awalker@topaz.ARPA (*Hobbit*) (03/03/85)
Apparently my message about transfer case spider gears/diff ratios was somewhat misunderstood. The way to figure out exactly what you have under there and what it can and cannot do is use a little logical common sense. First of all, even if they made the front and rear punkins the same ratio, you'd still wind up because of different tire inflations, paths the wheels take when turning, bumps in the road, etc. Therefore the manufacturers either make the front end ''switchable'' or use a middle spider as in full-time 4x4. Chevy fulltimers also have a CV joint on the front shaft, and a straight pair of U-joints on the back. When a U-joint is turned at a fairly hairy angle, transmission of rotation is not fixed -- e.g., when the transmission rotates at a fixed speed, the rear will alternately lead and lag the transmission slightly, twice per rotation. Think about how a U-joint works and you'll understand why this happens. In stock Chevy suspension, the most acute angle occurs at the junction between the front of the transfer case and the front shaft, so they use a CV to smooth it out a little. So what happens when you lift it? You change driveline angles, especially the angle at the rear of the transfer case. Because of the increased lead-lag cycle extent, you start killing off U-joints right and left, because the wheels have to slightly accelerate and decelrate the engine every time the shaft goes around. All this geometry notwithstanding, it is only the sensible thing to do to *not* lock both shafts together when on dry pavement. With *any* kind of fo-by, you're only begging for death if you do this. If you lock 'em up, if you don't skrag your transfer case, you'll at the very least be doing accelerated wear tests on your tires. If you want to figure out just how different your ends are, jack up one whole side of your rig, put the trans in neutral, and spin the back tire a few revolutions while noting how far the front one spins. Your effective front-rear ratio will be the observed one divided by two ... I think ... No, wait, it'll be a direct reading since you're only dealing with *ratios*. Useful tip: If you lock up the whole driveline, it makes your truck virtually impossible to tow [if the grunt doesn't have the presence of mind to unlock your front hubs]. Neither end will roll!! _H*