PaulR Posted October 17, 2000 Share Posted October 17, 2000 I've seen references here to people re-drilling the rear flange from 4-bolt to 5-bolt. I took a look at the flange on my 240Z and I am wondering if there is enough "meat" to do this. I generated the attached drawing (to scale) and as you can see, 2 of the new stud locations are only about 1/8 inch from the flange edge. I would appreciate any comments or feedback from anyone who has already done this as I would like to do the same. Paul Quote Link to comment Share on other sites More sharing options...
alsil Posted October 17, 2000 Share Posted October 17, 2000 The 2 lugs that will be .125" fromt he edge should hold well. the flange thickness is around .375", right? So with 5 lugs evenly distributing the force, it should hold up just fine. I'm doing the same thing, and I was worried about breakout, but it will be more than strong enough. ------------------ http://refuse.netdojo.com/Zcar Quote Link to comment Share on other sites More sharing options...
pparaska Posted October 17, 2000 Share Posted October 17, 2000 Ya know, this bothered me at first when I heard of it years ago, but considering the forces on the studs will be along the direction of the bolt circle for acceleration (and braking, but that goes from the disk, to the stud, to the wheel mostly) the 1/8" to the outside isn't too much of a factor. As for taking up cornering and dead weight loads, you have 5 studs taking the shear forces all in one direction. The worst case is when those 2 studs that are close to the edge are on top of the axle taking upward vertical loading from the tire, they get pushed towards the outer edge. But the material is thick and the other 3 studs share the load. Other than that there are loads that want to pull out the stud under the weight of the car and cornering, but the flange is pretty thick and a good 80% of the circumference of those 2 studs near the edge are in a meaty area of the flange away from the edge. The above is a mechanical engineer's point of view. I haven't done any calculations to back this up one way or another. I'd love to get some feed back on my thoughts above. I'm beginning to not have a problem with this swap. But just looking at it does make one feel a bit uneasy at first. Of course, racing the setup is the ultimate test. Any data on this? [This message has been edited by pparaska (edited October 17, 2000).] Quote Link to comment Share on other sites More sharing options...
Modern Motorsports Ltd Posted October 18, 2000 Share Posted October 18, 2000 Well I have a hunch my 280ZX flanges are a touch smaller than others as mine were v. tight. Either way, if you're concerned at all it's a small matter to have those two edges welded up a bit BEFORE you drill them (so's not to risk any warp effect on stud axial dirxn). I had mine filled and edges built up prior to drilling just so's I'd never have to wonder, I had a LOT less than an 1/8", ZX's must be smaller. FWIW, IMO I'd drill for larger studs and use PROPER slip on spacers. I have both bolt on and slip on with my setup and much prefer slipon for serviceability and easier change of offset with proper 'shims' behind them. Quote Link to comment Share on other sites More sharing options...
pparaska Posted October 18, 2000 Share Posted October 18, 2000 Morgan, I was picturing my car's setup with a 1/2" thick Wilwood Disc hat tha unfortunately does away with any center ring/puck that the stub axles have. So my setup uses only the studs and friction to oppose the vertical shear forces across the flange. Some quick calcs: - (5) 1/2-20 lug studs (large for the sake of an upper bound - I have 4 1/2"-20 studs) - Assume 150 ft-lbs (again, probably high) for the torque spec of the lug nut - coefficient of friction at flange/disc/wheel flange = 0.15 (this is generous, as the surface is uneven and might be greased, etc. Torque = 0.130 * (bolt diamater) * (clamping force) (Design of Machine Elements, M.F. Spotts) Solving for clamping force: (Clamping Force) = Torque / (0.130 * bolt diameter) Clamping Force = 150 / (0.130 * 0.5") Clamping Force = 2310 lbf Times 5 lugs -> 11550 lbf clamping force Friction Force due to clamping of 5 lugs = (coefficient of friction) * clamping force = 0.15 * 11550 = 1735 lbf This is assumed to resist the wheel rotation on the disc/stub axle flange. Assume a 2.25" bolt circle radius Torque to overcome friction = 2.25 * 1735 = 3900 in-lb = 325 ft-lb Well, I guess that with two wheels sharing the load, you'd need 650 ft lbs to overcome the friction due to bolting. But remember how generous I was with bolt size, friction coefficient, etc. If there's dirt or grease on the mating surfaces, all bets are off. Back off to more reasonable lug stud diameter (7/16"), torque (100 ft lb), and coefficient of friction (0.05 - 0.10) and the numbers get down to the a few hundred ft lbs before you over come the friction at both wheel/hub interfaces. I guess I just don't believe that automotive engineers depend on clamping force and friction to take the brunt of the accelerative reactions during take off and braking. But I've been wrong before. There's probably a more accurate way of calculating this, but I'm not interested in looking that far for the truth I guess. You point on preload is well taken. But the head of the lug stud still needs to not pull out. I think your idea of a ring behind the axle or just using large thick washers would work. Welding the area near the edge sounds good also. All in all, I still think the idea of taking the Z stubs and doing the 5 lug drilling is failry sound. The thickness of that flange makes up for alot of the drawbacks of those two studs being near the edge. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted October 18, 2000 Share Posted October 18, 2000 I think most are misunderstanding the forces involved... Studs merely hold the wheel tightly to the hub/rotor/flange/whatever. Studs take little or no force in directions other than axially. Friction between the wheel and the mounting surface as well as proper centerbore sizing takes all of the shear force. The way torque specs are derived is to pre-load the bolt enough so that the maximum force exerted on it doesn't surpass the pre-load force. This greatly reduces fatigue failure of the fastner and prevents the fastner from moving around(which is very bad). Is there enough room to put a steel ring behind the flange? Drill it and press the studs into the steel ring and when the wheel is tightened, the steel ring will be drawn snug against the flange. Kinda lame, but it will definately prevent any problems. I would try it and keep a tight inspection schedule on it for 5-10k miles(like check them out every 100 miles to start with) and feel pretty good about it. What does the rear flange on a 280ZX look like? I know Michael redrilled his 280ZX flanges for 5 lugs on his 510 and never had a bit of a problem. ------------------ Morgan morgan@z31.com http://carfiche.com http://z31.com Quote Link to comment Share on other sites More sharing options...
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