Mikelly Posted January 19, 2001 Share Posted January 19, 2001 Welded up the perches for the coil overs last night and started to put hte assemblies in the rear back together when I found a broken adjuster on the right rear strut was broken... Looks like I'm gonna be ordering some rear struts... I'm selling one "Like New-low mileage" Koni D series adjustable rear strut if anyone needs a spair. If you currently have these, Koni doesn't make them anymore (As I found out) so you might want to think about an extra... Moving onto doing the bump steer mod and the rest of the welding... I ordered up some straight tubing from S&W for $2.28 per foot, total of 40 Ft. to do some more structural support. Mike ------------------ http://hometown.aol.com/dat74z/myhomepage/auto.html "I will not be a spectator in the sport of life!" mjk Quote Link to comment Share on other sites More sharing options...
Evan Purple240zt Posted January 19, 2001 Share Posted January 19, 2001 Mike, bummer dude that really sucks when you find out something like that has happened. Ususally its either an expensive part, or a cheap one you have to wait forever for LOL. Please fill me in man, what is the bumpsteer mod you are speaking of? Inquring minds want to know Thanks buddy- Evan Quote Link to comment Share on other sites More sharing options...
Mikelly Posted January 19, 2001 Author Share Posted January 19, 2001 Evan, Per Jags That Run you take the bolt hole on the front crossmember where the control arm bolts in and you move it 7/8th inch straight up. This allows better geometry for the front control arms and cures some of the bumpsteer issues! Mike ------------------ http://hometown.aol.com/dat74z/myhomepage/auto.html "I will not be a spectator in the sport of life!" mjk Quote Link to comment Share on other sites More sharing options...
Modern Motorsports Ltd Posted January 19, 2001 Share Posted January 19, 2001 quote: Originally posted by Mikelly: Evan, Per Jags That Run you take the bolt hole on the front crossmember where the control arm bolts in and you move it 7/8th inch straight up. This allows better geometry for the front control arms and cures some of the bumpsteer issues! Now is it the same effect to put a 7/8's spacer under your strut b/t control arm end instead? (assuming your wheels clear etc..). This should achieve same geometry change. Are your front coilovers installed Mike with top hats? Just wondering if your struts/control arms are in their final position/configuration yet to see how it all settled out to do your final bumpsteer mods etc? Quote Link to comment Share on other sites More sharing options...
Mikelly Posted January 19, 2001 Author Share Posted January 19, 2001 Ross, My perches have been welded, but I haven't assembled the springs yet. I'll get to that this evening or over the weekend. Interesting side note, I mounted the camber plates I got from Randy in the rear since I already have adjustable control arms up front. I'll keep the aluminum camber bushings in the rear only to aid with toe issues. Mike ------------------ http://hometown.aol.com/dat74z/myhomepage/auto.html "I will not be a spectator in the sport of life!" mjk Quote Link to comment Share on other sites More sharing options...
Danno74Z Posted January 19, 2001 Share Posted January 19, 2001 Mike, A couple of questions for you. 1. Are you sectioning your strut tubes. 2. If the front suspension has a bumpsteer issue does the rear suspension of the Z have this problem? Danno74Z Quote Link to comment Share on other sites More sharing options...
