Spacenut Posted November 29, 2009 Report Share Posted November 29, 2009 Well, I got my modified uprights back from the machine shop last week. They've done a nice job of machining off the spindles and drilling and tapping the front face. The replacement spindles look really hefty and there is a Nylock backnut to keep everything together. Nice. With the spindle removed from the upright the flat surface makes an ideal datum for my magnetic base laser level, with which I tried to set up my bump-steer geometry 2 years ago. I got some conflicting results then, so I just set the steering rack height at the same ratio of upper wishbone to lower wishbone as the steering arm is between the top balljoint and bottom balljoint. Can't go far wrong, I thought Anyway, projecting the laser crosshairs vertically onto the underside of the wheelarch, and moving the suspension through its full travel by hand, the full extent of my ignorance is clear... The wheels are toeing out on bump, by quite a lot! I guess roll understeer too. The problem is that the steering rack is too high in the chassis. Its fixed in place using thick steel shims, so all I need to do is take some out until the steer component is minimised - the trouble is, to get to the steering rack I have to drain the coolant, remove the radiator, then drain and remove the fuel tank Not a pleasant prospect, but at the end of the day I'm delighted to have found such a major goof in my setup. I was beginning to think that I'd just wasted 20 years of my life designing a fully adjustable chassis that handled no better than the VW Beetle it was intended to replace, now at least I can get the bump-steer under control I'm currently waiting for a set of alloy hubs to arrive, to replace my heavy and corroded originals. I might just throw it all together to go to Goodwood next Sunday for the last breakfast club of the year, depending on the weather. Then get the tank out and blitz it over the Christmas holidays. I'll get some pictures of the offending article together soon! Lauren PS - any thoughts on whether to leave the disc backing plates on or off? They're rusty, and weigh more than thin air. I don't have any specific forced-air cooling on the brakes... yet. Quote Link to comment Share on other sites More sharing options...
Tony Posted November 30, 2009 Report Share Posted November 30, 2009 Blimey your not having much luck on this project are you!!...... Did you know you can get height adjustable track rod ends, this would stop the bump steer. Quote Link to comment Share on other sites More sharing options...
Spacenut Posted November 30, 2009 Author Report Share Posted November 30, 2009 Hi Tony - I suppose I could ream out the taper on the steering arms and replace the track rod end with a Rose joint and shim it. But in order to dial out the bump steer in this case the track rod end needs to pass through the steering arm, as opposed to being either above or below it. Its my mistake, I designed height adjustment into the steering rack to address this issue, I just didn't make it particularly accessible! I'm going to spend the Christmas period getting the bump-steer as close to zero as possible, that way it shouldn't be a major factor when I book into WIM in the New Year. If I need to make any further fine adjustment I can consider Rose jointing the track rod ends, we'll see what your computer says. I'm guessing the caster angle will make a small difference to the position of the steering arm. I currently have +5° dialed in. Is this about right, or should I anticipate using more (or less)? I guess luck (or a lack of it) has to be a factor. As you know, I am not a vehicle designer, but most aspects of my design seem to have worked out OK, so I guess I shouldn't be too disappointed! Lauren Quote Link to comment Share on other sites More sharing options...
Tony Posted November 30, 2009 Report Share Posted November 30, 2009 The castor depends on the SAI and camber positions and the weight on the front.... The attaching pin from the TRE to the hub is it vertical or horizontal? Quote Link to comment Share on other sites More sharing options...
CIH Posted November 30, 2009 Report Share Posted November 30, 2009 I plan to bin the brakedisc dustshields when I "do" my Silvia. Doubt they're really necessary with decent pads and giving the surrounding areas a decent clean periodically ? Quote Link to comment Share on other sites More sharing options...
Tony Posted November 30, 2009 Report Share Posted November 30, 2009 I plan to bin the brakedisc dustshields when I "do" my Silvia. Doubt they're really necessary with decent pads and giving the surrounding areas a decent clean periodically ? Arn't they also air rams to cool the brakes. Quote Link to comment Share on other sites More sharing options...
Spacenut Posted December 1, 2009 Author Report Share Posted December 1, 2009 The castor depends on the SAI and camber positions and the weight on the front.... The attaching pin from the TRE to the hub is it vertical or horizontal? Hi Tony - I appreciate it's a bit of a "chicken and egg" question, I just wondered if I was in the right ball-park with the caster angle I have been using to date. The corner weight is ~191 kg at the front, and 20 kg of that is unsprung, so 171 kg sprung corner weight, SAI = 4.9° (standard Cortina), camber 0°. Should I budget for more or less caster than the current +5°? The TRE is a standard taper balljoint at the moment, mounted below the steering arm (one-piece forging integral to the upright) with a vertical taper pin axis. I can make gross adjustment of the bump-steer using the packing shims under the steering rack (that's what I designed it for), its only if I need really fine tuning that I would drill out the taper in the steering arms and use a Rose joint... which hopefully won't be necessary once I fix my mistake! Lauren Quote Link to comment Share on other sites More sharing options...
Spacenut Posted December 1, 2009 Author Report Share Posted December 1, 2009 I plan to bin the brakedisc dustshields when I "do" my Silvia. Doubt they're really necessary with decent pads and giving the surrounding areas a decent clean periodically ? Arn't they also air rams to cool the brakes. I think in my case (and probably Cam's too) the backplates aren't for brake cooling. The idea of the Cortina back plate seems to be to fill the air gap between the inside wheel rim and the hub. That was with a standard 13" wheel, Green Machine uses 15" rims. Even with my ET16 RWD offset the brake disc is still shielded by the wheel rim (7" rim width helps), so I suspect that without forced air cooling, which I haven't used and the Cortina donor never had, my brakes would be better off without the backplates, as they hinder circulation around the disc and air movement through the wheel. If I use ducting from the nose intakes (currently feeding the cabin ventilation system) for forced-air cooling in future (perhaps for that trip over the Alps that I always promised myself) I can quickly fabricate a cowl to go around the disc with an air hose spigot. With an all-up weight of 830 kg (54% over the rear axle) and exclusive road useage, I haven't needed to upgrade my brakes from solid discs yet! I get a lot of brake dust on the wheels at the moment (standard pads, I've got a set of green fast road pads to replace them), but I quite like that in a car - it shows it gets used, unlike most Novas that only come out two or three times a year for some gentle cruising... Lauren Quote Link to comment Share on other sites More sharing options...
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