Spacenut Posted December 24, 2009 Report Share Posted December 24, 2009 Hi guys - as some of you know, I have this modified Nova kit car... which is in dire need of Tony's ministrations. But first, I need to fix the geometry damage sustained during an altercation with embankment at the Devil's Punch Bowl 2 years ago. It just would not have been worthwhile having the suspension aligned with the NSF spindle 2° out of whack. This is what I did... About 2 months ago now I checked the front suspension ride height on the Green Machine and it seemed a bit low – the lower wishbones weren't parallel to the ground, and neither were the steering trackrods, which don't bode well for bump-steer. Easy job, I thought – simply wind the suspension up on the coil-overs. Ahh, if only it were that simple! To cut a long story short, I finally managed to release my OSF coilover (the upper bush sleeve had cold-welded to the bolt and had to be pressed out), wound up the ride height, which gained positive camber, so I popped off the top balljoints and wound them in, but ran out of adjustment on the NSF. Removed the entire top wishbone and wound in the inner Rosejoints, only to run out of clearance around the coil spring at full droop. Removed the axial shims on the top wishbone to increase clearance, which ruined the caster adjustment. Result? Steering pulls strongly to the left when driving straight ahead. Just like it did after I stuffed the nose into the banking at the Devil's Punch Bowl 2 years ago. With me so far? Good. This is where it gets more interesting. As you may have guessed by now, the cause of my woes is that bent NSF spindle, which I skilfully compensated for, but only at the expense of some adjustment. Upon realising this painful truth, many vile oaths were uttered (“fiddlesticks†and “oh, botherâ€), and I resolved to fix the problem once and for all. This is my front suspension arrangement... It was raining when I did all this, no wonder I lost my temper at the end of the day Basically, the wishbones are custom Rosejointed items which Lee Noble (yes, that Lee Noble) sold for a Lotus 23 replica that he designed in the late 80s. Like all of Lee's designs, the 23 was honed on the racetrack and shares its geometry with the legendary Ultima, which of course Lee also designed. I had the top wishbone balljoint mounting modified to take a Ford Transit steering drag link instead of using the taper pin and high angle Rosejoint specified originally. This in turn dropped the outer balljoint height down a bit, necessitating the repositioning of the inner chassis mountings. With the geometry set, the Transit balljoint fits into a Ford Cortina suspension upright (spindle/stub axle), with a modified Cortina balljoint in the lower wishbone. The disc is standard Cortina, as is the brake caliper, which is the popular M16 (no relation to a machine gun as far as I know). The steering rack is also from the Cortina. Quote Link to comment Share on other sites More sharing options...
Spacenut Posted December 24, 2009 Author Report Share Posted December 24, 2009 OK, so you know what my suspension looks like now. I reversed the car into the garage and propped it up on blocks at the vehicle ride height. Although my driveway slopes to one side by a couple of degrees for drainage, the garage floor, although rather pitted, is relatively level, which I confirmed using a spirit level on the chassis. With the wheels off I was able to remove the brake caliper and the hub nut (held in place by a split pin and catellated nut cover to stop it coming loose) and withdraw the disc and hub carrier. I then popped the uprights off the balljoints and had a good look at them. This is what I saw... The NSF spindle is on the left, and you're eyes are not playing tricks on you... it is bent... ...However, it is clear from the other pictures, and detailed comparison measurements, that in every other respect the two uprights are identical mirror-images of each other. Why was this important? Well, I don't need to tell you how unlikely it is to see a Mk3, 4 or 5 Cortina about the place. Equally rare is their appearance in scrapyards, as most have been stripped to supply donor parts for Westfields, Robin Hoods and other 7even clones. So my plan was to send the uprights to Randall Motorsport, an outfit in Norfolk who prepare stock car racers. As stock car is a contact motorsport, and the Cortina is the suspension donor of choice in BRISCA Formula 3, Randall modify the uprights by machining off the spindle, and then drilling and tapping the forging to accept a high tensile steel screw-in spindle. So instead of throwing away the uprights if they get bent, stock car racers can simply replace the spindles and carry on racing. I think you can see where this is going... Quote Link to comment Share on other sites More sharing options...
