For tarmac events, especially if you have Bilstein dampers, you can run much stiffer front springs. I've heard of people running 300lb front springs; I'm up to 250lb.
There are two types of spring seat in use on the Sunbeam. The earlier Avengers had flat spring pans top and bottom, and it seems like most competition dampers are based on this. These can be identified by the fact that the springs have their top and bottom faces ground flat, and the lower seat curves downwards from it mounting on the damper tube to the spring pan. Later Avengers, and most Sunbeams as far as I am aware, used a cup seat to locate the spring, and this is identified by the spring pan rising up from the damper tube to meet the spring. The spring ends are also left unfinished and not ground off.
Bilstein and Leda (the only units I have first hand experience of) both produce a selection of damping rates, depending on which motorsport discipline you are after. The Bilstein units differ in that they have a larger damper tube and thus can cope better with stiffer spring rates. The damper unit is separately removable (no idea how easy this is).
There is one common modification to the dampers; units which have been modified are generally known as 'wedged'. A reinforcing bar is welded in between the cast stub axle unit, to help the stub axle unit stay attached in the correct place. It's a modification definitely worth having.
It's worth keeping an eye on the stub axle condition. It's a common failure point - it simply snaps off, taking the wheel with it and breaking the brake caliper in the process. It can get a bit exciting when this happens! There is a ring press fitted onto the stub axle, which the wheel bearing inner seal runs on. This can be removed to check the stub axle by a bit of heat and gentle tapping.
Another problem you get with dampers is that the damper tube or rod bend. This normally only happens when you hit something with them, but it is something worth checking if you are getting strange alignment problems.
The bearings on the top mounts do wear out, especially those mounted in aluminium mounts, and you can often find that there is play in the mounting.
A common addition to the uprated bushes is the use of oversize washers which form a cap round the bush. This helps to stop the bush deforming during heavy braking.
It's worth keeping an eye on the retaining nut for these bushes, as it can easily work loose. A good sign that the nut is loose is that the car pulls instantly under braking, but straightens up immediately the brake pedal is released. A common modification, which is actually standard on the early Avengers, is to use a castellated nut instead of the more common nylock.
If you do hit anything hard-ish, it is worth checking to see if the TCA has bent. I found that even though the car seemed to be handling OK, the post event check showed that the TCA had bent and twisted slightly, between the drag link mounting and the ball joint.
Rear Suspension
Tarmac events will require something a little more substantial. First step on the Sunbeam is to use the Avenger 240lb springs. After that, it's all down to how serious you want to be. I'm currently running 300lb 9" springs, and the back of the car seems to be pretty well nailed down - almost too well for the 250lb fronts (too much understeer on the Longcross hills).
One thing to beware of if you are using Bilstein dampers is that they are a substantially bigger diameter than the standard units, and clearance between them and the handbrake cable brackets is limited. If you are running rear disc brakes this isn't a problem as the brackets are redundant and can simply be removed. Otherwise, the standard items might have to be removed and replaced with fabricated parts which give the dampers more clearance. One car I navigated for had the damper bracket break in half, which I suspect was down to the axle moving around too much and levering the damper against the handbrake cable bracket.
None of the bushes are particularly easy to replace. First step can often be to remove the bolt, as they often rust in. A bush pulling kit will be needed to remove the bushes - the kit can be made using some solid pipe (mines about 3mm wall thickness), some substantial washers (once again, 3mm+) and some half inch/12mm studding. Once the bushes are removed, the holes will need cleaning out. A wire brush on a drill is one of the best ways, and a screwdriver to chisel the larger lumps of rust out. Keep an eye out for the outer casing of the bushes rusting in place, especially the bushes on the top link. They often have to be hacksawed out separately from the rubber.
I've seen some Bilstein rear dampers which have rose joints at the bottom instead of bushes. Whilst this is probably good for tarmac events, I'm not so convinced for forest events - I've seen the damper mounting break off the axle in these circumstances.
I've seen one set of axle links where the bushes have been replaced with rose joints. This is probably good for tarmac events, but the owner did say that on forest events the bolts were working loose on pretty much every stage.
Some of the rear bushes are available from Superflex. Details to follow...
Next thing to pay attention to is the mountings on the car for the axle links. The holes in these can become oval, especially if the bolts have rusted in place. These are simple to strengthen.
The first things to bend are the track rod ends, where they go into the steering arm. Triumph Dolomite Sprint items are the same threads but a bit longer, which is usually sensible to get more of the track rod engaged in the track rod end. The alternative is to weld a nut onto the track rod end but that's probably not as strong.
