Castor Angle

tonymce · Posted: Fri Dec 04, 2015 8:58 am Post subject: Castor Angle

Can anyone advise what the ideal castor angle is for a 4.5 Litre with 10' 10" wheelbase. I can see no data on this in the technical facts or in the forum and I'd like to lighten the steering if possible which, I believe, would result from a reduced castor angle.

Chris Card · Guest

Tony - the caster angle is set by the spring pad cast into the axle, and I think is 2.5 degrees. You can alter that by putting a wedge.either under the front or back of the spring.
If you put it under the front, you reduce the caster angle, which lightens the steering, but will make the steering more wayward - not to be recommended.
So - check that you don't already have a wedge Under the back of the spring pad, as this will increase the caster return action, making the steering heavier.
The other things to check are that the track rod and drag link ball joints are not too tight - you should be able to rotate the track rod and drag link with your hand against moderate resistance.
Tyre pressures have an effect, I run at 36psi, set when cold.
I hope this helps.
Chris

tonymce · Posted: Fri Dec 04, 2015 9:55 am Post subject:

Thanks Chris. I have always had a wedge put in the back of the spring and the steering is not at all bad, but the castor angle "looks" too much. None of the original drawings would appear to show a wedge under the springs so I was wondering if removing the wedge to see the effects would be a wise thing to do. I assume that it is and if that resulted in excessive "wandering" a thinner wedge could be tried. I was hoping someone might have done some experimentation on this and could advise that a castor angle of x degrees had been shown to be ideal.

Chris Card · Guest

I have a thin (about 3/32) wedge under the back of the spring clamp and I have quite strong caster action. I'm not convinced that it has any real effect on the weight of the steering unless it is much thicker.
In fact, the next time that I'm feeling energetic, I'm going to remove them.

Chris

Robert Zannetti · Guest

I have heavy steering on my 3 litre 1925 which I put down to the high gearing (one turn lock to lock). If you have a wedge at the back (giving an increase to the castor action and increasing the weight) can you see it without dropping the axle?

Christopher Carnley · Posted: Sat Dec 05, 2015 11:03 am Post subject:

There is a brief mention of this at section 18A of the 1984 Tech Facts,under Wheel Wobble at , s(9).

Your ideas would appear to be correct.

tonymce · Posted: Sat Dec 05, 2015 4:25 pm Post subject:

I see that, thank you. I will report in due course once I have done some experimentation.

Robert Zannetti · Guest

Earlier I mentioned my heavy steering on my 3 litre and resolved to try to improve the weight. I went to see Chris Card (not an onerous journey - he lives less than a mile away) and he showed me the shims he had used to increase his castor action by putting them at the back. I dropped my axle cleaned it all up and put 1mm shim at the front to reduce castor angle. I took advantage of today's pleasant conditions and did a road test over roads ranging from motorway to convoluted lanes. The results were much greater than I expected and can report that the steering has lightened quite a bit and there is a reduced steering wheel wobble. The action is now a little more 'darty' particularly on the potholed lanes with strange cambers, strange animals and strange octogenarians, but not off-putting. Technical Facts suggest that experimentation is necessary (as with friction shock settings) to get the best set up. I think it is particularly so with early 3 litre high geared steering which can be very heavy if not correctly set up.

tonymce · Posted: Thu Dec 24, 2015 5:58 am Post subject:

I did promise to update you on my experiment. I removed the wedges from underneath my front springs to have them as originally designed. These wedges were 6mm at the thick end. The steering has been markedly improved with no evidence of "wandering" and it is significantly lighter and more direct.

However, another issue was addressed that may have contributed to the huge improvement. Table 1.11 in the Technical facts shows the steering box requiring Hoffman ACD 130 bearings. The SKF equivalent is 7206 BEP. These are an "Angular Contact Ball Bearing" and are what were in my steering box. I had noticed some slight movement on the wheelshaft and examination of the bearings showed that because of the angular nature of these bearings, this movement could occur. I therefore changed the bearings on the wheelshaft to SKF 6206 (as indicated in 2.10.11 of the Technical facts) and all movement was immediately eliminated.

Overall it seems to have been an excellent result.