Guest HBskinheadZ Posted June 24, 2003 Share Posted June 24, 2003 Does anyone have details on this modification? I am looking to lower 1.25" to 1.5" and I am considering what my options are. Does the strut spacer availabe at MSA or on ebay eliminate the need to do the bump steer Mod shown in the JTR book? which is best or do both? Any more dumb questions Quote Link to comment Share on other sites More sharing options...
Guest MistressMotorsports Posted June 24, 2003 Share Posted June 24, 2003 IMO, if you are just street driving, you don't need to worry about moving the control arms or the rack. In fact, many racers don't even do it, although it does help make the car more predictable. If you are racing seriously or just "have to have it because it's trick," then you can go with the spacers first, moving the control arm mounts next, then possibly even move the rack up a bit. Mike Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted June 25, 2003 Share Posted June 25, 2003 lol just because racers don't do it doesn't mean much. there are quite a few race Z's out there on a budget diet. -Ed Quote Link to comment Share on other sites More sharing options...
j260z Posted June 25, 2003 Share Posted June 25, 2003 check out this site http://240z.jeromio.com/frontcross.html he is a member of this forum and may have some input into this. Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted June 25, 2003 Share Posted June 25, 2003 I'm interested to hear his results. Quote Link to comment Share on other sites More sharing options...
Oltmann Posted June 25, 2003 Share Posted June 25, 2003 There have been several long threads about this subject, so I will take a shot at synthesizing them here. The "bumpsteer mod" should really be called the "camber gain and also possibly but not nessecarily in a good way bumpsteer mod." Moving the control arm attachment point up will correct camber gain in lowered cars (which is good) and it might decrease bumpsteer, but it might increase it too, depending on the history/configuration of the front suspension. The only way to find out is to measure it which is painstaking. Correctly setting up bumpsteer is fairly difficult, which is why some racers don't bother. edit: The only way to find out is to measure it which is painstaking. By "it" I mean bumpsteer. Quote Link to comment Share on other sites More sharing options...
jeromio Posted June 25, 2003 Share Posted June 25, 2003 I did it because I felt (rightly or wrongly), that in daily driving I was experiencing adverse bumpsteer. In particular, there is a long sweeper on my freeway commute which has 2 bumps and a dip. Car would get very squirrely in this turn and in other situations. After the mod, it seems (to me, seat of the pants) to have very much improved the behavior of the car in these same situations. Also, since my car is lowered, moving the pivot up helps to return the camber gain lost. So, in summary, thumbs up for the pivot raising mod. The other part of the mod that I don't recommend is the moving of the pivot Out. The car now has lots and lots of camber (great metrics there, eh? ) up front. Visually, it has the same camber front and back now. So, the turn in is very dynamic. I know caster is supposed to be the key for turn in and I didn't change that, but little steering inputs go a long way now. And it is very grippy - I haven't really pushed it (no track days or autox yet), but it seems to me that there is zero push (and I have a stock front and no rear sway bar). It's just that the transitions from straight line to turn are maybe a little too quick. In summary, the car takes a little more concentration to drive now. I don't think I'm explaining it well. And of course there will certainly be tire wear issues. I have only got about 5K miles on this setup and I don't see a visual treadwear issue, but I rotated the tires at around 4K and I could definitely tell - I had thought I had just gotten used to the car at some point, turns out that the tires had bedded in (or whatever you wanna call it) and when I switched them front to back, I was back to square one. I'd really like an experienced driver to take my car for a spin at some point (like a John Coffey or Doug Hayashi type) and give me some feedback. In the meantime, I am saving my pennies for some adjustable front control arms. Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted June 25, 2003 Share Posted June 25, 2003 We have lost so many posts when we went to the new software. There was a thread some time back detailing the steps needed to precisely locate the pivot point to eliminate bumpsteer. The only thing I can't remember was the role of "bumpsteer spacers", those MSA spacers that bolt onto the bottom of the strut housing. If I remember right, the spacers really don't correct bumpsteer, but on a lowered car are necessary to retain the correct camber gain curve (whatever that means). The upshot is a lowered car may need both the bumpsteer mod and the spacers. What I do remember is how to compute the relocation point because the idea makes sense. The idea was to put the car on jack stands and remove the front springs. This allows you to move the front suspension through it's full range of travel. With the front tires removed, connect some type of device that allows you to measure the change in front toe as the spindle in moved up and down. Some guys were doing it with dial indicators, I figured attaching a laser pointer to the brake rotor and tracing the dot along the garage wall would work best. Just move the front spindles up and down while tracing the dot to make a line on the wall. If you do this for both sides, measuring the distance between the two lines will tell you how much the rotors point in or out as the suspension travels up and down. What you then need to do is, by trial and error, move the lower pivot point in and out, up and down, while redoing the test. Once the lines go up and down the same distance apart, that is where you want to place the new pivot point. I would take a rod the diameter of the control arm bolt and sharpen both ends to a point. This could then be placed in the control arm bushing, and the cross member C clamped against this to hold everything while the test is being done. Theoretically, JTR did just this when then came up with their "7/8 up, 1/4 out" (or what ever the exact numbers were). I would think that once it is figured out for one Z, then it should be true for all Z's. BTW, the thread also said Datsun purposely mislocated the pivot point to try and compensate for all the rubber isolators they put in the front end. Quote Link to comment Share on other sites More sharing options...
CruxGNZ Posted June 25, 2003 Share Posted June 25, 2003 Jim, I remember that post. If I'm correct John Coffey chimed in about the bumpsteer spacers and pivot relocation. He said that you should only do one, not both. John, if you see this, could you refresh our minds about bumpsteer modifications? !M! Quote Link to comment Share on other sites More sharing options...
Guest HBskinheadZ Posted June 26, 2003 Share Posted June 26, 2003 Thanks to all who replied, I am going to go by what JTR recomend in thier book, I have seen some posts of members saying theirs was close to where JTR recomends by looking at the picture in the bookand they did not have a bumpster problem with their lowered Z (any comments?). It kinda makes me wonder if the factory did changes on different years to correct the problem. Mine is a 74 (early) and I also have another 74 (early) that is lowered 1 1/2 to 2" and it does have some unwanted bump steer so I will assume it needs to be done on my v8z. If the suspension is the same from 70-78 than someone smarter than me should be able to find the correct location for the hole and all would benefit. (come on all you engineer types get out your pocket protectors and solve this Mystery ) Has anyone done this suspension from ZF racing http://www.zfracingsuspensions.com/ I would like to hear some feedback from guys (or gals ) who have done this.I am also talking with Ross about his coil over and 240sx rear disc brake conversion,front Brake,and Honda wheel adapters. Spring rates are my next concern but I,m sure Ross will be able to help me Quote Link to comment Share on other sites More sharing options...
DavyZ Posted June 26, 2003 Share Posted June 26, 2003 ... Has anyone done this suspension from ZF racing http://www.zfracingsuspensions.com/ I would like to hear some feedback from guys (or gals ) who have done this.I am also talking with Ross about his coil over and 240sx rear disc brake conversion,front Brake,and Honda wheel adapters. Spring rates are my next concern but I'm sure Ross will be able to help me Although I have not purchased ALL their equipment, I can tell you they are great guys to do business with and I have met both of them I have the rear 240SX brackets from Ross and a 240SX brake package as well--not mounted yet... Davy Quote Link to comment Share on other sites More sharing options...
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