Spacenut Posted December 24, 2009 Author Report Share Posted December 24, 2009 Well, about three weeks ago, I finally received my reworked uprights. As you can see, the machined face was a good opportunity to check the suspension and steering geometry – I can use it as a suitable surface for my magnetic laser-level, and look at camber gain in the vertical plane, and bump-steer geometry in the horizontal. You can also see the three mounting holes for the brake backplate. I decided to leave these off when I rebuilt the suspension, ostensibly because they contribute nothing to brake cooling and provide little protection to the brake disc (which is completely covered by the roadwheel), but also because the backplates were rusty and add extra unsprung weight, even if they only weigh a few grams. I also decided to replace the wheel bearings at the same time, as the NSF ones were almost certainly damaged from running askew for two years. I remember having to adjust the bearing preload countless times in the first few months of road use following the accident. Lifting the cast steel hub carriers got me thinking, why don't I replace the factory units with machined aluminium hub carriers? A plan slowly dawned... The trouble is, you can't just use any old alloy hub carriers – my researches into aluminium Cortina uprights had found that, while there are several suppliers of really neat alloy replacements, they are all designed for 7even clones weighing 600 kg or less; the manufacturers refused to guarantee them for any other application (particularly when I mentioned the Green Machine weighs 831kg), which is why I have stuck with the forged steel originals, albeit modified. It was much the same with the alloy hub carriers, which were all flimsy items designed for ultralight applications. I needed something heavier-duty. I needed Hi Spec Brakes. This outfit hail from Essex and supply big brake kits, mainly to Ford enthusiasts. They also do a neat line of aluminium CNC-machined hub kits for Cortinas, Escorts/Capris and Granadas. I called them up and asked what applications these hub kits were for, and intially I was disappointed to hear that they were intended primarily for the kit car market. My heart sank, until I was told, after a little more prodding, that several customers had used these hubs in their World Cup rally Escorts. As far as I was concerned, if they were good enough for rally cars they were good enough for me. The hub kits came complete with new bearings, grease and split pins, and the inner and outer bearing races pre-fitted. All I had to do was fit my own discs, grease up the bearings and voila! The Beast lives again! The other aspect I really liked was the centre hub nut caps, hammer-on pressed steel items originally, are chrome plated aluminium screw caps on the Hi Spec hubs. As these caps are exposed with my road wheels they make the whole car look much more presentable. Now all I need is something as neat for the back wheels Nearly up to date now... Quote Link to comment Share on other sites More sharing options...
Spacenut Posted December 24, 2009 Author Report Share Posted December 24, 2009 I screwed in the new spindles once I had established I could still use the adjacent machined face for alignment checks. The spindles have standard RH threads both sides, so in one case I was backing the spindle out of the upright while I tried to tighten the fat Nylock backing nut supplied with the kit. Of course you can't grip the spindle with anything without ruining the precision machined surface, so I took both the hub nuts and locked one against the other and clamped the assembly in the vice. That did the trick, new spindles in place and locked down. I then reassembled the uprights onto the suspension wishbones. I removed the discs from my old hub carriers and bolted them up to the new units. 42 lb/ft on each of the four bolts and bend over the locking washer tabs. I haven't weighed the new hub carriers, but subjectively they feel at least 2 kg lighter than their steel counterparts. That should bring the unsprung weight at the front down from 25 kg to 23 kg per side, a saving well worth having! I greased up the bearings, fitted the inner grease seal into each hub carrier and offered the assembly up to the spindle. The OSF went on like a charm; the NSF was more problematic – the outer bearing wouldn't pass over the spindle. Initially I feared that Randall had sent me the wrong spindle on one side, but closer inspection revealed that the milled slot in the spindle, used to locate a keyed thrust washer, had been machined in the opposite direction and had left small burrs along its length. Some quick work with a file and both hubs were in place. This is where the pictures run out, as I have yet to get the second roll of film developed. Suffice to say, once the new hubs were in place, it was a simple job to set the bearing preload (8 lb/ft on the hub nut and lock off with the castellated cover and split pin), refit the brake calipers (two-stage torque to 60 lb/ft and bend over the lockwasher tabs) and replace the asymmetrically worn brake pads with a set of nearly new EBC Green Stuff fast road items. I set the nominal suspension and steering geometry with the lower wishbone horizontal. Camber at zero, toe-in at zero, then refitted the coil-over dampers and checked the torque on all fittings. With the AROC Christmas meal looming the following day, the Green Machine finally roared into life at 5 pm on a cold, wet and dark Saturday afternoon. Cinderella did go to the AROC Christmas lunch Post run checks showed the ride height was still a tad high (which was cambering both wheels positive). The required change was about 5mm which I dialed in last weekend, between bouts of frostbite. I still need to sort out the bump-steer issue before I venture out to WIM, but I'm still hoping the Nova will be in a fit state to drive over early in the New Year. Lauren Quote Link to comment Share on other sites More sharing options...
Tony Posted December 24, 2009 Report Share Posted December 24, 2009 Superb post......... Back in a week once i consume all the information.... Quote Link to comment Share on other sites More sharing options...
