jrlichina.
I gotta’ beg to differ….and from my conversations with a PhD' retired professor of engineering, and JD engineer in the ‘50s…my Father.
First, I'm not supporting the theory that the change in the tractors caster angle would be the sole cause of the problem, (nor would my Pop’), but there is merit to the principle. That is, a slight change to a reasonably neutral caster angle in a CUT under a heavy load might have a dramatic effect on steering effort. Lots of other factors here, most have been covered earlier, i.e. ballast, tire pressure, surface conditions, hydraulic oil pressure, etc. Pressure now being increased with shims... /forums/images/graemlins/grin.gif
Second, to your statements....
<font color="blue"> Caster is important on higher speed vehicles like cars, trucks, and obviously race cars, but it is NOT an issue as it pertains to CUTs. </font>
Our slow-moving equipment is designed to carry a wide-ranging amount of weight in a variety of conditions, including slope, tilt, varying surface conditions, etc. Engineers spend an incredible amount of time testing and tweaking all of the steering dynamics in CUTS, not the least of which is caster angle. everything is BALANCED for safety, straight-line stability, and steering effort. Because of the fact that the tractor may creeping, or moving at over 10 MPH, and the fact that the front axle load can vary as much as 400% in a matter of moments, caster is more critical than ever and more sensitive than ever. Slight changes in a reasonably neutral caster condition, coupled with a dramatically increased load and even a slightly a modified downward thrust angle from the larger tires rear tire and inadequate ballast can make the steering effort increase exponentially
<font color="blue"> In general caster comes into play when the vehicle is in motion not in static situations. </font>
This is simply incorrect. Caster is in play all steering conditions, dynamic and static. Changes in caster angle primarily affect two things: stability in motion and required steering effort from a static position. Camber is affected secondarily by changes in caster.
<font color="blue"> The only time it would have an effect in a static situation is if the caster angle was changed drastically (greater than +- 20 degrees). </font>
An exaggerated 20 degree change in the caster angle, under load, and under-ballasted on a John Deere 4110 would render a very precarious stability condition in motion, and definately a completely inoperable steering condition from a static position. Whereas a 3 to 5 degree change might realistically have a dramatic effect on steering effort, ESPECIALLY from a static condition with inadequate ballast.
Most people know of caster, camber, and toe from automobile alignment training and discussions, but they are basic steering dynamic principles for racecars, bicycles, grocery carts, mining equipment, and little red wagons. If you consider the wide spectrum of steering applications from creeping mining equipment to an open-wheeled car going over 200 MPH, you will find the sensitivity level is exponentially greater at the ends of the spectrum. That is, a minor tweak to caster in a high speed car will have dramatic effects on stability, and a minor tweak to caster in a slow, heavily loaded vehicle will also have a dramatic effect, but in required steering effort.
I’ve even bored myself here, so I’ll just end by reminding everyone that JClark has (had?)to force his steering in static conditions, not while he’s moving. This symptom leads trained engineers to begin diagnosis by asking about these specific steering dynamics. I’m sure the RM was just parroting what an engineer told him, but that doesn’t make the principle absurd. It just isn’t the first blush answer anyone wanted to hear. The added pressure from the shims should overcome any possible imbalance from the changes to the steering and thrust dynamics. That's what we're all hoping for here, afterall. /forums/images/graemlins/grin.gif
