Hi Lloyd.
I cross posted this in the forum, but being "The man" on ZF's, I wanted your opinion on this theory. The copy and paste is below.
Hi Ron;
The easiest way to explain the misalignment is to picture two parallel lines, just a few thousandths of an inch apart. Your ZF is aligned to the back of the block by the factory dowels, or I should say, the case is. Your input shaft , supported by bearings with a small amount of slop, is inserted into a pilot bushing or bearing in the crankshaft. IF the parts are not in perfect alignment, again my gut feeling is .001-.004, bad things will happen. Normally, it will manifest itself in a synchro-dragging, noisy shifting kind of way as a means of identification. The oil pressure problem will come afterwards, when the whipping crank has had time to cause wear on the bearings. Another primary identifying clue will be front seal leaks on the transaxle, or uneven wear on the bearing retainer, in most cases, the guiding surface for your throw-out bearing.
Your note made it sound like this was a common problem among all Pantera owners, and I know this problem does not often occur in Boss 351 or other 351-C or 400-M installations.
That makes me question factory tolerances and installation procedures. I just can't believe that there is an inherent flaw in the Cleveland. I do feel that the misalignment of the bellhousing/case is causing the input shaft to enter the pilot bushing at a slight angle, and the holding pressure of the clutch is distorting the crankshaft flange, causing a slight whipping of the crank. The rear main bearing is the pivot point, as it is closest to the flywheel, and # 4 journal is the flex point, therefore taking out the surface of the bearing and spreading the main cap in the process. If excess wear has caused any saddle wear, an align hone process will be needed to salvage the block. Experience has taught me to square ALL surfaces in relation to the crankshaft centerline, head, front cover, rear flanges, starter mounting bosses, etc.. Once square, with the bearings and crank installed, measured and torqued to spec, install the flywheel bare. This will allow placement of a magnetic stand for a dial indicator. Transmissions and more specifically, their front bearing retainer, which centers the input shaft, fit tightly in the hole in the bellhousing. By using a dial indicator on a magnetic stand, you can rotate the crankshaft and read the runout. Dowels are available to aid in alignment, or you may need to machine some in severe cases. I don't recommend doing this on a complete engine, as it takes considerable force to overcome the friction caused by piston rings. A bare crank swings pretty easily. Mark the areas of severe misalignment on the bellhousing face ( here I need to ramble a minute. If the ZF does not have a removable clutch can or bellhousing, just find a factory unit for a regular passenger car. All bellhousings are machined relative to the input shaft, it shouldn't make a difference), calculate the movement necessary to bring the housing into alignment, replace the dowels and recheck to confirm your math. This will take time, not to mention a trip or two to the machine shop for dowels made to your specs. Many racers center punch the back rail on the block to give it a little more grip to hold the bellhousing or scattershield in place after alignment. If the housing is torqued correctly, that should not be necessary, but a couple of marks sure are cheap insurance. I just reread this explanation, and saw a gap in the explanation. The dial indicator is mounted in a position to read the inside dimension of the bearing retainer hole. The gauge itself will be centered in the hole, and the pin should be parallel with the flywheel surface AND the bellhousing surface. Another quick check to do with a dial indicator is mount it above the transmission mating flange, touch the surface, zero the gauge, and rotate the crankshaft. This check will tell you if the trans is mounted perpendicular to the crankshaft centerline. Again, not being all that familiar with a ZF, I don't know how possible all this is. That last measurement will sure tell you of angularity and crankshaft flex possibilities present in transmission manufacturing tolerances. My first experience with this was eye-opening, and it did not get far enough to cause bearing damage. The misalignment caused the input shaft to drag in the pilot bushing, therefore rendering smooth, quick shifting impossible. Back to the garage! We haven't spoken about the shifting characteristics of your car, and with the remote, front mounted linkage, you probably would not notice a misalignment unless it was severe. The same whip your crankshaft experiences can occur in the main shaft of your transmission, for exactly the same reason. The front bearing is the pivot point, etc.. I am trying to figure out a way to illustrate this with the keyboard, so bear with me.
*-/___ would force the crankshaft up at #4 , bellhousing low
__\--- would force the crankshaft down at #4 , bellhousing high
*-|--- on the same plane, should eliminate engine bearing wear, and trans wear
The pattern shown above could be detected by wear on the front and back edges of the rear main bearing, with the center surfaces basically unmolested, and the seam in the split bearing halves again being unmarked, as the flex will be an up and down whip, not side to side.
Hope this is clear enough to understand, I tend to ramble when I find a fascinating problem like this. I'd like to hear what the others experiencing this problem have to say, because I feel it is a matter of basics, not a flaw in the design.
Again, rereading this note pointed out that I failed to mention the possibility of the bellhousing flanges not being parallel. This can be checked on a surface table at a machine shop, and any misalignment corrected by a good old broaching cutter. If this is a contributing factor to the problem, be sure not to remove any excess material. If the input shaft is placed too deeply in the pilot bushing/bearing, the splines will contact and create one hell of a racket, for a minute, anyway.
Thats all for now, talk to you soon. Have fun shopping this theory around, it may remind some people of the basics.
Dave
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