pparaska Posted January 19, 2001 Share Posted January 19, 2001 quote: Originally posted by Ross C: Now is it the same effect to put a 7/8's spacer under your strut b/t control arm end instead? In a word, no. Putting a spacer under the strut, above the steering knuckle (and therefore above the ball joint AND tie rod end) lowers the ball joint and tie rod end, changing the angle that the control arm makes with the horizontal. This changes the rest position along the car's bumpsteer curve only, and changes the camber gain curve and roll center height. Since it changes the rest position in the bumpsteer curve, it will change the at rest toe. IT IN NO WAY CHANGES THE SHAPE OR SLOPE OF THE BUMP STEER CURVE. I know MSA and others call these "bumpsteer" spacers. I wish they'd cal them "roll center" spacers instead. They do not correct the usually fairly nonlinear and non-constant character of the bumpsteer curve for the Z. All they do is change the at rest position along the curve, and extend one end of the curve, shortening the other end. This can be advantageous, but really doesn't correct the overall shape or slope of the curve (the variation in toe as the wheels move up and down). The reason is that it moves BOTH the ball joint and outer tire rod end at one time. To change the bumpsteer curves shape/slope, you need to move either end of the control arm (CA) OR the tie rod (TR) to the correct direction, not the outer end of each at the same time in the same direction. Zero bumpsteer occurs when the CA and TR are parallel (when view in a front or rear view) and the lengths between the pivot points are equal. (They do not have to be co-planar, or one in front of the other when viewed from the front.) The real problem with the Z is that they are not parallel. Adding the spacers below the strut moves the outer pivots of BOTH the CA and the TR the same amount, so the non-parallel relationship between them is not changed. To get rid of the non-parallelism, you can lower the outer TR end (using a rod end and spacers) or raise the inner pivot of the CA. The latter is what JTR is advising. Of course, you could lower the steering rack to lower the inner TR end, but that's a bit of work! (Al [alsil], be careful of this when you're doing that Ford pwer steering rack swap!) After you make the JTR bumpsteer mod and drive the car around some bumpy curves, you'll love it! All that jerking of the steering wheel will be gone (or mostly gone), and the car is MUCH more enjoyable. I hope I cleared this up. The issue of bumpsteer mods and the false belief by many that the "bumpsteer" spacers fix the problem is at least 10 years old, as I've been trying to correct this misconception for at least that long on the various email lists, etc. ------------------ Pete Paraska - 73 540Z - Marathon Z Project pparaska@home.com Pete's V8 Datsun 240Z Pages Quote Link to comment Share on other sites More sharing options...
Evan Purple240zt Posted January 19, 2001 Share Posted January 19, 2001 Man i love this site, i would have never known about the whole issue. I never really payed attention. Does bump steer get worse when you lower the car? I assume so. I may just do that to my front control arm crossmember this summer. With my wide tires and lowered car I am sure i will benefit. Is there anything else i should know before i attempt this during the summer? Thanks guys- Evan PS You will be seeing my post alot more frequently on here now. I finally got my name etc . cookied in for this site. So its way easier to post Quote Link to comment Share on other sites More sharing options...
pparaska Posted January 19, 2001 Share Posted January 19, 2001 Evan, lowering the Z with shorter springs and or coilovers or by using camber plates and top spring perch that is shorter than the stock isolator and spring perch will drop the strut tower and therefore the frame rail and crossmember. Adding the JTR crossmember to frame rail spacer will also lower the crossmember. The effect of one or both of these is to lower the inner control arm (CA) pivot AND the steering rack (and therefore, the inner tie rod (TR) end). So the effect of lowering the car and/or putting in the JTR-recommended frame rail to crossmember spacer changes the roll center height (lowers it), changes the camber curve, and moves the rest position of the car on it's original bumpsteer curve. On the Z it moves it away from the more constant OE center area of the curve to the more largely sloped bump end of the curve. That's why people advise putting in "bumpsteer" spacers between the strut and steering knuckle - it moves th eat rest position of the car back toward the at rest position it was originally at (before lowering) of the original bumpsteer curve. It helps, but in my experience, not much or enough. Quote Link to comment Share on other sites More sharing options...
Mikelly Posted January 19, 2001 Author Share Posted January 19, 2001 Danno, To answer your question I didn't section my struts and don't think I will need to. As for the rear, no, there is no bumpsteer issue in the rear to worry about. As for the other question on removing the motor, My answer is no. Get the car up on stand high enough to get under it with a drill and mark and centerpunch the holes and then drill them out. Mike ------------------ http://hometown.aol.com/dat74z/myhomepage/auto.html "I will not be a spectator in the sport of life!" mjk Quote Link to comment Share on other sites More sharing options...
jeromio Posted January 20, 2001 Share Posted January 20, 2001 Unfortunately, if you're going to keep the stock arm, there's more work to the task of moving the pivot point up than re-drilling the hole. You must also remove the washers that are spot-welded to the inner sides of the crossmember. I have just now started this task. I had tried before to air-chisel them out - no luck. The grinding is an extra pain because I don't want to grind away any of the crossmember metal. I got a selection of various washers to use to try and replace the old ones once I drill the new hole. Most 1/2 inch washers seem nice and tight around the swing-arm pivot bolt. It's a matter of matching the thickness. Quote Link to comment Share on other sites More sharing options...