CIH Posted December 24, 2009 Report Share Posted December 24, 2009 What kind of camber gains are you seeing ? Quote Link to comment Share on other sites More sharing options...
Spacenut Posted December 25, 2009 Author Report Share Posted December 25, 2009 Superb post......... Back in a week once i consume all the information.... Thanks Tony - at least now you can see what I've been working with! What kind of camber gains are you seeing ? Hi Cam - the camber gain is quite rapid. When I rebuilt the suspension I set 0° camber with the lower wishbones parallel to the ground at the nominal ride height. When I put the car back on its wheels the ride height was around 10mm too high each side, and that resulted in about +1° positive camber. Clearly the suspension is only intended to work with a very short travel, which is just as well as I only have 2" of travel from bump to rebound, but assuming the camber gain remains broadly linear that still equates to more than 5° camber change I worked out that 225lb springs at the front would give an acceptable natural resonance, but would still allow adequate movement. They certainly work better than the 300lb springs that were on there before, that was like riding on rocks Lauren Quote Link to comment Share on other sites More sharing options...
Tony Posted December 25, 2009 Report Share Posted December 25, 2009 This is the problem with old school configuration and positive migration on bump. Is there room to install this type of adjuster on the top mounts? Not this actual one but something along this line? Quote Link to comment Share on other sites More sharing options...
Spacenut Posted December 26, 2009 Author Report Share Posted December 26, 2009 Hi Tony - not sure it was clear from the above, the camber migration is negative in bump, positive in droop. So in a corner the outside tyre gains negative camber with body roll. Isn't that correct for a performance double wishbone arrangement? I'm not sure how I would adapt the slotted strut mount to a double wishbone geometry. The only way I could alter the rate of camber gain would be to vertically slot the top wishbone frame mounts, which would require a significant stripdown of the front end Latest news is I've been out in the car today and one of the spindles worked loose Fortunately the Nylock back nut stopped it coming out altogether, and I was able to retighten the spindle and back nut with the assembly on the car (whew!). Dialed another 5mm out of the coilovers, as the camber was still +0.5° after a good run. It's reading zero now, but that is with reserve fuel so I guess it will go ever-so-slightly negative when I brim the tank... Lauren Quote Link to comment Share on other sites More sharing options...
Tony Posted December 27, 2009 Report Share Posted December 27, 2009 Yep, bump/droop and roll transition is perfect for the configuration.... But.... the trim height, wishbone radii, steering arm radii and camber gains on bump are out if sync and i'm not even going to think about the roll centre..... If we are going to have any chance to calibrate the chassis we need adjustabilty, camber is a must, castor would be nice but not essential. Quote Link to comment Share on other sites More sharing options...
Spacenut Posted December 27, 2009 Author Report Share Posted December 27, 2009 Hi Tony - its not as bad as you think... I think. Here's what's available in terms of adjustment... (1) All of the Rose joints are adjustable, with a little bit of work. Both top and bottom wishbones have one at each end. These allow (within reason) the length of each wishbone to be altered, and the caster to be adjusted by adjusting one joint in or out relative to the other - for each wishbone (2) The outer balljoint is threaded and allows coarse adjustment of camber without having to remove the entire wishbone. (3) Because the inner top frame mountings were dropped, there was clearance either side of the joint, which allows axial movement of the top wishbone. I have used various thickness washers either side of the Rose joints to set the top balljoint position relative to the bottom balljoint, i.e. another form of caster adjustment. I used the same track dimension as the Cortina donor, so I am confident that the steering arm radii can be brought into line with the wishbone arcs - that is what they were designed for, after all. I just need to remove some shims under the steering rack to drop it down a bit. That's the next job on the to-do list. The static roll centre height is about 1.5" above ground level. It obviously moves around with body roll, and with the top wishbone half the length of the bottom the lateral movement would be quite significant but for one thing - the overall suspension travel is less than 2" under all operating conditions. So again, I'm hoping it will not be as bad as you think. Look at it this way - if you can sort this one out, everything else will be a walk in the park Latest news is that the spindles are holding up, but after re-checking the camber (as best I can), tyre pressures and ride height I am still getting a slow drift to the left. I measured the caster and the NSF is +4° while the OSF is only +3.5°, which might explain it. I'll see what I can do to equalise the settings side for side. Maybe I will try a lower caster value, the steering is heavy enough as it is - maybe I can reduce the steering effort at the expense of some directional stability... +2.5° perhaps??? Lauren Quote Link to comment Share on other sites More sharing options...
CIH Posted December 27, 2009 Report Share Posted December 27, 2009 does it have power steering ? or manual ? Quote Link to comment Share on other sites More sharing options...
