Castor Wedges

By Michael Beswick

It was whilst filming "Ultimate MG", that I got to hear about "Castor Wedges".

The MGB is heavy to steer at parking speeds, even if you do grease the steering rack and king-pins regularly! This is particularly noticeable in comparison with a modern car. Part of the attraction of a classic is the absence of modern gimmicks, but sometimes a bit of modern engineering can help!  (Note - the MGOC offer a power steering kit which may be of more interest to owners with physical difficulties who still wish to use a MGB.)

The castor angle was designed for use with Cross-ply tyres. The slip angle (the amount the wheel turns before gripping and turning the car) is much less with modern radials. However the castor angle remained unchanged despite the fitting of radials as original equipment.

Castor Wedges are a wedge with a slot down it's length-a bit like a tuning fork without the handle. They are inserted between the cross member and the main chassis, by loosening the 4 bolts, sliding the wedges in and re-tightening the bolts. The effect is to tilt the cross member front edge slightly downwards and therefore rotate the king pin and wheel assembly slightly forwards to alter the castor angle.

Fitting was easy - You loosen the steering rack first and then loosen the 4 chassis bolts. The wedges slide in, using the suggested silicone sealer to reduce the level of electrolytic corrosion between the steel cross member and the aluminium wedges. Having re-tightened the 4 bolts, the steering rack is tightened using the supplied washers to compensate between the front mounting and the chassis.

Out on the road it seemed to make a small difference when manoeuvring but as I hadn't driven the B over the winter it is difficult to tell!

The wedges are expensive, but reflect the design cost. It has been suggested that washers could do the same thing. They could - but (a) you would have point loads, not evenly spread as with the wedges, and (b) you would have to remove the 4 bolts to fit them, and (c) how do you know how many to use. (I didn't measure the thickness of the wedges!

They work but are probably under the "nice to have" not "need to have" category, unless you do a disproportionate amount of parking!

Note:

Castor wedges are supplied by Frontline Costello in Bath.

Also, when reviewed by Roger Parker in Enjoying MG in 2005, he commented that the biggest improvements were on the MG RV8.