Spacenut Posted February 21, 2010 Report Share Posted February 21, 2010 OK, so things have been a little quiet again of late, so I thought it would be a good idea to bring you up to date on the latest happenings in the world of hurt that is the Green Machine. Being mostly about bump-steer I thought it warranted a separate thread. As you know, I managed to get the new spindles and alloy hubs installed before the AROC Christmas meal in December, and a break in the snow allowed me to get to the New Years Day classic car event at Elsted on January 1st. But in spite of the improvements, the front suspension still wasn't right, so a couple of weeks into the New Year I reversed the Green Machine back into the garage and put the front end back on blocks. This time I would get it right... So, armed with a piece of string I first tackled the wishbone geometry, rebuilding top and bottom wishbones ensuring all the joints had the minimum thread penetration (1.5 x thread diameter for the Rose joints I was using). The only exceptions were the upper wishbone front joints, which have the biggest influence on caster angles – I set these with an additional 3 turns in to pull the caster angles forward. Eventually I got both sides equalised at +2.75°, quite a lot less than the +5° I have been using to date. With everything lined up nicely, it was time to put the springs back on, but while I had the coils off I used my laser crosshairs to check the bump-steer geometry and couldn't quite believe how much I found! Lacking a proper DTI bump-steer gauge, this is the technique I used; The drawing board is used to draw three parallel lines, which represent the nominal ride height, full bump and full droop positions. The laser crosshairs are attached to the brake disc face (magnetic base), and the suspension moved through its travel on the scissor jack under the bottom balljoint. With the suspension at nominal ride height, I set the nominal line on the drawing board to line up with the laser line, then move the jack smoothly up and down. Not as accurate as a DTI, but I was able to take readings down to less than 0.25° - not that I needed that much accuracy to start with! The bump-steer was in fact a massive 2° of toe-out as the suspension moved through its range. What was even more galling was the knowledge that I was responsible for making it that bad in the first place, courtesy of a set of 5 and 6mm steel plate shims under the steering rack. And to cap it all, although the bump-steer is at least adjustable on the Green Machine, access to the steering rack mounting bolts is only possible with the cooling system drained and the fuel tank removed! The direction of toe change suggested that the rack was too high; removing the shims was therefore the order of the day. So, determined to do the job properly this time, I took a deep breath and drained the cooling system, removed the radiator and used the electric fuel pump to siphon the fuel into an empty C16 fuel bowser borrowed from my friend Sean. It's graduated in litres and US gallons, so I was able to determine that my reserve fuel capacity is a handy 11 litres after the gauge reads zero – not bad! With the fuel tank removed I could at last access the steering rack. As you can see, the rack itself is mounted on additional chassis longitudinals. About 15 years ago I determined that the steering rack (its a Cortina unit) needed to be raised up a bit, and welded on these pedestals out of 4mm steel plate. The top plate has captive nuts welded on underneath so that longer rack bolts can be used with spacers. It seemed like a good idea at the time... So, with 3 spacers removed (dropping the rack down a not insignificant 17mm), I bolted the rack down thus and repeated the bump-steer measurement. It was better, but alas still too large, and still in the same direction – the rack needed to be even lower... (Notice the slightly pink colour of the undertray below the chassis – that's the original red gel coat peeking through) There was nothing for it – I took the guard off my trusty Sealey angle grinder, put a fresh 5†grinding disc on and got to work. Two hours later, with my ears still ringing and a grinding wheel the size of a £2 coin, I had managed to remove the tops of the two pedestals, complete with captive nuts, and cleaned up what was left. The pedestals had been reduced in height by 10mm. Not wishing to have to repeat the exercise again, I securely ty-wrapped the rack onto the top of the plates and re-measured the bump-steer on both sides. This time the toe-out changed to toe-in on bump, confirming that I had indeed lowered the rack sufficiently. It was time to get the welder going... So, here are the new, improved mounting pedestals from the front... ...And from the side, looking through from the nearside front wheel arch. I know its very sloppy welding, but the thick metal allowed me to use a really hefty current setting and a fast wire speed, so they are at least strong enough. Also notice how the originally pink tinged undertray has turned charcoal black from all the grinding! I put several coats of Hammerite on the chassis and allowed it to cure for a week before finally setting the rack height. In the end, the best bump-steer geometry was obtained by using 3 x 1mm shims on the offside, and one 5mm plate plus a single 1mm shim on the passenger side. You can see the rack is not exactly level due to the unequal shimming. I can only assume that this unevenness is due to minor variations in the suspension pick-up points on each side. The final bump-steer figures, with the rack centred, were <0.25° toe-out on bump and droop, both sides. The very slight toe-out on bump means that if any effect manifests itself in roll, the outside wheel will tend toward understeer in a