Guest Frank280z Posted January 20, 2001 Share Posted January 20, 2001 I failed to do the jtr bumpsteer mod when I had the heart out. Can I do this without removal of the engine? Quote Link to comment Share on other sites More sharing options...
johnc Posted January 20, 2001 Share Posted January 20, 2001 What Pete said, only with a few more subtleties. A lowered 240Z front suspension will toe-in in bump slightly. Its not that much and if you have to have any toe change as a result of bumpsteer then toe-in is what you want. Toe-out in bump is dangerous. Bumpsteer spaces work very well to get rid of that toe-in in bump, but they take away the 1/4 of a degree in camber gain (more negative camber) in bump that is built into the 240Zs front suspension. Moving the lower control arm pivot point up reduces the toe-in in bump, but not as much as bumpsteer spacers. You will still have some toe-in in bump, but you will also not lose the 1/4 degree (or more depending on where the hole is) of camber gain. Now, as we can see, both of these changes are good things in one way or another. Which change is appropriate in which situation? For autocross, where your suspension is constantly moving, its a low speed course, short radius turns, etc. then the camber gain is very important and the bumpsteer issue is less important. In this applicaiton, moving the lower control arm position is the best choice. For road racing where you are traveling at high speeds, and speed maintenenace/smoothness is critical, then the bumpsteer spaces are the best choice. And to answer the obvious next question: no, I don't know if doing both is good or bad. I'll have to put that in my little computer program, but at first glance it looks like it might be a bad idea. FYI... when I am talking about bumpsteer spacers, I'm not talking about the ones sold by MSA. They are the wrong thickness and shape. ------------------ John Coffey johnc@betamotorsports.com [This message has been edited by johnc (edited January 19, 2001).] Quote Link to comment Share on other sites More sharing options...
Mikelly Posted January 20, 2001 Author Share Posted January 20, 2001 Interesting thing about mine is that when Zdr. made my control arms up he actually made them shorter than they should have been, causing me to adjust the heim joint out past the 3/4 inch amount most builders allow for a heim joint. I didn't realize this until Chris and I pulled them for the project we are working. Now I'm gona move the hole further outboard so I should clear the washer all together, allowing me to leave it and just weld in the new ones. Mike ------------------ http://hometown.aol.com/dat74z/myhomepage/auto.html "I will not be a spectator in the sport of life!" mjk Quote Link to comment Share on other sites More sharing options...
TimZ Posted January 20, 2001 Share Posted January 20, 2001 quote: Originally posted by Mikelly: (snip)...Now I'm gona move the hole further outboard so I should clear the washer all together, allowing me to leave it and just weld in the new ones. I've been meaning to comment on this for a while now, and this looked like as good a place as any to jump in... I agree with most of the comments that have been made so far, and agree that there are definite benefits to increasing the camber gain, but I have no faith whatsoever that either of these mods will 'cure' your Z's bumpsteer (at least, not on the first try). I've done this adjustment, both on my Z, and on several of my prototype vehicles at work. To actually achieve zero bump steer, or close to it, takes a fair amount of trial and error positioning, and very small changes in the location of the pivot point can and does make noticeable changes in the bump steer curve. When I first started being interested in this, I bought the spacers, and tried them - they actually made by bump steer worse. This was most likely exacerbated by the fact that my suspension pickup points had been moved laterally in order to adjust camber - which is exactly the situation that you are talking about above. If you were to start out with known stock suspension geometry, then either of these mods might be directionally correct, although I still have my doubts. Otherwise, all bets are off. With all of this in mind, I can't envision any way that moving the pickup point 'about 3/4"', or adding a pre-made spacer will get you there. It might get you closer, it might not. The only way to know for sure is to measure the bump steer before and after, which isn't that hard or expensive to do - just time consuming. A better option would be to remove the stock reinforcement washer, slot your holes vertically, and assemble the inner pivot assembly with new washers on the bolt. Adjust the pivot point until you are happy with the bump steer curve, and then weld the washers down in this position. The drawback to this would be that you might end up with different camber gains right to left if the optimum pivot points end up appreciably different. A better still option would be to go ahead and relocate the pivot points as you originally intended, and fab some heim jointed tie rod ends, and make your bump steer adjustments by shimming the tie rod ends. This decouples the camber gain adjustment from the bump steer, and allows easier adjustment of both. The drawback, aside from having to fab up the tie rods, is that I'm not sure about the legality of this mod (or any or the others, for that matter) for any specific racing classes. I'm sure that JohnC could enlighten us on this... [This message has been edited by TimZ (edited January 20, 2001).] Quote Link to comment Share on other sites More sharing options...
