Building The Front Suspension

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Now back to things more or less in the order in the manual.

The front suspension is next, and is probably the most critical part of a 12th scale car to get absolutely correct. You can see all the parts required to build up the 12x front end in the picture below, just as they are supplied.

There are a few other non standard parts I use to build up the front end. I'll explain these below.

Just about everyone in the UK uses Associated front springs instead of the ones supplied in the kit, which tend to be too soft for the carpet we race on. Associated, CRC and BMI all supply the same springs. I have shown the CRC ones below. 0.020 springs are the baseline though it is a good idea to have some 0.022 and maybe 0.018 springs around for unusual circumstances.

Instead of using the steel screws supplied in the kit to screw the lower arms to the chassis I use the Hot Bodies titanium version, mainly to save weight. These are part number 61683 as can be seen in the picture below.

I also replace the upper arm turnbuckles with titanium ones. I use the Tamiya ones shown below, though there are others just as good. Doing this is by no means essential, I just like doing it!

On to building the suspension up. First carefully cut all the parts from the trees they are attached to and carefully remove any excess material with a very sharp knife. There shouldn't be much, the moulding quality is pretty good. You should end up with the parts below.

The next thing I normally do is to build up the upper arms. It is absolutely critical to get the turnbuckles straight in the arms. If you don't the static caster of the car will be different from left to right. The way I do it is to tap the parts with a 3mm tap just in far enough to know the turnbuckles are going in straight. Remember though, one side needs a right handed tap and the other side a left handed tap! The way I do it is as follows. Looking from the front of the car in the same way as the manual it goes ball joint, arm, arm, ball joint. In the same order I use left handed, right handed, left handed, right handed. This ensures both sides are adjusted in the same direction. Tapping the arm is shown here.

Remember not to tap too far. It only needs to be enough to make sure the turnbuckle is going to go in straight. If you go too far the turnbuckle will be too loose.

Tapping the ball joint is shown below. The way I make sure it is straight is to tap in very slightly, eye up to large right angles such as pieces of furniture, walls etc. Then adjust as necessary, turn the tap slightly again, turn the part 90 degrees and check again. Seems an unusual technique but it works for me!

The lower arms need preparing next. The bottoms of the arms need to be absolutely flat. If they are not they will tweak the chassis. To do this, sand them on an absolutely flat surface with 600 grade wet and dry. This is complicated by the fact that the arms do not lie horizontally, they are supposed to droop downwards slightly towards the ball joint, so it is necessary to make sure you maintain this droop when you are sanding. Sanding an arm can be seen in the picture. I find that if you do this lightly and slowly the arm finds it's natural angle and ends up correct.

Also when sanding the arms it is essential that both end up the same height at the ball joint or the car will be tweaked. Compare them while sanding to make sure the tops of the arms are an identical height as seen in the picture below.

Keep sanding the arms until there is no shiny part left on the two circular sections. In the picture here you can see the left section has no shiny part left but the right one does, so sand more until this is gone.

 A finished arm is in the picture below.

It is worth trial fitting the arms to the chassis in order to double check the droop and the height of the arms as can be seen below.

If the arms are correct the front brace will fit naturally without the chassis bending at all. The height of the tops of the arms at the ball joint end can be checked with calipers.

The balls then need to be put into the ball joints. For the top ones it is best to use a pivot ball tool as can be seen below so the balls are not marked. It is just about possible to fit the lower ones with fingers but the tool can be used also.

A screw is used in the lower arm to adjust the tightness of the pivot ball in the arm. If this ends up too loose it is possible for the pivot ball to pop out of the arm while running so it is essential to get this tight enough. What I do is to put the pivot ball in, over tighten it slightly, put the kingpin though the pivot ball and move it around for a couple of minutes so it seats the pivot ball in the arm. Then I loosen it so it is possible to move the ball with a little effort. A rough and ready technique but it seems to work.

Time to build up the steering blocks and axles next. There's not much to do to these really. You can see below though that I've used titanium ball cups in order to save weight. Also you will see lots of purple alloy screws and nuts used throughout the article, also to save weight while building the car. They look good as well! The screws and nuts are from www.fastener-express.com and I replace the steel ones with the alloy equivalents in most places. I will say so for a particular area if I don't.

The rest of the assembly  can be put together now. Always fit the cross brace, the car is much better with it.

When fitting the upper arm mounts use the centre hole that gives 5 degrees of static caster. These can move slightly so I like to push them upwards as far as they will go when tightening them so they cannot move any further. When fitting the upper arms put a 1mm spacer clip at the front of the arms and a 2mm one at the rear.

If using the Associated springs you will only need a single shim above the top pivot ball rather than the two shown in the manual. The steering block will also be quite a tight fit on the kingpin. Unlike some other cars this is exactly as it should be, just make sure the block is pushed up against the top pivot ball.

The titanium nitride coated parts are very nice indeed and really do help the overall smoothness of the assembly.

The suspension can now be mounted on the car. You will need the spacers underneath. The size will depend on the diameter of the front tyres you will be using. In the pictures I have used the 2mm spacers until the car is fully built and ready to run. It will be adjusted properly at that point. The arms need to be tightened carefully. Too tight and they can tweak the chassis. Just tighten it until you feel the screw grab the chassis.

The front suspension is now built and fitted and should be both smooth working and accurate.

 

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