Next to bend is the steering arm, which can be replaced fairly easily. Slide the gaiter back, find and drill out the pin which has been used to secure the locking ring against the ball joint cover. Finding the pin can be a little tricky, careful examination is required to spot the pin - easiest with the rack off the car. There are two lengths of standard arm, and it is best to use the longer of the two if you are running negative camber to get some more of the track rod engaged in the track rod end. I've seen people run some kind of tubing along the track rod to strengthen it, but I'm not sure whether this is good or bad - it probably stops the track rod bending, but causes something else bend instead.
I've seen one occasion where the universal joint in the steering column started to dismantle itself; that was on a tarmac stage car where the loadings are probably the worst, what with sticky slicks etc. Something worth keeping an eye on.
The camber is increased by relocating the TCA mounting holes in the crossmember. The holes move downwards and outwards, but I can't remember by how much off the top of my head. Something like down a quarter of an inch and out by a half inch, but don't quote me on that. The old holes should be welded up and the mountings plated.
The rest of the crossmember also benefits from stitch welding, especially if the sumpguard is seeing serious use. Also worth keeping an eye on are the steering rack mounts, I've seen these break after forestry use.
The first step to uprating the calipers is to go to the M16 calipers, as used on the Lotus Sunbeam. Although the basic size of the calipers is the same as the M16 caliper used on the Mk2 Escort RS2000, the Cortinas and the Capris of the era, the offset of the caliper is different to the Lotus. Fortunately, the offset is in the direction which is easy to correct; spacers can simply be used to move the caliper inboard to centralise it on the disc. [measurements will go here when my calipers next come off...]
Next comes vented discs. Capri 2.8 vented discs (230mm?) are the easiest to get hold of, and it is a simple modification to make them fit. They are also available cross drilled and grooved if that takes your fancy. The diameter of the inner hole is fractionally too large, and although spacer rings used to be available, they have been found to be unnecessary. The bolt holes for attaching the discs to the hub are different on the Capri, and there are two methods to tackle this problem. I reckon that the easiest is to get some holes drilled at the correct PCD at 45 degrees from the Ford holes. The alternative is to get some Ford hubs and some suitable bearings to fit them to the Talbot hubs. Either way, you'll find that you have to grind the stub axle casting back to give the disc some clearance - see the rusty bits on the photo.
If you want better front brakes than this - and I'm finding that I need this to restore the brake balance between the front and rear whilst running Chrysler C180 calipers - then the options start getting expensive.
One option I've seen is a bracket which spaces the caliper out a small distance, which in conjunction with slightly larger discs (257mm?) gives a bit more braking effort. This conversion can work with 13 inch rims - but I've never tried this setup so I can't comment.
Another relatively cheap option is to use Austin Princess 4 pot calipers with a spacing kit. With a small bit of effort fabricating pipes, the calipers will bolt straight on (once again, requiring spacers, this time slightly different in thickness to those required for the M16). The brake pads require a bit of angle grinding to allow them to sit slightly closer to the centre of the hub than they would normally if you are using the Capri 2.8 vented discs, although I believe that this is not required if you have the larger discs described above. I once borrowed a set of calipers like this for one event and did find that they provided a better brake balance front to rear than the M16 calipers, but they do flex a surprisingly large amount when you lean on them hard (you can see this when you bleed them!).
Beyond this then you are talking custom aluminium alloy calipers from a manufacturer such as Wilwood or AP Racing. And this starts meaning loadsa money. I've no idea how well these work, but I'd guess that they work pretty well. Contributions please!
If you're happy staying with drums on the rear then drums from the larger engined Ford Capris fit and provide more effort for stopping the rear. I've not had any direct experience of this combination so I can't provide any further details than this.
The next common modification is to use the rear brake calipers and mountings from a Chrysler C180. For those who don't know what one of these is, they're kind of like an Avenger which has been enlarged about 20%. And they're rarer than rocking horse p00, although they do come up for sale in the back of Motoring News etc. from time to time. The bracket to mount them onto the axle is pretty simple, and up until recently the discs were pretty readily available. The calipers have to mount on top of the axle to clear the shock absorbers, which means that they are sitting at a strange angle which makes bleeding them difficult. The easiest way to do this is to remove them from the mounting and put a block of wood in them to stop the piston moving out. And for those of you unfamiliar with rear calipers with handbrake attachements, to push the piston back in when fitting new pads, the piston must be screwed back in, whilst pressing it back in. It's often easier to remove the dust seal whilst doing this.
