Posted by David Sherman on Monday, September 17, 2007 at 01:19:25 :
A couple years ago, my Spicer 3053 tranny blew out while climbing a steep grade with a heavy load. I managed to limp the rest of the way up the hill in 1st gear, though it made a lot of noise. I finally got around to tearing the tranny apart to see if I could fix it using parts from another 3053. I knew the collar around the output shaft was cracked because I saw that as soon as it blew. When I tore into it, I found that the output shaft bearing outer race was broken clean through and the transmission case was cracked near the output. The first/reverse and 4th gears on the mainshaft were badly chewed up. The reverse shaft looks good, and the countershaft looks okay at first glance as well. The real problem is that the mainshaft broke! This is a 1-3/4" shaft, presumably made of good steel. The front bearings, countershaft bearings, and the bearings where the mainshaft spins inside the input shaft are all fine. I was probably in 2nd or 3rd gear when it blew. My guess is that the mainshaft broke first, which caused it to loose those gears completely, but since the input shaft was still turning the countershaft, held in alignment by the input bearing and crankshaft pilot bushing, and the 1st gear was near the output shaft and so couldn't get too far out of alignment even with the front end of the mainshaft flailing around, I still had some use of 1st gear. I suspect that continuing to drive another 5 miles or so up a steep grade in that condition is what broke the output collar, its bearing, and the transmission case. With a broken mainshaft, the tranny is pretty much junk anyway, so the broken case is no great loss. The tranny had oil in it and there's no obvious signs of overheating.
I was just wondering if anybody else has ever had any shaft inside a transmission break and if they have any idea what could cause it. It seems like it would take a tremendous amount of torque to break a 1-3/4" shaft of top-quality steel. There's no obvious corrosion, scoring, nicks, or discoloration at the point of the break.
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