Tony Posted December 27, 2009 Report Share Posted December 27, 2009 Happy days with the camber/ castor adjusters.... So to hit the list here goes.. 1: See this often, Maserati/ Ferrari trait. 2: Very happy days 3: Same "I used the same track dimension as the Cortina donor" but it's not a Cortina, the track, width, wheelbase and DI are stand alone..... Move away from the parent car and visualize your own build. Quote Link to comment Share on other sites More sharing options...
Spacenut Posted December 27, 2009 Author Report Share Posted December 27, 2009 does it have power steering ? or manual ? 100% human muscle powered. Cortina/Pinto manual rack, with a VW bus telescopic steering damper to take the sting out of the steering kick-back. I basically copied the design used by the Lamborghini Miura. Happy days with the camber/ castor adjusters.... So to hit the list here goes..1: See this often, Maserati/ Ferrari trait. 2: Very happy days 3: Same "I used the same track dimension as the Cortina donor" but it's not a Cortina, the track, width, wheelbase and DI are stand alone..... Move away from the parent car and visualize your own build. Very true - I just tried to ensure the rack length was compatible with the wishbone geometry, to minimise bump-steer. The wheelbase is certainly different, which has made the already poor Ackermann worse... um, what's DI? Lauren Quote Link to comment Share on other sites More sharing options...
Tony Posted December 28, 2009 Report Share Posted December 28, 2009 DI.... Is Dynamic Index, by calculating the corner weight plus the wheel base you can estimate the handling expectations -V- the human natural frequency. A perfect DI is 1.0 meaning the Hz of 2 allows everyone to comfortable drive the car, an Evo on the other hand might have a DI of 1.5 which runs at 3 or 4Hz, if my natural frequency is 2Hz then i would say the Evo is undrivable, if my frequency is 4 or 5Hz i would say the car handles fantastic. If again the DI is .5 then i could comfortably drive the car but it's handling would be slow and unresponsive, a Bentley for example. The DI is established at the design stage, perfecting the corner weight improves DI moving the sloppy .5 to a 1.0, now we understand the chassis frequency and the human frequency could be in conflict?..... At this point the chassis calibration comes into account. With good communication the chassis can be tuned to suit the owner, the intention for the car and indeed the modifications. In summery DI: categorizes the handling group Human: frequency is our comfortable 2Hz Chassis frequency impacts on the human frequency as the DI is calibrated Chassis calibration tunes all the above. Quote Link to comment Share on other sites More sharing options...
Spacenut Posted December 28, 2009 Author Report Share Posted December 28, 2009 DI.... Is Dynamic Index, by calculating the corner weight plus the wheel base you can estimate the handling expectations -V- the human natural frequency. A perfect DI is 1.0 meaning the Hz of 2 allows everyone to comfortable drive the car, an Evo on the other hand might have a DI of 1.5 which runs at 3 or 4Hz, if my natural frequency is 2Hz then i would say the Evo is undrivable, if my frequency is 4 or 5Hz i would say the car handles fantastic. If again the DI is .5 then i could comfortably drive the car but it's handling would be slow and unresponsive, a Bentley for example. The DI is established at the design stage, perfecting the corner weight improves DI moving the sloppy .5 to a 1.0, now we understand the chassis frequency and the human frequency could be in conflict?..... At this point the chassis calibration comes into account. With good communication the chassis can be tuned to suit the owner, the intention for the car and indeed the modifications. In summery DI: categorizes the handling group Human: frequency is our comfortable 2Hz Chassis frequency impacts on the human frequency as the DI is calibrated Chassis calibration tunes all the above. I see - hmm. Corner weight plus wheelbase. Not sure what units to use, or which corner weight to take, but I have calculated the natural resonant frequency of the Green Machine: the front suspension is 122.39 CPM, or 2.04 Hz, and the rear is 128.75 CPM, or 2.15 Hz. That's with 1 occupant and reserve fuel, i.e. the highest the frequency is likely to be. I don't know how those numbers tie in to DI, if at all. Lauren Quote Link to comment Share on other sites More sharing options...
Tony Posted December 28, 2009 Report Share Posted December 28, 2009 2Hz front/ rear is an excellent DI at near to 1.0 without the weigh scales... CPM reads very well calculated, where did these figures come from? Quote Link to comment Share on other sites More sharing options...
