Shoptalkforums.com

I picked up a spare "T" frame for the suspension the other day and an interested in modifying it to get additional caster. To get one additional degree of caster I would have to move the frame forward 1/2 inch if my numbers are correct. Even at that point I will have to relocate the mounting point for the steering stabilizer to keep it from hitting. This of course is not hard to do.

Is there any reason to shoot for more caster than an extra 1°? Doing this would essentially double the stock caster angle, but is still way less than many other cars. Any thoughts, has anyone successfully gone for more than an additional degree? Was it worth it?

I have been scratching my head for a while on the caster issue. I am now thinking that I could get the most caster by relocating the top of the strut tower back and inch or so. With a little welding I could probably do this over a weekend. A lot of careful measuring, cutting and welding with a few fishplates added as needed. I think that my total caster would end up about 3° by doing so, should be pretty noticeable. Sounds fun to me.

Thoughts?

Sure, lots of cars have aftermarket "camber/caster plates" that offer adjustment through altering the strut mount position available. Probably something could be adapted of going through so much fabrication. I google image searched "camber plates" and found tons of great pics showing different setups for different types of cars. Shoot, something might be able to be done without body modifications.

I had thought about trying to go this route, but I don't think that there is enough room in the top of the strut tower for any offset in the location of the bearing and spring. To get the needed clearance you pretty much need to move the top of the strut tower itself.

There is not enough room to do it with the strut mount on the 411/412.
Actually you can get about 1.5+ castor by slotting the forward mounting holes for the "T" frame. You can pick-up just a slight amount from the strut mount by slotting the holes in the body and grinding away the edge of the center hole.

The calculations don't quite tell the whole tale. If I remember right the correct calculation for the castor angle uses the poinjt where the ball joint bolts to the arm and measures movement forward from vertical axis. Its a triangle calculation. Just slotting the bottom holes should be enough.
You need somewhere around 2.5-3.0* castor. 2.5 will be enough.

This is a VAST improvement. It gets rid of all bump steering and almost all of the wandering that we normally associate with crosswind. It also makes cornerng at speed more precise.

Also..don't confuse static castor calculation with active castor while driving. You get a bit of flex to the suspension parts when you put weight on them. Also the active castor affects the change to the angle of the wheel when you are turning. With more static castor, the active castor improves and keeps more contact patch on the pavement throuh turns. That is all much improved when you add static castor like we are doing.

Someting else to bear in mind. All of the late 412's had modified control arms and steering knuckles that had something like and added 5*static castor. By using late 412 trailing armsand steering knuckles on any other car you get an automatic improvement.

Also adding 5* static castor with the late control arms and knuckles is not teh same as adding 5* active castor. It helps....but since there were several angular relationships changed...partly at the ball joint mount point...and partly in the angles and shape of the steering knuckle.....it gave the most change in the cornering aspect of the active castor. But it is a slight multiplier for other angular changes made to static castor like moving the "T" frame forward. If you get or have the late 412 knuckles and control arms....3/8" to 1/2" slotting of the T frame will give you right at 3*+ of castor as measured on an alignment rack. You should not have to relocate the steering damper but it will be very close. Ray

I can't picture how they could have gotten an extra 5° if the shock towers were not changed. To get that kind of a change in camber would require the wheels to move so far forward I would think they would no longer fit the fender opening. By my calculations which show a need to move the wheel forward a half inch for each degree difference in castor, 5°s would require two and a half inches of movement.

Tell me if I am wrong, but I don't see how they could have done it.

Its decieving. The castor is calculated based upon the pivot point of the very bottom of the shock unit.....in conraste to a straight vertical line drawn through that same pivot point perpendicular to the pavement.

In our case the point at which the ball joint stud joins the control arm....or actually just above it....is our privot point. So....from the center of the ball joint....go straight up....all the way to the poin where the strut rod joins the plane of the ball bearing in the strut mount.

That is a very long vertical line. 20 something inches. It is the bottom leg of the triangle. The short leg.....starts at the bearing plane in the strut bushing and goes toward the cars rear. Now.....with a clinometer...measure the angle on the side of the strut tube...making sure that you are on the rearward side exactly (make sure car is on the ground and the gas tank is ay least half full with whatever you normally carry in the trunk). Shoot that line all the way up to the bearing plane...extend the short leg until it meets. Draw the triangle.

The thing is...with only one degree or so available...the angled line does not land to far from the vertical line.

But bear this in mind.....yu are measureing loaded. To get a real feel for the castor in various states...you must also draw this triangle with the strut unloaded (longer length) and fuly compressed (shorter length). It really does not take to much forward movement of the T frame to get a bot more out of the equation.

There is another aspect that affects castor. The actual position of the axle center relative to the center of pivot (the ball jont). I beleive the difference in the later steering knuckle ..was to move the axle pin slighly forward and up....putting the axle actually forward and higher than the pivot point. This technically gives a very slight affect the same as lowering the front end.
But what it really does it make the live castor effect (the tilting outward of the wheel through turns to keep contact patch) with reference to change of direction....greater.
Static castor...the actual tilt of the strut tube is not actually the same as active castor...or the affect that static castor lends when the car is in motion.

Put bluntly...the struts are so long that any extra amount of castor is greatly magnified. Ray

Ray, do you have the exact VW part numbers of these very late 412 steering knuckles and trailing arms with improved static caster? Also, do you know whether there is a letter code stamped in the knuckles to identify them (my 411 ones have a "B"). Thanks, Jan Peter