mclark999 Posted July 23, 2011 Share Posted July 23, 2011 (edited) I have just pulled out my front cross member and am getting ready to relocate the LCA pivot point to lessen bumpsteer ala the JTR manual. In the JTR manual it is recommended that you reinforce the cross member with a "doubler" before you drill the new holes. Is this reinforcement needed? Does it matter which model Z, 240, 260, 280 you are working with? Additionally, given very little fabrication experience with metal and close tolerances, (I've built homes, but that's very different), what is the best way to measure to get the exact 3/4 up, 1/4" out from the original hole center? Thanks as always to the brilliant guys who have lead the way and remember, a picture is worth a thousand words. Michael Edited July 23, 2011 by mclark999 Quote Link to comment Share on other sites More sharing options...
mclark999 Posted July 24, 2011 Author Share Posted July 24, 2011 Now that I have it all apart I can see that the doublers are needed. The doubler washer looks to be about 50% thicker than the actual crossmember. And without it, the LCA bushings would slop around forward and back. Time to find a welder buddy. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 24, 2011 Share Posted July 24, 2011 Not a big fan of the 3/4" up and 1/4" out because on my car 7/16" up got rid of the bumpsteer. 1/4" out has a minimal effect on camber, but is not really doing much of anything else. As to how I got the hole straight up, I just laid a square on the table and marked it and then eyeballed it a couple times to be sure it was as close as I could get it. When I did this I found that the rack was 1/8 or 1/4 lower on one side, so the tolerances are not super tight from the factory and it isn't necessary to be down to the .0001 on these. Quote Link to comment Share on other sites More sharing options...
mclark999 Posted July 24, 2011 Author Share Posted July 24, 2011 Not a big fan of the 3/4" up and 1/4" out because on my car 7/16" up got rid of the bumpsteer. 1/4" out has a minimal effect on camber, but is not really doing much of anything else. As to how I got the hole straight up, I just laid a square on the table and marked it and then eyeballed it a couple times to be sure it was as close as I could get it. When I did this I found that the rack was 1/8 or 1/4 lower on one side, so the tolerances are not super tight from the factory and it isn't necessary to be down to the .0001 on these. I will be lowering the car at least 2" using sectioned struts and coilovers. For the Velo Rossa, anything less than this much drop doesn't look very good. Maybe I will slot the crossmember providing me adjustable bump steer. I know some other guys have done this. Thanks for your thoughts. I know you have a lot of experience. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 24, 2011 Share Posted July 24, 2011 The amount you lower the car won't change how far the bumpsteer needs to be adjusted. If you're thinking roll center, then I'd suggest roll center spacers (aka bumpsteer spacers--but they really don't adjust bumpsteer). More info here: http://forums.hybridz.org/index.php/topic/38615-bumpsteer-faq/ Quote Link to comment Share on other sites More sharing options...
mclark999 Posted July 24, 2011 Author Share Posted July 24, 2011 Not a big fan of the 3/4" up and 1/4" out because on my car 7/16" up got rid of the bumpsteer. 1/4" out has a minimal effect on camber, but is not really doing much of anything else. As to how I got the hole straight up, I just laid a square on the table and marked it and then eyeballed it a couple times to be sure it was as close as I could get it. When I did this I found that the rack was 1/8 or 1/4 lower on one side, so the tolerances are not super tight from the factory and it isn't necessary to be down to the .0001 on these. From the picture above, it looks like you doubled the wall thickness by adding to the outside. Is that right? Regarding the 7/16" up removing the bumpsteer. Have you talked to others about this? Do you know what the consensus is? I won't be racing, just spirited street driving and trackdays at 80%. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 24, 2011 Share Posted July 24, 2011 I'm using rod ends on the control arms so I had to make new spacers anyway, and this meant that I wasn't concerned with the inner dimension of the crossmember. Since it is easier to weld on the outside of the crossmember, that's where I did my modifications. I haven't talked to anyone else about the bumpsteer figures. I think I might be the only person who has a slotted crossmember though. Maybe Pete Paraska has one too. Not sure, I know we were both talking about it in 1998 or 1999. I know there was a lot of concern when I initially did it that the adjustment would move around. Never happened to me in about 40K miles and 8 seasons of autox and a handful of track days on the previous crossmember. It would also be pretty easy to weld the washers to the crossmember once the happy spot was found if that was a serious concern. Quote Link to comment Share on other sites More sharing options...
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