Guest zfan Posted January 22, 2006 Share Posted January 22, 2006 I have a 1971 240Z with a 385 sbc/700r4 that I drag race. The car has been structurally reinforced, caged, braced etc. I went to an event last weekend and a friend happened to snap a couple of good shots of my car launching on slicks. The pictures showed the rear wheels moving forward and the tire ending up 2-3" forward and the slick coming in contact with the front of the rear fender wells. It appears that the rear control arm is giving way under stress on the launch. I have completely rebuilt the rear suspension in the last year, using urathane bushings everywhere. The struts and springs as well. I replace the drivers side rear control arm as it showed signs of damage from a previous misshap when a half shaft exploded on me. Has anyone experienced this type of failure or fatigue? The car is not a super high horsepower drag car. It runs high 6's in the 1/8th and low 11's in the 1/4, maybe high 10's at best. Dyno's 370rwhp and 430 rwtq. Mike Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted January 22, 2006 Share Posted January 22, 2006 I am going to try and post a picture of the launch I am talking about, here goes nothing! Quote Link to comment Share on other sites More sharing options...
Mikelly Posted January 22, 2006 Share Posted January 22, 2006 That's interesting. Looks like the whole suspension is shifting forward. Not good... Mike Quote Link to comment Share on other sites More sharing options...
JMortensen Posted January 22, 2006 Share Posted January 22, 2006 Cary (tube80z) has mentioned this before. I always assumed it was more of a bushing deflection than anything else, but poly shouldn't deflect too much. You could eliminate the bushings entirely and run monoballs and see what difference that makes, or you could stitch weld the control arms to make them a bit stiffer if you think that's what is deflecting. Then there are aftermarket control arms from MM and AZC if you find that it is the control arm itself. Could also be the strut housing itself twisting. Don't know how you'd address that... Quote Link to comment Share on other sites More sharing options...
johnc Posted January 22, 2006 Share Posted January 22, 2006 If nothing is broken or misaligned, I don't think the suspension is moving forward very much. I think what you're seeing is the normal suspension movement and the tire contact is the result of the large rear slick. Looking at the gap between the tire and the rear wheel well doesn't look that far forward. How tall is your rear tire? Look at the picture below of my old 240Z with the left rear fully compressed with 25.2" tall tires. It appears that the gap between the tire and the rear wheel well is about the same as on your car. Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted January 22, 2006 Share Posted January 22, 2006 The tire is a Mickey Thompson slick 25.5 X 8.5 X 15. I am using the Arizona Z springs/stock ride height but stiffer than stock with Tokico blue struts. I am using the 280Z perch bushing that fits under the strut tower, I believe it is 1" taller than the stock 240Z to give the car a little more clearance. I am going to take it to my buddies shop this week to get a good look underneath the rear end. I am looking at going coil over to stiffen things up out back but know I also need to address the other issues as well. Thanks Mike Quote Link to comment Share on other sites More sharing options...
fastzcars Posted January 22, 2006 Share Posted January 22, 2006 Is there any evidence of tire contact on the front of the wheel well? I know my Z has an offset look to the tire in relation to the wheel well to. It could be that the rear tire might just be too tall. The Z's only came with a 165/175 x14 tire from the factory. I think that's only 24 inches tall. I don't think there is anything wrong, unless you find some cracks/ bent items in your suspension system. Quote Link to comment Share on other sites More sharing options...
fastzcars Posted January 22, 2006 Share Posted January 22, 2006 You know if you stiffen the rear. you won't get as much weight transfer to the rear, and your 60 foot times might drop. By the way, those are impressive numbers on the strip! Quote Link to comment Share on other sites More sharing options...
tube80z Posted January 22, 2006 Share Posted January 22, 2006 Has anyone experienced this type of failure or fatigue? The car is not a super high horsepower drag car. It runs high 6's in the 1/8th and low 11's in the 1/4, maybe high 10's at best. Dyno's 370rwhp and 430 rwtq. I don't have any answers for you but I can tell you how to test to see what the problem truly is. You need to perform what is called a parasitic compliance test. To do this you will need to build a jig for the front and rear tires that bolts to the hub and is the same radius as the tire (quarter wall 2 inch square tube should suffice with some bracing). You will also put a toe plate on the hub to measure toe, camber, and lateral/logitudinal displacement can be measure with a plumb bob. These will be bolted to the hubs and then you will lock them in place using either brake pressure or some form of clamp to keep the hubs from rotating. Then at the bottom of the jig you will attach a porta-power with a pulling attachment (it also needs a guage). This will simulate the force of the launch of the rear tire and braking at the front. This should be configured so that you can slowly go up to 3000 to 4000 pounds of pulling force between the wheel pair. I would recommend going up 250 pounds of force at a time and measuring everything. Be careful doing this as you'll end up with a lot of force on things as you measure it but this should show if you have an issues that are force related. I know this sounds like a lot of work but it may show you things you can fix that will make your car even faster. I was curious what MPH you see in the 8th and what the time was. I've been trying to figure out 0-60 and 0-100 times for a high horsepower Z. Your car sounds like what I was looking for. Hope this helps, Cary Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted January 22, 2006 Share Posted January 22, 2006 With my current set up I have run: 1.55 60 ft. 4.48 330 ft. 76.70 mph 1/8th 6.94 98.89 mph The best 60 ft. to date is 1.53 The z runs 6.90's to 7.0's The 700r4 tranny is a hp pig, if I ran a th350 I would go faster but I like to cruise around too. Not just a drag car. The car weighs 2640 with full trim and cage. Hell it has a stereo, 2 amps, subs, speakers yadda, yadda. Even full exhaust. I think I will contact Chris aka Whiteboy in Ft. Worth, he has 3 Z's. One is a street car that still has the irs rear end and is deadly at the street races and 2 others that are dedicated track cars. One runs 5.50's in the 1/8th on 93 octane..pump gas. His street Z has the after market adjustable rear control arms. Maybe he can shed some light on the subject. Mike Mike Quote Link to comment Share on other sites More sharing options...
