall thickness on the tubing is only ~.080 or somewhere thereabouts. I'm going to start grinding the other side down, if anyone wants to stress the importance of preheating, do it now because I probably won't get to welding this stuff until tomorrow I'm thinking... Thanks all. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.