pparaska Posted January 21, 2001 Share Posted January 21, 2001 johnc & TimZ - good points. Me being the really nutso mod freak, I modified the crossmember to provide for adjustment of the inner CA pivots! The adjustments are in the range of 5/8" to 7/8" above and 1/8" to 3/8" outboard of the stock pivot bolt location. The adjustments are independent of one another. I do plan on measuring the bumpsteer curve when I get all the weight on the car and set the ride height, camber, caster, etc. One thing to realize is that if you move the inner CA pivots outboard, you'll need to lengthen the tie rods to get the toe back to where it was, assuming you don't have adjustable control arms (CAs). This changes the length of the tie rods (TRs). But the length of the CA's didn't change (unless you did something to them. What I'm getting at is that one change will trickle down to other changes, and the entire steering system has to be considered. The issue is that the distance between the outer tie rod pivot point, the distance between the ball joints, distance between the inner tie rod ends (fixed by rack selection), the distance between the CA inner pivot bolts, and the lengths of the tie rods and control arms are all related, if bumpsteer and static toe is to be held down. Change one dimension, and you need to change another to get the static toe back. But if that means making the effective length between the tie rod pivots per tie rod and the control arm pivots per CA unequal, then you've created a bumpsteer problem. Not because of the height of the pivot points, but because of the lengths of the links. Bending the steering knuckles could alleviate some of the problems. Quote Link to comment Share on other sites More sharing options...
Mikelly Posted January 21, 2001 Author Share Posted January 21, 2001 Well yesterday I did one side of the bump steer mod, and I had to remove the inner washers, which was VERY simple. Get a cole chisel, or other steel cutting chisel and good, heavy hammer and hit the washers at the spot welds... They pop right off, no problem what so ever! However, after marking and drillin my holes, I went back and remeasured and the hole is closer to 1 inch from center up and then 5/8th inch outboard. The absolute best way to do this is with the Kmember out from under the car guys! Hopefully I won't have to bad an issue to deal with. I will slot them if need be... As for "Needing" to do this mod, my car was driven hard this past summer and I noticed no adverse bump steer. If I do now, I will go back to the factory pickup points. Mike ------------------ http://hometown.aol.com/dat74z/myhomepage/auto.html "I will not be a spectator in the sport of life!" mjk Quote Link to comment Share on other sites More sharing options...
jeromio Posted January 22, 2001 Share Posted January 22, 2001 All I can say is that either you are really lucky or I am really not (or some combination there of). When I put in the coil overs this past summer, I wanted to move the pivot point up at the same time. I hammered, chiseled, air hammered, etc. Got nowhere. This time I am using a grinder. Those washers will not deafeat me! Too cold out right now though. Brrr. Quote Link to comment Share on other sites More sharing options...
Mikelly Posted January 22, 2001 Author Share Posted January 22, 2001 Yup, I even re-used the washers in the new holes. Had to trouble with them at all. I even removed 2.5 of the washers from the Kmember I delivered to BLKMGK yesterday! No kidding, it took less than 5 minutes to get all four of them off mine. a Large coal chissel with a 2-3# hammer and they popped right off. It was much easier with the unit on the car though, as the one I did for Jim was on a bench vise and was more difficult. Also re-measured with a dial caliper and my holes are 7/8th inch up and 5/8th inch further outboard. The unit on the right side had to be slotted a bit though. Mike ------------------ http://hometown.aol.com/dat74z/myhomepage/auto.html "I will not be a spectator in the sport of life!" mjk [This message has been edited by Mikelly (edited January 22, 2001).] Quote Link to comment Share on other sites More sharing options...
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