The FSM says you should use the fancy special tool to simultaneously measure camber and castor. If you can get hold of one I'm sure it will save you lots of time. So far I haven't worked out how to make an equivalent DIY tool – that's a project for the winter. So the only other way is to measure camber of the front wheels when they are turned by 20 degrees (as data for this is given in the FSM)
Preliminary steps:-
1.Assemble a camber gauge as described above in step 8.
2.Lock the steering in a straight ahead position
3.Set the toe in / out to zero degrees
4.REMOVE THE SPREADER BAR
5.Set the camber to zero degrees
6.Check the toe in / out and adjust the camber again if necessary
7.REMOVE THE SPREADER BAR
8.Remove your steering wheel lock – or the method of which you've locked the steering
9.Draw a line parallel to the rim when it is in its straight ahead position so that you have a convenient measurement datum point for the measurement a 20 degree angle. (You may be able to use your box of string datum for this too)
When you've got the camber set to the prescribed value and you've got your toe in / out set correctly then you are ready to check / measure / adjust the caster. Because you've got the car on slip plates you can easily turn the front wheel one way or the other. WARNING if your car is not on a level surface you will probably find that the wheels will slip off of the slip plates – this can be DANGEROUS!!!
Another problem that you may encounter is that when you turn the front wheels they catch on your carefully made box of string reference point. If this happens I recommend going back to step 6 above and make a wider box around the car, as if you adjust the caster you'll need to check the toe in / out again, and it is a good idea to check the distance from a point on the chassis to the string during the caster measurements.
To measure caster you:-
1.Recommended:- Measure from a point on the chassis to your box of string datum so that you have a way of checking if the car has moved after you've done the next step. I measured from the front jacking holes.
2.Turn the front wheel to the right by an angle of 20 degrees – you need to measure this with a protractor. Some people make up a template out of cardboard for this.
3.Recommended:- Check that the car has not moved – measure from your chosen points on the chassis again.
4.Using your camber gauge measure the angle of camber and record the value. If you are using the DIY camber gauge described above then 10mm = 1 degree.
5.Turn the front wheel back through the straight ahead position to an angle of 20 degrees left
6.Recommended:- Check that the car has not moved – measure from your chosen point on the chassis again.
7.Using your camber gauge measure the angle of camber and record the value.
Add the values of your measured camber together to get the caster for that wheel (Add positive values of camber together – don't get confused about positive or negative camber). You now need to do the same for the other wheel – if you get yourself organised you can incorporate the measurements of both wheels in such a way that you only the turn the steering wheel once to the right and once to the left. If you do this though I recommend that you measure the angle of turn of both front wheels as it is possible that when one wheel is at 20 degrees the front wheel on the opposite side is not!
To find the values of caster have a look at this link you might find values for your car here (you might not):-
W123 Caster / castor settings for a sedan / saloon?
To adjust the caster you need to alter the length of the stay that connects from the chassis to the lower control arm (FSM calls this the brake support). When you do this though you are also altering the camber. So for each alteration in caster you ideally need to follow the tedious process of:-
1.Measuring toe in / out and setting it to zero
2.Measuring camber and setting it to the correct value
3.Measuring caster and correcting it to the correct value
4.And finishing off with a check of toe in / out and camber!!!
Round and round you go until you don't need to adjust any more...