Now for a discussion of the Achilles Heel of the 289 and the 427 Cobra. The bearing spacers. Space does not permit me (or the rules of this forum
) to accurately describe my feelings toward these spacers. Suffice it to say they are an abomination (right next to the McLeod hydraulic throw out bearing).
The original Cobra (including 289 FIA, 427 Comp, 427 S/C, and 427 Street) used tapered roller bearings in the rear upright. (Just for interest's sake, the 289 street car used 2 standard roller bearings). Tapered roller bearings have to have a certain amount of preload on them to run right. If the bearings are too loose, then your rear hub will be loose and wander all over the place. (Not good unless you like saying your Hail Mary's at the end of the strait). If your bearings are too tight, they will burn up in short order, probably seizing the rear bearing and then spinning it on your rear hub. (Not good unless you like calling Kirkhams on the phone and begging them to custom make you some extremely expensive rear hubs.) There is an extremely fine line between too tight and too loose. It is only about 0.001 inches. You want the hubs to have about 25 inch pounds of resistance on them when you turn the hub and have it all preloaded correctly. The preload is set by the length of that stupid shim. When everything is right--it makes a marginally acceptable solution to the problem of rear hub bearings. Today we have MUCH better solutions--like double row angular contact bearings that come on a Porsche. But that is a story for another day.
In our experience, the rear upright bearing shims are seldom--if ever--set up correctly. Because the shim must take up the preload of the bearings, it is itself a bearing of sorts. As such, it MUST be made out of HARDENED STEEL!!! Everyone makes them out of mild steel and then prays to the bearing shim gods that they will hold up. They will not. They will FAIL after as little as 10-100 miles. Expecting them to hold up is much the same as praying to the Turn 1 god in hopes you will make the turn after you missed your braking point. Let's face it, if you have resorted to praying you will make the turn, you are probably going to shortly experience 4WD in a Cobra. Not so bad a Miller Motorsports Park (probably just humiliating as you spin off in a cloud of dust the size of Hurricane Katrina) but quite probably DEADLY at most other tracks.
If you look closely at the inner portion of the surface of the shim you can see it is colored differently than the outer portion. That is because 0.010 inches has been WORN OFF THE SURFACE!!!
We make our shims out of hardened 4340! Absolutely bulletproof. Pun intended...
OK, let me explain the pun. 4340 is the mil spec used for armor. It is hell on tools (and Osama's buddies) but it is about the ONLY thing that will stand up the the beating.
