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Showing results for tags 'bump steer'.
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Cary (tube80z) has been mentioning this idea of the dual ball joint front end off and on for the last couple years. I hadn't really given it too much thought until I autoxed my car and was really lifting the inside rear tire, and Dan (74_5.0L_Z) suggested that the problem might be scrub radius and caster related. I guess the idea is that the outside wheelbase increases significantly enough due to scrub that the car leans over in that direction and the inside rear comes off the ground. Recently this thread popped up talking about swapping front suspensions and it quickly devolved into a pissing match for reasons beyond my comprehension, but it did get me thinking more seriously about the dual ball joint idea. Cary seems to think it's doable with the ball joints in the same plane, and had thought of a modified bumpsteer spacer as a possible way to do it. That got me thinking that it might be easier to just make a square tube knuckle and bumpsteer spacer combo, so that's where I'm at right now. Thinking square tube with simple clevises welded to it for the ball joints, and then taper the front end and have it open and then use shims above and below the tie rod to adjust bumpsteer. I have absolutely no idea how to figure out the spacing on the clevises to minimize scrub and that sort of thing but I'm very interested to see if I can make it work, and to see if it would be as easy as I think it should be.- 38 replies
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- dual ball joint
- scrub radius
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This is not a how to,It is what I have done. Mesuring the 240 rack I came up with 24.230" from center to center of ball scokets (iner tie rod pivot point) and a travel of 5.125". The pinion is 7.5" from the center of the housing. The Miata rack's I reviewed are from a 92 and 97. The 92 has a vavle body cast with the gear case and is held togeather with C-clips. This makes it harder to modify. The 97 has a vavle housing bolted to the gear case and the end cap screws into the housing. This is what I will cover here. The Miata rack is 26.040"center to center of ball scokets with a travel of 4.704". The pinion is 8.75" from the center of the housing. Ball scoket threads are 17x1.0MM RH. Center of ball scoket to mating face of rack is (including lockwasher) .740".The travel is limited by ball scokets contact with the housing. Removing the ball scokets allows more travel that is now limited by the distance between the fluid lines less the with of the piston inside 5.354"-.287"=5.067" max travel for this rack. Not as much as the 240's 5.125",But with power steering I will go with shorter steering arms to make up for it. To get Center to center of 24.230" I removed 1.812" off the right end of the rack remachined the end with the exception of the lenght of the small OD witch was shortened to .25". This aera and the vent hole must be polished to prevent seal damage. The housing was cut down 1.582" on the right side and remachined. The thread is 40x1.0MM RH, I used 1.575"x24TPI RH (My lathe is english) A new shorter end cap was made alowing an extra .385" travel. It stops the piston befor it blocks the fluid port on the left. Using a face pin spaner insted of a hex alowes more of the housing to be left in place for the rubber mount. This made up for cutting less off the housing than the rack. On the left end of the housing a counter bore 1.5" DIA x.150"deep alowing the ball scoket to travel inside the housing,and the piston to travel to the edge of the right fluid port. The tie rod's were cut down 2.25" and threaded 12x1.25MM RH. Miata outer tie rod's will be used. I now have a rack with the same center to center as the 240z, and a travel of 5.067". Other problems to address will be the pinion is now 6.562" from the center of the housing (15/16" closer to the motor), steering shaft and mounting made.