I have a Mk2 1964 with a rack and pinion conversion using the original pump mounted on the dynamo the steering is so light you could drive it with one finger, any one know of a way to give it more weight?

 

There was no adjustment on the original Burman steering boxes and only limited adjustment on the Adwest Marles box. There is no adjustment on the actual pump other than I suppose you could change the pulley on the front of the generator to slow the rotation and there by reduce the PSI being produced by the pump but this would then effect the electrical power being produced by the generator as well as making the steering very heavy for parking. The pump produces 800 to 1000 PSI depending on the revs the generator is spinning at so the more RPMs the easier the steering becomes. My S Type with the Adwest Marles has heavy steering when parking because it is an Auto and therefor the RPMs produced at stand still by the engine are very low in turn producing low PSI at the pump. With a manual you have the ability to rev the engine a bit and then slip the clutch to get more PSI at the pump and easier steering for parking. At speed with higher RPM the steering is very light.
If you can tell us what rack and pinion was fitted to the car there might be a way that the R&P can be adjusted but I doubt it as it is still dependent on the PSI produced by the pump.

 

A pressure reducing valve should do the trick. The valve connects the pressure and return lines so there's some plumbing involved. Here's an example of one made here in the States.

 

The level of assistance is usually controlled by a torsion bar and sort of cylindrical valve at the input to the rack. Aston Martin often used the same racks as Jaguar, but with stiffer torsion bars giving weightier steering. Later Jaguar models also used stiffer bars.

The original front suspension and steering geometry was, of necessity, designed to minimise unassisted steering effort. The steering arms could be shorter in the horizontal direction (also reducing the turning circle), but there's not much possibility of change there (unless the standard PAS arms were shorter?). However, you can increase caster, preferably to the absolute maximum. That should increase steering effort and improve feel. It's also possible to change wheel offset: moving the wheel out relative to where the kingpin axis intersects with the road surface may help.

 

Forgot to mention: I have seen a MK2 with an XJ PAS rack and no pump or power assistance. To my surprise, it didn't seem heavier than a standard car to steer! However, that wasn't a side by side test.