Spacenut Posted December 28, 2009 Author Report Share Posted December 28, 2009 They are? That's good. Subjectively they feel right too. I used the formulas in Allan Staniforth's Race and Rally Car Sourcebook. The corner weights were measured on the Green Machine prior to it getting on the road - 831 kg with reserve fuel and fluids, distributed 46% front, 54% rear. I whistled up a spreadsheet to factor in weight of fuel, driver etc., and used a target CPM of 120 - or 2 Hz. The spreadsheet allowed me to iterate the spring rates to achieve the desired natural frequency - 225 lb/in front and 325 lb/in rear, to give the resonant frequencies quoted above. I just had to do something, this was my third complete set of springs, at £30 a corner. Previous attempts at getting the spring rates right relied on pure guesswork and got me nowhere. I took some in-car video last year, and while I am not one to publicise my amateur efforts to a wider audience, the camera fixed its anti-vibration reference on the horizon, so you can see the movement of the chassis on the bumpy bits. The video shows that there is travel, and the damping is adequate... I used the same spreadsheet to calculate the spring rates for another Nova, this time all VW based, so the owner could decouple the front torsion bars and replace with coilover dampers. He was very satisfied with the resulting ride and handling too, although the video below was acquired when he had 120 lb/in springs on the front (target was 110 lb/in, but 1.9" diameter springs are only available in 20 lb increments). Onboard footage was hand-held in his car, but the ride still wasn't bad. Nigel eventually changed the front springs to 100 lb/in with a corresponding improvement in ride comfort. Both videos are rubbish, but it was my first attempt with a borrowed camcorder... Lauren Quote Link to comment Share on other sites More sharing options...
Tony Posted December 28, 2009 Report Share Posted December 28, 2009 Vid one showed great steady state stability with very little yaw and no bump issues i could see..... Vid two is just car porn "nuff said". To me it looked like you had a very good build then it got hurt, logic suggests you return the wounded to where it was, which looked great Quote Link to comment Share on other sites More sharing options...
Spacenut Posted December 29, 2009 Author Report Share Posted December 29, 2009 Thanks Tony - I'm glad the overall performance looked OK. I did video 2 for the other Nova club members mainly, but the driveby footage (particularly Nova Nigel's car) shows how the suspension deals with some of the bumps along that part of the road... I've just been out and re-shimmed the NSF top wishbone to correct the caster on that side. Both sides now +3.5° near as dammit. Steering still has a very slight pull to the left, I've eliminated brake and bearing drag, tyre pressure and caster. Camber may be slightly asymmetric (I was shooting for zero, NSF may be slightly positive, changing camber thrust), also the wheelbase may not be equal side-to-side (I compensated for this in the post-crash alignment, something else to check... if it ever stops raining ). I suppose the other possibility may be the tracking, I centred the rack and aimed for zero toe, but there may be some crabbing in the geometry somewhere... need to redo the chassis squaring measurements... That's the trouble with having Rose joints everywhere, its infinitely adjustable Lauren Quote Link to comment Share on other sites More sharing options...
hms Posted December 29, 2009 Report Share Posted December 29, 2009 Nice Vid lauren. I have to ask though, is your steering wheel on upside down? h Quote Link to comment Share on other sites More sharing options...
CIH Posted December 29, 2009 Report Share Posted December 29, 2009 Remember Toe won't cause an actual pull, just put the steering wheel off-centre. Shame you can't measure SAI as that would be interesting. Quote Link to comment Share on other sites More sharing options...
Spacenut Posted December 29, 2009 Author Report Share Posted December 29, 2009 Nice Vid lauren.I have to ask though, is your steering wheel on upside down? h Thanks H - yes, I had noticed I get better visibility of the instruments that way. Nova Nigel was so impressed, he used the same trick. Its a bit different Remember Toe won't cause an actual pull, just put the steering wheel off-centre. Shame you can't measure SAI as that would be interesting. You're right. Straight ahead is straight ahead. But if I let go of the wheel on a non-cambered surface, the steering just drifts to the left. Seems to go only so far before self-centring forces take over. Given that dimensionally everything else about my uprights was equal, I am assuming that the SAI is the standard factory 4.8° both sides. I'm thinking my wheelbase might be different on each side - if front and rear wheels are at zero toe, but the offside wheelbase is longer then the car will steer to the left. I'll check the chassis and wishbone triangulation again... Lauren Quote Link to comment Share on other sites More sharing options...
Tony Posted December 29, 2009 Report Share Posted December 29, 2009 I really advise you swap the front wheels side-to-side just the prove the pull is not pneumatic. Quote Link to comment Share on other sites More sharing options...
CIH Posted December 29, 2009 Report Share Posted December 29, 2009 I really advise you swap the front wheels side-to-side just the prove the pull is not pneumatic. Doubled My Silvia suffered a tyre induced pull and I never really believed it untill I experienced it for myself. Quote Link to comment Share on other sites More sharing options...
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