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Okay, so the trans has arrived and I have taken it apart and found the problem. The owner said that about 20 years ago it had a diff carrier failure that was repaired. It does have an upgraded diff carrier. I asked because it was clear the trans had been apart. I found the lay shaft ring nut was tight and staked but took very littler torque to remove it. I didn't actually check the torque but my impact wrench whipped it off with not issue at all. The main shaft nuts were much tighter and took an appropriate amount of impacting to remove. As I took everything apart, it was clear that second gear was indeed seized on the lay shaft. However, the lay shaft slid out easily as it should, after hammering passed the pressed on bearing anyway. I pulled the gears from the case and found that second was not seized on the shaft but it had welded itself to fifth gear which is splined. Image Unavailable, Please Login I was able to clamp it in my lathe and break it apart. Image Unavailable, Please Login I found that the loose nut allowed the stack on the lay shaft to float enough to wear down some and create a tight condition for second gear. second gear floats on a bearing between fifth and a washer the keeps the thrust movement in check. With the wear from the float, this allowed the clearance to be eliminated and second and fifth wear rubbing very hard against each other. Eventually the metal smeared and that took all f the clearance away. Any time the car is moving and not in second gear, second gear spins at a different speed than fifth. So as he was driving second gear smeared its face against fifth and super heated which started the welding process. As soon as he clutched the car the two gears matched speed and cooled the weld. Thus welding second to fifth. Here are some pictures of the worn shims and gear. Image Unavailable, Please Login Above is the spacer on the other side of second, as you can see it was smearing metal as well. Image Unavailable, Please Login Image Unavailable, Please Login The razor blade shows the wear line created be the spacer being loose. As a repair, the plan was refinishing the gears and shims to restore a flat surface and then re-shim the trans to establish proper clearances and preloads. Changing the stack shim thickness alters the preload for the lay shaft taper bearings. I was able to use resurface the shims and gears with diamond lapping, they are really hard. I then re-shimmed the stack and restored the proper preload and gear mesh. I also had to use a diamond wheel to regrind the second gear face to remove damage from the welding. There is no cracking on any of the parts and the heat was surface only. This is the second reshim I have had to do because of loose nut on stacked gears. The other was Daytona and it was just shifting poorly and had not damaged the gears. So, at this point, I am ready to start the final cleaning and re-assembly process.
thank you wade for all the info and good that not much was wrong, so need nearly no parts but a lot of work so you will change now all the bearings also? makes sense I think what do you think what happened? the nut not right tighten 20 years ago? never before I had such a problem. so I say: very unusual
The bearings are not hurt and have no need to be changed. I have seen this before with nuts coming loose. This damage and the welding of gears is unusual in my opinion. The clearance is very small and it takes very little change to make the parts start to smear. The wear was only on parts that were not spinning against each other but just moving slightly back and forth. This generated no heat, and took 20 years to remove the needed clearance and cause an issue. The previous one I repaired with a loose nut had the nut actually loosen completely and was not a staked nut. This one was staked so it did not rotate to loosen but had no clamping on the shaft. This allowed the spacers to wear and then allow the gear to have no clearance.
