Tuesday, 11 December 2007

't Kreng's front suspension upgrade (old news)

As I am ill at home at the moment I’ve time to put some older info in my weblog which has been lying about but wasn't used yet. Might be old news put maybe someone finds some inspiration from it!
Under the pretence off further improving the handling of 't Kreng I had a go at the front suspension last year. As I had ordered some new front brakes and they took a while to arrive I had some time to work out a new front setup. For this I used the following starting points;
  • Front struts with adjustable spring platforms;
  • Replace original thrust collar (part nr. UKC329) with a proper thrust bearing;
  • Use universal 2¼ inch coil springs, for easier choice of spring rates;
  • Stiffen up the front as much as possible;
To start with I got myself an adjustable coil over kit for an Opel Corsa (as these had the smallest inside diameter from the available kits). After which I hacked up some perfectly good OS front struts;

And welded up the threaded tubes. As the inside diameter of the Corsa tubes was slightly larger than the outside diameter of the struts I had to make up some slim rings. These went between the strut and the threaded tubes to centre these and fill the gap to allow for a better weld.
After the welding was done it was time to move my attention to the top of the conversion. As I had decided on some decent and simple "off-the-shelf" thrust ball-bearings (standard SKF item) combined with the 2¼ inch coil springs I needed something to house these. Something to replace the standard TR7 upper spring pan. A few hours behind the computer solved the problem;

To keep the weight down as much as possible I used an aluminium alloy for the spring pans. And while I was working at the spring pans I thought it a good idea to also replace the sub frame mounting rubbers with solid aluminium alloy ones. Knowing someone who knows how to use a lathe certainly helps with this kind of work. The end product certainly looks good;

And by the time these parts were finished the dampers and the springs I ordered from AVO had arrived. So as I now had all the parts for the suspension struts it was time to get them assembled which was rather straightforward;

And after that there was the (seemingly) extreme long wait for the brakes to arrive, so I could assemble everything and fit it to the car. When they did arrive I started with dismantling the old suspension and brakes from the car. First thing to do was fit the alloy spacers between sub-frame and chassis leg. Here I found out that I had overlooked something. The original rubber mountings have steel inserts. The top ones of which were binned because the hole in the spacer was ø12 mm. As a result the original lower inserts were too short, which is bad as you can't machine something on! So a pair of new inserts were made for the sub frame’s front lower mounting bushes. On the right the original one, on the left the new one;

I also used the new alloy spacers to lower the sub-frame and thus the engine by some 5 mm by simply making the spacers 5 mm thicker than the original ones. And as the suspension is completely adjustable any geometry changes resulting from this lowering can easily be adjusted;

With the sub-frame mountings sorted it was at last time to put the new struts and brakes on the car. As expected this was rather straightforward;

So after everything was fitted it was time to bleed the brakes (and align the callipers at the same time). After which it was a matter of tightening the calliper mounting bolts and putting the wheels back on. Before I could start with any testing I first had to set the ride height properly. To get it were I wanted it I had to wind down the lower platforms quiet a lot though. As they are so far down they are only a few mm’s free from the inside tire wall, but then that's more than enough.

The odd thing is, on both sides the fitted length of the springs is more or less the same (225 lbs/inch, free length 254 mm) being 181/179 mm respectively). Also the distance between lower spring platforms and axle are the same. But there is nevertheless a difference in ride height off 10 mm between left and right;

But as the car doesn’t behave strange I still don’t worry too much about that!

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