corner, which is of course safer than going into oversteer! You can also see my steering damper, which was based around the unit from a VW bus, together with a split alloy clamp which fits around the end of the nearside rack bar, just behind the track rod inner balljoint. I designed it to help counter the kick-back in the steering which (at the time) I thought was mainly due to the poor scrub radius geometry of the Cortina suspension uprights. (Hehe – there's news on that front as well...) I removed the front grille to show the modifications I have made to the stock undertray – I have fitted ABS brake cooling collectors either side of the nosecone, although these connect to the cabin ventilation system, and cut a nice radiused aperture for the radiator cooling. You can also see why I had to fit remote fluid reservoirs for my brake and clutch master cylinders! This is the view looking forwards. That's my radiator in the background, with the twin electric fans (the Alfasud has a single fan, I simply drilled and tapped the upper radiator flange to take a second unit, “just in caseâ€). I rarely have to use the fan override switch, even in the hottest weather. Anyway, back to the story. With the rack now (finally) in the right place, I bolted it down, re-measured the bump-steer (unchanged), reconnected the steering column UJ and clamped everything up, refitted the fuel tank, refitted the radiator and re-filled with fuel and fluids, refitted the coil-overs, put the car back on the ground and very gingerly went for a gentle drive around the block. This revealed that the tracking was all over the place, and the camber was a bit off as well, but the steering effort was markedly improved due to the reduction in caster angles. There was also no pull to the left, which has been bugging me ever since I rebuilt the suspension last year. A second journey last Friday settled the suspension and allowed me to determine how much camber adjustment was required. I removed both front wheels, centred the rack, refitted the steering wheel (it was one spline off to the left), popped the top balljoints off and made the necessary adjustments to the camber (1 turn = 0.25° camber change). With the car back on its wheels I used my trusty Longacre trammel bar to set the toe to zero. Job done A longer drive yesterday confirmed what I had hoped would be the case – a significant reduction in steering effort at all speeds, steering kick-back reduced by half, no pulling to the left and best of all, no instability under heavy braking (because the toe setting doesn't change with suspension travel). Its been a long hard slog to just get this far, but the car feels sooooo much nicer to drive, it really does feel like its been worth the effort! Lauren Quote Link to comment Share on other sites More sharing options...
Tony Posted February 21, 2010 Report Share Posted February 21, 2010 Stunning blog................ Back in a few days once i've analysed all the information. Quote Link to comment Share on other sites More sharing options...
hms Posted February 23, 2010 Report Share Posted February 23, 2010 Well done Lauren. Great write up. Put together the full posts and re-purpose it as an article for one of the car mags. You might get some petrol money from them! I like phrases like 'popped the top balljoints off' I've never worked on any car where something 'just popped off'! Everthing for me is a right pain in the 'arris, the simplest ones taking the longest time! h Quote Link to comment Share on other sites More sharing options...
Spacenut Posted February 24, 2010 Author Report Share Posted February 24, 2010 Thanks H - not sure there is any magazine out there that would be interested in my paltry chassis engineering efforts "on the cheap", but thanks anyway! The balljoints pop off relatively easily mainly because I have to do it so often, although the Nylock nuts look a little the worse for wear as I use them as packing for the balljoint separator (saves me having to re-dress the threads on the balljoint). Lauren Quote Link to comment Share on other sites More sharing options...
hms Posted February 24, 2010 Report Share Posted February 24, 2010 Thanks H - not sure there is any magazine out there that would be interested in my paltry chassis engineering efforts "on the cheap", but thanks anyway! Lauren Why not? You've generated enough interest on here with your threads. I would have thought any of the kitcar mags would be interested. It's not your 'paltry chassis engineering efforts' (your phrase not mine, I'd settle for 'superior chassis engineering efforts') but how you solved the issues, used the lasers etc. Drop the editors of the Kit Car mags a link to these threads, they may be interested in working them in to an article. h Quote Link to comment Share on other sites More sharing options...
Tony Posted February 24, 2010 Report Share Posted February 24, 2010 +1, i deal with the end results of the engineering work, never could we solve the sort of issues you've had, in truth we would just tell you what issues you have. Quote Link to comment Share on other sites More sharing options...
Spacenut Posted February 24, 2010 Author Report Share Posted February 24, 2010 I could give it a go I suppose - they can only say no Quote Link to comment Share on other sites More sharing options...
hms Posted February 25, 2010 Report Share Posted February 25, 2010 I could give it a go I suppose - they can only say no Let us know when it's published h Quote Link to comment Share on other sites More sharing options...
CIH Posted March 1, 2010 Report Share Posted March 1, 2010 Do it! This thread has been bloody impresive so far Quote Link to comment Share on other sites More sharing options...
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