DavyZ Posted January 22, 2006 Share Posted January 22, 2006 Mike, I noticed mas280's rear wheels looked like they were moved farther forward than usual just sitting still, but what do you expect from a 400+ RWHP LS1? On some of the higher HP Z cars I notice that the rear ties look like they are set farther forward for some reason. This might be an optical illusion, but it really does look that way. Sitting still do your wheels appear to farther forward than another relatively stock Z car? Just thinking outloud... Davy Quote Link to comment Share on other sites More sharing options...
mark Posted January 23, 2006 Share Posted January 23, 2006 I have seen video of my car on a dyno and I can tell you, the rear tires did move foward. I had new stock rubber bushings on the rear. Arizona Z makes some nylon rear bushing that I have used to replace the rubber ones with. I have not seen video of the car since so I don't know if it has helped but that had to be what was giving on my car. Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted January 23, 2006 Share Posted January 23, 2006 I was wondering too if I was to reinstall my rear swaybar if that would help. Also I think I will install coil overs this next week. Maybe the stiffer springs will help as the Arizona Z springs do not appear to be up to the job and from what I hear they are just about as stiff as I can go before just going coil over anyway. I checked the slicks and they do have some very superficial cuts to the tire, nothing too deep but still enough to worry me. Maybe a solid axle would be the way to go...hell who knows?????? Thanks, Mike Quote Link to comment Share on other sites More sharing options...
260DET Posted January 23, 2006 Share Posted January 23, 2006 Looks like its squatting a fair bit causing the alignment to go into significant negative camber. That plus the fact that strut suspension does not hold its angles as well under heavy loads as more sopisticated suspension like double wishbone or Nissan's own multilink does. I know bugger all about drag racing but is'nt it the usual thing to set the rear of the car a fair bit higher than the front, a lot of rake? I guess so that the car can squat under acceleration giving good weight transfer to the rear without dragging its arse. A bit more rear height may help here? Keep the rear tyres tread flatter on the ground too. Lower the front as well? Quote Link to comment Share on other sites More sharing options...
Dave Posted January 23, 2006 Share Posted January 23, 2006 If your using the stock 240Z control arms (Transverse Links) it is possible they are deflecting. The 280Z control arms are much more robust. If you compare the 2 side by side you can see a big difference. They are bolt for bolt interchangeable. Quote Link to comment Share on other sites More sharing options...
fastzcars Posted January 23, 2006 Share Posted January 23, 2006 Dave, this is first time I heard that the 240 and the 280 had differnet arms? Does anybody have some pictures comparing the two ? If so maybe some reinforcements can be added to the a-arms. Quote Link to comment Share on other sites More sharing options...
Guest JAMIE T Posted January 23, 2006 Share Posted January 23, 2006 I have had the two side by side and can assure you, they ARE different. Quote Link to comment Share on other sites More sharing options...
jbc3 Posted January 23, 2006 Share Posted January 23, 2006 Hmm, My rear tires rub the front of the fender lip on launches and hard acceleration. The front of the tire only sits about an inch or less from the front fender lip when sitting still. I was thinking it was all in the squat and large tires. I welded in large gussets in my LCA to hopefully prevent any deflection on launch. Looks like I will be ordering poly bushings. BTW I am running the 255-50-16 MT ET Drag radials. Quote Link to comment Share on other sites More sharing options...
dj paul Posted January 23, 2006 Share Posted January 23, 2006 anyone want to spare these rear arms for me? on one of mine the swaybar end link had ripped apart that welded washer. it looks like i could fix it easily. but considering im going to be around 450 rwhp eventually and spindle pins are PITA (as i did mine the other night, sounded easier than your guys experience tho, lol) that i might as well get some better ones. i do not have the money for the AZZcar or the MM ones. im going to college and i work at radioshack. cant quite drop 800 or more dollars right now. oh and jbc, could you show me these gussets? id rather spend no money and use my welding skill to pull me outta this mess. i can show you all pictures later. about the wheels going up forward, i was looking at the 240sx rear subframe and saw upper control arms and another bar up there. any way we could design this on our rear subframes without spending 1000+ on a 240sx rear. using monoballs and such with some bent tubing bolted in to a gusset extending off of the subframe? Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted January 23, 2006 Share Posted January 23, 2006 Keep in mind the tires get taller as they spin. It is a little hard to say where the deflection is taking place. Obviously the poly bushings will compress and expand, but you could also have the strut tube twisting/bending. I would think a few times about what exactly needs to be strengthened before I started welding gussets on whatever I thought was deflecting. BTW, if your quarter mile times are good and your prerace inspections show nothing is breaking, then is this really a problem? Quote Link to comment Share on other sites More sharing options...
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