A more recently discovered option would appear to be the rear calipers from Sierras and Granadas used in conjunction with Ford Fiesta front discs. Having said this, I have heard that some of the parts for these calipers are starting to get difficult to come by, with problems arising with the handbrake mechanism getting sticky. The caliper also has a larger piston and I'm not sure what that does to the brake balance and master cylinder choice.
Whilst we're here, a word of warning about handbrake cables. If you motorsport discipline requires an MOT, or you use the car on the road, then the UK law says (something like) that it should have a mechanical means of stopping the car rolling away - ie. hydraulically operating the rear brakes doesn't count. I've been pulled up on this once in pre-event scrutineering, which wasn't a problem since I keep the cables attached anyway. I also know of a rally car which failed its MOT because it had no handbrake cables.
This means that if you have rear calipers, you've basically got to have some sort of cable provision. This is easy if you use the C180 calipers since the cables are(were?) available. The standard cables can also be mullered to fit as well, although watch for them corroding into the calipers. I'm sure that the same holds true if you use the Ford rear calipers. But I've seen a number of vehicles around which have XR3 front calipers on the rear, and these don't have this facility. I've heard tell that if you try hard enough, you can hook the cables onto brackets welded onto the pads, but I wouldn't like to try this myself. Another way of circumventing this rule is, theoretically at least, having a small slot in the transmission tunnel where you can drop a bolt through the propshaft. But this is another technique I've never tried.
The simplest way of doing this is to remove the Pressure Conscious Restricting Valve (PCRV), and fit an adjustable restrictor in the rear circuit. The standard master cylinder and servo can then be retained unmodified. There are two types of pressure restrictor I've seen; one is lever operated and the other has a screw in knob. The lever type is obviously quickest to adjust from one of it's half a dozen or so positions, but I have known one which failed to restrict the pressure at all (mention no names here). I found that the adjusting knob type which I had for a few years only actually made any difference over a couple of its dozen or so turns, but it did make a noticable difference.
The better (but more involved) solution is to use a pedal box which has been converted to use two master cylinders (known as a bias pedal box). This allows the braking effort to be adjusted between the two circuits. This also has the advantage that the front and rear braking systems are two completely separate circuits, which means that if one springs a leak, you don't pump the shared reservoir dry... The servo is normally dumped, although I've seen installations with remote servos in the back. This gives you a very very firm pedal - it almost feels like it is locked solid, which takes some getting used to - which gives you much better feel for whether the car is locking up or not.
The choice of master cylinder size is fairly limited, basically to 0.625" or 0.7" bores. Experience has shown that you will probably want to run 0.625" on the front circuit and 0.7" on the rear. And yes, I mean the smaller cylinder goes on the front circuit - that way you get more effort on the front circuit. I've found that with M16 calipers on the front, Chrysler C180 rear calipers and the above combination of master cylinders, that even with the bias wound all the way to the front, I've still got too much rear brake bias. (This has temporarily been cured by hacksawing bits off the rear pads...).
If you are a complete animal, there is another method for reducing the rear brake bias. I'm going to say no more than it involves a pair of mole grips...
The first 'level' of modification is to convert it so that the release button works the opposite way round. This means that when you grab hold of it in the heat of the moment, it only stays on if you push the button in - known as a fly-off handbrake. It's a relatively simple modification which can be achieved in one of two ways. The most basic way is to simply drill a small hole so that a pin of some kind (the stem of a pop rivet works well) can be pushed through to stop the rachet engaging onto its teeth. This is fine, but won't pass an MOT (but of course you'd remove the rivet before the MOT, wouldn't you ;-).
The more professional way of achieving the same end is to extend the rachet (weld an extra bit on) and bend the release 'wire' (the bit connected to the button) so that the rachet is kept away from the teeth unless the button is pushed in. The spring will release the rachet when the handbrake is lifted slightly with no pressure on the button.
The next modification is to convert the handbrake so that it works hydraulically. This is a fairly simple modification, and kits suitable for Mk2 Escorts can be fitted pretty easily (see photo). The only problem I've found is that the cylinder sits too high, which means that the lever only comes up a click or two before stopping dead - which can hurt if you are pulling too hard. The Sunbeam specific kit mounts the cylinder on its side which then allows the lever more travel by attaching closer to the pivot.