BRB's Really! they are Cross head braces and stop the top of the cross head moving either fore or aft.
Do they make a difference? You bet they do!
Firstly: Under hard braking the cross head suffers a rotational force the tends to try and tip the top of it forward. Not just as a force which remains stationary but it actually moves directionally forward. This results in the axel tube remaining in it's true plane as its stabilized by the lower stays but the top tubes from the center square cross bracing are pushed forwards at their outboard ends. This alters caster, cator and tow settings and creates that juddering sensation felt through both the body of the car and the steering wheel. This is as a result of the shimmy created at the tyre as it loses and regains traction much like ABS in feel but hugely undesirable!
Secondly: Driving on the ever increasingly poor and broken surfaces we find ourselves on these days, every time one side or the other of the cross head receives a shock through the suspension it upsets the steering geometry and causes what is akin to bump steer with the associated symptom of shot shock absorbers. That rattle at the steering wheel. This is caused by the high frequency spring effect of the top tube resuming its correct position.
So, fitting cross head top bracing stops a lot of this effect. It was fine when the cars were made for a different era of motoring but they now require a far greater level of stability and certainly finesse!
How do they actually work then? Well they work in both compression and tension in that they help prevent all but the most extreme rotational forces on braking and acceleration from having to great an effect on the top tube and thus the suspension element of the front end geometry. They also have a damping effect when extreme shock happens at one or both sides of the car in that they reduce greatly any spring vibration that the top tube would suffer from in recovery of that shock.
Most drivers will feel a 'more solid' sensation that these braces will achieve. They will quickly forget just how jittery and unpleasant their steering was before fitting them and will quickly go on to seek more finesse out of these old chassis designs that the classics have! Those wise amongst you who have described them as the cheapest and best improvement you can make have absolutely nailed it!
Just a couple of other things i picked up on. Those cars with the one shot oiler system removed have not always had pillar changes and the oilway is not adequate for greasing purposes . use a thick oil in a grease gun if this is the case.
For the post 2011 cars with adjustable camber and having dome topped pins. I agree with those who say that the cross head braces should be fitted above the conical washers. the minute amount of movement at this point were the camber to be adjusted would be easily accommodated by the brace. If this exercise is undertaken, it is first vital that the oiler bolt is loosened. The only difference that it will make not being fitted directly above the top shock absorber mounting plate is its slightly different location point on the chassis rail! and as all cars vary slightly here that's not an issue. I also feel that putting anything that irregular and not fully supporting under the conical washers is asking for trouble!
